6th 8th january @ university college london · 2016-01-13 · microtectonics workshop with cees...

Tectonic Studies Group Annual Meeting London, January 2016

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Tectonic Studies Group Annual Meeting 2016

6th–8th January

@ University College London

Sponsored by:


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Welcome to London!!

The Tectonic Studies Group Annual Meeting, TSG 2016, is co-hosted by

University College London and Birkbeck University of London.

Co-convenors:

Tom Mitchell, University College London ([email protected])

Gerald Roberts, Birkbeck, University of London ([email protected])

Penelope Wilson, Kingston University, London ([email protected])

https://tsg2016.wordpress.com/

This conference is sponsored by:

Midland Valley and Badley Geoscience

For information about TSG, including future events, visit:

http://tectonicstudiesgroup.org/

https://twitter.com/TSG_since1970

https://www.facebook.com/tectonicstudiesgroup

https://www.linkedin.com/groups/4928216/profile

Follow the conference and TSG on Twitter @TSG_since1970

[email protected]

[email protected]

[email protected]

https://tsg2016.wordpress.com/

http://tectonicstudiesgroup.org/

https://twitter.com/TSG_since1970

https://www.facebook.com/tectonicstudiesgroup

https://www.linkedin.com/groups/4928216/profile


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Conference Schedule

Pre-conference Workshops

Tuesday, January 5th

Move Workshop with Midland Valley

Time: 10:00–16:00

Venue: Petrology Laboratory, Birkbeck, University of London

Wednesday, January 6th

Microtectonics Workshop with Cees Passchier

Time: 09:00–12.30

Venue: Petrology Laboratory, Birkbeck, University of London

TSG 2016 Conference

Wednesday, January 6th

12:30–14:00 Conference registration opens (lunch/ tea/ coffee)

14:00–15:45 Session 1: Fractures and Fluid Flow I

16:05–18:30 Session 2: Rift and Passive margins

18:30–20:00 Icebreaker drinks and Posters

Thursday, January 7th

08:30–09:30 Session 3: Geodesy and Structural Geology I

09:30–10:30 Session 4: Fractures and Fluid Flow II

10:30–11:15 Morning break and Posters

11:15–12:45 Session 4: Fractures and Fluid Flow II (continued)

12:45–14:00 Lunch and Posters

14:00–16:35 Session 5: Palaeoseismology and Earthquake Geology

16:35–17:50 Session 6: Geodesy and Structural Geology II

19:30–Midnight Conference Dinner/ Party Boat

Friday, January 8th

09:00–10:30 Session 7: Regional Tectonics

10:30–11:00 Morning break and Posters

11:00–12:00 Session 7: Regional Tectonics (continued)

12:00–13:00 Session 8: Fault Rocks and the Brittle-Ductile Transition I

13:00–14:00 Lunch and Posters

14:00–14:45 TSG AGM

14:45–17:05 Session 9: Fault Rocks and the Brittle-Ductile Transition II

17:05–17:30 Closing Remarks and Student Prize Presentations

Session Time Speaker Title SP

14:00 D. Healy Connectivity of polymodal fault patterns

14:15 J. EllisImportance of bed-parallel fractures in flexural slip folds at the Grasberg-

Ertsberg mining district, Papua, Indonesia.

14:30 T. Fukunari A new model of bed-scale fracture development during basin burial Y

14:45 A. Bubeck Void geometry as a control on rock strength anisotropy Y

15:00 G. WangThe influence of gouge thickness and grain size on permeability in macro-

fractured basaltY

15:15 R. Murray The architecture and frictional properties of faults in shale Y

15:30 J. Browning Cooling-induced cracking in thermally stressed volcanic rocks

16:05 T. PhillipsFault interactions above a deep-seated crustal lineament – The multiphase

evolution of the Farsund BasinY

16:20 D. McCarthy Deformation of a Passive Margin, Southern Falklands

16:35 L. Pérez-Díaz Kinematic and paleobathymetric evolution of the South Atlantic Y

16:50 T. Dalton Deepwater fold-thrust belts in the Orange Basin; a balanced review. Y

17:05 M. ReeveThe Stratigraphic Record of Pre-breakup Geodynamics: Evidence from the

North Carnarvon Basin, offshore Northwest AustraliaY

17:20 D. CresswellUntangling the faults: Using 3D data at the Galicia margin to determine

faulting historyY

17:35 R. GrantGeometry and kinematics of a salt-detached fault system, Santos Basin,

offshore BrazilY

17:50 R. BellAre current models for normal fault array evolution applicable to natural

rifts?

18:05

Session 2: Rift and Passive margins

Rift and

Passive

margins

Discussion

18:30 to 20:00 Icebreaker and Posters

15:45 to 16:05 Afternoon Break - Refreshments

Day 1 - Wednesday, January 6th

12:30 to 14:00 Conference Registration - Lunch and Posters

Session 1: Fractures and Fluid Flow I

Fractures

and Fluid

Flow I

Session Time Speaker Title SP

08:30 R. Walker Igneous sills as a record of horizontal shortening

08:45G. Degli

Alessandrini

Deformation mechanisms of a sheared mafic granulite infiltrated by melt: an

example from the Seiland Igneous Province (N Norway)Y

09:00 C. ReillyThe importance of compaction in considering the movement history of

growth faults

09:15 Y. Wirtz

Integration of Outcrop-, Map-, and Regional-Scale Structural Analysis to

More Accurately Measure Tectonic Shortening in the Santa Maria Basin,

California, USA

Y

09:30 C. Nixon Contributions of sub-seismic faults to deformation in the Earth’s crust

09:45 D. Peacock Fault interactions and associated damage

10:00 C. GiorgettiFault geometry and mechanics within sealing horizons consisting of

carbonate multilayersY

10:15 A. Rotevatn

Deformation bands in carbonate grainstones (Miocene Globigerina

Limestone Formation, Malta): structure, kinematics, petrophysical properties

and impact on fluid flow

11:15 K. McCaffreyNatural seismogenic pumping processes in near surface fractured basement

gneisses

11:30 T. KristensenBreaking it down: mechanical and chemical damage zones. A case study

from the Dombjerg Fault Zone, Wollaston Forland, NE GreenlandY

11:45 P. Meredith The impact of compaction localization on fluid flow in rocks.

12:00 R. RizzoPredicting Bulk Permeability Using Outcrop Fracture Attributes: The Benefits

of Maximum Likelihood EstimatorsY

12:15 S. WeihmannPredicting Hydraulically Conductive Fractures: A Quantitative Comparison of

MethodsY

12:30

14:00 A. FagarengHang on a moment: If slow slip events are not earthquakes, how do we

interpret their source parameters?

14:15 A. Gudmundsson Statistical physics, active fault zones, and earthquake ruptures

14:30 M. DemurtasStructure of a seismogenic normal fault zone in carbonates: Campo

Imperatore, Central Apennines (Italy)Y

14:45 J. WilliamsDamaged beyond repair? Characterising the damage zone of the Alpine

Fault, New Zealand, a fault late in its interseismic cycle.Y

15:00 L. Wedmore

Coulomb stress modelling of an exceptional record of historical earthquakes

in the central Apennines, Italy: Lessons for fault interaction and earthquake

occurence

Y

15:15T. Rockwell

(Keynote)

Is the Southern San Andreas Fault Really Overdue For a Large Earthquake or

Just Late in the Cycle?

Lunch and Posters

Session 5: Palaeoseismology and Earthquake Geology


Day 2 - Thursday, January 7th

Session 3: Geodesy and Structural Geology I

Morning Break - Refreshments and Posters10:30 to 11.15

Session 4: Fractures and Fluid Flow II (Continued)

Session 4: Fractures and Fluid Flow II

Geodesy and

Structural

Geology I

Fractures

and Fluid

Flow II

Fractures

and Fluid

Flow II

Palaeo-

seismology

and

Earthquake

Geology

12:45 to 14:00

Discussion

16:05 M. Meschis

Investigating tectonically-deformed Quaternary marine terraces using

synchronous correlation to determine faulting activity: the Capo D’Orlando

Fault as a case study (NE Sicily, Italy).

Y

16:20 S. PavlidesActive tectonics of the northern Gulf of Corinth (Central Greece) and the

Delphi-Arachova Fault geometry and kinematics.

16:35 A. Bladon3D modelling and structural analysis of the Grasberg-Ertsberg mining district,

Papua, Indonesia.

16:50 T. Blenkinsop Visualising Second Order Tensors in Virtual Globes

17:05 P. SmithConstraining the vertical surface motions of the Hampshire Basin, south

England During the CenozoicY

17:20 C. Talbot We need a 2nd Stone Age when molten rocks replace concrete and bricks

17:35

Session 5: Palaeoseismology and Earthquake Geology (Continued)

Session 6: Geodesy and Structural Geology II

Palaeo-

seismology

and

Earthquake

Geology

Geodesy and

Structural

Geology II

Discussion

19:30 to 00:00Conference Dinner: Viscountess Pleasure Boat, Thames River Cruises (meet at Waterloo/ Millennium

Pier, South Bank, opposite Westminster)

Speaker Speaker Title SP

09:00 J. Dewey Four shear zones; their structure and evolution

09:15 A. Kemgang GhomsiContribution of the Geophysics to the Structural Study of the Mbere Basin

using GOCE Gravity Measurements:Implication to the Regional Tectonics.Y

09:30 C. MottramFrom micron to mountain-scale, using monazite and titanite Petrochronology

to quantify the rates of deformation in the Himalaya and beyond

09:45 S. Boulton When did the Moroccan High Atlas Mountains get high?

10:00 X. YangDynamic growth of fold and thrust belts: insights from numerical modelling

tested against a natural example from SE Asia Y

10:15 Y. Tian

Understanding long-term strain accommodation in the Longmen Shan

region: Insights from 3D thermo-kinematic modelling of thermochronometry

data

11:00D. McKenzie

(Keynote)The deep structure of continents

11:30 L. White Rapid orogenesis driven by crustal extension in eastern Indonesia

11:45 R. Butler Basement-cover tectonics, structural inheritance

12:00 B. FernandoMicrostructural evolution of plagioclase during shear zone formation in a

lower-crustal gabbroY

12:15 L. CampbellLithological controls on coseismic behaviour shown by frictional melting

experiments on wall rocks of the Outer Hebrides Fault Zone.Y

12:30 Z. Shipton ‘Pseudotachyl_te’ – a case study of ambiguous terminology in geoscience Y

Regional

Tectonics12:45

14:45C. Trepmann

(Keynote)

Long-term dissolution-precipitation creep at low stresses and transient high-

stress crystal plasticity of quartz in the subduction zone

15:15 N. TimmsThe effects of anisotropic elastic properties on shock deformation

microstructures in zircon and quartz

15:30 T. Tesei Friction and deformation of mineralogically controlled serpentines.

Session 7: Regional Tectonics (Continued)

Session 8: Fault Rocks and the Brittle-Ductile Transition I

Session 9: Fault Rocks and the Brittle-Ductile Transition II


14:00 to 14:45 TSG AGM

13:00 to 14:00 Lunch and Posters

Discussion

Regional

Tectonics

Fault rocks

& the BDT I

Fault rocks

& the BDT II

10:30 to 11:00 Morning Break - Refreshments and Posters

Day 3 - Friday, January 8th

Session 7: Regional Tectonics

Regional

Tectonics

16:05 L. MenegonBrittle-viscous deformation cycles in the dry and strong continental lower

crust

16:20 A. Cartwright-TaylorSpontaneous Electric Current Flow in a Deforming Non-Piezoelectric Rock at

Conditions Spanning the Brittle-Ductile Transition

16:35 P. MeredithStrength recovery and vein growth during self-sealing of experimental faults

in Westerly granite.

16:50

17:05

17:30 Close

Closing Remarks and Student Prize Presentations

Session 9: Fault Rocks and the Brittle-Ductile Transition II (Continued)

Discussion

Fault rocks

& the BDT II

Poster

BoardAuthors Abstract Title Theme SP

1 J. Gardner et al.What kind of creep would do that? Investigating the influence of diffusion on texture development in

rocksFault Rocks and the BDT Y

2 A. Castagna et al. Frictional and mechanical properties of volcanic and sedimentary rocks. Application to Mt Etna (Sicily) Fault Rocks and the BDT Y

3 I. Blaekkan et al. Evolution of normal faults and fault-related damage: insights form physical experiments Fault Rocks and the BDT Y

4 B. Vogt and Z. Shipton Enormous volumes of pseudotachylites on Barra, Outer Hebrides Fault Rocks and the BDT Y

5 I. Korneva et al.Deformation mechanisms and petrophysical properties of fault rocks within slope-to-basin carbonates

(Gargano Promontory, southern Italy)Fault Rocks and the BDT

6 K. Farrell et al. Estimating strain from CPO in ductile shear zones: the Uludağ Massif, NW Turkey. Fault Rocks and the BDT Y

7 A. Minor et al. Mechanical Twinning and Microstructures in Experimentally Stressed Quartzite Fault Rocks and the BDT Y

8A. Ayan Misra and S.

MukherjeeReview on spheroidal weathering and associated fractures Fractures and Fluid Flow

9 V. Dimmen et al. Structural controls on fluid flow and differential cementation in carbonate rocks Fractures and Fluid Flow Y

10 L. Millar et al. Faults in dirt: a comparison of deformation bands in sand and sandstone. Fractures and Fluid Flow Y

11 L. Smeraglia et al. Fault zone evolution and fluid circulation within active extensional faults in carbonate rocks Fractures and Fluid Flow Y

12 M. Stillings et al.Investigating the dynamic response of a Granitoid rock mass to reservoir draining at Grimsel Test Site,

Switzerland, as an analogue for Glacial RetreatFractures and Fluid Flow Y

13 K. Nærland et al. Topology of small-scale fault damage zones Fractures and Fluid Flow Y

14 R. Rizzo et al. Get the ‘Maximum’ out of it: Maximum Likelihood Estimators for Fracture Attributes Fractures and Fluid Flow Y

15 H. Watkins et al. Discrete Fracture Network (DFN) modelling of a folded tight sandstone reservoir analogue Fractures and Fluid Flow

16 C. Bond et al.The Structural Geology of the Bongwana Natural CO2 Release: an analogue for fracture controlled CO2

migration.Fractures and Fluid Flow

17 A. Chadderton et al. A high temperature experimental insight into permeability evolution in silicic volcanic systems Fractures and Fluid Flow Y

18 C. Bond et al. Utilizing Drones, Virtual Outcrop and Digital Data Analysis to Input into Fracture Models Fractures and Fluid Flow

19 O. Duffy et al. The Topology of Evolving Single Phase and Multiphase Rift Fault Networks Fractures and Fluid Flow

20G. Eggertsson and Y.

LavalléePermeability of geothermal reservoir rock near the Krafla magma Fractures and Fluid Flow Y

21 M. Bazargan et al.Multi Physics Modeling Of Hydraulic Fracturing and Fluid Transfer in Fractured Porous Medium to

Monitoring Enhanced Oil Recovery and Engineering Geothermal SystemFractures and Fluid Flow

22 N. Farrell et al. Effects of Porosity on Geomechanical Risk Fractures and Fluid Flow

23 S. Sosio de Rosa et al. Predicting fault permeability at depth: data pooling from multiple field sites Fractures and Fluid Flow Y

24 T. Mitchell The influence of initial damage on microcrack healing at hydrothermal conditions Fractures and Fluid Flow

25 P. Wilson et al.Fracture analysis of deformation structures associated with the Trachyte Mesa intrusion, Henry

Mountains, Utah: implications for reservoir connectivity and fluid flow around sill intrusionsFractures and Fluid Flow

26 T. Kawanzaruwa et al. Sill Geometry and Distribution in Contractional Settings: the San Rafael Sub-Volcanic Field, Utah, USA Fractures and Fluid Flow Y

27 M. Webb et al.The age and character of magmatism in the Netoni Intrusive Complex, Bird’s Head Peninsula, West Papua,

Indonesia.Geodesy and Structural Geology Y

28 T. Stephens et al. Sill emplacement controlled by stress state rather than host layering Geodesy and Structural Geology Y

29 M. Hoggett and T. Reston An explanation of the sill-forced fold amplitude discrepancy. Geodesy and Structural Geology Y

30 A. Cawood et al. A workflow for the structural analysis of virtual outcrop models Geodesy and Structural Geology Y

31 J. Alcalde et al. Two Hundred and Fifty Six Shades of Grey: Impact of seismic image quality on interpretation uncertainty Geodesy and Structural Geology

32 S. B. Willan Workflows and techniques for building a 3D model in Move: a case study from North Arran Geodesy and Structural Geology

33 Y. Totake et al. Uncertainty in seismic depth conversion and structural validation Geodesy and Structural Geology Y

34 A. Jihad et al.Seismic characterization of the root zones of km long blow-out pipes using time lapse surveys: examples

from the Loyal field (West Shetland, North Sea)Geodesy and Structural Geology Y

35 L. Pérez-Díaz and J. Adam Dynamic growth and linkage of extensional faults in detached half-grabens Geodesy and Structural Geology Y

36 R. Butler et al.Interpreting deformation structures formed beneath submarine gravity flows– a kinematic boundary layer

approach. Geodesy and Structural Geology

37 S. Mukherjee Review on Symmetric Structures in Ductile Shear Zones Geodesy and Structural Geology

38 T. Cain et al. Investigating fault zone development and architecture in mixed carbonate and clastic sequences. Geodesy and Structural Geology Y

39 K. Papapavlou et al.Titanite petrochronology of ore-controlling shear zones: Insights from the Sudbury mining camp (Sudbury,

ON)Geodesy and Structural Geology Y

40 E. Papaleo et al. What is the structure of the North Anatolian Fault below the Moho?Palaeoseismology & Earthquake

GeologyY

41 E. Kent et al.Geomorphic and geological constraints on the active normal faulting of the Gediz (Alaşehir) Graben,

Western Turkey.

Palaeoseismology & Earthquake

Geology

42 R. Normand et al. Last interglacial marine terraces reveal extreme surface uplift rates in the Iranian MakranPalaeoseismology & Earthquake

GeologyY

43 I. Tsodoulos et al.Palaeoseismological history of the Gyrtoni Fault (Thessaly, Central Greece). Preliminary results and

problems.


Geology

44 T. Snell et al.The Impact of Fault Zone Architecture in Modelling the Fluid Overpressure Driven Faulting and Seismicity

of the Colfiorito Seismic Sequence


GeologyY

45 Z. Mildon et al.Using fault orientation to study the links between slip at depth and the surface for the 1997 Colfiorito

earthquakes.


GeologyY

46 G. Wang et al. The Cenzonic tectonic evolution and genetic mechanism of Liaodong Bay Depression, East China Regional Tectonics Y

47 A. Lee et al. How does partial melt effect the seismic properties of orogens? Regional Tectonics Y

48 B. Andrews The Stuctural Evolution of Panticosa, Spanish Pyrenees. Regional Tectonics Y

49 D. McCarthy et al. Internal Thrust Sheet Deformation in the Sevier FTB, insights from AMS Regional Tectonics

50 E. Scott et al. Plate controls on the location of arc volcanoes Regional Tectonics Y

51 C. Goddard et al. Earthquakes, elevations and the construction of continental plateaux Regional Tectonics Y

52 B. Jost et al. Deformation and metamorphism of Australian basement rocks in the Bird’s Head, West Papua, Indonesia Regional Tectonics Y

53 A. Obaid and M. Allen Landscape maturity and fold growth timing in the Kirkuk Embayment, northern Iraq Regional Tectonics Y

54 Amy ElsonA structural interpretation of the Genestosa strike-slip fault zone, Cantabria, Spain: Evidence for influence

of a pre-thrust template on thrust sheet development?Regional Tectonics Y

55 G. Henstra et al.Evolution of a major segmented normal fault during multiphase rifting: the origin of plan-view zigzag

geometryRift and Passive Margins

56 D. Astratti et al. Geometry and kinematics of normal faults in a salt-related minibasin, Santos Basin, offshore Brazil Rift and Passive Margins Y

57 T. Dodd et al. The Falkland Plateau; a rotated slice of the Cape Fold & Thrust Belt Rift and Passive Margins

58 J. NorcliffeUsing structural reconstructions to constrain volcanic passive margin evolution; a case study from the

Orange Basin, offshore SW AfricaRift and Passive Margins Y

59 M. Siegburg Tectono-magmatic interaction at the Boset volcanic complex in the Main Ethiopian Rift Rift and Passive Margins Y

60 M. Marvik et al.Eocene evolution of fault populations in the northern Sørvestnaget Basin related to North Atlantic break-

upRift and Passive Margins Y

61 M. Hodge et al. Stress and displacement of overlapping active normal fault segments Rift and Passive Margins Y

62 M. Ordemann et al.Structure and Cretaceous evolution of the multiphase East Røst Fault Zone, Lofoten Margin, Northern

NorwayRift and Passive Margins Y

63S. Dasgupta and S.

MukherjeeReview on Tectonics of Barmer rift Basin, Rajasthan, India Rift and Passive Margins


1

Oral Presentation Abstracts

(In order of talks)


2

Connectivity of polymodal fault patterns

D. Healy

1, R. Rizzo

1, and P. Jupp

2

1School of Geosciences, University of Aberdeen, Aberdeen AB24 3UE UK.

[email protected] 2School of Mathematics & Statistics, University of St. Andrews, St Andrews KY16 9SS

UK.

Conjugate, or bimodal, fault patterns dominate the geological literature on shear failure.

Based on Anderson’s (1905) application of the Mohr-Coulomb failure criterion, these

patterns have been interpreted from all tectonic regimes, including normal, strike-slip and

thrust (reverse) faulting. However, a fundamental limitation of the Mohr-Coulomb failure

criterion – and others that assume faults form parallel to the intermediate principal stress –

is that only plane strain can result from slip on the conjugate faults. However, deformation

in the Earth is widely accepted as being three-dimensional, with truly triaxial stresses and

strains. Polymodal faulting, with three or more sets of faults forming and slipping

simultaneously, can generate three-dimensional strains from truly triaxial stresses.

Laboratory experiments and outcrop studies have verified the occurrence of the polymodal

fault patterns in nature.

The connectivity of polymodal fault networks differs significantly from conjugate fault

networks, and this presents an opportunity to improve our understanding of fluid flow in

fractured rock. Polymodal fault networks have, in general, more connected nodes in 2D

and more branch lines in 3D than comparable conjugate (bimodal) patterns. The

anisotropy of permeability is therefore expected to be very different in rocks with

polymodal fault patterns in comparison to conjugate fault patterns, and this has

implications for the development of hydrocarbon reservoirs, the genesis of ore deposits

and the management of aquifers. In this contribution, we briefly assess the published

evidence and models for polymodal faulting before presenting a novel kinematic model

for general triaxial strain in the brittle field. The geometry of branch lines of polymodal

fault systems is then explored with reference to bulk permeability.


3

Importance of bed-parallel fractures in flexural slip folds at the

Grasberg-Ertsberg mining district, Papua, Indonesia.

J. Ellis*

1, C. Seiler

1 and E.Macaulay

1

1Midland Valley Exploration, 2 West Regent Street, Glasgow, G2 1RW

*[email protected]

The identification and modelling of fracture systems is key in the design and development

of block caves. Detailed analysis of the structural geometries and geological history of the

Grasberg-Ertsberg district in Papua, Indonesia, was completed by Midland Valley during

2014 and 2015, with the aim of creating a geological Discrete Fracture Network (DFN)

within a 2.1 km3 GeoCelluar Volume. Results of the geologcial approach to fracture

modelling show that beddding-parallel fractures are important.

The Grasberg-Ertsberg district is located in the Central Ranges of Papua, an ~WNW-ESE

trending fold-and-thrust belt that is the result of collision between the Australian plate and

a Mesozoic island arc terrane. The district comprises a sequence of shallow water

limestone and sandstone deposits that were deformed into a series of WNW-ESE trending

folds and reverse faults starting in the Late Miocene. This period of deformation was

followed by the intrusion of the minersalised Ertsberg and Grasberg igneous bodies (~3.2-

2.7 Ma), which were cut by later NE-SW trending faults.

To account for lithological heterogeneity in the block cave, the GeoCelluar Volume was

divided into three primary geotechnical domains: country rock (limestone), skarn and

intrusion. The country rock domain represents the southern limb of a tight chevron fold,

with abundant evidence for bedding-parallel flexural slip folding. Fracture measurements

recorded within this domain were tightly clustered along tunnels and were restricted to a

small portion of the full domain. A geological approach to fracture modelling was

therefore applied as a statistical extrapolation of data would carry high risk.

By combining fracture sets predicted from attributes captured during geological modelling

and restoration of folding and faulting, ~94% of fractures within measured statistical

populations can be accounted for. Of these, bedding-parallel fractures account for ~43%

and are therefore a significant proportion of observed fractures. The importance of

bedding-parallel fractures are discussed, as the significance of these fractures is currently

not recognised in published theoretical models.

Acknowledgements: The authors would like to thank Sugeng Widodo and Richard

Hudson of Freeport McMoRan who provided us with data used in the structural modelling

project.


4

A new model of bed-scale fracture development during basin burial

Tetsuzo Fukunari1,2

and Agust Gudmundsson1

1Department of Earth Sciences, Royal Holloway University of London, Egham, Surrey

TW20 0EX, UK. [email protected] 2Japan Oil, Gas and Metals National Corporation (JOGMEC), Toranomon Twin Building,

2-10-1 Tranomon, Minato-ku, Tokyo 105-0001, JAPN

Fracture networks have significant impact on, and sometimes likely control, permeability

and fluid transport in subsurface reservoirs. For understanding the development of such

fracture networks in relation to geological history, it is of fundamental importance to

assess the fracture characterisics such as fracture displacement mode (I, II and III),

geometry, frequency, as well as fracture size-distribution and orientation.

We present the results of detailed field studies of networkds of bed-scale orthogonal

fractures in alternating sand-shale layers in the South Wales coalfield, forming a part of a

foreland basin associated with the north-northeastward progression of the Variscan

Orogen. Both map-scale and outcrop-scale folds trending ESE-WNW are common in the

study area. Relative age relationships between the folds and the bed-scale fractures were

determined based on their geometrical features complemented by numerical modelling.

The results suggest fracture formation predates or coincides with that of folding. The

timing of fold formation in this area is constrained by field observations which suggest

that folding occurred at the later stage of basin burial and partly induced by

compressional stress associated with the Variscan Orogen.

Based on the above field results, we propose a new model of fracture formation in

mechanical layers in relation with burial history of a foreland basin. Many models on

fracture-network formation focus on horizontal external stresses in association with

formation of, or opening up of existing, fractures. By contrast, in the present model the

focus is on external vertical stress generating layer-parallel stresses whose magnitudes

depend on the variation in mechanical properties among the layers (Figure 1). Analytical

results suggest that increase in the vertical stress in mechanical layers during their burial

in the basin may account for mode I (extension) fracture formation in relatively stiff layers

during sedimentation, provided the volume of soft layers exceeds that of stiff layers.

Figure 1

mailto:[email protected]


5

Void geometry as a control on rock strength anisotropy

A. Bubeck

1, 2, R.J. Walker

2, D. Healy

3, M. Dobbs

4 and D.A. Holwell

2

1 Department of Geology, University of Leicester, Leicester, UK

2 School of Earth and Ocean Sciences, Cardiff University, Cardiff, UK

3 School of Geosciences, King’s College, University of Aberdeen, Aberdeen, UK

4 Rock Mechanics and Physics Laboratory, British Geological Survey, Keyworth, Nottingham, UK

Studies of material strength across material sciences, biomechanics, and geology, show

that there is a strong link between porosity and strength in both natural and manufactured

porous materials: an increase in porosity or pore size is typically associated with a

decrease in brittle strength and fracture toughness. Most rock strength studies involve

materials with assumed isotropic porosity, or anisotropic foliated materials. Here we

consider the control of anisotropic voids on rock strength, using 2D elastic stress field

modelling, and laboratory uniaxial compressive strength (UCS) measurements of basaltic

lava samples. Voids were imaged in 3D using high resolution X-ray computed

tomography (CT). CT imaging highlights the presence of flattened gas bubbles in the base

of the lava, that have aspect ratios of 0.1-0.4. Numerical models for flat ellipsoidal voids,

using an aspect ratio of 0.3, show that compression applied to the minimum curvature

results in relatively broad amplification of stress, compared to compression applied to the

maximum curvature. UCS results provide support for this; samples that contain flattened

voids show their strength is dependent on the compression direction relative to the void

short axis. Samples are significantly weaker with the compression applied along the short

axis (i.e. across the minimum curvature) compared to compression applied across the

maximum curvature, which implies that certain void shapes – in relation to the orientation

of in situ stress – may be relatively stable in the upper crust, whereas others are inherently

weaker. Constraining pore shape is therefore a critical step in characterising the strength

and elastic properties of porous materials. This study has significant and broad

implications across the geosciences, including studies related to fluid flow and

mineralization, volcanotectonic monitoring, and the deep biosphere.

Figure 1. CT scans for (a) the top of a lava and (b) the lava core where samples show roughly equant

vesicles, with no preferred shape orientation. (c) Samples from the lava base sample show flattened vesicles

that are aligned in the horizontal plane.


6

The influence of gouge thickness and grain size on permeability in

macro-fractured basalt G. Wang

1,2, T. Mitchell

2, P. Meredith

2, and Z. Wu

1

1School of Geosciences, China University of Petrolem, Qingdao, China.

[email protected] 2Department of Earth Sciences, University College London, London, UK.

Fractures are ubiquitous on all scales in crustal rocks and are commonly filled with detrital

material, such as the comminuted gouge observed in many shear fractures. Fracture

networks in crystalline rocks allow both the storage and transport of geofluids, and so the

investigation of fracture-fills and how they influence fracture transport properties is

important in understanding various many key problems in geosciences. Here, we

conducted several steady-state flow permeability measurements on a 38mm diameter and

length, single-macro-fractured sample of Seljadur basalt, an intrusive basalt from SW

Iceland with no visible cracks and exceptionally low initial matrix permeability.

Measurements were made under a range of different fracture fills and pressures: (1)

Baseline measurements on unfilled macro-fractures at effective pressures up to 60 MPa.

(2) Fracture filled with a 0.6mm thick artificial fault gouge layer prepared from ground

and sieved basalt particles and varying maximum grain sizes of 63, 125, 250, 500μm to

explore the influence of grain size of gouge; (3) to investigate the influence of gouge

thickness, measurements on the same sample with 0.2- 2mm thick gouge layers with

maximum grain sizes of 63 and 250μm were done, respectively. In order to explore any

compaction processes, both the change in thickness and grain size distribution pre and

post-test were also measured.

The results show that the presence of a fine grain sized (63μm here) gouge layer in the

fracture decreases its permeability by several orders of magnitude relative to unfilled

fractures and minimal change with increasing effective pressure. While that filled with

coarse sized gouge (125-500μm here) has very similar permeability, and the gouges

decrease its permeability under lower effective pressure, while increase its permeability

instead under higher effective pressure (above 45MPa here). Generally with the increase

of the thickness of gouge, the permeability of gouge will also increase, but permeability of

fractured filled with fine sized gouge has some variations. As to the thickness reduction,

but bigger of the grain size or the thicker the gouge layer, the bigger of the thickness

reduction. And the grain size distribution of the gouges barely change during the test as

their grain sizes are smalller or equal to 125μm, while it will change a lot as their grain

size become bigger.

Overall, filled with gouge, especially fine sized one and under lower effective pressure,

the permeability of fracture will decrease dramatically, but as the gouge grain size up to

some points(108μm here), the gouge layer will prevent the closure of the fracture under

higher effective and the grain size make no difference even it become larger. Gerneall, the

thicker of the gouge layer, the bigger of the permebaility of fracture filled with gouge, but

there are some variations for fine sized gouge. The reduction mechanism of the fracture

permeability is closely related to the porosity changes of the gouge packs due to the grain

reshuffling, and the bigger of the grain size and the thicker of gouge pack, the huger of the

porosity, for bigger grain size gouge, grain crushing is also an important factor influence

porosity reduction.


7

The architecture and frictional properties of faults in shale

Rosanne Murray

1, Nicola De Paola

1, Mark Stillings

1, Jonathan Imber

1, Robert E.

Holdsworth1

1Rock Mechanics Laboratory, Earth Sciences Department, Durham University, South

Road, Durham, DH1 3LE, UK.

The geometry of brittle fault zones and associated fracture patterns in shale rocks, as well

as their frictional properties at reservoir conditions, are still poorly understood.

Nevertheless, these factors may control the very low recovery factors (25% for gas and

5% for oil) obtained during fracking operations.

Extensional brittle fault zones (displacement ≤ 3 m) cut exhumed oil mature black shales

in the Cleveland Basin (UK). Fault cores up to 50 cm wide accommodated most of the

displacement, and are defined by a stair-step geometry. Cores typically show a poorly

developed damage zone, and a sharp contact with the protolith rocks. Their internal

architecture is characterised by four distinct fault rock domains: foliated gouges; breccias;

hydraulic breccias; and a slip zone up to 20 mm thick, composed of a fine-grained black

gouge.

Velocity-step and slide-hold-slide experiments at sub-seismic slip rates (microns/s) were

performed in a rotary shear apparatus under dry, water and brine-saturated conditions, for

displacements up to 46cm. Both the protolith shale and the slip zone gouge display shear

localization, velocity strengthening behaviour and negative healing rates. Experiments at

seismic slip rates (1.3 m/s), performed on the same materials under dry conditions, show

that after initial friction values of 0.5-0.55, friction decreases to steady-state values of 0.1-

0.15 within 10 mm of slip. Contrastingly, water/brine saturated gouge mixtures, exhibit

instantaneous low steady-state sliding friction of 0.1.

Field observations show that brittle fracturing and cataclastic flow are the dominant

deformation mechanisms in the fault core, where slip localization may lead to the

development of a thin slip zone composed of fine-grained gouges. The velocity-

strengthening behaviour and negative healing rates observed during laboratory

experiments, suggest that slow, stable sliding faulting should take place within the

protolith rocks and slip zone gouges. This behaviour will cause slow fault/fracture

propagation, affecting the rate at which new fracture areas are created. During slipping

events, fluid circulation may be very effective along the fault zone at dilational jogs –

where oil and gas production should be facilitated by the creation of large fracture areas –

and rather restricted in the adjacent areas of the protolith, due to the lack of a well-

developed damage zone and the low permeability of the matrix and slip zone gouge.

Finally, experiments performed at seismic slip rates show that seismic ruptures may still

be able to propagate in a very efficient way within the slip zone of fluid-saturated shale

faults, due to the attainment of instantaneous weakening.


8

Cooling-induced cracking in thermally stressed volcanic rocks

John Browning

1&2, Philip Meredith

1, Agust Gudmundsson

2

1 Department of Earth Sciences, University College London, London WC1E 6BT

[email protected] 2 Department of Earth Sciences, Royal Holloway University of London, Egham TW20

0EX, United Kingdom

Several hypotheses have been proposed regarding the role of thermo-mechanical

contraction in producing cracks and joints during cooling of volcanic rocks. Nevertheless,

most studies of thermally-induced cracking to date have focused on the generation of

cracks formed during heating and thermal expansion. In this latter case, the cracks are

formed under an overall compressional regime. By contrast, cooling cracks are formed

under an overall tensile regime. Therefore, both the nature and mechanism of crack

formation during cooling are hypothesised to be different from those for crack formation

during heating. Furthermore, it remains unclear whether cooling simply reactivates pre-

existing cracks, induces the growth of new cracks, or both.

We present results from experiments based on a new method for testing ideas on cooling-

induced cracking. Cored samples of volcanic rock (basaltic to dacitic in composition) were

heated at varying rates to different maximum temperatures inside a tube furnace. In the

highest temperature experiments samples of both rocks were raised to the softening

temperature appropriate to their composition, determined using thermal mechanical

analysis, forcing melt interaction and crack annealing. We present in-situ acoustic

emission data, which were recorded throughout each heating and cooling cycle. It is found

consistently that the rate of acoustic emission is much higher during cooling than during

heating. In addition, acoustic emission events produced during cooling tend to be

significantly higher in energy than those produced during heating. We therefore suggest

that cracks formed during cooling are significantly larger than those formed during

heating. Seismic velocity comparisons and crack morphology analysis of our cyclically

heated samples provide further evidence of contrasting fracture morphologies. These new

data are important for assessing the contribution of cooling-induced damage within

volcanic structures and layers such as sills and lava flows. Our observations may also help

to constrain evolving ideas regarding the formation of columnar joints.


9

Fault interactions above a deep-seated crustal lineament – The

multiphase evolution of the Farsund Basin

T. B. Phillips

1, C. A-L Jackson

1, R. E. Bell

1, and O. B. Duffy

2

1 Basins Research Group (BRG), Department of Earth Science and Engineering, Imperial

College, South Kensington Campus, Prince Consort Road, London, SW7 2BP, UK

,. [email protected] 2 Bureau of Economic Geology, University of Texas, Austin

Non-colinear fault populations may form in rift basins subject to multiple phases of non

coaxial extension. Such populations display a wider array of fault interactions than

typically observed in single-phase systems, producing more complex rift geometries.

Understanding the growth of and interactions between these fault systems is fundamental

to understanding the evolution and physiography of multiphase rift basins.

This study uses borehole-constrained 2D and 3D seismic reflection data to constrain the

structural style and evolution of the Farsund Basin, offshore southern Norway. The basin

is situated above the westernmost termination of an E-trending lower crustal lineament,

the Sorgenfrei-Tornquist Zone, which may have controlled the E-W orientation and

evolution of the overlying basin. Perpendicular to this, a regional N-S-striking fault

system partitions the basin into a series of terraces. Using isopachs and quantitative fault

analysis techniques, including throw-distance (T-x) and throw-depth (T-z) plots, we

unravel the evolution of the Farsund Basin, with particular focus on how the two fault

populations interact during multiphase rifting.

By examining the interactions between non-colinear fault populations through time, we

constrain the evolutionary history of the Farsund Basin. We find that the N-S fault

population was initially active prior to the Triassic. Following a period of quiescence in

the Jurassic, these faults were cross-cut by major E-W striking faults, forming in response

to reactivation of the underlying crustal lineament. We observe both cross-cutting and

abutting intersections between the two fault populations, in addition to isolated faults. A

number of N-S faults were reactivated as hanging wall release faults during the formation

of the E-W faults. In addition some of the N-S faults, acted as transfers between the E-W

structures.

In this study, we document interactions between two perpendicular fault systems and show

how this can control the evolution and physiography of a multiphase rift basin.

Furthermore, we offer insights into how deep-seated crustal lineaments are expressed

within rift systems.


10

Deformation of a Passive Margin, Southern Falklands

D. McCarthy

1, T. Dodd

1, and P. Richards

1

1British Geological Survey, Murchison House, Edinburgh, UK.

[email protected]

The eastern Falkland Plateau represents a passive margin with a complex history. The

Falkland Islands rifted from the rest of Gondwana by Late Triassic (190 Ma) accompanied

with extensive volcanism. Initial displacement was accomodated by oblique extension of

South America and clockwise rotation of the Falklands, which completed by 165 Ma. As

rotation completed, the Falkland plateau was stretched synchronous with the opening of

the Weddell Sea and oceanic crust formation by the Late Jurassic, with continued

volcanism accounting for the widespread Tobifera Formation. The opening of the South

Atlantic occurred at 130 Ma, accomodated by oblique extension. The mid to Upper

Cretaceous was relatively quiet tectonically with deposition on a passive margin not being

interupted until the Cenozoic.

Subduction beneath the South American plate along the Magallanes –Fagnano Fault

becomes dominantly strike slip along the North Scotia Ridge, whereby the Burdwood

Bank, a continental block, is thrust over the southern margin of the Falkland Plateau. This

resulted in the downwarping of the Cretaceous shelf and development of normal faults that

displace the top basement and Miocene sediments. The uplift of the Burdwood Bank and

adjacent downwarping resulted in the development of a fold and thrust belt and foreland

basin, the South Falkland Basin. The South Falkland Basin has experienced multiple

phases of deformation and as a result displays a number of dominant fault sets. The

northern part of the basin is dominantly comprised of N-NW normal faults, whilst the

southern part is mainly characterised by an array of E-W of normal, strike-slip, and

compressional faults. The E-W structures are associated with Tertiary transpression,

which overprinted the NNW Mesozoic normal faults.

This study draws on modern 2d and 3d seismic reflection data as well as recent

exploratory well data to provide new insights into regional stratigraphy, the interplay

between structure and sedimentation as well as the polyphase deformation of this complex

passive margin.


11

Kinematic and paleobathymetric evolution of the South Atlantic

L. Pérez-Díaz

1 and G. Eagles

2

1COMPASS Consortium, Department of Earth Sciences, Royal Holloway University of

London, Egham, UK. [email protected] 2Alfred Wegener Institute, Helmholtz Centre for Polar und Marine Research,

Bremerhaven, Germany.

The opening of the South Atlantic Ocean is one of the most extensively researched

problems in plate kinematics. In recent years focus has shifted to the early stages of

continental separation. General agreement exists about ocean opening being the result of

the diachronous separation of two major plates, having involved a certain degree of

intracontinental deformation. However, in order to achieve their best fits, most modern

models assign most of this intracontinental deformation to narrow mobile belts between

large, independently moving plate-like continental blocks, even though timings and

motions along their boundaries are not well known. Aiming to step away from the very

large uncertainty introduced by this approach, here we present a model of oceanic growth

based on seafloor spreading data (fracture zone traces and magnetic anomaly

identifications) as a context within which to interpret intracontinental tectonic motions.

Our model results are illustrated by an animated tectonic reconstruction. Spreading started

at 138 Ma, with movement along intracontinental accommodation zones leading to the

assembly of South America by 123 Ma and Africa by 106 Ma. Our model also provides an

explanation for the inception and evolution of the Malvinas plate and its connection with

the formation of a LIP south of the Falkland-Agulhas Fracture Zone. Finally, we challenge

the view of narrow deformation belts as the sole sites of stress accommodation and discuss

the implications of our model in terms of the distribution of intracontinental strain.

However, paleobathymetry (depth variations through time) also needs to be considered for

a fuller understanding of the ocean’s evolution and development of its petroleum systems.

At first order, this is controlled by plate tectonics, which determines changes in the

geographical location of the lithosphere, along with thermal subsidence, which controls

changes in its vertical level. Thermal subsidence is modelled by applying plate-cooling

theory to a high-resolution seafloor age grid derived from the plate kinematic model.

Then, this thermal surface is refined to account for other factors that affect bathymetry at

smaller scales or amplitudes, both within the ocean and the continent-ocean transition

zones. The results are a series of paleobathymetric reconstructions of the South Atlantic,

which provide a fuller picture of its evolution from Cretaceous times to present.


12

Deepwater fold-thrust belts in the Orange Basin; a balanced review.

T. J. S. Dalton

1, D. A. Paton

2 and D. T. Needham

1,2

1School of Earth and Environment, University of Leeds, West Yorkshire, UK.

[email protected] 2Needham Geoscience Ltd., Ilkley, West Yorkshire, UK

Shale detached deepwater fold and thrust belts (DWFTBs) exist on many of the world’s

passive margins, they grow through a combined process of gravity spreading and gravity

gliding. The behaviour and timing of these systems are attributed to a range of factors

such as inherited structural geometry, lithology and detachment thickness. Previous

research has tended to concentrate on isolated systems or single 2D seismic lines to

understand their wider 3D complexity. This presentation seeks distil the findings of 3

years of PhD research into multiple DWFTBs extant throughout the Orange Basin

offshore Namibia and South Africa.

Through seismic interpretation and balanced restorations of multiple 2D seismic sections,

using Midland Valley Move software, we are able to build an accurate 3D model of these

systems. This allows us to see how these systems develop and grow over time in 3D, as

well as build an understanding of the larger scale passive margin development. We find

that timing relationships exist between separate DWFTBs across the entire margin which

implies larger plate scale movements.

.


13

The Stratigraphic Record of Pre-breakup Geodynamics: Evidence from

the North Carnarvon Basin, offshore Northwest Australia

M. T. Reeve

*, R. E. Bell, C. A.-L. Jackson, Craig Magee and I. D. Bastow

Basins Research Group (BRG), Department of Earth Science and Engineering, Royal

School of Mines, Prince Consort Road, Imperial College London, SW7 2BP, UK.

* [email protected]

Our understanding of the geodynamic evolution of divergent continental margins is

primarily derived from the sedimentary record. Although the structural and stratigraphic

evolution of rift basins and passive margins has been widely studied, the processes

governing the transition from continental rifting to oceanic crust formation remain poorly

constrained. In order to assess the factors controlling this transition in extensional style, it

is crucial to evaluate the timing and distribution of uplift and subsidence operating during

the final stages of continental break-up.

The Lower Cretaceous Barrow Group of the North Carnarvon Basin, offshore NW

Australia is a unique example of a major delta deposited in the last stages of continental

rifting, and interpreting this sedimentary archive of uplift, subsidence and erosion can give

unparalleled insight into the processes operating during continental breakup on the

northwest Australian margin. In this study, we employ an integrated geological and

geophysical approach, using a large database of high-quality 2D and 3D reflection seismic

and well data to constrain the structural and stratigraphic evolution of the Barrow Group,

and its implications for break-up.

Our results suggest that: (i) substantial uplift took place along the flanks of the North

Carnarvon Basin during the final stages of rifting; (ii) anomalously rapid tectonic

subsidence occurred during Barrow Group deposition; and (iii) classic models of uniform

extension cannot adequately account for the observed subsidence and uplift patterns. We

conclude by presenting an integrated model of the geodynamic evolution and potential

rifting mechanisms operating in the North Carnarvon Basin during the Early Cretaceous,

which may also be applicable to understanding the breakup mechanisms of other passive

margins worldwide.


14

Untangling the faults: Using 3D data at the Galicia margin to determine

faulting history

D.J.F. Cresswell

1, G, Lymer

1, T.J. Reston

1, C.T.E Stevenson

1, J.M. Bull

2, D.S.Sawyer

3 &

Galicia 3D Working Group4.

1Geosystems Research Group, School of Geography, Earth and Environmental Science,

University of Birmingham, UK: [email protected]. 2Ocean and Earth Science, National Oceanography Centre, University of Southampton,

Waterfront Campus, European Way Southampton, SO14 3ZH, UK. 3Department of Earth Science, MS-126 Rice University, 6100 Main Street, Houston, TX

77005, USA: 4Lamont Doherty Earth Observatory, Columbia University, New York, USA & Institute of

Marine Science, Barcelona, Spain in addition to the named institutions.

The western Iberian margin, due to its limited post-rift sedimentary cover and limited

volcanic activity, has provided significant data to aid the formulation of 2D models of

continental extension and breakup. Structural elements characteristic of such highly

extended post-breakup continental margins include: rotated faults blocks and associated

syn-kinematic sedimentary wedges, low angle detachment faults, exhumed and

serpentinised continental mantle and allochthonous blocks. The mechanisms postulated to

account for these characteristic structures include: depth-dependent thinning, sequential

ocean-ward faulting and polyphase faulting. These mechanisms have resulted in a range

of, often complex, evolutionary models that are 2D representations of an inherently three

dimensional process.

A ~680 km2 3D seismic survey (the largest academic one of its kind) consisting of 800

inline and 5000 crosslines has provided high resolution images of the edge of the Iberian

continental crust.

Detailed 3D interpretation of the deformation seen within the rotated fault blocks and their

corresponding syn-kinematic sediments are presented and reveal a complex structural

history. Changes in the style and relative ages of the dominant faulting imaged within the

rotated fault blocks vary along the strike, revealing spatial and temporal variations in the

accommodation of strain. More recent (steeper faults) are seen to dissect large blocks and

cut earlier faulting. Steep antithetic faults seem to suggest structural collapse within

discrete segments of some blocks. Fault linkage and the reactivation of earlier phases of

faulting are essential characteristics of the progressive deformation. Furthermore the

interaction between intra-block faults and a low angle detachment demonstrates the

complex patterns generated by the rifting process. This interaction is investigated using

maps of the detachment fault amplitudes showing the major fault intersections.

Untangling the fault movements both spatially and temporally will enable various breakup

mechanisms to be tested. Such mechanisms are essential in the development of accurate

heat and fluid flow models in the heavily interconnected fault network.



15

Geometry and kinematics of a salt-detached fault system, Santos Basin,

offshore Brazil

A. Ross J. Grant

1,∞,, B. Donatella Astratti1,2

, and C. Christopher A.-L. Jackson1

1Basins Research Group (BRG), Department of Earth Science and Engineering, Imperial

College, Prince Consort Road, London SW7 2BP, UK.

2Schlumberger, P.O. Box 8013, N-4068 Stavanger, Norway

∞Present Address: Centre for Exploration Geoscience, School of Energy, Geoscience,

Infrastructure and Society, Heriot Watt University, Edinburgh EH14 4AS, UK.

Email: [email protected]

Normal faulting above thick salt causes salt to flow and typically results in the

development of structures such as diapirs. However, the exact three-dimensional geometry

and kinematics of supra-salt-detached faults is relatively poorly constrained, especially in

settings where salt movement and extension and protracted and multiphase. This study

uses high-resolution 3D seismic reflection data to to investigate an array of Cenozoic

normal faults developed above a salt wall in the deepwater Santos Basin, offshore Brazil.

We interpret the observed structural style and fault growth history in the context of the

regional halokinetic history of the Santos Basin, before considering the implications of our

observations for the development of crestal fault systems in other salt provinces. The

studied fault array is ~17 km long, trends parallel to and detaches downward onto the

underlying, NNE-trending salt wall. The array consists of 71 closely-spaced segments that

display a left-stepping, en-echelon geometry. Individual segments are up typically 1-1.5

km long, have 40-60 m of throw, and define a 500 m wide crestal graben.

A lack of seismic-scale evidence for fault growth by segment linkage, and the lack of

hard-linkage between such closely spaced (<0.5 km), high aspect ratio, overlapping

segments is striking and has implications for established models of normal fault growth.

Analysis of throw-distance (T-x) and throw-depth (T-z) plots, expansion indices, and

growth strata isopachs suggest the fault array formed in three phases; (i) a Palaeocene-

Early Eocene phase of initiation, rapid growth stage and basal detachment within the salt;

(ii) a subsequent Late-Eocene–Early Oligocene phase during which new faults nucleated,

and old faults were reactivated and rotated on the salt wall flanks; and (iii) a Miocene

phase of fault reactivation and growth. We conclude by discussing the mechanisms

responsible for nucleation, growth and, ultimately, the final geometry of the suprasalt fault

array. We suggest faulting was initially driven by active diapirism with purely dip-slip

movement. Later faulting involved involved oblique-slip slip driven by a combination of

ongoing active diapirism and differential horizontal displacements of flanking minibasins

during basin-scale, thin-skinned extension.



16

Are current models for normal fault array evolution applicable to

natural rifts?

Rebecca E. Bell* and Christopher A-L. Jackson

Basins Research Group (BRG), Department of Earth Science & Engineering, Imperial

College, London, SW7 2BP, UK

*corresponding author email: [email protected]

Conceptual models predicting the geometry and evolution of normal fault arrays are vital

to assess rift physiography, syn-rift sediment dispersal and seismic hazard. Observations

from data-rich rifts and numerical and physical models underpin widely used fault array

models predicting: i) during rift initiation, arrays are defined by multiple, small, isolated

faults; ii) as rifting progresses, strain localises onto fewer larger structures; and iii) with

continued strain, faulting migrates toward the rift axis, resulting in rift narrowing. Some

rifts display these characteristics whereas others do not. Here we present several case

studies, including examples from the northern North Sea, documenting fault migration

patterns that do not fit this ideal. We show that strain migration onto a few, large faults is

common in many rifts but that, rather than localising onto these structures until the

cessation of rifting, strain may ‘sweep’ across the basin. Furthermore, crustal weaknesses

developed in early tectonic events can cause faults during subsequent phases of extension

to grow relatively quickly and accommodate the majority if not all of the rift-related

strain; in these cases, strain migration does not and need not occur. Finally, in salt-

influenced rifts, strain localisation may not occur at all; rather, strain may become

progressively more diffuse due to tilting of the basement and intrastratal salt décollements,

thus leading to superimposition of thin-skinned, gravity-driven and thick-skinned, plate-

driven, basement-involved extension. We conclude that complexities such as the thermal

and rheological properties of the lithosphere, specific regional tectonic boundary

conditions, crustal weaknesses and intrastratal rheology variations, need to be

incorporated into fault array numerical models to more accurately predict the evolution of

rift-scale normal fault arrays. The ability to better model fault array evolution will

improve predictions of tectono-stratigraphic setting and seismic hazard.


17

Igneous sills as a record of horizontal shortening

Richard J Walker

1, D. Healy

2, KA Wright

3, RW England

1 and K.J.W. McCaffrey

4

1 Department of Geology, University of Leicester, Leicester, LE1 7RH, UK

2 School of Geosciences, King’s College, University of Aberdeen, Aberdeen, AB24 3UE,

UK 3 DONG E&P (UK) Ltd, 33 Grosvenor Place, London SW1X 7HY, UK

4 Department of Earth Sciences, Durham University, Durham, DH1 3LE, UK

Igneous sills make a significant contribution to upper crustal magma systems, but the

mechanisms of sill emplacement remain ambiguous. Analogue experiments that simulate

sill emplacement, involve a mechanically layered host, comparable to stratigraphic

layering, but notably this mechanism cannot explain how sills can be kept open to allow

magma transport over large distances: thousands of km in some instances. Here we use a

combination of mechanical modeling, supported by key field examples in the Faroe

Islands and San Rafael Sub-Volcainc Field (Utah), to show that sills are a result of

horizontal shortening rather than host mechanical layering. The two field localities are

well characterized in terms of tectonic setting, but both regions are dominated by

extensional strains. Local sill contacts do activate some host layer interfaces, but

regionally intrusion is at a low angle to layering, broadly parallel to small (<1 m

displacement) thrust faults. Mechanical models show that these geometries are favoured in

the upper crust during mild horizontal compression, and with only a relatively negligible

magmatic pressure (i.e., 10 MPa). Importantly, our model implies that sills can be used as

an indication of regional and local stress state during their emplacement, as is commonly

done from dike geometries, presenting a new and useful tool in plate tectonic studies.


18

Deformation mechanisms of a sheared mafic granulite infiltrated by

melt: an example from the Seiland Igneous Province (N Norway)

G. Degli Alessandrini

1, L. Menegon

1, N. Malaspina

2, A. Dijkstra

1 and M. Anderson

1

1School of Geography, Earth and Environmental Sciences, Plymouth University,

Plymouth, UK.

[email protected] 2 Department of Earth and Environmental Sciences, Milano-Bicocca University, Piazza

della Scienza 4, 20126 Mi, Italy

This study investigates the deformation mechanisms of a metagabbroic dyke experiencing

syn-kinematic melt-rock interaction in a continental lower-crustal shear zone of the

Seiland Igneous Province (northern Norway). Solid state shearing occurred at T ≈750-

820ᵒC, P ≈0.75-0.95 GPa and was coeval with melt infiltration from dehydration melting

of adjacent metasediments, as is evident from thin leucosome veinlets within the dykes.

Microstructurally, the mylonite consists of cpx [Ca0.47,Mg0.35,Fe0.18]Si2O3 + opx

[Ca0.1,Mg0.5,Fe0.4]Si2O3 + pl (An77Ab22Or1) porphyroclasts with localized grt and ilm

coronas, embedded in a fine grained matrix of cpx + opx + pl + qtz + ilm ± k-fs.

Porphyroclasts range in size (diameter) between 25 to 650 µm, whereas the fine grain

matrix is consistently below 10 µm (average 4-7 µm). Porphyroclasts show varying

degrees of elongation, with the opx reaching aspect ratios of 1:16 and the cpx reaching

rare maxima of 1:7. Cpx and pl porphyroclasts are micro-fractured and micro-boudinaged

with fine-grained material infill. Texturally, opx porphyroclasts display a marked

crystallographic preferred orientation (CPO) and activity of the {100}<001> and

{100}<010> slip systems, whereas cpx and pl porphyroclasts are randomly oriented. All

porphyroclasts have strong internal misorientations (undulatory and sweeping extinction)

and lack recovery features (subgrains). The fine-grained polyphase matrix wrapping the

porphyroclasts displays no-to-weak CPO, with the exception of opx that shows a {100}

poles-to-planes maxima perpendicular to the foliation. Based on the microstructure, we

argue that a large part of the matrix is the product of metamorphic reactions in the

presence of melt. To test for this hypothesis, the interaction between the studied mafic

dyke (using a calculated bulk composition) and an adjacent felsic leucosome was

modelled using Connolly’s Perple_X for P-T conditions ranging between 7-9kbar and

700-1000 °C. Results show that the syn-kinematic mineral assemblage (opx + cpx + pl +

qtz + ilm ± k-fs) can be the product of melt-rock interaction for melt fractions up to 40

wt%. Further constrains using the biotite abundance indicate melt infiltration below 5wt%.

We believe that melt infiltration during shearing has strong implications on the rock’s

rheology, as it promotes weakening by dramatic grain-size reduction through nucleation of

fine-grained material. Interconnected fine grained material deforms by grain size sensitive

creep (GSS) imposing high strain rates and hampering dislocation creep and recovery.

Deformation by GSS creep is supported by the small grain-size (7µm average diameter),

by lack of CPO in the matrix (except for opx, interpreted as a result of oriented grain

growth) and by phase mixing. We ruled out recrystallization as a mechanism to produce

the fine grained pyroxene matrix as there are no evidences of subgrains in the

porphyroclasts.


19

The importance of compaction in considering the movement history of

growth faults

C. Reilly

1 and H. Anderson

1

1

Midland Valley Exploration Ltd., West Regent St., Glasgow, UK.

[email protected]

Structural restoration techniques, including backstripping and retro-deformation of

faulting, have long been recognised as important practices in assessing structural evolution

on regional to local scales. However, in many previous studies of temporal fault analysis,

the effect of compaction has been overlooked or downplayed, resulting in calculated

displacement magnitudes which may not accurately represent the true history of fault

movement. Here, structural restorations that incorporate differential across-fault sediment

compaction are used to provide a more accurate constraint on temporal fault activity and

across-fault juxtaposition. Furthermore, using a combination of synthetic and real-world

models, a new, more representative method of measuring backstripped displacements

across growth faults is outlined. These results allow quantitative assessment of fault seal at

key times during the development of a petroleum system; a technique which is we

compared with traditional backstripping methods. Analysis of multiple models and

scenarios also allows the validity of the technique to be investigated.

The principal natural dataset is a seismic section across the Parihaka Fault, located in the

Taranaki Basin, offshore New Zealand. Previous studies have used displacement

backstripping to infer that the fault accommodated normal movement during two periods

of extension, either side of regional tectonic quiescence. Temporal fault analyses have

been repeated using the methods presented in this study and have revealed a period of

previously unidentified reverse movement on the fault. This is indicative of a period of

inversion, which has been observed contemporaneously on other large faults in the

Taranaki Basin and is in agreement with the recognised regional tectonics. The Parihaka

Fault is also used to demonstrate analysis of temporal fault sealing capacity. Restored

cross-sections allow definition of across-fault palaeo-juxtapositions and calculation of

shale gouge ratio values at restored time-steps. This is a workflow rarely employed in fault

displacement and sealing studies.

This work demonstrates that the implications of neglecting across-fault compaction can

result in invalid fault growth histories and temporal sealing capacities; thus necessitating

the use of the presented practices in all studies of temporal displacement and seal on

growth faults.


20

Integration of Outcrop-, Map-, and Regional-Scale Structural Analysis

to More Accurately Measure Tectonic Shortening

in the Santa Maria Basin, California, USA

Yannick Wirtz

1, Richard Behl

1, Nate Onderdonk

1, and Thom Davis

2

1Department of Geological Sciences, California State University, Long Beach, CA, USA.

[email protected] 2Thomas L. Davis Geologist, Geologic Consulting, Ventura, CA, USA.

The Santa Maria basin (SMB), California, USA underwent a complicated tectonic

history from Miocene basin development to the formation of a fold-and-thrust belt by

several phases of north-south shortening. Accurate quantification of structural deformation

in the SMB is essential to unraveling the tectonic history of the California active plate

margin and test models of major block movements and rotations. Namson and Davis

(1990) quantified shortening across the basin by balancing regional-scale cross-sections.

However, constructing a regional-scale balanced cross-section has limited capabilities

to account for the different mechanical behaviors of individual deformed units as this

method assumes structural panels that maintain constant volume in the reconstruction.

The objectives of this study are to assess the quantitative contribution of km-scale and

outcrop-scale structures of the diagenetically distinct siliceous sedimentary rocks of the

Monterey and Sisquoc formations at the southern boundary of the SMB to existing

regional-scale balanced cross-sections and evaluate how integration of structural analysis

at smaller scales affects the assessment of the regional deformation and tectonic history.

The Monterey and Sisquoc formations are well suited for this study because (1) they

were deposited during the Miocene to early Pliocene prior to regional contraction, (2) their

thinly bedded character and diverse rock mechanics produced smaller structures that allow

the quantification of tectonic shortening at km-scale and outcrop-scale, and (3) they are

well exposed. In general, the Sisquoc Formation is composed of highly porous

diatomaceous rocks that compact by regional shortening, whereas the underlying

Monterey Formation is largely composed of more competent opal-CT or quartz phase

diagenetic siliceous rocks that deform by folding, faulting and layer-parallel slip.

Namson and Davis used surface mapping and data from numerous oil field and

exploration wells to create a regional-scale balanced cross-section across the SMB. A 7.7

km segment of their section that includes both Monterey and Sisquoc rocks yields 7.25 %

of total shortening. In this study, quantification of km-scale structures contributes up to an

additional 20% shortening to the regional-scale balanced cross-section giving a total

deformation of 27.25 %. However, quantification of map-scale structures of the Monterey

and Sisquoc formations have also shown that by focusing on structures related to

particular mechanical units, significant differences arise with respect to the amount of

shortening. Structural mapping and restoration of continuous outcrops will document how

much deformation at outcrop-scale will be further additive to the map-scale.


21

Contributions of sub-seismic faults to deformation in the Earth’s crust

C. W. Nixon

1, D.J. Sanderson

2,3, M. W. Putz-Perrier

4, and J. M. Bull

5

1Department of Earth Sciences, University of Bergen, Bergen, Norway.

[email protected] 2Faculty of Engineering and the Environment, University of Southampton, Southampton,

UK 3Reservoir Development, BP, Sunbury-on-Thames, UK

4Egis-Tunnels, Park Nord Annecy, Annecy-le-Vieux, France

5Ocean and Earth Sciences, University of Southampton, Southampton, UK

Fault imaging techniques, such as seismic reflection surveys, are limited in their spatial

extent and resolution. As a result, small faults and fractures (sub-seismic) being missed in

low resolution datasets, which is particularly important when using conventional seismic

reflection surveys since these typically only detect faults down to 10-20m displacement.

In such surveys the majority of fault intensity is not observable and studies often

underestimate extension within basins and reservoirs. This is important as the abundance

of these sub-seismic faults and fractures controls important rock properties, such as

porosity and permeability, affecting predictions of fracture controlled properties within

reservoirs and aquifers.

The significance of extension accommodated by sub-seismic faults and fractures is widely

debated and difficult to accurately quantify. We use a compilation of different fault

datasets (normal and strike-slip faults; low and high strain regions) that provide direct

measurement of extension on structures across a wide range of displacement (0.1-100m

displacement). These provide a complete record of extension on faults across the

resolution cut-off of many seismic reflection datasets (i.e. ~10m displacement). Thus we

focus on comparing the extension on sub-seismic faults (<10m displacement) with

seismically resolvable large faults (10m displacement). This approach vastly improves

on previous studies that rely heavily on the application of general scaling laws to limited

fault size data in order to extrapolate extension up and down scale.

Results highlight new empirical relationships indicating that the total extension on sub-

seismic faults changes as strain increases. In low strain regions sub-seismic faults are of

greater importance, whereas in high strain regions the majority of extension is

accommodated by seismically resolvable faults. This is attributed to strain localization

onto larger structures as a fault population grows, resulting in sub-seismic faults

generating a background strain of ~3% extension. We introduce a potential ‘universal’

relationship that provides a new and alternative method for estimating total extension from

observable extension on seismically resolvable faults. This will improve predictions of

fracture controlled properties within reservoirs as well as reconcile estimates of extension

within basins and reservoirs.


22

Fault interactions and associated damage

D.C.P. Peacock1, C.W. Nixon

1, A. Rotevatn

1 & D.J. Sanderson

2

1 Department of Earth Science, University of Bergen, Allégaten 41, 5007 Bergen, Norway

2 Engineering and the Environment, University of Southampton, Highfield, Southampton,

SO17 1BJ, UK.

The way that faults interact with each other will control fault geometries,

displacements and strains, which in turn affects fluid flow and mineralisation. This is

important as faults rarely occur individually but as networks of numerous faults. The

arrangement of these faults (i.e. the topology) and their development can produce a variety

of different fault interactions, including but not limited to fault splays, abutments, relay

zones and cross-cutting relationships. What are the characteristics of these different

interactions? How do we interpret them? What are their implications for fault behaviour?

To answer these questions, we describe and analyse different fault interactions, focussing

on improving our understanding of their development and the resulting fault damage.

Fault interactions can occur between two or more faults of any orientation or

relative age. They are defined by the geometric and kinematic relationships that form

between the interacting faults (e.g. Fig. 1). For example the faults may or may not be

geometrically coupled, when fault planes share an intersection line (or branch line); and/or

kinematically coupled, where the displacements, stresses and strain of one fault influences

those of the other. Thus fault interactions are analysed in terms of the following: 1)

Geometry and topology – describing the arrangement of the faults and whether the faults

share an intersection line or not. The topology describes the geometric relationships

between the faults and can be linked to connectivity. 2) Kinematics – describing the

displacement distributions of the interacting faults and whether the slip directions are

parallel, perpendicular or oblique to the intersection line, and if the faults have the same or

opposite slip directions. 3) Stress and strain – whether extension or contraction

dominates in the acute bisector between the faults. 4) Chronology – the relative ages of

the faults.

We explore a variety of fault interactions that illustrate the use of this classification

scheme in understanding fault-related structures, discussing the implications for the

analysis of damage zones. We introduce the terms intersection damage zone for structures

created around the intersection line of geometrically coupled faults, and approaching

damage zone for the zone between geometrically uncoupled faults (Fig. 1).

Fig. 1 Schematic of different geometric and

kinematic relationships that might form

between interacting fault planes, with shape

proportional to the along-strike displacement

profiles. Note geometrically coupled faults

share an intersection line and kinematically

coupled faults affect each other’s displacement

profiles.


23

Fault geometry and mechanics within sealing horizons consisting of

carbonate multilayers

C. Giorgetti

1, M. M. Scuderi

1,2, M. R. Barchi

3, and C. Collettini

1,2

1Department of Earth Sciences, Sapienza University, Rome, Italy.

[email protected] 2Istituto Nazionale di Geofisica e Vulcanologia, Rome, Italy

3Department of Physics and Geology, University of Perugia, Perugia, Italy.

Sealing horizons are often sedimentary sequences characterized by alternating clay-rich

weak lithologies and strong lithologies. These mechanical multilayers when involved in

faulting processes develop complex fault geometries, strongly influencing their sealing

maintenance. Here we investigate fault nucleation and evolution along a natural

mechanical multilayer that represents a potential sealing horizon. To do this we integrate

field observations on outcropping faults characterized by different displacement and rock

deformation experiments conducted on lithologies collected in the field. Our study aims at

the understanding of how the mechanical properties of multicompetent layers influence

the overall deformation style and fluid circulation.

Figure 2. Faults nucleation and evolution. a) Faults with an initial staircase trajectory, with θi ranging from

10° to 70°, tend to progressively straighten and widen with accumulating displacement. b) Experimentally-

derived Mohr-Coulomb envelop showing θi = 26° for one of the tested marly horizons. c) Enhanced

permeability during stress drop.

Faults enucleate with a staircase trajectory refracting at competent contrasts (Fig. 1a). The

angles of fault initiation θi in thick calcite-rich layers are concentrated around 21°-37°.

Triaxial compression experiments on marly limestones (Fig. 1b) confirm θi values in the

same range. However, the variabily of θi down to ~10° suggests a possible role of pre-

existing joint surfaces or a possible occurrence of hybrid, transitional from tensile to shear,

fractures in influencing faults geometry. In weak clay-rich layers, θi values concentrate

around 45°-56° with several examples extending up to ~70°. These high θi values are not

explainable considering only the low friction μ of marls, μ ≈ 0.4, suggesting an important

role of the foliation in inducing layer parallel propagation of faults. With increasing

displacement, fault trajectory evolves towards a more straight geometry and overall wider

fault zones, characterized by a strong marly foliation embedding calcareous sigmoidal

fragments (Fig. 1a). We observed that the straightness of the trajectory depends not only

on the amount of displacement, but also on the scale of anisotropy. All the investigated

faults are characterized by calcite mineralizations within cataclastic fault rocks, dilational

jogs and slikenfibers, suggesting that within these sealing horizons fluid flow is mainly

controlled by faulting. This is further supported by the strong increase in permeability

observed only at failure during triaxial deformation experiments (Fig. 1c).



24

Deformation bands in carbonate grainstones (Miocene Globigerina

Limestone Formation, Malta): structure, kinematics, petrophysical

properties and impact on fluid flow

Rotevatn, A.

1, Thorsheim, E.

1*, Fossmark, H.S.

1*, Bastesen, E.

2, Torabi, A.

2

1

Department of Earth Science, University of Bergen, Allégaten 41, 5007 Bergen, Norway 2 Uni Research CIPR, , Allégaten 41, 5007 Bergen, Norway

* now at: Statoil ASA, Sandsliveien 61, 5055 Sandsli, Norway

Corresponding author (email: [email protected])

Deformation bands in porous sandstones have been widely studied for four

decades. Deformation bands in carbonate rocks are comparatively less studied, although

during the last decade, deformation bands in carbonates rocks have been reported in

contributions covering natural as well as laboratory examples. Nevertheless, their

structure, kinematic evolution and petrophysical properties are not as well understood as

their sandstone counterparts. Motivated by this, we investigate deformation bands in

remobilized carbonates of the Miocene Globigerina Limestone Formation in the hanging-

wall of the Maglhlaq Fault in Malta. Three band types are described; pure compaction

bands, solution-dominated compactive shear bands, and cataclastic-dominated compactive

shear bands.

Pure compaction bands (CB) are orientated sub-horizontally, parallel to bedding,

and are only localized within a select few intervals in the studied stratigraphy. The CB are

1-2 mm thick, and are associated with compaction evidenced by a porosity reduction from

~10% in the host rock to ~1% in the bands. Compaction appears to have been

accomplished by grain reorganization and pressure solution at the grain contacts.

Solution-dominated compactive shear bands (SCSB) and cataclastic-dominated

compactive shear bands (CCSB) are both orientated at high angles to bedding and occur

throughout a larger stratigraphic proportion of the studied stratigraphic intervals compared

to the very localized CB. SCSB record compaction (porosity halved compared to host

rock) and shear; the dominant deformation mechanism in SCSB is grain reorganization

and intergranular pressure solution, evident as discrete, wavy, low-amplitude seams within

the SCSB.

CCSB record compaction and shear offsets up to 6 mm; the dominant deformation

mechanism in CCSB is cataclasis, with grain breakdown selectively affecting specific

bioclasts. Survivor grains in the bands are predominantly sphere-shaped foraminifers.

The studied deformation bands are interpreted to have formed sequentially during

a single phase of extensional slip along the Maghlaq Fault. SCSB and CCSB abut against

CB, which indicates CB formed first, due to burial induced loading caused by syn-tectonic

sedimentation in the hanging-wall of the Maghlaq Fault. Subsequently, SCSB and CCSB

appear to have formed more-or-less coevally, though there are some observations that

indicate that CCSB were the last to form. We suggest that the CCSB may represent the

most advanced stage of compactive shear bands, and that SCSB may represent a precursor

stage to CCSB formation.

Deformation bands in carbonate rocks may affect subsurface fluid flow; image-

processing and core-plug analyses showed that permeability is reduced by up to two

orders of magnitude within SCSB and CCSB compared to host rock.


25

Natural seismogenic pumping processes in near surface fractured

basement gneisses

K. McCaffrey

1, R. Holdsworth

1 and D. Oxlade

2

1Department of Earth Sciences, Durham University, Durham, UK. DH1 3LE

[email protected] 2Geospatial Research Limited, Office Suire 7, Harrison House, 1 Hawthorne Terrace,

Durham, UK, DH1 4EL

The fluid transport and storage properties of fractured crystalline rocks are relevant to

understanding water and hydrocarbons resources and potential containment of radioactive

materials and carbon dioxide. Crystalline lithologies have virtually non-existent primary

porosity therefore any porosity and permeability is secondary originating from fractures

and/or surface weathering. Here, we report a study on the kinematics, geometry and

topology of naturally formed fractures in the Lewisian gneisses complex (LGC) of NW

Scotland. The fracture systems show good evdence for near surface seismogenic faulting,

including the local generation of thin psuedotachylytes, reactivation and pulsed fluid

transport that was likely to be epsiodic in nature. The evidence points toward the presence

of short term high flux and long term persistent fluid transport pathways.

We studied exposures within and adjacent to the Canisp shear zone exposed on the coast

near Achmelvich Bay, NW Scotland. At Alltan Na Bradhan, regionally recognised

Neoproterozoic Stoer Group-age fractures associated with rifting are particularly well

developed as hematite-stained faults, with many containing iron-stained breccias,

cataclasites and epidote-mineralised ultra-cataclasites. Clastic material is found locally

within these fractures consisting of fine red mudstone and sandstone of Stoer Gp age. The

Stoer Group-aged faults partly reactivated pre-existing foliation parallel faults that locally

carry pseudotachylytes. These so-called Late Laxfordian structures were extensively

developed in the nearby Canisp shear zone and are themselves a brittle reactivation of

earlier formed ductile shear zone fabrics. The Stoer Group age faults are mainly N-S or

NW-SE trending (3 main sets) and display oblique/down dip normal-sense offsets up to a

metre. 1D fault intensities show power law scaling with typically 10 structures per metre

for 1mm apertures. In 2D, structures are highly connected in both map and section views.

Fault rocks are chaotic breccias with local sediment fills and vuggy quartz-calcite-epidote-

prenhite mineralised voids.

We interpret the Stoer Group age faults to be near-surface rift-related structures that cross

cut and partially reactivate pre-existing faults. Importantly, we suggest that some of the

structures were periodically highly dilational. Seismogenic slip along reactivated foliation-

parallel faults could lead to instantaneous fracture dilation in fracture sets cross-cutting the

foliation at high angles, leading to fracture wall implosion forming chaotic breccias up to

1 m across. The dilation is likely to have sucked in surface water and sedimentary material

from the surface a few tens to hundered of metres above. Elastic rebound triggered partial

collapse of breccia-, sediment- and fluid-filled voids. The collapsed breccia fills could

then have acted as natural props holding open the fractures systems thereby facilitating

longer term fluid flow in otherwise impermeable basement.


26

Breaking it down: mechanical and chemical damage zones. A case study

from the Dombjerg Fault Zone, Wollaston Forland, NE Greenland

Kristensen, T.B.

1, Rotevatn, A.

1, Peacock, D.C.P.

1, Ksienzyk, A.K.

1, Henstra, G.A.

1,

Midtkandal, I.2, Grundvåg, S-A.

3† and Wemmer, K.

4

1Department of Earth Sciences, University of Bergen, Norway.

(Corresponding author: [email protected]) 2 Department of Geosciences, University of Oslo, Norway.

3 Department of Arctic Geology, University Centre in Svalbard, Longyearbyen, Norway.

4 Geowissenschaftliches Zentrum der Georg-August Universität, Germany.

† now at: Department of Geology, University of Tromsø, Norway.

The terminology associated with damage in and around faults is currently lacking clear

definitions that separate between mechanical effects and chemical alteration of the

protolith. Chemical alteration includes mineralisation and cementation related to fluid

flow in the fault zone. By introducing the terms mechanical damage zone and chemical

damage zone, we suggest that the systematic description and classification of fault damage

is improved by separating i) mechanical/structural damage (faults, fractures, veins,

stylolites) from ii) chemical damage (cementation, mineralisation) related to fault-

controlled fluids. Such a classification is helpful to understand and describe the mutual

interaction between deformation and chemical alteration of host rocks, including in

hydrocarbon or other reservoirs.

To demonstrate the proposed damage zone classification and its applicability, we

use an outcropping basin-bounding fault located in Wollaston Forland, NE Greenland. The

fault has c. 3 km throw and separates Caledonian crystalline metamorphic rocks in the

footwall from late Jurassic to early Cretaceous deepwater syn-rift clastics in the hanging-

wall. Pervasive calcite cementation and mineralisation of the basinal clastics define an

undulose chemical damage zone that is 300-500 m wide. The mechanical damage zone

extends c. 500 m into the footwall. Where the mechanical damage zone coincides with the

cemented clastics of the chemical damage zone, it is characterised by faults and calcite

veins, while shear bands and thick disaggregation zones characterise the mechanical

damage outside the chemical damage zone. This suggests that the chemical damage zone

formed early and controlled the spatial and temproal distribution of mechanical damage by

changing the rock mechanical properties.

Chemical damage inflicted by fault-related fluid flow is commonly under-reported

at the expense of mechanical damage; the proposed classification scheme may contribute

to a more holistic approach to fault zone characterisation, and may lead to an increased

focus on the mutual interaction between chemical alteration and deformation during

faulting.


27

The impact of compaction localization on fluid flow in rocks.

Philip Meredith

1, Michael Heap

2, Patrick Baud

2, Thierry Reuschlé

2 & Ed Townend

1

1Rock and Ice Physics Laboratory, Department of Earth Sciences, University College

London, London, UK. [[email protected]] 2Institut de Physique de Globe de Strasbourg UMR 7516 CNRS, Université de

Strasbourg/EOST, Strasbourg, France

Common compaction localization features in carbonate and clastic rocks - namely

stylolites and compaction bands - hold the potential significantly to impact permeability

and fluid flow. Stylolites are complex column-and-socket interdigitation features that form

as a result of intergranular pressure-solution. They form laterally extensive features that

can reach lengths of 100s of metres. Compaction bands are tabular structures with a

significantly lower porosity than their adjacent host rock. In limestones and sandstones,

respectively, this porosity reduction is accommodated by grain crushing and pore collapse.

Both localisation features are generally found to be orientated normal or sub-normal to the

maximum principal stress direction.

Although knowledge of the influence of compaction bands and stylolites on fluid flow is

an important consideration in geomechanics and structural geology, there have been very

few measurements of permeability in these structures. We therefore measured

permeability of limestones containing stylolites from the ANDRA underground research

laboratory at Bure in SE France. We show that the permeability follows the same power

law porosity-permeability relation as that of stylolite-free material. The stylolites

comprised perforated layers constructed from numerous discontinuous pressure-solution

seams that comprised minerals of similar or lower density to the host rock. We also found

that samples containing stylolites parallel to the direction of fluid flow generally exhibited

permeabilities that were about an order of magnitude higher than the stylolite-free host

rock. We therefore suggest that flow-parallel stylolites commonly act as conduits for

enhanced fluid flow.

In contrast, we also show that mechanically-induced compaction bands in sandstone can

reduce permeability by three orders of magnitude or more. Permeability was measured

sequentially during triaxial compression of Diemelstadt sandstone samples under effective

pressures appropriate to reservoir depths and compaction band formation. The results

show that, for samples deformed at an effective pressure of 150 MPa, the permeability

dropped from 10-12

m2 to 10

-16 m

2 following propagation of the first compaction band.

Taken together, we conclude that the growth of compaction bands is likely to severely

reduce fluid flow within reservoirs, while the growth of stylolites is unlikely to affect fluid

flow in any significant way.


28

The Benefits of Maximum Likelihood Estimators

R. E. Rizzo

*, D. Healy

*, L. De Siena

*

* Department of Geology and Petroleum Geology, School of Geosciences, King’s College,

University of Aberdeen, UK. [email protected]

The success of any predictive model is largely dependent on the accuracy with which its

parameters are known. When characterising fracture networks in fractured rock, one of the

main issues is accurately scaling the parameters governing the distribution of fracture

attributes. Optimal characterisation and analysis of fracture attributes (lengths, apertures,

orientations and densities) is fundamental to the estimation of permeability and fluid flow,

which are of primary importance in a number of contexts including: hydrocarbon production

from fractured reservoirs; geothermal energy extraction; and deeper Earth systems, such as

earthquakes and ocean floor hydrothermal venting.

This work focuses on linking outcrop fracture data to permeability estimation and fracture

network modelling. The study area is a highly fractured upper Miocene biosiliceous mudstone

formation, cropping out along the coastline north of Santa Cruz (California, USA). These

unique outcrops have recently experienced seepage of bitumen-rich fluids through the

fractures, which makes them a geological analogue of a fractured top seal. Using outcrop

fracture networks as analogues for subsurface fracture systems has several advantages,

because key fracture attributes such as spatial arrangements and lengths can be effectively

measured only on outcrops [1]. However, a limitation when dealing with outcrop data is the

relative sparseness of natural data due to the intrinsic finite size limits of the outcrops. We

make use of a statistical approach for the overall workflow, starting from data collection with

the Circular Windows Method [2]. Then we analyse the data statistically using Maximum

Likelihood Estimators, which provide greater accuracy compared to the more commonly used

Least Squares linear regression when investigating distribution of attributes. Finally, we

estimate the bulk permeability of the fractured rock mass using Oda’s tensorial approach [3].

The higher quality of this statistical analysis is fundamental: better statistics of the fracture

attributes means more accurate permeability estimation, since the fracture attributes feed

directly into the permeability calculations.

These procedures are aimed at understanding whether the average permeability of a

fracture network can be predicted, reducing its uncertainties; and if outcrop measurements

of fracture attributes can be used directly to generate statistically identically fracture

network models, which can then be easily up-scaled into larger areas or volumes.

1 Gale et al. “Natural Fracture in shale: A review and new observations”, AAPG Bulletin 98.11 (2014).

2 Mauldon et al. “Circular scanlines and circular windows: new tools for characterizing the geometry of fracture traces”,

Journal of Structural Geology, 23 (2001). 3 Oda “Permeability tensor for discontinuous rock masses”, Geotechnique 35.4 (1985).


29

Predicting Hydraulically Conductive Fractures: A Quantitative

Comparison of Methods

S. Weihmann, D. Healy

Department of Geology and Petroleum Geology, University of Aberdeen, Aberdeen, UK.

[email protected]

Previous work has suggested that the hydraulical conductivity of fractures depends on the

magnitude and orientation of in-situ stresses through shear or tensile instabilities (eg.

Zoback, 2007). A correlation of fracture orientation, in situ stress field and fluid

conductivity is therefore predicted (sensu Zoback, 2007). Our analysis quantitatively

evaluates the two established prediction methods for fluid flow through fractures.

The Critically Stressed Fracture (CSF) approach correlates high fluid flow rates with

fractures stressed beyond their frictional shear strength (μ = 0.6) (Barton et al., 1995). The

Dilatation Tendency (Td) approach links high fluid flow rates with fractures optimally

oriented for tensile opening: Td = (σ1-σn)/(σ1-σ3) (Ferrill et al., 1999). We compare

predictions from both methods against intervals of flow and non-flow in 3 oil & gas wells

to measure their significance with respect to hydraulical conductivity.

Fracture and stress data derived by Dove Energy from resistivity and acoustic image logs,

open hole log suites and associated reports are used to compare the CSF and Td methods.

Flow and non-flow intervals were distinguished based on fluid flow at locations classified

as “oil inflow zones”. No distinction between fracture types were made.

Results suggest that neither method correlates well with apertures and location in the flow

zone of the well:

● CSF is a poor predictor of fluid flow; 98% (weighted average) of the fractures are

predicted not to be critically stressed; yet occur within a flow zone.

● Td is also a poor predictor of fluid flow; 67% (weighted average) of the fractures in the

flow zone have an insufficient (<0.5) Td for fluid flow.

● In non-flow zones CSF seems to predict accuractely (94% are non-CSF) but only 73%

(weighted average) of fractures demonstrate a sufficiently low (<0.5) Td.

Parameters including lithology or variations in in-situ stress, friction coefficient and

cohesion factors may influence results. Sensitivity analysis shows that variations of 5% of

σ3 affects uncertainty by 5%. Uncertainty increases with any change in cohesion factor.

Uncertainty reduction can only be achieved by a decrease in friction coefficient. Further

quantification of uncertainty, sensitivity and variation will better establish risk estimation

and finally improve predictions of hydraulically conductive fractures.

Method CSF Td

Uncertainty, flow 98% 67%

Uncertainty, non-flow 6% 27%



30

Hang on a moment:

If slow slip events are not earthquakes, how do we interpret their source

parameters?

A. Fagereng

1

1School of Earth & Ocean Sciences, Cardiff University, Cardiff, UK.

[email protected]

Slow slip events (SSEs) represent transient fault slip velocities slower than earthquakes

but faster than steady, average plate motion. SSEs are detected geodetically and do not

emit detectable seismic waves, although they are commonly, but not always, accompanied

by tectonic tremor. Tremor is defined as weak, persistent, low-frequency (< 10 Hz)

seismic signals lacking impulsive body wave arrivals. Within the tremor signal are low

and very low frequency earthquakes, interpreted as shear slip on faults parallel and

kinematically consistent with the hosting fault. An increasingly common interpretation is

that SSEs are a form of transient fault creep, and associated low frequency seismic

phenomena represent shear failure of stronger asperities embedded in the creeping fault

segment. A geological analogue to the coupled phenomena of slow slip and tremor is then

a tabular heterogeneous shear zone with rigid, relatively competent lenses in a less

competent matrix. This analogue has some significant differences compared to a discrete

slip surface in an elastic medium.

Where slow slip and tremor spatially and temporally coincide, the total seismic moment of

tremor and superimposed low frequency seismic events is negligible compared to the

geodetic moment of the SSE. Thus, the geological analogue is restricted to shear zones

where the majority of finite strain is accommodated by deformation of the relatively

incompetent matrix. It follows that the geodetic moment of an SSE is representative for

the elastic strain converted to finite displacement by the SSE (centimetres), whereas

tremor represents coincident frictional failure with small (sub-mm) slip magnitudes. This

interpretation assumes that SSEs, like earthquakes, represent a form of stick-slip motion

associated with elastic strain build-up and release in the surrounding elastic rock volume.

If this assumption is correct, and geological analogues implying SSEs may form by

viscous shearing flow are also correct, then SSE source parameters can be considered in

terms of viscous deformation of a tabular shear zone.

Analogous to 'characteristic earthquakes', SSEs repeating at the same location have

approximately characteristic slip magnitude and duration. Contrary to earthquakes,

however, average slip relates to neither duration nor area, and average slip velocity is

considerably greater in shallow events than in deep events. Considering SSEs as viscous

shearing flow, and assuming that SSEs accommodate slip deficit equivalent to the elastic

strain in surrounding rock, it is possible to calculate their effective viscosity from the

geodetic moment. In this paradigm, variations in duration, slip, and slip rate between SSEs

can be tied to variations in effective viscosity. That deep SSEs are slow and long implies a

relatively high effective viscosity; this may be interpreted as caused by a wider shear zone

with lower strain rate than in shallow events, consistent with a viscous shear zone model

for SSEs if shear zones widen with depth, as is commonly inferred.


31

Statistical physics, active fault zones, and earthquake ruptures

Agust Gudmundsson

Department of Earth Sciences, Queen’s Building, Royal Holloway University of London,

Egham TW20 0EX, UK ([email protected])

The seismogenic (brittle) part of an active major fault zone may contain of the order of

1013

outcrop-scale (≥ 0.1 m strike or dip dimension) fractures and perhaps 1023

grain-scale

(≥ 1 mm) fractures. In active fault zones, the outcrop-scale fractures would be mainly in

the damage zone whereas the grain-size slip planes would be primarily in the core. A fault

zone receives energy mostly through plate-tectonic forces that drive the movement across

the fault. For a fault zone of (temporary) constant volume, the available energy for work,

and thus for producing earthquakes through fault slip, can be estimated from the

Helmholtz free energy, F, given by F = U - TS. Here U is the internal energy of the fault

zone, T the absolute temperature, and S entropy. TS represents the energy transformed,

dissipated, as heat and unavailable. Alternatively we have F = -kBT ln Z, where kB is the

Boltzmann constant (1.38 × 1023

J K-1

) and Z is the partition function. Differentiation of F

with respect to temperature (at constant volume) then yields the Gibbs entropy formula

i

iiB ppkS ln . Here pi is the probability of a fault falling in a particular bin in the

distribution. This equation can be used to calculate the entropies of the size and orientation

distributions of fractures in fault zones.

We present results showing that fault dimensions and slips/displacements in some fault

zones may follow partly exponential and partly power-law size distributions. Using the

Gibbs-Shannon formula I show that the configuration entropy in a fault zone increases

with time. It is proposed that as a fault zone evolves more and more of its energy is

transformed into low-grade or unavailable energy through the term TS, implying that the

fault-zone slip is gradually accommodated by creep or aseismic faulting. The results also

suggest that if energy input into a fault zone increases, the tail of the fracture-size

distribution becomes proportionally longer, that is, the fault zone generates more long

fractures and large earthquakes, meaning that the length range increases. We show that the

entropy increases with increasing fracture-length range. Since fault slip and earthquake

magnitudes depend on earthquake-rupture size, it follows that if we can explain the

rupture size distribution, we should be able to explain the earthquake-magnitude

distribution. Exponential parts of size distributions follow directly from the Boltzmann

distribution law. While there are no generally accepted explanations for power-law parts

(proposed explanations for power laws include ‘preferential attachment’ and ‘self-

organised criticality’), there are indications that maximising the Gibbs-Shannon entropy

subject to certain conditions results in a power-law size distribution. Here we explore

these ideas in relation to energy budgets of major fault zones.

Gudmundsson, A., 2014. Elastic energy release in great earthquakes and eruptions. Front.EarthSci. 2:10.

doi:10.3389/feart.2014.00010.

Gudmundsson, A., Mohajeri, N., 2013. Relations between the scaling exponents, entropies, and energies of fracture

networks. Bull. Geol. Soc. France, 184, 377-387.

Gudmundsson, A., De Guidi, G. and Scudero, S., 2013. Length–displacement scaling and fault growth. Tectonophysics,

608, 1298–1309.


32

Structure of a seismogenic normal fault zone in carbonates: Campo

Imperatore, Central Apennines (Italy)

M. Demurtas

1, M. Fondriest

1, L. Clemenzi

2, F. Balsamo

2, F. Storti

2, A. Bistacchi

3, G. Di

Toro1,4

1Department of Geoscience, University of Padua, Italy.

[email protected] 2NEXT – Natural and Experimental Tectonics research group, Department of Physics and

Earth Sciences “Macedonio Melloni”, University of Parma, Italy. 3Dipartimento di Scienze Geologiche e Geotecnologie, Università degli Studi di Milano

Bicocca, Italy. 4School of Earth, Atmospheric & Environmental Sciences, University of Manchester, UK.

Fault zones cutting carbonate sequences represent significant seismogenic sources

worldwide. Most of the earthquakes associated to the L’Aquila 2009 extensional seismic

sequence (main shock MW 6.1), probably nucleated and surely propagated through

carbonate-bearing rocks. Though seismological and geophysical techniques (e.g., double

differences method, trapped waves) allow us to investigate down to the decametric scale

the structure of active fault zones, further geological field surveys and microstructural

studies of exhumed seismogenic fault zones are required to support interpretation of

geophysical data, quantify the geometry of fault zones and identify fault processes active

during the seismic cycle.

Here we describe the fault geometry and fault zone rock distribution of the

footwall-block of the active Campo Imperatore Fault Zone (CIFZ). The CIFZ was

exhumed from 2-3 km depth and accommodated a normal throw of 1-2 km since Early-

Pleistocene. In the studied area, the CIFZ dips N210/60° and puts in contact Quaternary

colluvial deposits in the hangingwall with dolomitized Jurassic platform carbonates in the

footwall. The following structural units were distinguished within the ~300 m thick CIFZ

footwall-block, based on density of the fracture/fault network, clast/matrix proportion,

preservation of sedimentary features and relative abundance and geometry of veins:

"cataclastic unit",

"breccia unit",

"low-strain damage zone" (mean fracture spacing ~10 cm), and,

"high-strain damage zone" (mean fracture spacing <2-3 cm).

The "cataclastic unit" is up to 40 m thick and associated to the master and major

faults. Fault rocks are ultra- to cataclasites derived from the progressive deformation of

adjacent structural units; shear strain is partitioned among multiple sub-parallel normal

faults. Slipping zones include microstructures suggestive of coseismic deformation such as

mirror-like slip surfaces with truncated clasts, mixed calcite-dolomite foliated cataclasites,

fluidized granular layers. The "breccia unit" includes low angle normal faults re-activating

pre-existing reverse faults and consists of mosaic-crackle breccias cut by dolomite veins.

The (1) overall distribution of the structural units, (2) the attitude of newly-formed

faults and joints, (3) the re-activation of reverse faults inherited from the Miocene-

Pliocene compressional phase, are kinematically consistent with the post-Pliocene

extensional activity of the CIFZ. The depicted structures compare well with the fault

network highlighted by hypocentre relocation of the L’Aquila 2009 seismic sequence.



33

Damaged beyond repair? Characterising the damage zone of the Alpine

Fault, New Zealand, a fault late in its interseismic cycle.

Jack Williams

1, Virginia Toy

1, Cecile Massiot

2, and D. McNamara

3

1Department of Geology, University of Otago, Dunedin, New Zealand.

[email protected]

2 School of Geography, Environment and Earth Sciences, Victoria University of

Wellington, Wellington, New Zealand

3 GNS Science, Lower Hutt, New Zealand

Fault damage zones are the heavily fractured and faulted protolith rocks that surround a

fault core. Although they accommodate only a small proportion of fault displacement,

damage zones influence fluid flow around a fault, its stress state and the dynamics of

earthquake rupture. We are characterising the damage zone of the Alpine Fault, the major

structure bounding the Pacific and Australian plates in the South Island of New Zealand.

Since it is statistically late in its interseismic cycle and has well-constrained

transpressional kinematics, the Alpine Fault is an attractive target for damage zone study.

We documented all damage zone structures observed in X-ray computed tomography (CT)

scans of core recovered from the first phase of the Deep Fault Drilling Project (DFDP-1)

through the Alpine Fault. These scans provide a near continuous record of its damage zone

(Figure 3). Structures are categorised into two types: (1) “off fault damage” induced by

stress changes associated with the passage of seismic rupture and (2) “off fault

deformation,” which are small faults that accommodated shear displacement that was not

localised on to the principal slip zones (PSZs). The distribution of these structures was

calculated using a weighted moving average technique to account for orientation bias

when picking structures. We find that, within the part of the damage zone sampled by

DFDP-1, there is no increase in the density of the structures towards the PSZs. This is

consistent with analysis of damage zone structures picked in borehole televiewer data. We

suggest instead that the density of damage zone structures is systematically related to the

rock type within which they are observed.

Figure 3: Example CT scan of DFDP-1 core and typical damage zone structures that are

observed.

For the interval of core recovered <40 m from the PSZs, we observe no systematic

relationship between fracture density and P-wave velocities obtained from wireline logs.

This interval is identified as a zone of extensive fluid-rock interaction, ie. an ‘alteration

zone,’ in which we interpret that extensive cementation of fractures has diminished their

expected ability to reduce the elastic modulus of the rock. We welcome discussion of how

this might influence the dynamics of future Alpine Fault earthquakes.

11 cm

Minor

fault Open

fracture

Clay filled

fracture

Partially

open

fracture

DFDP-1A 55-1

75.25-75.50 m

500 2500

CT Number Key:

4000


34

Coulomb stress modelling of an exceptional record of historical

earthquakes in the central Apennines, Italy: Lessons for fault interaction

and earthquake occurence

L. Wedmore

1, J. Faure Walker

1, G. Roberts

2, K. McCaffrey

3 and P. Sammonds

1

1Institue for Risk and Disaster Reduction, University College London, London, UK.

[email protected] 2Department of Earth and Planetary Sciences, Birkbeck, University of London, London,

UK 3Department of Earth Sciences, Durham University, Durham, UK

Our understanding of the effects of co-seismic stress changes on fault interaction and

earthquake occurence is currently limited by the short temporal duration of historical

earthquake catalogues. This is particularly a problem in low strain-rate continental settings

where earthquake recurrence intervals are long, fault slip-rates are low and strain is

distributed between a number of faults. While our understanding of the effects of fault

interaction on fault growth and fault displacement rates over 104-10

6 year timescales is

relatively well developed, the effects of stress changes on fault activity over hundreds to

thousands of years are less well known. Faults in the central Apennines, Italy, show

evidence for clustered earthquakes and temporally variable slip-rates over timescales of

102-10

3 years. We use the exceptional records of historical earthquakes available for the

region that extends from 1349 A.D. for 660 years and includes 27 Mw>5.8 earthquakes

along with an extensive slip-rate database that constrains interseismic loading, to explore

the effects of both co-seismic and interseismic stress changes on expected earthquake

recurence intervals. We also investigate the structural controls on the interaction over this

timescale.

We use palaeoseismic records alongside historical records of damage to reconstruct the

fault ruptures for 27 earthquakes since 1349 A.D. In addition, we model each of the 97

faults in the central Apennines that show evidence of activity during the Holocene. The

co-seismic Coulomb stress changes for each earthquake are resolved on all faults in the

region for each of the events. We also calculate interseismic stress accumulation from a

model of viscous shear zones that underlie the upper crustal brittle faults. The model of

interseismic loading is constrained by field measurements of fault slip-rates, fault

geometry and fault kinematics.

We show that during the historical period studied earthquakes occurred on faults where

the combined co-seismic and interseismic stress was positive prior to each event.

Calculated interseismic stress accumulation suggests fault recurrence intervals that are

consistent with palaeoseismology in the region. Whilst co-seismic stress changes are small

(<10-1

MPa) relative to interseismic stress accumulation rate (c.10-3

MPa yr-1

), co-seismic

stress reductions are not overcome by interseismic stress accumulation. Consequently, co-

seismic stress shadows leave a lasting imprint on the fault system and imply changes in

expected earthquake recurrence of up to 103 yrs. We show how fault length places a key

constraint on how much faults are affected by co-seismic Coulomb stress changes.

Consequently, we suggest that fault size population statistics should be incorporated into

seismic hazard estimations.


35

Is the Southern San Andreas Fault Really Overdue For a Large

Earthquake or Just Late in the Cycle?

Thomas K. Rockwell1

1Department of Geological Sciences, San Diego State University, San Diego, CA, USA.

[email protected]

Compilation of paleoseismic data from several dozen trench sites in the southern San

Andreas fault system (Figure 1), along with more precise dating of Lake Cahuilla

sediments that cross many of these sites, allows for sequencing of the past 1100 years of

large (M6.5 and larger) earthquakes for

the southern 150 km of the main plate

boundary system. Major faults capable of

larger earthquakes include the San

Andreas, San Jacinto, Elsinore, Imperial,

Cerro Prieto, Laguna Salada, and possibly

the Earthquake Valley faults.

Displacement data have been generated

for most of these faults for the past one to

several events. Using these observations

on timing and displacement in past large

earthquakes, and assuming reasonable

seismogenic thicknesses, estimates of

moment release through time can be

made. Based on these estimates, at least

three generalizations are clear: 1) M7 and

larger earthquakes account for most of the

moment release in the southern San

Andreas fault system over the past 1100

years; 2) large earthquakes on individual

faults are quasi-periodic but display a

relatively high coefficient of variation in

recurrence time, similar to most long

California records; and 3) moment release

has temporally varied during the past

1100 years but within potentially

predictable bounds. A forth observation is

that inundation of Lake Cahuilla may

have triggered some large earthquakes, as

previously suggested, and that the lack of

a lake in the past 300 years may partially

explain the relatively long quiecence of

the southern San Andreas fault system. Together, the record suggests that the southern San

Andreas fault is late in the cycle but not necessarily “overdue”, and that a systems level

approach may be more accurate in long term earthquake forecasting than data generated

from a single element of the fault system.

Figure 1. Map of the major elements of the southern

San Andreas fault system. The dashed box defines the

area of consideration. Yellow stars are paleoseismic

Sites used in this analysis.

Figure 2. Moment release in the southern San Andreas

fault system for the past 1100 years. Occurrence of

freshwater Lake Cahuilla shown as blue bars. Note

possible effects of lake loading as a trigger for some

large southern San Andreas faul earthquakes.


36

Investigating tectonically-deformed Quaternary marine terraces using

synchronous correlation to determine faulting activity: the Capo

D’Orlando Fault as a case study (NE Sicily, Italy).

M. Meschis

1 , G. P. Roberts

1 and J. Robertson

1

1Department of Earth and Planetary Sciences, Birkbeck, University of London, WC1E

7HX, UK.


Quaternary tectonic vertical movements can be used to estimate long-term crustal

extension rates accommodated by active normal faults. Sequences of marine terraces

deformed by active faults capture the interplay between sea-level changes, tectonics and

active faulting throughout the Quaternary (e.g. Armijo et al., 1996, Giunta et al, 2011,

Roberts et al., 2013). By mapping the palaeoshorelines of these tectonically-deformed

Quaternary terraces, both in the hangingwall and footwall, we can calculate crustal

deformation over multiple seismic cycles (Roberts et al., 2013).

The key to this process is the synchronous correlation method (insert references) which

exploits the facts that (a) sea-level highstands are not evenly-spaced in time, yet must

correlate with palaeoshorelines that are commonly not evenly-spaced in elevation, and (b)

that older terraces may be destroyed by younger highstands, so that the next higher or

lower paleoshoreline does not necessarily correlate with the next older or younger sea-

level highstand (c.f. Armijo et al., 1996).

We studied a sequence of Late Quaternary palaeoshorelines deformed by normal faulting

as a result of the Capo D’Orlando Fault in Sicily (e.g. Giunta et al., 2011). This fault lies

within the Calabrian Arc which has experienced damaging earthquakes such as the 1908

Messina Straits earthquake ~ Mw 7. Our mapping demonstrates changing palaeoshorelines

elevations along the strike the NE – SW oriented normal fault. This confirms active

deformation on Capo D’Orlando Fault, indicating that it should be added into the

Database of Individual Seismogenic Sources (DISS, Basili et al., 2008). While Giunta et

al. (2011) successfully mapped this fault and the deformed palaeshorelines, the long-term

uplift rates were calculuated using a sequential correlation method which does not take

into account overprinting terraces, yet suggested time-varying uplift. Our results show

instead that uplift rates were constant through the Late Quaternary, suggesting that slip-

rate controlling seismic hazard have also been constant.

Reference Armijo, R., Meyer, B. G. C. P., King, G. C. P., Rigo, A., & Papanastassiou, D. (1996). Quaternary evolution

of the Corinth Rift and its implications for the Late Cenozoic evolution of the Aegean. Geophysical

Journal International, 126(1): 11 – 53.

Basili R., Valensise, G., Vannoli, P., Burrato, P., Fracassi, U., Mariano, S., Tiberti, M.M., Boschi. E. (2008).

The Database of Individual Seismogenic Sources (DISS), version 3: summarizing 20 years of research

on Italy's earthquake geology, Tectonophysics, doi:10.1016/j.tecto.2007.04.014

Giunta, G., Gueli, A.M., Monaco, C., Orioli, S., Ristuccia, G.M., Stella, G., Troja, S.O. (2011). Middle-Late

Pleistocene marine terraces and fault activity in the Sant’Agata di Militello coastal area (north-eastern

Sicily). Journal of Geodynamics. 55, 32 – 40.

Roberts, G. P., Meschis, M., Houghton, S., Underwood, C., & Briant, R. M. (2013). The implications of

revised Quaternary palaeoshoreline chronologies for the rates of active extension and uplift in the upper

plate of subduction zones.Quaternary Science Reviews, 78: 169 – 187


http://dx.doi.org/10.1016/j.tecto.2007.04.014


37

Active tectonics of the northern Gulf of Corinth (Central Greece) and

the Delphi-Arachova Fault geometry and kinematics.

Valkaniotis Sotiris1 and Pavlides Spyros

1

1 Department of Geology, Aristotle University of Thessaloniki, 546 21, Thessaloniki.

[email protected], [email protected]

The Gulf of Corinth, is a very active seismic area as it is documented from the intense

earthquake activity. New field mapping, aerial photos, morphotectonic analysis and DEMs

help to better study the Northern Gulf of Corinth land (Sterea Ellada) tectonics mainly.

Our study, showed that, in the region exist in both on land and offshore, at least 65 active

and probably active faults possibly associated with 46 known potent earthquake region

size Μw>6.0. They have been classified and categorized as Seismogenic Sources in order

to be used in the Greek Database of Seismogenic Sources (GreDaSS). Using known

empirical relationships of Magnitude vs Surface Rupture Length, it is estimated that the

maximum potential faults can cause earthquakes of magnitude up to M = 6.8, which is the

maximum magnitude observed in the area. The major and more complicated structure in

the studied area is the Delphi-Arachova fault zone, which was remapped in detail and also

in the archaeological area of the Delphi Oracle. It is a dip-slip typical normal active fault

zone, E-W trending and S dipping of ~ 15 Km long, which crosses and branching the

archaeological site. Associated with major historical earthquakes, the Delphi-Arachova

fault zone, an Aegean type active structure, forming a distinct landscape, is the largest and

most active structure direct to the north of Corinth Rift. The post-Glacial fault surfaces

and scarps with sub-vertical slickensides are covered by four generations of scree material

and talus cones, evidently the result of successive movements and rock falls. The surfaces

of the faults contain a zone of cataclastic rock of fine material. A number of secondary

sub-parallel faults (strike 60-120° and dip 60–80°) also affect the alpine and post-alpine

formations in the broader area, forming a rather complex fault pattern.



38

3D modelling and structural analysis of the Grasberg-Ertsberg mining

district, Papua, Indonesia.

A. Bladon

1*, C. Seiler

1, J.F. Ellis

1, A.P.M. Vaughan

1, S. Widodo

2

1 Midland Valley Exploration, Floor 9, 2 West Regent Street, Glasgow, G2 1RW, UK.

2 Freeport-McMoRan, 333 N Central Ave, Phoenix, AZ 85004

* [email protected]

The Sudirman Range of Papua, Indonesia forms part of the collisional suture zone

between the Australian Plate and the Caroline and Bismark microplates. The range

contains a number of large ore deposits, including the Grasberg and Ertsberg

porphyry/skarn Cu-Au deposits. Here we describe the construction, validation and

quantitative structural analysis of a 3D model of the Grasberg-Ertsberg mining district.

The results of this study have significantly improved our understanding of the structural

development of the district and the emplacement of the 2.7 Ma Ertsberg intrusion.

The rocks in the mining district consist of Triassic to Cretaceous Kembalangian Group

clastics overlain by carbonate rocks of the Paleogene to Neogene New Guinea Limestone

Group. The sedimentary succession was folded and faulted during the 12 Ma to 4 Ma

Central Range Orogeny and between 4 Ma to 2 Ma there was a period of increased

oblique plate convergence between the Australian Plate and the Caroline microplate. The

Grasberg Igneous Complex was erupted at 3.2 Ma and the Ertsberg intrusion was

emplaced at 2.7 Ma.

The dominant structural trend in the district is WNW-ESE, with gentle (inter-limb angle

(α) = 160° to 130°) and concentric anticlinal folds in the north and south of the district.

These folds are separated by the close to tight (α = 85° to 25°), chevron-style Yellow

Valley Syncline. The variations in fold class and tightness indicate that the Yellow Valley

Syncline forms a high strain zone against a background of comparatively low-strain

compressional deformation. Total NNE-SSW shortening ranges between ~50% (west) and

~30% (east) and peaks at ~55% adjacent to the Ertsberg intrusion. The folded strata are

cut by WNW-ESE orientated reverse faults that accommodated up to 3,000 m of throw

and show strong along-strike displacement gradients. The faults have throw:length ratios

that vary between 1:5 and 1:6. Cumulative throw ranges from ~3,000 m (west) to

~5,000 m (east) and peaks at ~6,000 m adjacent to the Ertsberg intrusion.

Quantitative structural analysis revealed previously unrecognised fault relay zones and

linkages. Additionally, the correspondence between peak shortening (~55%), peak

cumulative fault throw (~6000 m), and the Ertsberg intrusion suggests that emplacement

of the Ertsberg intrusion locally influenced strain patterns and deformed the enclosing host

rock.


39

Visualising Second Order Tensors in Virtual Globes

T. Blenkinsop

1, I. Merrick

1, H. Jelsma

2 , T. Mochales

3

1School of Earth and Ocean Sciences, Cardiff University, Cardiff, UK.

[email protected] 2Anglo American, Exploration Technical and Business Planning, Johannesburg, South

Africa 3Spanish Geological Survey IGME, Spain.

Many important properties in structural geology are second order (rank 2) tensors.

Examples include stress, deformation (the position and displacement gradient tensors), the

velocity gradient tensor, magnetic susceptibility and permeability. Representing such

properties in a readily understandable way is challenging, particularly when spatial

variations in such properties also need to be displayed. Mohr diagrams are in common use,

but they are not very accessible to the inexperienced, especially in three dimensional

versions. Direct representation of ellipsoids defined by the principal axes is more intuitive

(e.g. Mookerjee and Nickleach 2011), but even in this case, conventional two dimensional

illustrations convey a limited impression.

We have developed a method to represent second order tensors in virtual globes. The

ability of virtual globes to visualise three-dimensional objects makes them a natural way

to represent the inherently three-dimensional nature of second rank tensors. Figure 1

shows strain ellisoids around the Chinamora batholith, Zimbabwe, which were used to

demonstrate the ballooning/diapiric effects of emplacing the batholith (Jelsma et al. 1993).

Relationships between the batholith margins and the adjacent greenstone belt are clearly

visualised in a virtual globe.

Fig. 1. Strain ellipsoids around

the margin of the Chinamora

batholith, Zimbabwe. Long

axes plunge away from the

margin of the batholith to the

south (right) of the view, which

looks east. There is a general

tendency for ellipsoids to be

more prolate in the centre of the

greenstone belt.

Jelsma, H. A., van der Beek, P. A., Vinyu, M.L., 1993. Tectonic evolution of the Bindura-

Shamva greenstone belt (northern Zimbabwe): Progressive deformation around

diapiric batholiths. J. Struct. Geol. 15, 163–176.

Mookerjee, M., Nickleach, S., 2011. Three-dimensional strain analysis using

Mathematica. J. Struct. Geol. 33, 1467–1476.



40

Constraining the vertical surface motions of the Hampshire Basin, south

England During the Cenozoic

Philip G. Smith

1, Richard. W. England

2, and Jan. Zalasiewicz

2.

1Department of Geology, University of Leicester, Leicester, UK.

[email protected]

The potential effect of rising sea level on the UK has received considerable attention in

recent years. However, the ongoing long-term changes in surface topography of the UK

driven by regional tectonics and the mechanisms responsible are not fully understood. It is

thought that glacial loading/unloading is the primary influence. However, this is

inconsistent with present-day vertical surface motions recorded from Continuous Global

Positioning Stations (CGPS) across the UK. The lateral variations in the present day

motions are too complex to be explained by glacial isostatic rebound. We are investigating

the hypothesis that the vertical motions of SE England also reflect the long term tectonic

history by backstripping the Cenozoic geological record. So far the Paleogene

stratigraphic record of the Hampshire basin in southern England has been investigated and

using a series of deep boreholes that reach the chalk basement, a 2-D backstripping

method has been applied.

Subsidence analysis of cliff sections and boreholes reveal a short lived period of rapid

subsidence from 42Ma, at a time when Eustatic sea level remained low. This requires

tectonic mechanism for the increase in accommodation space at this time. The data

developed so far also suggests that any major periods of uplift and denudation to the

present day state must have occurred from the mid Oligocene onwards, post 33.7Ma and

there is no early Tertiary uplift in this area, in contrast to other parts of the UK. Additional

deep boreholes from the London basin and East Anglia will be backstripped to produce a

comprehensive 3D tectonic map of vertical surface motions during the early to mid

Cenozoic. From this we may be able to understand the major tectonic controls influencing

southern England at this time and modifying the current surface elevation change on short

wavelengths.


41

We need a 2nd

Stone Age when molten rocks replace concrete and bricks

Christopher Talbot

Hans Ramberg Tectonic Laboratory, Department of Earth Sciences, Uppsala University

Now at 14 Dinglederry, Olney, MK46 5ES, UK. <[email protected]>

Half of everything produced today consists of an artificial rock called concrete:

broken rocks and sand cemented together. Roasting special rocks at 1500°C to produce

cement is our 3rd

dirtiest industry and accounts for between 5 and 7% of all man’s

greenhouse gasses currently cooking Mother Earth too fast for comfort. Producing every

tonne of Portland cement spews about a tonne of CO2 into the sky. The EU estimated that

man produced ~3.7 billion tonnes of concrete in 2013. US cement-makers alone dump

about 3,750 tonnes of carbon dioxide into the atmosphere every minute. Much is being

done to clean up our two dirtiest industries, energy and transport, but not enough to clean

up our construction industry. And yet it could be surprisingly easy to replace concrete and

brick by materials far more friendly to Mother Earth: the molten rocks with which she

built herself.

We left our 1st Stone Age by turning flint weapons into tools long before we ran

out of flints. Similarly, we need to advance into our 2nd

Stone Age long before we run out

of fossil fuels. Melting and reshaping almost any rock on any scale would allow us to live

comfortably in alien environments on Earth and in space where the ingredients of pozolan

cement are missing. Organising the shapes, sizes and arrangements of different

proportions of bubbles would allow re-shaping man-molten rocks into products with a

huge range of material properties. These could range from robust solids through porous

solids and foams light enough to float, to loose particles and rock fibres or films. The

various risky proposals to bypassing our potentially “apocalyptic” future at 2.7°C or above

by geoengineering our atmosphere should be supplemented by the far less risky approach

of geoengineering a new , cleaner construction industry.

The concept of slip forming molten rock instead of concrete for highways between

busy city centres in which hi-rise towers are slip formed by molten rocks would light a

fire under the nuclear power industry that has been promising inherently safe nuclear

reactors small enough to be mobile for decades. The need for safe small rock melters and

some imagination should revolutionise both the nuclear power industry and tectonics (the

science or art of construction and architecture).

A 10MW HTR-10 pebble bed nuclear reactor modified to melt rocks.


42

Four shear zones; their structure and evolution

John Dewey

1, Richard Lisle

2, and Paul Ryan

3

1University College, Oxford, UK; [email protected]

2University of Wales, Cardiff, UK

3University College Galway, Galway, Ireland

The structure and evolution of four shear zones are described. 1. 26 x 2 cm zone with

Anti-Riedel-bounded rotated blocks in red Keuper siltstones at Watchet, Somerset. 2. 2

cm wide transtensional zone with tension gashes and spaced solution cleavage in

Carboniferous mudstone at Hartland Quay, Devon. 3. Conjugate shear zones, with tension

gashes and spaced solution cleavage, that merge into coaxial cleavage zones at their tips,

at Marloes Bay, Pembrokeshire. 4. 1 x 0.5 km transtensional zone of shear-banded

Silurian siltstones with kink bands and P-shears at Emlagh Point in County Mayo.

Outcrop-scale transtensional and transpressional shear zones are monoclinic/plane strain

and change volume by solution transfer, in contrast to triclinic lithospheric-scale zones

where body forces dominate. Foliated transtensional zones are characterized by kink

bands and P-shears whereas transpressional zones are dominated by S/C fabrics;

transecting foliations may occur in both.

[email protected]


43

Contribution of the Geophysics to the Structural Study of the Mbere

Basin using GOCE Gravity Measurements:Implication to the Regional

Tectonics.

A. KEMGANG GHOMSI Franck Eitel

1, B. NGUIYA SEVERIN

2, C. NOUAYOU

Robert2, and D. TOKAM KAMGA Alain Pierre

3

1Department of Physics, Faculty of Science, The University of Yaounde I, Yaounde,

Cameroon

[email protected] 2Industrial Engineering Faculty, University of Douala, Douala, Cameroon

3School of Geosciences, University of Witwatersrand, Witwatersrand, South Africa

We used the GOCE (Gravity Field and Steady-State Ocean Circulation Explorer, 2009–

2013) measurement data sets to analyze the regional gravity anomalies and to study the

underground structures in the Adamawa volcanic uplift.

The Adamawa volcanic uplift which include the Mbere Basin in central Cameroon forms

the eastward termination of the Cameroon Volcanic Line (CVL) in West-Central Africa.

This line is unique among intra-plate volcanic provinces in that it straddles a continental

margin and has both oceanic and continental volcanic centres. The uplift is characterised by

a long-wavelength negative Bouguer anomaly similar in shape and amplitude to those of

other African basement uplifts.

Two gravities profiles derived from the Bouguer gravity map of Adamawa plate,

perpendicular to the anomaly associated with the uplift shows a broad negative and an axial

positive Bouguer anomaly. These profiles are used the logarithmic power spectrum

technique to obtain detailed images and corresponding source depths as well as certain

lateral inhomogeneity of structure density. The broad negative and central positive

anomalies beneath the Adamawa uplift are interpreted as a consequence of lithospheric

thinning (27.5 - 35 km) and crustal thinning (3.67 – 11.5 km), respectively. Compared to

the Kenya dome, the Adamawa uplift may be in an early stage of continental rifting, along

the site of a pre-existing basement weakness, the Central African Shear Zone (CASZ).

A comparison of gravity anomalies difference (GOCE TIM_R5 and TIM_R4) and

climatological data reveal a strong link and the possible impact of hydrography and

moisture on the variation of the gravity on the gap of the Mbere basin.

Our results are in good agreement with previous investigations.


44

From micron to mountain-scale, using monazite and titanite

Petrochronology to quantify the rates of deformation in the Himalaya

and beyond

C.Mottram

1,2,3, J. Cottle

2

1Department of Earth Sciences, Dalhousie University, Halifax, Nova Scotia, Canada.

[email protected] 2Department of Earth Science, University of California, Santa Barbara, California, U.S.A

3Department of Environment, Earth and Ecosystems, The Open University, Milton

Keynes, U.K.

Mountains form where the Earth’s plates collide; during this upheaval rocks are deformed

by massive forces. The rates and timescales over which these deformational processes

occur are determined from tiny accessory minerals that record geological time through

radioactive decay. There remain major unresolved challenges in linking the dates yielded

from these accessory phases to specific deformation events and discerning the effects of

deformation on the isotopic and elemental tracers in these phases. The Himalayan orogen

represents the ideal natural laboratory to decode the record of the deformational processes

encrypted in the rocks.

Here, we use combined laser ablation (split-stream) U-Pb and REE analysis of deformed

monazite and titanite along with Electron BackScatter Diffraction (EBSD) imaging and

Pressure-Temperature (P-T) phase equilibria modelling to (1) link accessory phase ‘age’

to ‘metamorphic stage’ and (2) to quantify the influence of deformation on monazite

(re)crystallisation mechanisms and its subsequent effect on the crystallographic structure,

ages and trace-element distribution in individual grains, and (3) to understand how along-

strike variations in orogenic processes can be revealed using titanite petrochronology.

These data provide links between ages and specific deformation events, thus helping

further our understanding of the role of dynamic recrystallisation in producing age

variation within and between crystals in a deformed rock and thus help develop further

understanding of the deformational history of the cores of evolving mountain belts.


45

When did the Moroccan High Atlas Mountains get high?

Sarah J. Boulton

1 and Justin H. VanDeVelde

1

1School of Geography, Earth and Environmental Sciences, Plymouth University,

Plymouth, U.K.

The surface uplift of mountain belts can have profound effects on precipitation patterns

and moisture distribution, potentially resulting in the development of orographic rain

shadows and aridification. Understanding the timing and magnitude of uplift can also

inform models of plate tectonic evolution and allow understanding of the underlying

mechanisms of uplift. However, deriving measurements of palaeoelevation is difficult and

traditionally has relied on the presence of uplifted marine and coastal sediments or

complex modelling of hydrological cycles.

The uplift history of the Moroccan High Atlas has been a matter of debate for many years.

Although, it is apparent that ~1000 m of elevation have been gained during the Plio-

Quaternary, two main models have been poroposed for the timing of previous uplift. One

model advocates a pulsed uplift history for the High Atlas, with initial mountain growth in

the Eocene or Oligocene followed by rapid Quaternary uplift. By contrast, the second

model suggests that uplift has been fairly continuous since the Eocene/Oligocene. Here we

apply a new method for determining palaeoelevation, which utilizes dual carbon and

oxygen isotope ratios from lacustrine carbonates to quantitatively constrain the mean

upstream catchment altitudes for the High Atlas Mountains, Morocco.

We show for the first time that the High Atlas had a mean altitude of 1200 ± 500 m

through the Middle-Late Miocene, demonstrating that it was a modest topographic feature

at this time and did not gain any significant altitude during the latter part of the Miocene.

Subsequently, ~ 1000 m of elevation was achieved through the Plio-Quaternary to reach

the present mean altitude of ~ 2200 m. These data suggest either that the Miocene was a

period of tectonic quiescence or that erosion balanced rock uplift. Previous research on

apatite fission track data and structural observations indicate that exhumation and

thrusting was active during the Micoene ruling out a pause in deformation. Therefore,

these data support a model for pulsed surface uplift but continuous rock uplift in the

Moroccan High Atlas since the Eocene/Oligocene. These new data provide independent

constraints on the timing and magnitude of orogenic development and landscape

development. These data also form an important case study that validates the dual isotope

method illustrating the high potential of this method for palaeoelevation research.


46

Dynamic growth of fold and thrust belts: insights from numerical

modelling tested against a natural example from SE Asia

X. Yang

1, F. Peel

2, D. Sanderson

3, and L. McNeill

1

1School of Ocean and Earth Science, University of Southampton, Southampton, UK.

[email protected] 2National Oceanography Centre, Southampton, UK.

3 Faculty of Engineering and Environment, University of Southampton, Southampton, UK.

The Coulomb Wedge model of Davis simply and elegantly describes the mechanics of

fold and thrust belts (FATBs) driven by orogenic processes, by considering the system as

an orogenic wedge at the point of compressional failure, like a snow wedge pushed by a

snowplough. The model can be applied alike to thrust belts driven by plate convergence,

or by gravity collapse of a passive margin. The Critical Coulomb Wedge model is a good

starting point which describes part of the system, part of the time, but it does not apply all

the time, and it does not predict what happens in front of the wedge.Most importantly, the

Coulomb Wedge approximation does not define the dynamic processes of FATB

development.

To investigate these, we used a 2D numerical FEM model built with Abaqus© 6.14 to

show how wedge development is a cyclic process, in which the region in front of the

wedge plays a critical part. In the FEM model, we can track the propagation of the stress

front, the displacement front, and the failure front in an simulated thrust belt. These are

physically separated and quite distinct: the stress front leads the system, followed in turn

by the displacement front and the failure front. They advance cyclically at a non-uniform

rate.

When a wedge achieves critical taper, thrust movement within the wedge slows, and the

displacement in front of the wedge accelerates until a new thrust can initiate at the failure

front. But as soon as this happens, the taper angle is reduced below critical state. Motion

becomes concentrated on the new thrust, and propagation of the displacement and stress

fronts slows down until critical taper is re-established. Our model shows that there is an

essential activity in front of the thrust wedge which is an important part of the overall

process. The the wedge cannot propagate without this precursor activity, which may be

hard to identify in natural examples.

Observations on 3D seismic reflection data from a passive margin FATB in Baram Delta

system, NW Borneo, SE Asia reveal that there are up to 8-10 obvious fault related folds

developed with an orientation of NE-SW in the thrust belt, slight shortening (characterised

by detachment folding) in front of main thrust wedge demonstrates the displacement front

lies ahead of the thrust fault, and, we infer, it lies behind the stress front. We observe

along-strike variations in the structural style of the FATB: these appear to mirror the

proximity of a potential barrier to the FATB, in the form of a major carbonate platform,

which lies some way ahead of the apparent deformation front. In a classical coulomb

wedge model, the FATB should not yet be interacting with the platform, so the apparent

mirroring is inexplicable. Is it possible that the stress and displacement fronts ahead of the

FATB have already reached the carbonate barrier, and this interaction explains the

observed variations?


47

Understanding long-term strain accommodation in the Longmen Shan

region: Insights from 3D thermo-kinematic modelling of

thermochronometry data

Yuntao Tian

1, Pieter Vermeesch

1, Andy Carter

2

1

Department of Earth Sciences, University College London, UK

[email protected] 2 Department of Earth and Planetary Sciences, Birkbeck, University of London, UK

The Longmen Shan marks the steep eastern margin of the Tibetan Plateau and three

parallel NW-dipping fault zones define its structural geometry. From foreland (southeast)

to hinterland (northwest), the main faults are the Guanxian-Anxian fault, Yingxiu-

Beichuan fault and Wenchuan-Maowen fault. The exhumation pattern constrained by 1-

dimensional modelling made from a compilation of published and unpublished

thermochronometry data shows a strong structural control, with highest amounts of

exhumation in the hinterland region, a pattern that is characteristic of out-of-sequence

thrusting (Tian et al., 2013, Tectonics, doi:10.1002/tect.20043). Three-dimensional

thermo-kinematic modelling of these data suggests that the listric Longmen Shan faults

merge into a detachment at a depth of ~20-30 km. The models require a marked decrease

in slip-rate along the frontal Yingxiu-Beichuan in the late Miocene, whereas the slip-rate

along the hinterland Wenchuan-Maowen fault remained relatively constant. These results

reveal the long-term pattern of strain accommodation and have important implications for

hazard risk assessment in the region. Further, the out-of-sequence thrusting architecture

highlights the importance of upper crustal shortening and extrusion in forming this plateau

margin.


48

The Deep Structure of the Continents

Dan M

cKenzie

1

1 Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge,

CB2 3EQ

[email protected]

For 50 years we have had an excellent understanding of how oceanic crust and lithosphere

is produced, by passive upwelling and melting on ridges, and how it moves as a rigid

spherical cap until it is destroyed by subduction. But we still have no similar

understanding of the evolution and tectonics of continental lithosphere. Part of the

problem is that, until recently, we had no method of imaging its three dimensional

structure. But now we do, using surface wave tomography, and especially by using higher

modes. This new technology allows us to produce global maps of lithospheric thickness.

Some features of such maps simply confirm what we already knew from mantle nodules

brought up by kimberlites: that most (but not all) cratons are underlain by thick

lithosphere. But the lateral extent of such thick lithosphere is much greater than is the

surface outcrop of ancient rocks. However, what was unexpected was that the thickest

lithosphere is not beneath cratons but beneath Tibet. This feature is not consistent with

models of continental delamination, and in turn suggests how thick cratonic lithosphere is

generated. Out of curiosity Mike Daly and I reconstructed Gondwanaland, and to our

surprise found that thick lithosphere formed a contiguous arc behind the subduction zone

that consumed Panthalassa. The production of this feature must have involved extensive

deformation of thick lithosphere, and also suggests that lithospheric thickness exerts an

important control on continental assembly. So I think we are now beginning to understand

what controls continental evolution and deformation 50 years after we understood that of

the oceans.



49

Rapid orogenesis driven by crustal extension in eastern Indonesia

L. White

1, R. Hall

1, R. Armstrong

2, and I. Gunawan

3

1Department of Earth Sciences, Royal Holloway, University of London, Egham, Surrey

UK. [email protected] 2Research School of Earth Sciences, The Australian National University, Canberra,

Australia. 3Institut Teknologi Banding, Bandung, Indonesia.

Eastern Indonesia represents a complicated zone of interaction between several major and

minor plates. It represents a zone where we can study the early stages of orogenesis, prior

to “terminal” collision which may obscure or remove parts of the geological record. Many

have considered eastern Indonesia to be a largely accretionary zone dominated by crustal

shortening. Yet, recent and ongoing studies continue to demonstrate that many of eastern

Indonesia’s mountainous regions record evidence of signficant crustal extension, or record

multiple switching between periods of shortening and extension. We show examples of

some of these processes from Halmahera and West Papua. In West Papua, we have used a

combination of field studies and microstructural observations to document cross-cutting

relationships for a multiply deformed metamorphic core complex (the Wandaman

Peninsula). Previous studies report eclogite and amphibolite from the peninsula and

propose that the metamorphism and unroofing occurred in the Mio-Pliocene. Should this

be true, our observations of later deformation indicate that uplift and mode-switches

between shortening and extension must have been rapid, likely occurring on million year

time-scales. Similarily, on the island of Bacan, in Halmahera, we have dated some of the

world’s youngest granitoids (1.4 Ma). These granites are exposed at 2000 m above sea

level. Offshore of this small island, there is significant vertical displacement and a thick

pile of sediment accumulating in the space that has been created during the extentional

exhumation of these granitoids. This again indicates that extensional tectonics is driving

rapid uplift near the plate boundary between the Philippine Sea, Molucca Sea and

Australian plates. This work has implications for our understanding of mountain building

in other parts of the world, particularly as large parts of the Alps and Himalayan chains

likely involved the accretion of island arc systems and continental crust during the closure

of Tethys, with their history being incredibly difficult to resolve after ten’s of millions of

years of being sandwiched between larger continental plates (e.g. India/Eurasia).


50

Basement-cover tectonics, structural inheritance

and deformation migration in the outer parts of orogenic belts:

A view from the western Alps.

Rob Butler

Geology and Petroleum Geology, School of Geosciences, University of Aberdeen,

Aberdeen AB24 3UE, UK.

[email protected]

The structure and geology of former rifted continental margins can exert significant

influence on their subsequent incorporation into collision orogens. While thinned

continental crust attached to the subducting mantle lithosphere may be incorporated into

subduction channels, the weakly rifted parts of the margin are likely to resist subduction

and thus deform ahead of the main orogenic front. This expectation is corroborated by a

case study from the external western Alps. The former Dauphinois basins have inverted to

form external basement massifs. Recent research on the Ecrins (Pelvoux) – Vercors

transect has modified simple inversion descriptions: much of the deformation was widely

distributed, with few localised thrust structures. Using a total shortening of 54 km and

assuming conservation of cross-sectional area, the mean pre-orogenic crustal thickness

was c 22 km. While there is convergence on such estimates of pre-orogenic crustal

thickness and Alpine shortening, the timing and rates of contraction remain contested.

Existing models invoke distinct deformation events, separated in time by a major (late

Eocene, “Nummulitic”) unconformity. This is overlain by the regional “foredeep”

turbidite system (Annot-Champsaur-Aiguilles d’Arves) of late Eocece-Oligocene age (c

34 ±2-3 Ma). Recently acquired Ar-Ar deformation ages from basement tectonites in the

Ecrins straddle this depositional age. Integrating stratigraphic, paleothermal and

geochronological data reveals that basin inversion and deformation of the Ecrins massif

was protracted over 10-15 Myr, coeval with deformation in the more internal parts of the

Alpine chain. Through this period the syn-tectonic surface was at times sub-areal

(deformation accompanied by denudation), submarine (with growth strata) and finally

buried beneath internal thrust sheets. Episodic descriptions of orogenic evolution are

artefacts of these different surface states. Crustal shortening was continuous in time. The

notion of continuous, rather than episodic, deformation raises issues for how rates and

tectonic activity may be evaluated within ancient orogens.



51

Microstructural evolution of plagioclase during shear zone formation in

a lower-crustal gabbro

B. Fernando

1, D. Wallis

2, and L. N. Hansen

3

1Department of Earth Sciences, Oxford University, UK. [email protected]

(student) 2Department of Earth Sciences, Oxford University, UK. [email protected]

3Department of Earth Sciences, Oxford University, UK. [email protected]

The behaviour of plagioclase controls the rheological properties of Earth’s lower crust

during ductile deformation. This ductile deformation includes both large-scale,

homogeneous deformation and the formation of localised shear zones. Importantly, the

deformation of plagioclase depends intimately on its microstructural evolution, especially

in the context of strain localisation and shear zone formation.

Unfortunately, there are several areas where a more thorough understanding of plagioclase

deformation is needed. For instance, the timescales of the evolution of crystallographic

preferred orientations (CPOs) may prove key to the formation of long-lived shear zones

due to the development of plastic anisotropy. Although some attempts have been made to

simulate CPO development in plagioclase, few observational constraints exist. In addition,

the evolution of plagioclase grain size during deformation is thought to promote

weakening and localisation through the resulting influence on the dominant deformation

mechanism. However, the systematics of plagioclase grain-size reduction have not yet

been quantified, especially in compositionally complex rocks in which hydration may lead

to the nucleation of secondary phases that pin plagioclase grain boundaries.

We attempt to quantify the relevant parameters for microstructural evolution through

investigation of a centimetre-scale shear zone from a gabbro section of the Semail

ophiolite in the United Arab Emirates. Orientations of mineral foliation in hand sample are

used as proxy for the magnitude of shear strain, revealing a distinct strain gradient and

shear strains >10. This strain gradient is accompanied by a marked reduction in grain size.

Microstructural analysis was conducted with electron backscatter diffraction in a scanning

electron microscope. EBSD mapping was conducted in a 7.5cm transect across the shear

zone parallel to the strain gradient. The resulting dataset is used to quantify the mean grain

size, CPO strength and orientation, and modal proportions of different phases as a function

of shear strain. These data are compared to theoretical predictions and laboratory

observations of plagioclase microstructural evolution, with the aim of constraining those

models and allowing for new insight into lower crustal deformation.



52

Lithological controls on coseismic behaviour shown by frictional melting

experiments on wall rocks of the Outer Hebrides Fault Zone.

L.R.Campbell

1, N. De Paola

2, S. Nielsen

2, R.E. Holdsworth

2, G.E. Lloyd

1, R.J. Phillips

1,

R.C. Walcott3

1School of Earth and Environment, University of Leeds, UK

[email protected] 2Department of Earth Sciences, Durham University, UK

3Nation Museums Scotland, Edinburgh, UK

Recent experimental studies at seismic slip rates (≥ 1 m/s) suggest that the friction

coefficient of seismic faults is significantly lower than at sub-seismic (< 1 mm/s) speeds.

Microstructural observations have presented a range of thermally-activated mechanisms

(e.g. gel, nanopowder and melt lubrication, thermal pressurization, viscous flow),

triggered by frictional heating in the slip zone, that could control coseismic weakening.

The presence of pseudotachylyte within both exhumed fault zones and experimental slip

zones in crystalline rocks suggests that lubrication plays a key role in controlling dynamic

weakening during rupture propagation.

The Outer Hebrides Fault Zone (OHFZ), UK contains abundant pseudotachylyte along

faults cutting varying gneissic lithologies. Our field observations suggest that the

mineralogy of the protolith determines volume, composition and viscosity of the frictional

melt, which then affects the coseismic weakening behaviour of the fault and has important

implications for the magnitudes and distribution of stress drops during slip episodes.

High velocity friction experiments at 18 MPa axial load, 1.3 ms-1

and up to 10 m slip were

run on quartzo-feldspathic, metabasic and mylonitic samples, collected from the OHFZ in

an attempt to replicate its coseismic frictional behaviour. These were configured in cores

of a single lithology, or in mixed cores with two rock types juxtaposed. Metabasic and

felsic single-lithology samples both produce sharper frictional peaks, at values of μ = 0.19

and μ= 0.37 respectively, than the broader and smaller (μ= 0.15) peak produced by a

mixed basic-felsic sample. In addition, both single-lithology peaks occur within 0.2 m

slip, whereas the combined-lithology sample displays a slower transition to the steady

state, with the peak occurring after almost 2 m. Microstructural and compositional

investigations on the melt confirm that preferential melting of biotite and amphiboles,

where present, not only contribute disproportionally to the melt composition - and hence

viscosity - but also influence the roughness of the slip surface. Our results show that the

frictional behaviour of faults in crystalline rocks, where different lithologies are in contact,

is complex. Protolith composition determines the physical properties of the melt, which

controls the evolution of coseismic friction.


53

‘Pseudotachyl_te’ – a case study of ambiguous terminology in geoscience

B. Vogt

1, Z. K. Shipton

1, and J. Roberts

1

1Department of Civil and Environmental Engineering, University of Strathclyde, Glasgow,

UK. [email protected]

Pseudotachylites, also spelt pseudotachylytes, are aphanitic fault rocks that are commonly

dark in colour. They contain clasts of, and exhibit a sharp contact to their host rock. Their

name was coined by Shand (1916), who reported dikes (or dykes) from Vredefort

(Republic of South Africa), of an enigmatic rock type, which he described as “trap- or

tachylite-like”. Since their recognition as friction melts produced at seismic slip rates,

peudotachylites have been used to infer earthquake source parameters. These “tectonic”

pseudotachylites generally occur in thicknesses of millimeters to a few centimeters. On the

other hand, pseudotachylites from the type locality in Vredefort commonly occur in

massive dikes up to tens of meters in thickness (sometimes referred to as pseudotachylitic

breccias after Reimold, 1995). These large volumes of pseudotachylites are only matched

by a handful of places on Earth, such as the Sudbury impact structure, Canada. However,

the processes behind the formation of large volume pseudotachylites are still a matter of

debate.

We conducted a survey to explore how the term "pseudotachylite" is used amongst

geoscientists of different subdisciplines. The surveys were completed by delegates at two

conferences on the topics of (1) rock deformation and (2) impact cratering research in

2015. Our preliminary results find that one fraction of the scientists make a clear

distinction between tectonic (micro-fault) pseudotachylites and impact-related

pseudotachylites, whereas the other fraction does not make this distinction. The distinction

is based on size, geometry, and the inferred process(es) of formation.

Misconceptions behind terminology and language can hamper the research progress, as is

well known from interdisciplinary research endeavours. Here, we find that the same term

is used by two different communities of geoscientists to imply different formation

processes. This has, no doubt, confounded the debate on the origin(s) of these rocks.

Issues of miscommunication is particularly important when, for example, scientific reports

inform political or economic decision-making. For effective communication, potentially

ambiguous geoscientific terminology should be identified. This is particularly important

for sensitive or contentious topics, such subsurface engineering projects like shale gas

extraction or the geological disposal of radioactive waste. While the debate around the

origin of pseudotachylites is clearly not a contentious topic for the general public, this

study highlights the need for geological language to be better defined to enhance science

communication.

References:

Dressler, B. O. and Reimold, W. U. (2004). Order or chaos? Origin and mode of emplacement of breccias in floors of

large impact structures. Earth-Science Reviews, 67:1–54. Lieger, D., Riller, U., and Gibson, R. L. (2009). Generation of

fragment-rich pseudotachylite bodies during central uplift formation in the Vredefort impact structure, South Africa.

Earth and Planetary Science Letters, 279(1-2):53–64. Reimold, W. (1995). Pseudotachylite in impact structures -

generation by friction melting and shock brecciation?: A review and discussion. Earth-Science Reviews, 39:247– 265.

Shand, S. J. (1916). The Pseudotachylyte of Parijs (Orange Free State), and its Relation to ’Trap-Shotten Gneiss’ and

’Flinty Crush-Rock’. Quarterly Journal of the Geological Society, 72(1-4):198–221. Spray, J. (1997). Superfaults.

Geology, 25:579–582.


54

Long-term dissolution-precipitation creep at low stresses and transient

high-stress crystal plasticity of quartz in the subduction zone

C.A. Trepmann

Department of Earth and Environmental Sciences, Ludwig-Maximilians-University

Munich, Germany.

[email protected]

Subduction plays a first-order role in the dynamics of the Earth, where the down-going

plates undergo metamorphism and deformation as they descend to depth, accompained by

seismic activity. Exhumed high pressure – low temperature (HP-LT) metamorphic rocks

provide unique information on the pT-history, grain-scale deformation mechanisms and

state of stress during both, burial and exhumation. Though, the rock record is not easy to

correlate with the large-scale geodynamic processes because of the superposition of

(micro)structures generated during different transient stages at strongly varying

conditions. Deciphering the deformation record of HP-LT metamorphic rocks, i.e., to

resolve the different deformation stages during burial and exhumation, is vital to elucidate

the rheological evolution of subduction zones.

Here, quartz microfabrics from HP-LT metamorphic rocks at the base of the lowermost

known level of the Cretan nappe pile in the Talea Ori Mountains are presented. In

components of low-strain metaconglomerates, deformation microstructures originating

from the source rocks of the pre-Alpine basement are preserved or quasi-statically

overprinted during the later subduction history. A gradual transition from these low-strain

metaconglomerates, associated black shales and metacherts, to shear zones is observed.

The shear zones are characterized by a scaly foliation, shear bands and associated quartz

veins. The shear bands generally indicate down-faulting of the northern block. Associated

quartz veins taper wedge-shaped at a high angle to the foliation, decorating the shear band

boundaries and showing shear offsets. Microfabrics from these shear bands and related

vein quartz show indication of dislocation glide-controlled deformation of quartz by the

presence of deformation lamellae, deformation bands, short-wavelength undulatory

extinction and localized strings of recrystallized grains. The shear zones document at least

two different deformation stages: A first stage is characterized mainly by dissolution-

precipitation creep generating the scaly cleavage, representing low-stress viscous flow in

the subduction zone. A second stage is recorded by the shear bands and associated quartz

veins, indicating localized and episodic deformation at transient high stresses. This stage

is interpreted to be linked to the detachment of the subducted sediments from their original

substratum recording transient high-stress deformation, probably related to seismic

activity.


55

The effects of anisotropic elastic properties on shock deformation

microstructures in zircon and quartz

N. Timms

1 and D. Healy

2

1Department of Applied Geology, Curtin University, Perth, GPO Box U187, WA 6845,

Australia. [email protected] 2School of Geosciences, King’s College, University of Aberdeen, Aberdeen, AB24 3UE,

UK.

Impact shock metamorphism of minerals can result in thin (nanometers to micrometers)

lamellae with the same composition as the host crystal containing an amorphous phase

(planar deformation features, or PDFs), twins and/or high-pressure polymorphs. These

features all occur along a limited number of rational, low-index crystallographic planes,

specific to each mineral phase, if the yield condition is exceeded. Minerals respond

elastically before the yield condition is reached, and elastic behavior exerts some influence

on the nature of the plastic strain in many materials. All minerals exhibit anisotropic

elasticity governed by their intrinsic crystallography. In this study, we investigate the

effects of anisotropic elasticity on the formation of shock deformation microstructures

along specific {hkil} in zircon and quartz, chiefly for their importance in geochronology

and shock barometry, respectively.

Young’s modulus (E) scales a longitudinal strain into an equivalent stress, shear modulus

(G) describes a similar relationship for shear strains and shear stresses, and Poisson’s ratio

(ν) relates axial and lateral strain, and can be positive or negative in minerals. Full

descriptions of G and ν involve a range of different magnitudes in different directions

normal to each crystallographic direction. In this study, we calculate and visualise the

minimum and maximum magnitude of G and ν normal to each crystallographic direction

(Gmin and Gmax, and νmin and νmax, respectively), for the first time in two minerals.

Zircon has tetragonal symmetry and is highly anisotropic in its elastic properties (E,

63.4%; Gmin, 60.8%; Gmax, 20.7%), and non-linear increases in properties with pressure (to

24 GPa) with little effect on the anisotropy. The directions normal to common PDF and

micro-cleavage plane orientations reported in zircon (i.e., {001}, {100}, {112}) have a

combination of high values of E and ν, and low Gmin values. That is, zircon is elastically

more rigid in directions perpendicular to the PDF planes, and elastically soft in shear in

directions parallel to these planes. Our analysis also supports a shear mechanism for shock

twins along {112} in zircon. Lamellae of the high-pressure polymorph, reidite, most

commonly form along high-E, low-Gmin {100} in zircon. However, reidite formation is

impeded in radiation damaged (metamict) zircon in which all values and anisotropy of E

and G are significantly lower, highlighting the importance of elastic stiffness in the

formation of some shock features.

Quartz (trigonal) is also highly anisotropic in its elasticity, but with significantly different

responses for <r> than for <z>. The anisotropy of Gmin has an excellent correspondence

with the relative abundance of PDF planes {hkil} reported elsewhere, and no PDFs are

reported for planes with high Gmin values. We speculate that PDFs in minerals are shear-

induced damage planes, and that shear modulus anisotropy exerts a first order influence on

shocked planes such that {hkil} planes with the lowest shear modulus have the lowest

yield condition. This predicts a sequence of PDF formation with increasing yield

conditions, which could be used to refine the PDF-based shock barometer for quartz.


56

Friction and deformation of mineralogically controlled serpentines.

Examples from the Monte Fico ophiolitic shear zone (Elba Island, Italy)

T. Tesei1, C. Viti

2, E. Mugnaioli

2, and C. Collettini

3

1Istituto Nazionale di Geofisica e Vulcanologia, Rome, Italy.

[email protected] 2Department of Physical Sciences, Earth and Environment, Siena University, Siena, Italy.

3Department of Earth Sciences, La Sapienza university, Rome, Italy.

Serpentines are important constituents of faults in tectonic mélanges associated to

subduction and strike-slip settings, of obducted tectonic slivers in collisional orogens

(ophiolites), or along oceanic core-complex detachments. We present field and

microstructural observations coupled with friction experimens to gain insights into the

mechanics of these important tectonic features.

We studied deformed serpentinites from the Monte Fico shear zone (Elba Island,

Italy). The shear zone is an obduction thrust characterized by a complex array of lens-

shaped massive serpentinites separated by discrete shear surfaces coated by slickenfibres

of serpentine. Sliding along these surfaces occur in parallel with dissolution-

recrystallization processes that progressively alter the bastite-and-mesh texture of the

massive lenses. The compressive shear zone is cross-cut by normal faults that record

deformation of the serpentinites at shallower crustal levels. Normal faults are

characterized by the association of cataclastic deformation, calcite veins and serpentine

recrystallization along the sliding surfaces. These observations suggest that the strength of

the shear zone is bounded by the strength of the fibrous serpentine along the shear

surfaces.

We have tested the frictional properties of mineralogically controlled serpentinite

powders using a biaxial apparatus under various applied normal stresses and water-

saturated conditions. Friction of the three principal serpentine minerals, namely antigorite,

lizardite and chrysotile, has been extensively investigated under a large variety of P-T-

strain conditions. In the “brittle field” Lizardite and antigorite have been commonly

reported to have high friction μ>0.4, whereas chrysotile has been reported to be

frictionally weak μ<0.3. Conversely, Lizardite standards and the natural mixtures of

serpentintes from the Monte Fico shear zone yielded extremely low coefficients of

friction, i.e. μ<0.2.

Our data suggest that the preferred orientation of serpentinite fibres coupled with

their mineralogical texture controls the strength of natural serpentinites and inherent

weakness of serpentinite-bearing faults that can explain the apparent weakness of some

major tectonic features such as the San Andreas fault and OCC detachments.


57

Brittle-viscous deformation cycles in the dry and strong continental

lower crust

L. Menegon1, G. Pennacchioni

2, and N. Malaspina

3

1School of Geography, Earth and Environmental Sciences, Plymouth University, Plymouth,

UK. [email protected] 2Department of Geosciences, University of Padua, Padua, Italy. 3Department of Environmental and Earth Sciences, University of Milan-Bicocca, Milan, Italy.

Many rheological models of the lithosphere (based on “strength envelopes”) predict a

weak aseismic lower crust below the strong brittle upper crust. An alternative view, based

on the distribution of crustal seismicity, is that the lower crust could also be strong and

seismogenic. It has been suggested that a strong, seismogenic lower crust results from the

dry conditions of granulite facies rocks, which inhibit crystal plastic flow.

This study investigates exhumed networks of shear zones from Nusfjord (Lofoten,

northern Norway) to understand initiation and localization of viscous shearing in the dry

and strong lower crust. In the study area, different sets of ultramylonitic shear zones are

hosted in the massive coarse-grained anorthosite. Metamorphic conditions of 720° C, 0.9

GPa have been estimated for ductile deformation using amphibole-plagioclase

geothermobarometry and thermodynamic modelling. Field evidence indicates that viscous

shearing exploited pseudotachylyte veins (solidified frictional melt produced during

coseismic slip) and the associated damage zone of extensive fracturing. Field- and thin

section observations indicate that frictional melting occurred at the same deep crustal

metamorphic conditions of viscous shearing (mylonitization). Mutually overprinting

pristine pseudotachylytes and ultramylonites (derived from pseudotachylyte veins)

indicate that brittle (coseismic) and viscous deformation occurred cyclically in the lower

crust. Detailed microstructural analysis of the ultramylonites suggests that diffusion creep

and grain boundary sliding were the dominant deformation mechanisms. Nucleation of

hornblende in dilatant sites indicates that fluids were channelized in the ultramylonites.

However, intracrystalline water contents in nominally anhydrous minerals (plagioclase

and clinopyroxene) measured in (1) the damage zone flanking pseudotachylyte veins, (2)

survivor clasts within pseudotachylyte veins, and (3) large porphyroclasts within the

mylonitized pseudotachylytes, are of the same order as those measured in the massive

anorthosites (< 50 ppm H2O on average). Thus, we conclude that fracturing did not result

in intracrystalline fluid infiltration and hydrolitic weakening of minerals, and that fluid

infiltration in the fractured domains has rather promoted mineral reactions and grain

boundary diffusivity. This resulted in the activation of grain size sensitive creep and in

viscous strain localization.

In summary, this study indicates that brittle (coseismic) fracturing was essential to weaken

the dry and strong lower crust by activating grain size sensitive creep in the fine-grained

material resulting from grain size reduction. Coseismic fracturing resulted in the ductile

shear zones localized to the brittle precursors. In the absence of intense fracturing dry

granulites would not undergo deformation and metamorphism, and would survive

metastably in the course of Wilson cycles. This has obvious implications for long-term

continental dynamics and for strain localization at plate boundaries, and will need to be

included in future geodynamic models.


58

Spontaneous Electric Current Flow in a Deforming Non-Piezoelectric

Rock at Conditions Spanning the Brittle-Ductile Transition

A. Cartwright-Taylor

1,2, P. Sammonds

2, and F. Vallianatos

3

1School of GeoSciences, University of Edinburgh, Edinburgh, UK.

[email protected] 2Institute for Risk and Disaster Reduction, University College London, London, UK.

3Technological Educational Institute of Crete, Laboratory of Geophysics and Seismology,

Crete, Greece

We investigate spontaneous electric current flow in a non-piezoelectric rock (Carrara

marble) during triaxial deformation at conditions spanning the brittle-ductile transition.

Mechanical data, ultrasonic velocities and acoustic emissions were acquired concurrently

with electric current measurements to constrain the relationship between electric current

flow and damage. Under strain-controlled loading, spontaneous electric current signals

(nA) are generated and sustained at all the conditions tested. Localised electric dipoles are

responsible for these signals, evident from variations in current flow through different

regions of the sample. In dry samples, a detectable electric current arises only in the region

of permanent deformation beyond the yield point of the material and is correlated with the

damage induced by microcracking, with a contribution from other intermittent ductile

mechanisms. Current and charge densities are consistent with models of crack separation

charging. Both absolute and fluctuating components of the signal are related to stress,

mechanical damage and deformation mechanism.

Electric current and electric charge production depend strongly on the experimental

condition. Power-law relationships are seen with confining pressure and strain rate across

the brittle-ductile transition, with the first corresponding to microcrack suppression and

the second to time-dependent differences in deformation mechanism. In the brittle regime,

the signal exhibits a precursory change as damage localises and the stress drop accelerates

towards failure. Similar changes are seen in the semi-brittle regime, but the oscillatory

nature of the signal means a high probability of false alarms. The high-frequency electric

current fluctuations exhibit non-random, ‘heavy-tailed’ macroscopic distributions, with

characteristic parameter values for different deformation regimes across the brittle-ductile

transition. Evolution of the distribution parameter during deformation reveals a two-stage

precursory anomaly prior to sample failure, consistent with the observed acoustic

emissions b-value and the stress intensity evolution as modelled from fracture mechanics.

Our findings support the notion that electric currents in the crust can be generated purely

from deformation processes. Scaling the laboratory results to large stressed rock volumes

characteristic of those that produce M7 earthquakes (104 −10

5 km

3) at crustal strain rates,

and accounting for >99% dissipation, deformation-induced transient telluric current

systems may be as large as 106 A. This corresponds to a huge accumulated net charge of

1022

C and implies that a significant amount of charge from deforming tectonic regions

contributes to the Earth’s telluric currents and electric field. However, it is unlikely that

accumulated charge of this quantity could ever be measured in the field due to conduction

away from the stressed rock volume.


59

Strength recovery and vein growth during self-sealing of experimental

faults in Westerly granite.

Philip Meredith

and Nicolas Brantut

Rock and Ice Physics Laboratory, Department of Earth Sciences,

University College London, London, UK.

[[email protected]]

Numerous studies have shown that crustal deformation in the presence of chemically-

active pore fluid is commonly accompanied by selfpsealing processes that can occur

relatively rapidly compared with geological time-scales. This is consistent with earthquake

models involving transient fluid flow on faults during seismic slip. Followed by self-

sealing which may occur through physico-chemical processes suchs as the crack-seal

mechanism. Here, brittle deformation of water-saturated rock produces new fracture

surfaces that are out of chemical equilibrium with the pore fluid, leading to mineral

dissolution, mass transport and precipitation in a cycle of coupled deformation and fluid

flow.

We present direct experimental evidence for the rapid development of dilatant crack-seal

quartz veins during sequential stressing of rock samples containing pre-existing faults.

Right-cylindrical, pre-faulted samples of Westerly granite were held at a constant

temperature of 400°C and an effective confining pressure in the range 100 to 160 MPa in a

triaxial deformation apparatus. A differential axial stress was then applied cyclically to

the samples at a strain rate of 10-5

s-1

to induce frictional sliding under either saturated (λ =

0.4) or dry (λ = 0) conditions using distilled water as the pore fluid. The samples were

broken a number of times (5 to 7 depending on the test) over periods of up to several

months, and left to cook between loading cycles at constant temperature and hydrostatic

pressure for hold times varying between 1 hour and 78 d ays. On re-loading, all the

saturated samples exhibiuted sunstantial strength recovery for hold times greater than

about 100 hours, while dry samples showed no increase in strength for any hold time up to

the maximum of 34 days.

The reason for the strength recovery becomes clear from post-mortem microstructural

analysis of the deformed samples. All of the saturated samples showed evidence of the

developoment of quartz veins in the fault zones, whereas none of the dry samples showed

any evidence of such veining. The experimentally produced quartz veins are not due to

any influx of a supersaturated fluid from far away, as commonly invoked for crack-seal in

the crust, but have developed spontaneously by solution, transport and deposition from a

local source in the host rock during and after slip on the fault surface. A vein provides a

natural mechanism for both healing (strength recovery) and sealing (permeability

reduction). However, we would expect permeability to decrease before contact between

the vein and the fault walls leads to strengthening because permeability depends on the

cube of aperture.


60

Poster Presentation Abstracts

(Alphabatised by first author)


61

Two Hundred and Fifty Six Shades of Grey: Impact of seismic image

quality on interpretation uncertainty

Alcalde, J.

1,2, Bond, C.E.

1, Johnson. G.

2, Ellis, J. F.

3 And Butler, R. W. H.

1Geology and Petroleum Geology, University of Aberdeen, School of Geosciences,

Kings College, Aberdeen, AB24 3UE, UK. 2School of Geosciences, University of Edinburgh, West Mains Road, Edinburgh, EH9

3JW, UK. 3Midland Valley Exploration Ltd, 2 West Regent Street, Glasgow, G2 1RW, UK.

Uncertainty in interpretation of a seismic image is deeply affected by its image quality.

This uncertainty can have a strong economic impact in subsurface resource exploration.

Numerous studies deal with data quality affecting the interpretation, but usually only refer

to the quality of the seismic data in a qualitative way (e.g., “poor quality”). We analysed

fault interpretations carried out by 196 participants for a seismic image, presented both in

two-way traveltime (TWT) and as a depth-converted image. The depth conversion

stretched the image and reduced the image contrast and reflector continuity. Using image

analysis techniques we have quantified the differences in contrast and continuity of the

TWT and depth images, creating colour maps of image quality to compare with the spread

in the interpreted fault populations. Analyis of the results strongly suggest that differences

in image contrast and reflection continuity can form artificial (i.e. not data-constrained)

boundaries that impact interpretation outcome. The effects of image quality and

presentation should be taken into account by both those involved in the processing and

interpretation of seismic image data. The analysis suggests that quantitative assessment of

image quality can be used to feed into seismic processing models for the creation of

optimal images for interpretation, and to determine areas within seismic imagery that are

poorly constrained. This information can be used to inform areas in an interpretors model

where interpretation risk maybe high, and where interpretation and structural modelling

efforts should be focused.


62

The Stuctural Evolution of Panticosa, Spanish Pyrenees.

B. Andrews

1

1Department of Earth and Environment, University of Leeds, UK. [email protected]

This study describes the sedimentary, structural, igneous and metamophic evolution of a

section of the Axial zone, Spanish Pyrenees. This was achieved through 1:10,000 field and

the use of high resolution air photos to deduce the field retaltions and thin sections to

investigate the genesis of the zoned bathalith. The area of study covers a roughly 20 km2

area extending 6 Km NE from the village of Panticosa in the Spanish Pyrenees. The axial

zone of the Pyrenees consists of Precambrian to Carboniferous rocks with younger

Mesozoic highly folded strata to the north and south (Mcmillan 1985). The rocks

surrounding Panticosa consist of Devonian pelites and carbonates (Gleizes et al. 1998),

Veriscian batholith (e.g. Subías et al. 2015; Gil-Imaz et al. 2012) and Permian Dyke

swarms (Gil-Imaz et al. 2012).

The mapped area is charactorised by hectometer folded paleozoic calcic turbidites and fine

siliclastics split into five mappable sedimentary units laid down in lower shelf settings

prior to being folded. The sedimentary pile was intruded by a 12 Km2 veriscan normally

zoned bathalith ranging in composition from Quartz monzinite to Tonalite forming an up

to 400m metamorphic aureole. During the permian multiple generations of mafic dykes

were intruded of variable composition, either chlorite aultered or not. Alpine tectonics is

not clearly seen in the mapping area however may be visible through the multiple

cleavages seen in the fine siliclastics aswell as occationally in the carbonates. The area

was finally cut by a large number of normal faults, with offsets from meter to 500m

offsets.

Overall this study has revealed a complex geological evolution of an area with evidence of

numerous stress fields and complex history of dyking. The late stage normal faulting

complicates the internal structure and contact of the bathalith (Figure 1).

Figure 1 – Sketch of Batholith, Paleozoic sediment contact from GR 0725199 4737741


63

Geometry and kinematics of normal faults in a salt-related minibasin,

Santos Basin, offshore Brazil

Donatella Astratti, Christopher A-L. Jackson, and John W. Cosgove

Basins Research Group (BRG), Department of Earth Science & Engineering, Imperial

College, Prince Consort Road, London, SW7 2BP, UK

The geometry and evolution of halokinesis-related faults in structurally complex areas is

poorly understood. In this study we use high-quality 3D time-migrated seismic data to

investigate a normal fault array developed on a salt-cored anticline flanked by Cretaceous

minibasins in the Santos Basin, offshore Brazil. Three nearby wells provide information

on lithology and age of the faulted succession, and velocity data that we used to undertake

depth conversion of the time-migrated volume.

Our initial focus is an area of c. 35 km2 where the fault array can be subdivided in three

domains superimposed on the salt-cored anticline; (i) a northern domain –cross-cutting,

conjugate faults that strike NNE-SSW, sub-parallel to the anticline hinge; (ii) a central

domain –subparallel NNE-SSW-striking faults also sub-parallel to the anticline hinge; and

(iii) a southern domain –E-W-striking faults that are broadly perpendicular to the anticline

axis. The southwards change in fault strike is associated with an increase in dip, from 50-

60° in the northern and central domains to >70° in the southern domain.

Detailed mapping of throw patterns on >100 faults, whose maximum value is c. 30 m, is

key to understanding the Albian to Cenozoic growth of this salt-related fault array.

Many of the faults in the central and southern domains grew by lateral linkage, with

maximum throw occurring close to the top of the Albian. Their lower tips are located in

poorly reflective Albian shales, whereas their upper tips have variable upward extents: on

the western flank of the anticline, the faults die out within the Senonian, whereas the faults

along the hinge and on the crest of the anticline continued growing until the Oligo-

Miocene. The northern domain witnessed two episodes of fault initiation, during the

Albian and the Senonian. The upper and lower fault tiers locally dip-linked, and some of

these structures also grew by lateral linkage to connect with faults in the southern domain.

In the northern domain the upper tips of the faults are shallower than in the south and their

lower tips extend deeper into the Albian, locally reaching the top salt.

We speculate the hinge-parallel faults accommodate hinge-normal stretching related to the

growth of the anticline, and the abrupt change in fault strike in the southern domain is

related to hinge-parallel stretching related to salt evacuation from the south of the

anticline.We also interpret that faults are taller in the northern array because they

accommodated both the reactive rise and its later collapse of the salt wall on the northern

side of the minibasin.


64

Multi Physics Modeling Of Hydraulic Fracturing and Fluid

Transfer in Fractured Porous Medium to Monitoring Enhanced

Oil Recovery and Engineering Geothermal System

Mohsen Bazargan

1,2, Alberto Striolo

1, Tom Mitchell

1, Agust Gudmundsson

2, and Philip

Meredith1

1Department of Earth Sciences, University College London, UK.

[email protected] 2 Department of Earth Sciences, Royal Holloway University of London, UK..

Naturally fractured reservoirs make up a large proportion of the planet’s hydrocarbon

resources. The permeability of these reservoirs is controlled by the connectivity of the

fracture network. However, it should be pointed out that the development is still poorly

understood especially during hydraulic fracturing operation in oil/gas or geothermal

industry. Normally, in reality very high tensile stresses are generated around the tips of

fractures when the fluid pressure inside them is high enough. Fracture linkage occurs

when these areas of high stress within a minimum separation distance of each other and

are greater than the tensile strength of the rock.

Numerical modelling in this report focused on fluid mechanic and solid mechanic. The

solid mechanic part explores the key controls on fracture formation, propagation, linkage

and arrest,which determine network connectivity and consequently permeability.

Mechanical properties of host rock layers can determine whether a propagating fracture

either penetrates or arrests at a contact between layers or any existing fractures. Originally

softer layers for instance shale tend to cause arrest, but can stiffen over time with

increased burial and diagenesis. Changing mechanical properties of host rock layers mean

fracture network connectivity and associated permeability evolve and can increase or,

alternatively, decrease over time.

Furthermore, in fluid mechanics part of this research group series of computational multi

physics modeling, fluid flowing in a fracture network is channelled into segments with the

reasonable apertures. This is described mathematically by the well known cubic law. The

other main control on the flow pattern is fracture orientation relative to the fluid pressure

gradient. This has been shown to be more critical than aperture size. Fluid flow is

modelled through typical reservoir fracture network, illustrating how the rate of flow is

highest in fracture segments with the largest apertures and, more critically, whose

orientation is parallel with the fluid-pressure gradient. In this poster, this research group is

going to present numerical modelling and statistical analysis results of a reservoir

analogue.

Multi-phase fluid flow is tested in fractured reservoir analogue models to view the effect

of fracture networks in the case of optimizing enhanced oil recovery (EOR) and Enhanced

Geothermal System (EGS). The results show extensive connectivity of fractures is crucial

for efficient penetration of the injected phase into the reservoir. Finally, flowing fluid in a

fractured reservoir, fractures act as faster pathways for injected materials to travel through

than the matrix.



65

Evolution of normal faults and fault-related damage: insights form

physical experiments

Blaekkan, I.

1, Rotevatn, A.

1, Fossen, H

2, Bastesen, E.

3, Seim, M.H.

1, Bøyum, M.S.

1

1

Department of Earth Science, University of Bergen, Allégaten 41, 5007 Bergen, Norway 2 Natural History Museum, University of Bergen, Allégaten 41, 5007 Bergen, Norway

3 Uni CIPR, Uni Research AS, Allégaten 41, 5007 Bergen, Norway

Corresponding author (email: [email protected])

Our understanding of the growth of natural extensional faults is limited to the

study of a random snapshot in time, namely that of present day, aided by various

techniques to reconstruct fault growth history. Furthermore, whilst the growth of faults

may to some extent be reconstructed, the evolution of fault-related damage is harder to

reconstruct and less well understood. In this study we use physical analogue models to

study fault evolution in extensional regimes in time and space. In particular we are

interested in how footwall and hanging-wall damage evolves during fault growth. To do

this, we use Plaster of Paris, which is a well-suited material for this purpose. The

experimental setup is similar to that of Mansfield and Cartwright (2001), with an open top

wooden box with four rigid walls and a moveable internal wall. By moving the internal

wall, the plaster deforms under gravitational collapse, producing an evolving array of

extensional faults and joints. The resulting fault systems have been analysed based on

photos, videos, and the final preserved model itself. In the analyses we have focused on

three main questions: (1) How do faults grow and link to form longer, amalgamated

faults? (2) How does fault related damage evolve over time? (3) How does the topology,

and thus connectivity, of the studied fault systems evolve over time? Preliminary results

suggest that the connectivity of the fault and fracture system increases with strain; further

results from these analyses will be presented at the conference. The findings from the

present and similar studies may shed light on processes relating to fault growth that would

otherwise be difficult to elucidate through studies of natural fault systems.

References:

Mansfield, C., Cartwright, J. 2001. Fault growth by linkage: observations and implications

from analogue models. Journal of Structural Geology 23, 745-763.


66

The Structural Geology of the Bongwana Natural CO2 Release: an

analogue for fracture controlled CO2 migration.

C. E. Bond1

, G. Johnson2, N. Hicks

3, Y. Kremer

4, S. Gilfillan

2, D. Jones

5, R. Lister

5, T.

Maupa6, P. Munyangane

3, K. Robey

3, I. Saunders

3, Z. Shipton

4, Jonathan Pearce

5 and

Stuart Haszeldine2.

1School of Geosciences, Department of Geology and Petroleum Geology, Aberdeen

University, Aberdeen, UK. 2School of GeoScience, University of Edinburgh, Edinburgh, UK.

3Council for Geoscience, Pietermaritzburg, South Africa.


UK. 5British Geological Survey, Keyworth, Nottingham, UK.

6South Africa Centre for Carbon Capture and Storage, Johannesburg, South Africa.

Understanding the role of faults and fractures as fast pathways for CO2 through

overburden strata is critical for ensuring carbon capture and storage (CCS) site integrity.

For example, the veracity of the In Salah CO2 CCS site is questioned due to the role of

fractures in creating a conductive network through which CO2 can migrate. Here we

present data from a natural CO2 release in South Africa that supports the hypothesis that

faults and fractures can act as significant migration pathways for CO2 in the sub-surface,

and to the surface, and are a crucial consideration for CCS projects.

The natural CO2 release near the village of Bongwana in KwaZulu-Natal province in

South Africa was first described in the early 20th century as dry gas exhalations (98%

CO2) along a 150 m line cutting through farmland. Since then little work has been

reported, however other gas seeps and the formation of travertines have been noted. It is

thought that natural CO2 is being released along the length of an ~80 km fault that cuts

through tillite caprock above a potential carbonate hosted CO2 reservoir. A team of

Scottish and South African researchers performed initial fieldwork and reconnaissance in

September 2015. In the field sampling was undertaken for: stable isotope and noble gas

analysis of water and gases, travertines for dating and stable isotope analysis; as well as

soil gas chemistry and flux measurements. Structural geological mapping and sampling of

the fault zone was also undertaken and forms the main set of data presented here.

Three main localities at the northern end of the fault were visited, where CO2 springs and

gas bubbles in rivers had been reported. Structural characterisation of the sites documents

the change in nature of both the CO2 seeps and structural characteristics of the fault along

strike. The fault is generally defined by a broad fracture zone. Fractures predominantly

trend North-South and have dip-slip slickensides, but the fractures are locally re-oriented

NE-SW in an area where the fault trace bends. At this bend the fault is heavily

kaolinitised, and is recognised by a white, apparently pulverised, rock mass. CO2 flux

measurements demonstrate a clear spatial relationship with the fault/fracture zone. The

CO2 flux, is apparently controlled by fracture flow of the CO2 to the surface, associated

with faulting.


67

Utilizing Drones, Virtual Outcrop and Digital Data Analysis to Input

into Fracture Models C. E. Bond

1, Shackleton J.R.

2, Wild, T.

1 and Binti Zain, Z.

1

1 School of Geosciences, University of Aberdeen, Kings College, Aberdeen, AB24 3UE,

UK 2

Department of Geology and Geography, West Virginia University, Morgantown, WV

26506-6300, USA

Using outcrop analogues to understand subsurface rock geometries, and fault and fracture

attributes has the potential to enhance prediction of the geomechanical response of sub-

surface rock volumes to imposed stresses. For fractured rock volumes outcrop analogues

raise particular challenges including: understanding the difference in timing of fracture

systems, mineralization, and the effect of tectonic unloading on existing and new

fractures. The use of fractured analogues is further complicated by limited exposure and/or

accessibility of most rock outcrops that restricts full capture of the 3D fracture geometry.

Utilizing drone technology, photogrammetry and digital data capture we map and model

fracture networks in shale sequences to test the efficacy of these ‘new’ digital approaches

for the creation of better reservoir scale fracture models from outcrop data.

We present data from potential shale-gas resource field outcrops from the UK and USA, to

demonstrate our methodology at two analogue sites. Photography for photogrammetry has

been captured via drone, photo-pole and conventional techniques to create a layered set of

imagery at different scales. At both sites, creek-sections in the USA and coastal bench and

cliffs in the UK, the outcrop is only partially accessible. The virtual 3D models, created by

photogrammetry, allow a more complete picture of the outcrop and fracture network to be

built and interpreted. Interpretation of the 3D models is aided by fieldwork, linear scan

lines and mapping.

Digital interpretation of the models and subsequent analysis enables fracture attributes to

be assessed at a range of scales, using different techniques (e.g. linear and circular scan

lines). These traditional field techniques for assessment of fracture attributes can be

completed automatically on the digital models, enabling efficient assessment of the

efficacy of the techniques. The difference in scale of the digital imagery allows an

assessment of up-scaling, an issue for building effective fracture models from outcrop data

and predicting reservoir fractures and their geomechanical response. We assess the up-

scaling potential and the effectiveness of 3D model creation and interpretation, over

reliance on 2D linear or circular scans and traditional field data collection. Our focus is on

assessing the ability to predict and upscale fractures from outcrop analogues to a reservoir

scale to create effective fracture model predictions for unconventional resource

exploitation.


68

Interpreting deformation structures formed beneath submarine

gravity flows– a kinematic boundary layer approach.

Rob Butler

1, Joris Eggenhuisen

2, Peter Haughtonr

3, and Bill McCaffrey

4

1Geology and Petroleum Geology, School of Geosciences, University of Aberdeen,

Aberdeen, AN24 3UE, UK

[email protected] 2 Faculty of Geosciences, Utrecht University, P.O. Box 80.021, 3508 TA Utrecht, The

Netherlands 3UCD School of Geological Sciences, University College Dublin, Belfield, Dublin 4,

Ireland 4School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK.

Turbidite sandstones and related deposits commonly contain deformation structures and

remobilised sediment that might have resulted from post-depositional modification such as

down-slope creep (e.g. slumping) or density-driven loading by overlying deposits.

However, we consider that deformation can occur during the passage of turbidity currents

that exerted shear stress on their substrates (whether entirely pre-existing strata, sediment

deposited by earlier parts of the flow itself or some combination of these). Criteria are

outlined here, to avoid confusion with products of other mechanisms (e.g. slumping or

later tectonics), which establish the synchronicity between the passage of over-riding

flows and deformation of their substrates. This underpins a new analytical framework for

tracking the relationship between deformation, deposition and the transit of the causal

turbidity current, through the concept of kinematic boundary layers. Case study examples

are drawn from outcrop (Miocene of New Zealand, and Apennines of Italy) and

subsurface examples (Britannia Sandstone, Cretaceous, UKCS). Example structures

include: asymmetric flame structures, convolute lamination, some debritic units and

injection complexes together with slurry and mixed slurry facies. These structures may

provide insight into the rheology and dynamics of submarine flows and their substrates –

and have implications for the development of subsurface turbidite reservoirs.


69

Investigating fault zone development and architecture in mixed

carbonate and clastic sequences.

T. Cain

1, S. Clarke

1 and G. Leslie

2

1Geology, Geography and the Environment, Keele University, Keele, UK

2British Geological Survey, Murchison House, Edinburgh, UK

Predictions for the three-dimensional properties of faults and fault zones within highly

cyclical, mixed clastic and carbonate strata at, or below, the seismic scale are currently

poorly understood, despite being vital considerations for trap identification, exploration

risk and reservoir quality.

Detailed outcrop observations can help improve our knowledge of the controls on, and

subsequent properties of, fault zone architecture, aiding in risk and fault seal predictions.

This work presents data collected from fault zones in the mixed clastic and carbonate

stratigraphy of the Carboniferous rocks of the Midland Valley of Scotland, United

Kingdom. Using a series of highly detailed, three-dimensional fault observations

collected using photogrammetrically generated models, surveyed coal surfaces, LiDAR

data, geophysical wireline logs and field observations, we aim to investigate how

rheological differences within the host rock stratigraphy impact subsequent fault zone

development and properties such as the fault core and damage zone width.

We have observed multiple fault facies, with differences in fault architecture and

geometrical properties in both two and three dimensions depending on the stratigraphy

contained within the foot and hanging-walls. We propose that the rheological weaker

mudstones and siltstones operates as the main kinematic control during the earliest stages

of fault propagation, accommodating a large amount of deformation and reducing the

stress accommodated by more porous stratigraphy, limiting the formation of damage

zones and deformation bands. Fault connectivity appears reduced with increasing

thicknesses of mudstone packages and damagezone width has observed to be reduced

compared to fault sets contained within more brital strata.

Observations and initial hypothesis made within the Midland Valley are currently being

tested by examining the mineralised faults within the North Pennine Ore Fields where

undergound workings allow faults to be followed and observed for considerable distance

both along strike and down dip.


70

Frictional and mechanical properties of volcanic and sedimentary rocks.

Application to Mt Etna (Sicily)

A. Castagna

1, S. Vinciguerra

1,2, A. Ougier-Simonin

2, N. De Paola

3, P. Benson

4,

1Department of Geology, University of Leicester, UK [email protected]

2 Rock&Soil Physics Laboratory, British Geological Survey, Keyworth, UK

3Department of Earth Science, University of Durham, UK

4School of Earth and Environmental Science, University of Portsmouth, UK

Preferred presentation type: Poster

Sliding processes and flank instability affect volcanic edifices worldwide. Mt. Etna, Sicily,

is Europe’s largest active volcano, and is subject to flank instability in the south-eastern

area. Sliding is driven in the north-east sector by the Pernicana Fault System (PFS). This

fault system is the most active part of the entire flank to date with a slip rate of about 2

cm/y. Along its 20 km length, the PFS shifts from a stick-slip (e.g. upper section of the

system, near the summit) to an aseismic creep behaviour (lower section, towards the

Ionian Sea). The depth extent is unknown, but it is thought that the PFS represents a listric

fault that cuts the entire volcanic pile, decreasing in dip into the sedimentary basement.

The geometry and scale of displacement involves juxtaposition of the lithologies present,

from the basalt lava flows composing the edifice, through the quaternary deposit of clay

present underneath the volcano, to the sedimentary formations belonging to the

Appenninic-Maghrebian Chain (Europe domain) unit and the limestone belonging to the

Hyblean plateau (Africa domain). In this project we purposed to run mechanical and

frictional experiments to characterize frictional strength and deformation mechanisms

occurring on the unstable flank.

The sample collection of the twelve main lithologies belonging to the sedimentary units

present at Mount Etna has been completed, with an initial mechanical characterization

being conducted in the field by way of a portable Point Load Test and Schmidt Hammer

Test. The sedimentary sequences mainly show alternation of limestone, quarzarenite and

sandstone embedded in layers of clay and claystone. All these lithologies are strongly

deformed, fractured and mechanically weakened, apart from some exceptions represented

by the quarzarenite of the Monte Soro Unit (Appenninic-Maghrebian Chain).

A set of triaxial experiments in direct shear configuration will be run to test the main

properties of the end-member gouges and mixed gouges (e.g. clay and sandstone) in both

dry and saturated conditions. The aim of this is to represent the natural conditions and to

investigate the frictional and mechanical variations at different effective pressures of these

lithologies leading to seismic or aseismic behaviour.


71

A workflow for the structural analysis of virtual outcrop models

A.J. Cawood1, C.E. Bond

1, Y. Totake

1

1Geology and Petroleum Geology, University of Aberdeen, School of Geosciences, Kings

College, Aberdeen, AB24 3UE, UK

The use of structural data from geological outcrops has long been used in the Earth

Sciences to gain an understanding of structural geometries. Often these outcrop studies are

used to create maps and build cross-sections that together represent a 3D conceptual

model of the structural geometries observed; and how these extend beyond the outcrop

(into the sub-surface, or above ground). These analogue based conceptual models are used

to aid interpretation of sub-surface structural geometries. With the advent of new

techniques, such as terrestrial LiDAR and photogrammetry, greater automation of

structural data acquisition from outcrop is possible. However, the efficacy of these

technqiues in characterising structural features when compared to traditional methods has

not been tested.

Here we present a workflow for, and the results of, a quantitative analysis and

interpretation of structural data accquired from multiple technnologies. 3D models derived

from LiDAR and digital photogrammetry data are compared with traditional structural

data collection techniques. We have created models utilising both explicit (interpretation

lead) and implict (data interpolation) model building workflows. Emphasis is placed on

the analysis of key outcrop surfaces for comparative statistical analysis of the different

techniques. We find that while these methods potentially require time-consuming

processing and field acquisition time, the quality, amount of data, and digital format

provide a powerful tool for structural analysis. We predict that because of measurement

precision, realistic representation of outcrops and ease of collaboration and data sharing,

these tools will be used for structural analysis more frequently in the future.

Data for this study was acquired from the upright syncline in Carboniferous limestones at

Stackpole Quay, Pembrokeshire, sketched by Lady Murchison to illustrate Murchison’s

The Silurian System, published in 1839.


72

A high temperature experimental insight into permeability evolution in

silicic volcanic systems

A. Chadderton

1, P. Sammonds

1, P. Meredith

2, R. Smith

1 and H. Tuffen

3

1Institute for Risk and Disaster Reduction, University College London, UK.


3 Lancaster Environment Centre, Lancaster Unviersity, UK.

Experimentally determined permeability results have provided the basis for numerous

theories of magmatic degassing. Two recent eruptions in Chile, at Chaitén Volcano in

2008-10 and Cordón Caulle in 2011-12, allowed the first detailed observations of

rhyolitic activity and provided insights into the evolution of highly silicic eruptions. Both

events exhibited simultaneous explosive and effusive activity, with both lava and ash

plumes emitted from the same vent [1]. The permeability of fracture networks that act as

fluid flow pathways is key to understanding such eruptive behaviour. Here, we report

results from a systematic experimental investigation of permeability in volcanic rocks, at

magmatic temperatures and pressures, in the presence of pore fluids using our newly-

developed high-temperature permeability facility. Enhancements to the High

Temperature Triaxial Deformation Cell at UCL [2] have enabled us to make permeability

measurements on 25mm x 50mm cores at both elevated temperature and elevated

hydrostatic pressure [3]. We present results from several suites of permeability

measurements on samples of dome dacite from the 2004-08 eruption of Mount St Helens,

and rhyolite collected from the lava dome formed during the 2008-10 eruption of

Chaitén, Chile. Tests were conducted at temperatures up to 900oC and under an effective

pressure of 5 MPa, using the steady-state flow technique. Samples were cooled to room

temperature between each high temperature test, and the permeability of each sample was

re-measured before heating to the next temperature increment in the series. The results

show a complex permeability evolution that includes a reduction in permeability by

approximately 4 orders of magnitude up to 600oC. These new experimental permeability

results are applied to enhance our understanding of the complex issue of silicic magma

degassing.

[1] Castro JM et al, 2014 EPSL 405, 52-61

[2] Rocchi V et al, 2004 JVGR 132,137-157

[3] Gaunt HE et al 2013 IAVCEI Sci. Com. 1W_2K-P6


73

Review on Tectonics of Barmer rift Basin, Rajasthan, India

Swagato Dasgupta

1, Soumyajit Mukherjee

2

1 Reliance Industries Ltd., Navi Mumbai 400 701, Maharashtra, India.

[email protected] 2 Department of Earth Sciences, Indian Institute of Technology Bombay, Powai, Mumbai

400 076, Maharashtra, India.

The Barmer basin is < 50 km wide, ~ 200 km elongated trending NNW extending up to

Sanchor towards S. It is a part of NW segment of Indian plate in Rajasthan state, India.

The Fatehgarh fault limits the northernmost part of the basin. The Barmer basin consists of

Jurassic to Eocene shallow marine- and fluvial sediments. The basin separates from the

pericratonic Jaisalmer basin by a NE trending structural high: the Devikot-

Fatehgarh/Barmer-Devikot-Nachana ridge. While the eastern segment of the basin is fault

bound with thicker sedimentary cover, the western part comprises of basement uplifts with

thinner sediment layer. The Barmer rift extends southward towards Sanchor and into the

Cambay rift system. The Malani basement rhyolites are exposed in and around Barmer on

the western rift shoulder. Bouguer anomaly gravity lows occur distinctly along the

Cambay basin, which extends into the Barmer rift basin associated with high amplitude

gravity highs (0 to 50 mGal) along the rift shoulders on either side. The gravity low at

Jaisalmer basin (~ -20 to-50 mGal) is separated by a low-intensity gravity high (-5 to -

15mGal), trending NE, from the Barmer basin (~ -15 to -35 mGal). The residual magnetic

anomaly maps also depict similar geometry. Additionally, there are gravity- and magnetic

trends along NE-SW connoting flexed basement. The high magnetic anomalies, associated

with rift shoulders, resemble those produced by mafic intrusions in the basement.

Moreover a ~ 100 km deep linear NNW trending low velocity zone exists below the

Barmer basin. All these indicate that the Mesozoic rift basin reactivated ~ end Cretaceous

due to Reunion pluming resulting in Deccan volcanism thereby extending the second

rifting phase into the Cambay basin. A modelled NE-SW profile from Bouguer anomaly

map across Barmer basin identifies a mafic basement with large-scale intrusion along with

Moho upwelling up to 27-28 km beneath the basin like a typical rift basin. The dominant

fault system in Sarnoo hill area at the eastern rift shoulder strikes NE and accommodates

more deformation than its NW cross trend. Images from Google Earth Pro also shows

three sets of lineaments in the Sarnoo hill area. The NE trend is the most distinct one and

is followed by ENE and a less prominent ~ ESE trend. The Barmer hill section in the

western rift shoulder is of Malani igneous suite. The Google Earth Pro images of this area

depicts clear NW trending lineaments and an indistinct N-S one. The evolution of younger

lineament fractures like Rajkot-Lathi and Jaisalmer-Barwani lineaments might indicate

shallow crustal flexture. The Rajkot-Lathi lineament runs N-S along the NW limit of the

Barmer basin. The NW-SE trending Jaisalmer-Barwani lineament runs longitudinally

along the W margin of the Barmer basin. Few key unanswered issues for the Barmer rift

system are (i) scale of deformation; (ii) strain rates and mode of deformation- was it a

continuous rifting or was it pulsating; (iii) was initial rifting magmatic or amagmatic; and

(iv) genesis of neotectonic lineaments. This review speculates (i) the Barmer petroleum

basin is a failed continental rift; (ii) Deccan volcanism affected only the eastern rift

shoulder of the Barmer basin; (iii) the rift faults are at high-angle on the two rift shoulder

margins; and (iv) the rift faults are oriented in different (near perpendicular) directions on

the two rift shoulders.


74

Structural controls on fluid flow and differential cementation in

carbonate rocks

Dimmen, V. 1, Nærland, K.

1, Rotevatn, A.

1, Kristensen, T.B.

1, Nixon, C.W.

1, Peacock,

D.C.P. 1

, Bastesen, E.2


2 Centre for Integrated Petroleum Research, University of Bergen, Allégaten 41, 5007

Bergen, Norway

Corresponding author ([email protected])

Faults and fractures may exert strong controls on fluid flow and fluid-rock

interaction in the shallow crust, with locations of fault zone complexity such as relay

zones being particularly prone to act as loci for focused fluid flow. Various fluids can flow

at such locations, including hydrocarbons, magma, and hydrothermal and mineralising

fluids. Despite the wide recognition of faults and fractures as important controls on crustal

fluid flow, there are currently few studies that systematically and directly document and

quantify the relationship between structural complexity and fluid flow. In this study, we

use differential cementation and oxidation along small-scale faults and within damage

zones in carbonate rocks as a proxy for palaeo-fluid flow. The degree of structural

complexity is quantified by means of geometric and topological characterisation of the

studied fracture systems, fluid flow is quantified by measuring the widths of the

diageneticallly altered zones associated with each structure. The studied outcrops are

located in Malta and comprise Miocene-aged limestones of the Upper Globigerina

Formation.

Preliminary results show a direct relationship between the degree of structural

complexity and the amount of fluid flow. Our findings have scientific and economic

implications for understanding the fundamentals of the relationship between structural

complexity and fluid flow.


75

The Falkland Plateau; a rotated slice of the Cape Fold & Thrust Belt

T. Dodd

1, D. McCarthy

1, and P. Richards

1


[email protected]

The evolution of the Falkland Plateau details a complex rift history at the southern edge of

the South Atlantic passive margin, commonly described as a volcanic passive margin.

Volcanic passive margins are typically associated with the development of a thick

magmatic crust, characterised by a heavily intruded continental crust, overlain by flood

basalts and tuffs that extruded during rifting, the so called Seaward Dipping Reflector

Sequence (SDR’s). SDRs are commonly used to identify the transitional boundary

between continental and oceanic crust.

Previous research based on older regional seismic data described the presence of SDRs

within the Berkley Arch of the Falkland Plateau, a buried basinal-high that separates the

Volunteer sub-basin in the north and the Fitzroy sub-basin to the south. The evolution of

the Falkland Plateau and indeed the Lafonia microplate can be characterised by rifting

from south eastern South Africa due to rotation and translation along the Agulhas fault

zone at the initiation of the break-up of Gondwana at approx. 180Ma. This complex

history may account for a more appropriate explanation for these dipping seismic features.

Interpretation of modern seismic data suggests that the Berkley Arch structure could

represent a basement structure composed of the Devono-Carboniferous Cape Fold-Belt

sediments. In this model the dipping reflectors observed could represent an imbricate

thrust sequence within the fold belt.

Re-interpreting these dipping reflectors as a thrust sequence implies that the Berkley Arch

represents a missing slice of the Cape Fold thrust belt. Similarly the Fitzroy sub-basin can

be correlated with the Karoo foreland basin of the Cape Fold thrust belt, whilst the

Volunteer sub-basin towards the north of the Berkley Arch, can be interpreted as a piggy-

back basin occurring immediately behind the main thrust belt. Furthermore this

interpretation agrees with the Early-Middle Jurassic 180° rotation of the Falkland Islands

Plateau. This reinterpretation highlights some of the difficulties of interpreting basement

structures of complex passive margins. Improved understanding with regards to basement

composition and regional burial histories is essential in the determination of hydrocarbon

presence and perhaps more importantly hydrocarbon phase in frontier basins.


76

The Topology of Evolving Single Phase and Multiphase Rift Fault

Networks

Duffy, O.B.

1*, Nixon, C.W.

2, Bell, R.E.

1, Jackson, C.A-L.

1, Gawthorpe, R.L.

2, Sanderson,

D.J. 3, 4

and Whipp, P.S.5

1Basins Research Group (BRG), Department of Earth Science & Engineering, Imperial College,

London, United Kingdom 2 Department of Earth Science, University of Bergen, Bergen, Norway

3 Faculty of Engineering and the Environment, University of Southampton, Southampton

4Reservoir Development, BP, Chertsey Road, Sunbury-on-Thames

5Statoil ASA, Sandslivegen, Sandsli, Norway

*Present Address of Corresponding Author: Bureau of Economic Geology, Jackson

School of Geosciences, The University of Texas at Austin ([email protected])

Faults rarely occur individually, but instead develop and accumulate strain as a network of

interacting faults. Determining how fault networks behave, grow, develop and interact

through time is vital for establishing an understanding of seismic hazard, fault-fluid flow

relationships and the structural development of reservoirs and aquifers. Topology is essential

for characterizing fault networks as it describes the arrangement and relationships between

faults. The topology of a fault network is analysed in terms of branches (I-I, I-C, C-C

branches) between isolated tips (I-nodes) or intersections (Y- or X-nodes), the relative

proportions of which provide a topological signature and assessment of the degree of

connectivity. Thus determining how the topology of a rift fault network evolves will provide

significant insights into fault growth and development. Here, we investigate how the plan

view topology and connectivity of single and multiphase fault networks from rifts evolves

with increasing strain. Single phase rifts are limited to fault splays and along-strike linkage

(I-node and I-C branch dominated networks), whereas multiphase rifts develop abutting and

cross-cutting fault relationships providing across-strike linkage (Y-node and C-C branch

dominated networks). The topological pathways of these different fault networks evolve in a

largely predictable manner in response to increasing strain, progressing towards Y-node and

C-C branch dominated networks. Therefore, the degree of connectivity within any fault

network increases with increasing strain. In particular, a second phase of rifting considerably

increases the network connectivity as across-strike linkage promotes development of a more

interconnected topology.


77

Permeability of geothermal reservoir rock near the Krafla magma

G.H. Eggertsson1, Y. Lavallée

1

1Department of Earth, Ocean and Ecological Sciences, University of Liverpool, Liverpool,


The magmatic-hydrothermal system at Krafla Volcano, North-East Iceland, has been the

source of important geothermal fluids, exploited by Landsvirkjun National Power since

1977 to generate electricity (~60 MW). Since 2000 there have been plans to drill beyond

fluids at moderate temperatures (200-300°C) to source fluids in the super high enthalpy

hydrothermal system below. In relation to this, IDDP-1 was drilled in 2009. Drilling was

terminated at a depth of 2100m when the drill string penetrated a silicic magma body.

Above the magma chamber (~80m thick), granophyre and felsite are dominant. Felsite

rocks can be found scattered around the Víti crater, a few hundred meters away from

IDDP-1, and these rocks are thought to be the same as the ones found above the magma

chamber. They scattered around the area when the Víti crater formed in 1724. Here, we

present results of mechanical and permeability tests carried out on the felsite that is

thought to overlay the magma chamber.

The felsite is white, medium to course grained, with an average grain size around 2 mm. It

is composed of quartz, alkali feldspar, plagioclase, titanomagnetite and augite. Very close

to the bottom of IDDP-1, rock cuttings have revealed signs that indicate incipient melting,

with the melt quenched to interstitial glass by the drilling fluid.

Country rocks at distances beyond 30m of the intrusive contact are essentially unaltered,

implying that they have been emplaced very recently and/or are as yet unaffected by

hydrothermal fluid flow.

During a field survey in Krafla in Fall 2015, representative samples of felsite blocks were

collected, scattered mainly around the area NE of Víti. The samples had ranging porosities

from 10%-16%, determined using helium pycnometry.

Permeability measurements have been carried out using a hydrostatic cell. To simulate

stress conditions extended in the geothermal field, we performed permeability

measurements at a range of effective pressures (1 to 100 MPa), using a pore pressure

differential of 0.5-1.5 (at an average pore pressure of 1.25 MPa). The results are presented

with permeability-porosity relationship as a function of effective pressure, and we discuss

the permeability of the fluid reservoir as a function of effective pressure to constrain fluid

flow during different pressurisation events.

Complementary Brazilian tests were also performed to induce a fracture in the samples;the

permeability of these fractured rocks will be measured to describe the role of macro-

fractures in controlling fluid flow. Permeability measurements at high temperature (up to

~500 C) will also be presented . All experimental data will be discussed in terms of the

implications they have forfluid flow around the magma chamber.


78

A structural interpretation of the Genestosa strike-slip fault zone,

Cantabria, Spain: Evidence for influence of a pre-thrust template on

thrust sheet development?

Amy Elson

1, Stuart M. Clarke

1 and Graham Leslie

2

1 Basin Dynamics Research Group, Department of Geology, Geography and the

Environment, Keele University, Keele, Staffordshire, ST5 5BG, UK 2 British Geological Survey, Murchison House, West Mains Road, Edinburgh

Thrust belts over large distances are rarely uninterrupted, but are often complexly

deformed by localised ‘transfer zones’ that manifest themselves as shallow-seated

structures, such as strike-slip faulting, en-echelon folds and localised thrusting. The

position and geometry of transfer zones is commonly attributed to presence of deep-seated

and pre-existing variations or ‘complexities’ in the pre-thrust template (Krabbendam and

Leslie, 2004; Calassou et al, 1992).

This work presents the results of detailed geometrical and kinematic observations along

with high-resolution field mapping of the Genestosa Fault, an isolated strike-slip zone

contained within the Thrust and Fold Belt of the Cantabrian Mountains. The belt

incorporates stratigraphy from the lower Cambrian to the Carboniferous periods in north-

easterly verging, stacked thrust sheets formed by late-stage Variscan deformation that

subsequently underwent folding to form the Cantabrian Arc Orocline.

Detailed field mapping combined with kinematic and geometric observations expose

stratigraphically discrete lenses bounded by, and contained within, an anastomosing fault

zone. Stereonet and geometrical analysis produces a fault reconstruction, constrained by

different shears and geometries that identifies discrete fault lenses.

Stratigraphy is a clear control on the development of the strike-slip system. Towards the

west of the studied area, the system is spatially constrained and forced through a narrow

band in competent limestones of the Valdeteja Formation. In less competent units, the

fault zone widens significantly and splays through the softer sediments. The overall

system is sinistral, and displaces the thrusted stratigraphy westwards by nearly two and a

half kilometres.

The geometry, the transport-parallel nature, and stratigraphical separation contained

within the Genestosa Fault Zone suggest that it may have acted as a transfer zone during

the development and deformation of the Cantabrian Fold and Thrust Belt. Regional

variations in sedimentology, from north to south across the zone, suggest that it may be

seated upon, and controlled by, pre-existing variations in the pre-thrust template. Our

analysis offers new insight into the structural development of the Cantabrian Arc and

further evidence for the control of transfer zones by deep-seated and pre-existing

structures.


79

Estimating strain from CPO in ductile shear zones: the Uludağ Massif,

NW Turkey.

K. Farrell

1, G. E. Lloyd

1, D. Wallis

2, R. J. Phillips

1

1

Institute of Geophysics and Tectonics, School of Earth and Environment, University of

Leeds, LS2 9JT. 2

Department of Earth Sciences, University of Oxford, OX1 3AN.

[email protected]

Understanding the behaviour of active continental-scale fault zones at depth, and in

particular how displacements observed at the Earth’s surface are accommodated through

the crust, is crucial to improving understanding of the earthquake cycle. This behaviour

can be inferred by study of exhumed portions of ductile shear zones using methods that

record strain profile(s) across the fault zone. However, due to the nature of mid-crustal

rocks, strain markers tend to be rare and/or discontinuously distributed.

The intensity (I) of crystallographic preferred orientation (CPO) of deformed minerals

provides a proxy for strain that is continuous across fault zones. CPO are collected via

electron back scattered diffraction in the scanning electron microscope. The strength of the

CPO can be quantified using eigenvalue-based intensity parameters. Calibration of

intensity with strain is achieved via comparison with visco-plastic self-consistency models

of CPO evolution, although the temperature-dependent critical resolved shear stresses of

potential crystal slip systems must be known.

As an example, we consider the dextral strike-slip Eskişehir shear zone, NW Turkey,

which was active during the Oligocene and accommodated ~100km of displacement,

including a component of late oblique-normal slip. An exhumed mid-crustal section of this

fault zone is exposed in the Uludağ Massif, comprising of high-grade metamorphic rocks

of the Uludağ Group, intruded by the Central and South Uludağ granites. Sample transects

focussed on the pure calcic marbles that dominate the stratigraphy. Fortunately, the

availability of experimental data for calcite crystal slip behaviour at different

temperatures, particularly the temperature-dependent critical resolved shear stresses of

potential crystal slip and twining systems, makes the application of the CPO intensity

strain proxy method relatively straightforward.

The Uludağ Massif and Eskişehir shear zone provide a field based analogue for the ductile

shear zone beneath the currently active North Anatolian Fault. The results of our CPO

intensity-based strain profiles allow us to speculate on the current behaviour of the North

Anatolian Fault, a major seismogenic feature, at depth.


80

Effects of Porosity on Geomechanical Risk

N.J.C. Farrell1, D. Healy

1 and M.J. Heap

2

1Department of Geology, University of Aberdeen, Aberdeen, UK. [email protected]

2Institute de Physique de Globe, Universite de Strasbourg, Strasbourg, France.

Petrophysical and petrographical characterisation of reservoir quality around fault zones in

clastic reservoir analogues shows that tectonic deformation can change the amount of

porosity, as well as altering pore geometries. Development of fault-induced porosity has

also been measured as anisotropy of permeability in core plugs sampled around faults.

Using quantitative pore space characteristics combined with experimentally derived rock

strengths and elasticities we have modelled the influence of reservoir quality around fault

zones on the geomechanical behaviour of normal faults in subsurface reservoirs. Previous

research has shown that changes in pore fluid pressure, associated with fluid flow, can

induce changes in the stresses and potentially leading to fault reactivation. In these studies

pores are modelled as simple spherical voids. However, microstructural studies show that

real pores are more complex than spheres and are better represented by ellipsoids. In

addition, image analysis on thin sections of cataclastic fault rocks show that ellipsoidal

pores are commonly oriented, and therefore impart anisotropy. Theoretical work suggests

that depending on the orientation of anisotropic pore long axes with respect to the in situ

principal stresses, anisotropy of porosity may either increase or decrease the stability of

faulted rock. Geomechanical models presented in this study test this hypothesis using

petrophysical data (helium and mercury injection porosimetry, high pressure nitrogen

permeametry), image analyses (optical microscopy, BSEM and SEM-CL) and rock

strength and elasticity data (uniaxial and triaxial compressive strengths and seismic

velocities) from samples taken from normal faults hosted in clastic reservoir analogues.

Results from our geomechanical models show that increased pore fluid pressure in a

porous sandstone containing anisotropic pores oriented perpendicular to σ1 (as quantified

in undeformed aeolian host rock) decreases the effective stress and shear stress, making

the rock more stable. In comparison, pore fluid pressure increases in a cataclastic fault

rock comprising anisotropic pores oriented parallel to σ1 decreases the effective stress but

increases shear stress, potentially leading to fault reactivation (Figure 1).

Figure 1. Mohr diagrams showing the effects of increasing pore fluid pressure in a sample

of undeformed quartz rich sandstone (a) and a fault induced cataclasite (b).


81

What kind of creep would do that? Investigating the influence of

diffusion on texture development in rocks

Joe Gardner1, John Wheeler

1, Elisabetta Mariani

1

1Department of Earth, Ocean and Ecological Sciences, University of Liverpool, 4 Brownlow Street,

Liverpool L69 3GP, UK

A strong crystallographic preferred orientation (CPO), or texture, in rocks is generally

interpreted as evidence for crystal plastic deformation, whereas deformation

accommodated by diffusive processes is commonly thought to weaken or destroy any

existing CPO. Recent petrological studies have shown that diffusion-accommodated

deformation may be more common than previously recognised over a range of

temperatures (Wintsch and Yi 2002, Menegon et al 2008), and numerical modelling has

shown that in certain circumstances diffusive processes could in fact lead to CPO

development in rocks (Bons and ten Brok 2000). Heidelbach et al (2000) reported

evidence for CPO development in experimentally deformed albite aggregates attributed to

dissolution-precipitation creep.

Our study focuses on metagabbros from an extensional shear zone in the Western Alps in

which deformation has been accommodated by dissolution-precipitation creep. We use

electron backscatter diffraction (EBSD) analysis to show that diffusive processes have

contributed to the development of CPOs, and that the presence of a second phase exerts a

strong influence on the strength of the CPOs.

The metamorphic breakdown of Ca-rich plagioclase at greenschist facies produces a

predominantly two-phase mixture of albite plus Ca-bearing phase (clinozoisite). The

microstructural geometry and distribution of phases in the metagabbros suggests a

substantial solubility contrast between the two product phases. The less soluble phase (cz)

undergoes rigid body rotation within the more mobile phase (ab) to form anastamosing

albite-free bands that wrap around pyroxene porphyroclasts. Strong shape-preferred

orientations (SPO) develop in cz in these regions, and an associated CPO is also observed.

Where albite has precipitated into pressure shadows CPOs are weak or non-existent,

however in regions of the matrix that are essentially two-phase mixtures, and where

pressure shadow tails have been modified by continued deformation, variable strength

CPOs are observed.

Our results illustrate a natural example of significant CPOs developing during diffusion-

accommodated deformation. Additionally, our observations suggest that the presence of a

second phase can influence the development of a CPO. We will use these observations as

a starting point from which to develop models explaining how diffusion creep (wet or dry)

might lead to the development of CPOs, and how CPOs may develop in two-phase

mixtures deforming in the diffusion field.

Bons, P. D., & den Brok, B. (2000). Crystallographic preferred orientation development by dissolution–precipitation

creep. Journal of Structural Geology,22(11), 1713-1722.

Heidelbach, F., Post, A., & Tullis, J. (2000). Crystallographic preferred orientation in albite samples deformed

experimentally by dislocation and solution precipitation creep. Journal of Structural Geology, 22(11), 1649-1661.

Menegon, L., Pennacchioni, G., & Spiess, R. (2008). Dissolution-precipitation creep of K-feldspar in mid-crustal granite

mylonites. Journal of Structural Geology, 30(5), 565-579.

Wintsch, R. P., & Yi, K. (2002). Dissolution and replacement creep: a significant deformation mechanism in mid-crustal

rocks. Journal of Structural Geology, 24(6), 1179-1193.


82

Earthquakes, elevations and the construction of continental plateaux

C. Goddard, M.B. Allen, N. DePaola, S.Nielsen and C. Saville

Department of Earth Sciences, Durham University, Durham, UK.

[email protected]

It has long been noted that larger thrust earthquakes (M>~5) are rare at higher elevations

in continental fold-and-thrust belts. For example, the cut-off is the 1250 m elevation

contour in the Zagros fold-and-thrust belt, while thrust events are rare above 3500 m in the

Himalayas and other fold-and-thrust belts marginal to the Tibetan Plateau. There are

various possible explanations for this phenomenon, including aspects of the critical wedge

model, but one interpretation which has addressed the relationship is the recognition that

higher elevation regions resist major seismogenic thrusting due to the additional

gravitational potential energy (GPE) added from the increase in height.

Here we have investigated the elevation distribution of earthquake data sets for the Qilian

Shan (at the northeast margin of the Tibetan Plateau) and the Zagros, to identify a

relationship between elevation and earthquake magnitude. Preliminary findings show a

gradual reduction of larger thrust events rather than an abrupt termination. Regression

analysis has additionally been carried out on the plots created to test the strength of the

relationship found between elevation and magnitude. We aim to repeat this analysis over a

variety of different areas via the use of public–domain datasets for seismicity and

topography in an attempt to quantify this relationship.

We are also investigating an alternative model, where increase in height, and therefore in

lithostatic load, creates a thicker zone of distributed deformation above the temperature

dependent brittle-plastic transition. This could potentially suppress the ability of large

earthquakes to propagate through the entire brittle crust, while still allowing smaller

earthquakes to continue to develop above and also below the brittle-ductile transition.

Future work will involve laboratory analysis to mimic the increasing conditions of

confining pressure experienced by rocks as the regional elevations increase. This will aim

to quantitate understanding of how large earthquakes may evolve to distributed

deformation. An additional area of interest is what effects and modifies the gradient of

such curves.


83

Evolution of a major segmented normal fault during multiphase rifting:

the origin of plan-view zigzag geometry

Henstra, G.A.

1, Rotevatn, A.

1, Gawthorpe, R.L.

1, Ravnås, R.

2


2 Norske Shell, Tankvegen 1, 4056 Stavanger, Norway


This case study addresses fault reactivation and linkage between distinct extensional

episodes with variable stretching direction. Using 2-D and 3-D seismic reflection data we

demonstrate how the Vesterdjupet Fault Zone, one of the basin-bounding normal fault

zones of the Lofoten margin (north Norway), evolved over c. 150 Myr as part of the North

Atlantic rift. This fault zone is composed of NNE-SSW- and NE-SW-striking segments

that exhibit a zigzag geometry. The structure formed during Late Jurassic and Early

Cretaceous rifting from selective reactivation and linkage of Triassic faults. A rotation of

the overall stress field has previously been invoked to have taken place between the

Triassic and Jurassic rift episodes along the Lofoten margin. A comparison to recent

physical analogue models of non-coaxial extension reveals that this suggested change in

least principal stress for the Lofoten margin may best explain the zigzag-style linkage of

the Triassic faults, although alternative models cannot be ruled out. This study underlines

the prediction from physical models that the location and orientation of early phase normal

faults can play a pivotal role in the evolution of subsequent faults systems in multi-rift

systems.


84

Stress and displacement of overlapping active normal fault segments

M. Hodge

1, A. Fagereng

1, J. Biggs

2, and H. Mdala

3

1School of Earth and Ocean Sciences, Cardiff University, Cardiff, UK.

[email protected] 2School of Earth Sciences, University of Bristol, Bristol, UK.

3Geological Survey Department, Mzuzu Regional Office, Malawi.

Large, continental normal faults grow by interaction and linkage of fault segments.

‘Continuous’ fault systems consist of segments that interact, grow and slip synchronously,

whereas ‘segmented’ (non-continuous) fault systems comprise isolated fault segments.

Maturity is thought to be a control on fault continuity: immature faults have experienced

small total displacement and are typically assumed to be ‘segmented’. Alternatively, pre-

existing structures may influence or inhibit fault growth by providing a plane of weakness,

or a stress barrier. As seismic moment is related to fault length (Wells and Coppersmith,

1994), understanding whether fault systems are ‘continuous’ or ‘segmented’, and the

influence of pre-existing structures, is critical in understanding seismic hazard.

Here we study two overlapping segments of the NNW-SSE striking Bilila-Mtakataka

fault, Malawi, in the relatively immature, southern section of the East African Rift System.

Despite its relative immaturity, previous studies concluded the Bilila-Mtakataka fault is

continuous for its entire 100 km length, with the most recent event producing an average

slip of 10 m, equating to an Mw8.0 earthquake (Jackson and Blenkinsop, 1997). We

explore the extent to which differences in segment orientation and relationship to pre-

existing foliation has influenced segment growth and interaction. We chose two fault

segments, near the village of Golomoti, that have strikes differing on average by 10°, with

a maximum of 55° at their overlapping tips. The southern segment is sub-parallel to the

foliation, while the northern segment is oblique to perpendicular to the locally folded

foliation.

Fault scarp height and orientation is constrained by Digital Elevation Models derived from

SRTM 30 m satellite data and ‘Structure from Motion’ photogrammetry using an

Unmanned Aerial Vehicle (UAV), alongside direct field observations. Displacement-

length (D-L) analyses show bell-shaped appearances for both segments, with scarp height

maxima of 15 m closer to the overlap than the segment centre. Skewed scarp height

maxima indicate that this section of the Bilila-Mtakataka fault may be mechanically

‘continuous’ despite appearing as two geometrically separate segments. Next, we calculate

Coulomb stress changes and assess the influence of the pre-existing foliation. Our

preliminary results indicate that the orientation of the southern segment may be controlled

by reactivation of the local pre-existing foliation, which strike at a high angle of 70-90° to

the trend of the regional least principal stress (σ3). Results from the north segment do not

show a strong influence of foliation on fault orientation, likely because the angle between

strike of locally folded pre-existing foliation and the trend of σ3 varies significantly from

10 to 90°. Our findings show that at certain angles to σ3, pre-existing structures influence

fault growth, and geometrically separate overlapping segments may still be mechanically

linked. Such interactions develop ‘continuous’ fault systems, increasing fault length and

therefore seismic hazard.


85

An explanation of the sill-forced fold amplitude discrepancy.

M. Hoggett

1*, T. Reston

1.

1Department of Geography, Earth and Environmental Sciences, University of

Birmingham, Edgbaston, Birmingham, UK. *[email protected]

Forced folds are structures formed at the earth’s surface due to deformation during sill

emplacement. During emplacement igneous bodies inflate, and the space problem of such

volume increase is taken up at the free surface. These structures have recently gleaned

much interest due to them forming potentially attractive four-way dip closed petroleum

exploration targets, and also because similar ground deformation can preceede volcanic

eruptions.

Since the first published studies of forced folds above sills, it has been recognised that

there is a strong disparity between the amplitude of forced folds and the thickness of the

underlying causal magmatic intrusion. Assuming no removal of mass and no unexpected

host rock behaviour, we would expect the amplitude of the fold to be close to the thickness

of the underlying magmatic intrusion, however the amplitude of the fold is typically found

to be around 50% or less of the sill thickness. This has been explained in various

publications as due to (1) unobserved erosion, (2) seismic imaging difficulties, (3)

anomalous host rock compaction during emplacement, (4) host rock fluidization, and (5)

unrecoverable (plastic) strain in the host rock during emplacement. However none of these

models fully explain the presense or magnitude of the disparity.

In this study we model compaction post intrusion, and find the amplitude discrepancy can

be explained with the simple insight that forced folds as measured today are the product of

two processs. Firstly, the formation of the forced fold during intrusion, and secondly, post

intrusion modification of the fold during burial after intrusion, where the sediment

compacts significantly more than the sill. This has a number of implications for

hydrocarbon exploration of such plays in basins containing volcanic intrusions, and should

be included in models of ground deformation preceeding volcanic eruptions.


86

Seismic characterization of the root zones of km long blow-out pipes

using time lapse surveys: examples from the Loyal field (West Shetland,

North Sea)

Jihad A

1., Maestrelli

2. X, Iacopini D

1 , Bond C. E.

1

1 Geology and Petroleum Geology Dept, University of Aberdeen

2 Diaprtimento di Scienze della Terra, Universita degli Studi di Firenze,

Most of the available knowledge for fluid escape and blow-out pipes (Cartwright et al.,

2007) has been inferred from high resolution marine seismic studies. On seismic data fluid

escape pipes are recognizable as columnar zones of disrupted reflection continuity,

commonly associated with amplitude and velocity anomalies, and scattering, attenuation

and transmission artifacts (Loseth, et al 2009; Cartwright and Santamarina 2015). In some

cases, pipes consist of zones of deformed reflections related to minor folding and faulting.

In others, they simply appear to consist of stacked pockmark craters or stacked localized

amplitude anomalies that are likely to be small gas accumulations or zones of

cementation. In most cases, they tend to be localized at natural leak-off points for over

pressured pore fluids, for example at the crests of structures, above gas reservoirs, or at the

up-dip limits of aquifers. However the detailed structure of pipes is still poorly understood

and may be highly variable. Here we report on a detailed analysis of the seismic

expression of some blow-out pipes from the Loyal field affecting the late Paleogene-

Neogene overburden units, focusing on the root zones of the structures. The Loyal field in

the UK North Sea is an oil and gas producing field located in Quadrant 204 and 205 of the

UKCS, 130 km west of Shetland and is characterized by siliciclastic turbidite sandstones,

derived from the uplifted Scottish Massif to the southeast. In order to investigate the

internal structure and distribution of the root zone structuresthe major Cretaceous-

Neogene formations have been systematically mapped and interpreted to outline the blow-

out pipes . Initial results suggest that most of the pipe roots are triggered or fromthe over-

pressured units of the Montrose Group and Lista Formation. (the smallest) or from the

T31-T26 Paleocene reservoir units (the largest structures). The majority of the Lista

Formation related blow-out pipes show localized root structures (across both the near to

far offset seismic dataset) confined to the upper part of the sloping. basin structure, in

some case exploiting pre-existing faults. The largest and deepest fluid pipes are scattered

across the basin slope, apparently associated with the main reservoirs currently under

production. The internal structure of the root are imaged differently across the near to far

offset dataset and are often characterized by low signal/noise and a more diffuse geometry

with depth. Using the full, near, medium and far offset seismic datasets a classification of

the different root geometries observed across the different blow-out pipe structures is

proposed with models of their formation processes.

-Cartwright, J.A. 2007, Bicentennial Review: The impact of 3D seismic data on the understanding of

compaction, fluid flow and diagenesis in sedimentary basins. Journal of the Geological Society of

London, 164, 881-893.

-Løset H., Gading M., Wensaas L. 2009. Hydrocarbon leakage interpreted on seismic data. Marine and

Petroleum Geology, 26, 1304-1319.

-Cartwright J., Santamarina C. 2015. Seismic characteristics of fluid escape pipes in sedimentary

basins: Implications for pipe genesis. Marine and Petroleum Geology, 65, 126-140.


87

Deformation and metamorphism of Australian basement rocks in the

Bird’s Head, West Papua, Indonesia

B.M. Jost

1, L.T. White

1, R. Hall

1, M. Webb

1, and H. Tiranda

2

1Southeast Asia Research Group, Department of Earth Sciences, Royal Holloway

University of London, UK. [email protected] 2Geodynamics Research Group, Institute of Technology Bandung, Indonesia.

The Bird’s Head Peninsula is the northwesternmost region of New Guinea. It represents a

section of the boundary between the Australian and Caroline plates. This remote and

relatively unexplored mountainous region offers a unique opportunity to study the rate and

duration of tectonic events in a relatively young (~Eocene-Miocene) arc-continent

collisional setting. The highlands that developed as a result of this also offer a window to

better understand the Palaeo- and Mesozoic evolution of the north-western Australian

crust. The mountainous regions are dominated by exposures of variably metamorphosed

and multiply deformed basement rocks (the Kemum Formation). These poorly dated

Silurian-Devonian meta-turbidites have also been intruded by numerous granitoid

intrusions. Locally, the Kemum Formation is overlain by Pleistocene shallow marine to

terrestrial sediments. Their elevations of more than 1800 m a.s.l. indicate that the northeast

part of the Bird’s Head experienced dramatic recent uplift. The exact time and rate at

which these highlands developed, however, is a question still unresolved. We aim to

address this issue through detailed field studies combined with isotopic dating as well as

petrographic and microstructural analyses.

We present preliminary results from several months of fieldwork as well as petrographic

and geochronological analyses from this remote region. We have focused on the

northeastern exposures of the Kemum basement high, where the low-grade meta-turbidites

were intruded by granitoids and affected by a second, medium- to higher-grade

metamorphic event. Previous authors stated that the metamorphic grade of the second

overprint increased towards the Australian-Pacific Plate boundary (e.g. Pieters et al.,

1990). We show that this overprint was due to contact metamorphism, likely associated

with the intrusion of the granitoids. Our initial geochronological results indicate that the

granitoids intruded the Kemum Formation in the latest Devonian or earliest

Carboniferous, rather than during the Late Permian and Triassic as was proposed from K-

Ar data (e.g. Pieters et al., 1983). Such results indicate that we still have a lot to learn

about the timing of tectono-thermal events at the northern margin of the Australian Plate.

Pieters, P.E., Hakim, A.S., Atmawinata, S. 1990. Geologi lembar Ransiki, Irian Jaya.

Geological Survey of Indonesia, Directorate of Mineral Resources, Geological Research

and Development Centre, Bandung, 81pp.

Pieters, P.E., Pigram, C.J., Trail, D.S., Dow, D.B., Ratman, N., Sukamto, R. 1983. The

stratigraphy of western Irian Jaya. Indonesian Petroleum Association, Proceedings 12th

Annual Convention, Jakarta, 229–262.


88

Sill Geometry and Distribution in Contractional Settings: the San Rafael

Sub-Volcanic Field, Utah, USA

T. Kawanzaruwa

1, R. Walker

1, R. England

1, K. Wright

2 , N. De Paola

3 , K.

McCaffrey

3

[email protected]

1

Department of Geology, Leicester University, Leicester, UK 2

DONG E&P (UK) 3

Department of Earth Sciences, Durham University, Durham, UK

Complex sill networks in basin settings can have significant impact on subsurface fluid

flow (e.g., acting as aquitards or aquicludes to fluid systems), geothermal systems, and the

maturation of hydrocarbons. Models for these effects are critically dependent on the

mechanisms for sill emplacement, and the resulting geometry and distribution of the sill

network. This study focuses on the San Rafael Sub-Volcanic Field (SRSVF), Utah; the

subsurface plumbing system of a monogenetic basaltic volcanic field where magmatic

emplacement was focused along the transition zone between the Basin-and-Range and

Colorado Plateau. The SRSVF hosts dykes, sills, and volcanic breccia bodies, which were

intruded into Jurassic strata of the San Rafael Group between 3.7 to 4.6 Ma at an

estimated crustal emplacement depth of up to 1 km. Dykes in the SRSVF intrude joints

within the host sequence, leading to previous interpretations that the intrusive network,

including sills, was emplaced during a period of low deviatoric stress. Here we use a

combination of remote-sensed data such as high-resolution aerial imagery and airborne

lidar (1 m resolution respectively), and field characterisation of exceptionally well-

exposed sills, to constrain the geometry and spatial distributions of sills in the SRSVF. Sill

mapping using remote sensed data reveals that sill dip directions change across the area,

from NW-dipping in the north, to NE- and SW-dipping in the south. Field characterisation

of sill geometry in the south suggests sills were formed at two main scales: (1) gently

transgressive tabular sills ranging from 10-40 m that are laterally continuous for the extent

of exposure (~1-2 km); and (2) thin (0.04-1.0 m) anastomosing sills that can be traced in

section for 10-100 m. Small sills form linked networks of horizontal to inclined sheets that

indicate extension (mode I) and extensional-shear (mode II) mode failure respectively.

Sills cut and are cut by similarly oriented fractures and reverse faults suggesting intrusion

during compression, related to NE-SW shortening. On-going work aims to constrain the

relative timing of dykes and sills, and the influence of sill emplacement on the physical

and fluid flow properties of host rocks.


89

Geomorphic and geological constraints on the active normal faulting of

the Gediz (Alaşehir) Graben, Western Turkey.

E. Kent, 1 S. J. Boulton,

1, * I. S. Stewart,

1 A. C. Whittaker,

2 and M. C.Alçiçek

3

1

School of Geography, Earth and Environmental Sciences, Plymouth University,

Plymouth, PL4 8AA, UK. 2

Department of Earth Science and Engineering, Royal School of Mines, Imperial College,

London, UK 3

Department of Geological Engineering, Pamukkale University, Turkey.

The Gediz (Alaşehir) Graben is located in the highly tectonically active and seismogenic

region of Western Turkey. Extension due to regional geodynamic controls has resulted in

a broadly two-phase evolution of the graben; firstly, low-angle normal faulting relating to

the exhumation of the Menderes Massif metamorphic core complex took place between 16

- 2.6 Ma. Secondly, high-angle normal faulting initiated ~ 2 Ma resulting in the formation

of the Gediz and other E-W trending grabens in the region.

Using structural and geological constraints, the throw rate along the fault array over the

last 2 Ma has been quantified, along with analysis of topographic relief as a proxy for

footwall uplift. We derive, for the first time, time averaged rates of fault motion varying

from 0.4 mm/yr to 1.3 mm/yr along the strike of the Gediz Graben, with variation in

throw-rate associated with the geometry of individual fault strands. Variations patterns in

throw-rate along strike of the graben bounding fault array also suggest that the fault

segments have become linked during the last 2 Ma.

Furthermore, the rivers upstream of the normal fault-bounded graben each contain a non-

lithologic knickpoint, including those that drain through inferred fault segment

boundaries. Knickpoint heights measured vertically from the fault scale with footwall

relief and documented fault throw (vertical displacement). Consequently, it appears that

knickpoints were initiated by an increase in slip rate on the basin-bounding fault, driven

by linkage of the three main fault segments of the high-angle graben bounding fault array.

Fault interaction theory and ratios of channel steepness suggest that the slip rate

enhancement factor on linkage was a factor of 3. We combine this information with

geomorphic and structural constraints to estimate that linkage took place between 0.6 Ma

and 1 Ma. Calculated pre- and post- linkage throw rates are 0.6 and 2 mm/yr respectively.

Maximum knickpoint retreat rates upstream of the faults range from 4.5 to 28 mm/yr,

faster than for similar catchments upstream of normal faults in the Central Apennines and

the Hatay Graben, and implying a fluvial landscape response time of 1.6 to 2.7 My.

Climate variation and fault throw rate partially explain the variations in repsonse times

observed, lithology remains a potentially important but poorly characterised variable in

understanding the landscape response to base-level change.


90

Deformation mechanisms and petrophysical properties of fault rocks

within slope-to-basin carbonates (Gargano Promontory, southern Italy)

I. Korneva

1,2, E. Tondi

2, F. Balsamo

3, and F. Agosta

4

1 Department of Earth Science, University of Bergen, Norway

[email protected] 2 Geology Division, School of Science and Technology, University of Camerino, Italy

3 NEXT (Natural and Experimental Tectonic research group), Department of Physics and

Earth Sciences, University of Parma, Italy 4 Department of Sciences, University of Basilicata, Italy

In this work, we examine faults exposed in a slope-to-basin succession composed of

limestone and chert rocks, which crop out in the eastern Gargano Promontory (southern

Italy). Two stages of deformation have been recognized: i) faulting occurred within

sediments prior to their complete lithification (pre-lithification faulting stage); ii) faulting

tooked place in sediments that were already well-lithified (post-lithification faulting

stage). The structural properties of pre-lithification faults were likely controlled by the

competence contrast between limestone and chert sediments, due to their different timing

of lithification. In fact, faulting occurred when the chert was still not completely lithified

and hence smeared along fault planes, resulted in pre-lithification fault rocks being mainly

composed of chert clasts. On the contrary, post-lithification fault rocks are mostly made

up of limestone clasts or mixed lithology. The results of both microstructural and image

analyses show that carbonate fault rock is characterized by higher percentage of bigger

clasts and their lower angularity than chert fault rock. Mercury porosimetry confirmed that

pre-lithification fault rocks are characterized by bigger pore throats and greater

permeability than post-lithification ones. This study increases our knowledge in how

lithological heterogeneity and different lithification stage of the sediments where faulting

occur may influence the deformation mechanisms and resultant hydraulic properties of

fault zones.


91

How does partial melt effect the seismic properties of orogens?

A. L. Lee

1, T. Torvela

1, G. E. Lloyd

1, and A. M. Walker

1

1School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, UK.

[email protected]

The geological evolution of orogenies is partly controlled by partial melting in the middle

and/or lower crust. However, seismic methods cannot reliably quantify the amount of

melting at depth in tectonically active mountain belts. We have developed a method to

assess the impact of melt on seismic properties and applied this to samples from a transect

across a migmatitic shear zone in the Seiland Igneous Province, Northern Norway. These

rocks represent an analogue to lower crustal shear zones undergoing orogenic collapse.

Compressional and shear waves reduce when melt is introduced but the effect on seismic

anisotropy is unclear and recent evidence suggests the melt-seismic property relationship

is not simple.

We have measured crystallographic preferred orientations in sheared migmatites using

EBSD and use this data as input for multiple models designed to quantify the variation of

seismic properties with melt volume. Three ‘end member’ models have been developed: a

reference ‘isotropic model’ consisting of a rock matrix comprising randomly oriented

grains with distributed spherical melt pockets, the ‘matrix dominated model’ consisting of

a textured mineralogical matrix with randomly distributed spherical melt pockets, and the

‘shape fabric model’ an isotropic matrix with ellipsoidal melt inclusions.

The isotropic and matrix dominated models give end member seismic properties for the

isotropic and anisotropic dominated regimes. Importantly, these models do not consider

the shape of the melt fractions, and instead the melt is averaged over the whole rock. The

shape fabric model calculates the seismic properties of an isotropic inclusion within an

isotropic matrix. The results of this modelling show that an oblate ellipsoid has the

greatest effect on seismic properties. It is also the most likely shape for melt pockets as it

is an analogue shape for extensional melting during orogenic collapse; a large oblate

ellipsoid produces a high S-wave anisotropy.

These results indicate that partial melt can greatly affect the seismic response from the

lower crust and that this relationship is not linear with melt volume increase. Mineral

composition, melt shape and wave propagation direction can result in huge variations in

the same seismic property. Thus, multiple seismic properties should be used to predict

melt volume in the lower crust.


92

Eocene evolution of fault populations in the northern Sørvestnaget Basin

related to North Atlantic break-up

Marvik, M.

1, Kristensen, T.

1, Rotevatn, A.

1, Ravnås, R.

2, and Henstra, G.

1

1Department of Earth Sciences, University of Bergen, Allégaten 41, 5007 Bergen, Norway

2Norske Shell, Tankvegen 1, 4056 Tananger, Norway


Fault population evolution in the margin proximal basins along transtensional rift-

shear margins are complex compared to orthogonally extended rifted margins and is at

present poorly documented. The aim of this study is to investigate the structural style and

evolution of the Sørvestnaget basin during the Eocene, and examine the geometries and

style of fault arrays that formed during the opening of the North Atlantic along the sheared

margin of the western Barents Sea.

The study area is located in the northern part of the Sørvestnaget Basin, a major

Cenozoic depocenter situated along the NNW-SSE trending western margin of the Barents

Sea, at approximately 71°-73°N, 15°-18°E. To the north the basin is delineated by the

Vestbakken Volcanic Province and the southern part of the Stappen High. The

westernmost limit of the basin is defined by the oceanic crust of the oceanic Lofoten

Basin, and eastwards separated from the Bjørnøya Basin by a system of normal faults. In

the southeastern part, the Veslemøy High and Senja Ridge bound the basin. The main

structural grain within the study area is defined by a NNE-trending array of extension-

dominated faults.

Three-dimensional reflection seismic and well data from the Sørvestnaget Basin

have been used to examine the stratigraphic framework and the structural style of the

northern part of the Sørvestnaget Basin. By analyzing variations in lateral and vertical

throw distribution as well as the thickness distribution of syn-tectonic growth strata, we

shed light on the structural style and evolution of the studied fault populations and the

Sørvestnaget Basin.

Results from this ongoing work will be presented at the conference; preliminary

analyses indicate a complex basin history related to the opening of the North Atlantic with

partitioning of extension, compression and shear in space and time.

By constraining the kinematic evolution of the northern Sørvestnaget Basin we

conribute to an improved understanding of basin- and fault evolution in settings with

complex transtensional rift-shear margins, as well as to the regional evolution of the

Western Barents Sea margin.



93

Internal Thrust Sheet Deformation in the Sevier FTB, insights from

AMS

D. McCarthy

1, P. Meere

2, and M. Petronis

3


[email protected] 2School of Biological, Earth and Environmental Sciences, University College, Cork,

Ireland. 3Environmental Geology, New Mexico Highlands University, Las Vegas, New Mexico,

USA.

The Sawtooth Range of North-Western Montana represents the frontal range of one of the

world’s classic fold and thrust belts, the North American Cordillera. The range is

composed of numerous thrust sheets of Mississippian carbonates that were emplaced in

the footwall of the regional scale Lewis Thrust. Despite considerable bulk shortening, the

finite strain in the Mississippian carbonates has been largely limited to brittle deformation

with only minor development of a penetrative tectonic fabric. In order to determine the

extent of the development of this weak tectonic fabric, anisotropy of magnetic

susceptibility (AMS) studies have been carried out on five thrust sheets, exposed in the

Sawtooth Range.

AMS is capable of determining the orientation distribution of all the minerals contributing

to the magnetic fabric of a sample, and as a result can identify separate petrofabrics,

including incipient tectonic fabrics. The AMS fabrics recorded from the Sawtooth Range

vary from bedding controlled to a weak tectonic cleavage, through an intermediate stage

with blended fabrics. This evolution of fabric type is not clearly developed at an outcrop

scale. The poor development of penetrative fabrics in the Madison Limestones may be

attributed to the relatively low temperature deformation conditions they experienced.

Estimated deformation temperatures of 100˚C-175˚C are below the temperatures required

for intracrystalline plastic flow of calcite (200˚C-300˚C). When present a tectonic

stylolitic fabric is consistently perpendicular to bedding, suggesting that they developed

prior to thrusting and rotation of the carbonates. Similarly the AMS results suggest that

cleavage formation within each thrust sheet developed as a response to the over-riding

thrust.


94

Using fault orientation to study the links between slip at depth and the

surface for the 1997 Colfiorito earthquakes.

Z. K. Mildon

1, J. P. Faure Walker

1 and G. P. Roberts

2

1 Institute for Risk and Disaster Reduction, University College London, Gower Street,

WC1E 6BT. [email protected] 2

Department of Earth and Planetary Sciences, Birkbeck, University of London, Malet

Street, London, WC1E 7HX

The Mt Le Scalette fault, Umbria, ruptured during an earthquake sequence in 1997 and a

pale unweathered stripe appeared at the base of the bedrock fault scarp. The origin of this

stripe is debated in the literature. We have conducted detailed structural mapping to

determine whether this stripe formed by tectonic or landslide processes. The detailed

mapping highlights variability in strike and dip over a range of scales (10’s to 100’s of

metres) due to corrugations and breached relay zones along the fault scarp. The structural

data collected demonstrates a systematic relationship between the strike, dip and

coseismic slip (measured as the height of the pale unweathered stripe at the base of the

fault scarp). We interpret this relationship as evidence that slip during the earthquake

propagated from depth to the surface.

The central Apennines are undergoing active extension across NW-SE orientated normal

faults. These faults have been active since the Plio-Pleistocene (2-3Ma) when the regional

stress field switched from compressional to extensional (Cavinato et al., 2002, Roberts

and Michetti, 2004). Following the demise of the Last Glacial Maximum (LGM, 15±3ka)

and the reduction in erosion rates, limestone bedrock fault scarps have been exposed and

preserved at the surface. It has been debated

in the literature whether these fault scarps

are active (e.g. Blumetti et. al., 1993,

Schlagenhauf et al., 2010) or inactive (e.g.

Cinti et al., 1999, Chiaraluce et al., 2003).

This debate is important for the full

understanding of the seismic hazard of the

region.

Other fault scarps throughout the Apennines

show similar features to the Mt Le Scalette

fault, and hence we infer that they are also

active and representative of the seismogenic

fault. Through mapping the fault scarps, the

location and extent of active faults can be

mapped and used to infer the level of

seismic hazard within the region.

Figure 1: Structural data collected from the Mt Le

Scalette fault plotted against distance along the fault. a.)

strike against distance, black line is perpendicular to the

mean trend. b.) dip against distance, black line is the

mean plunge. c.) vertical height of the unweathered

stripe (analogous to coseismic slip) against distance.

Vertical grey bars indicate the regions of high and low

strike, dip and slip which we use to infer a systematic

relationship between the data.


95

Faults in dirt:

a comparison of deformation bands in sand and sandstone.

L.A. Millar

1, Z.K. Shipton

1 and A. Hamilton

1.



Deformation bands are mm-cm scale tabular zones of localized strain mostly found in high

porosity sand(stones). Deformation bands have been identified and widely studied in

sandstone field outcrops and boreholes across the world. More recently there has been an

increasing number of studies on the formation of deformation bands in poorly

consolidated and unconsolidated sands. In particular the identification of cataclastic

deformation bands formed in <500 m of the Earth’s surface is of interest as previously

cataclastic bands were perceived as forming deeper in the Earth.

Primarily deformation bands have been studied due to their impact as baffles and barriers

on fluid flow in reservoir rock. However, it is also important to understand their formation

in the shallow subsurface as their identification may also impact burial history estimates.

Furthermore, their identification could be a useful tool in paleoseismology research.

Here we present a review of recent literature on deformation bands found in poorly

consolidated and unconsolidated sandstones, and compare the features of these

deformation bands with deformation bands in sandstone. We characterise each of the

bands by their deformation mechanism and kinematic features, depositional environment,

burial depth and whether they are identified as single, zone or anastamosing at outcrop

scale.

In addition, we present first results from a multiscale comparative study of deformation

bands in Permian sandstone on Arran, Scotland, versus deformation bands found in poorly

consolidated, Oligocene-Miocene age sediments of northern Hungary. By comparing and

contrasting the physical properties of the deformation bands within sands and sandstone

we aim to grasp a clearer understanding of the processes which take place during their

formation in order to better constrain their application in subsurface fluid flow, tectonic

evolution and paleoseismology.


96

Mechanical Twinning and Microstructures in Experimentally Stressed

Quartzite

A. Minor

1, H.-R. Wenk

2, E. Rybacki

3, and M. Sintubin

1

1Geodynamics and Geofluids Research Group, KU Leuven, Belgium.

[email protected] 2Department of Earth and Planetary Science, University of California Berkeley, USA.

3German Research Centre for Geosciences GFZ, Potsdam. Germany.

Since Dauphiné twins in quartz, a 180° rotation about the crystallographic c-axis [0001],

have been identified as a stress-related intracrystalline microstructure, several electron

backscatter diffraction (EBSD) studies revealed that Dauphiné twins are present in

naturally deformed quartz-bearing rocks in a wide range of tectono-metamorphic

conditions. EBSD studies on experimentally stressed quartzite showed that crystals with

particular crystallographic orientations contain many Dauphiné twin boundaries (DTBs),

while neighboring crystals with different orientations are largely free of DTBs.

A detailed EBSD study was performed on experimentally stressed quartzite samples and

compared with an undeformed reference sample to understand the relationship between

stress direction and orientation of Dauphiné twinned quartz crystals. Cylindrical samples

(20 mm length, 10 mm diameter) of quartzite were stressed in triaxial compression in a

Paterson type gas deformation apparatus at GFZ Potsdam. Experimental conditions were

300MPa confining pressure, 500°C temperature and axial stresses of 145MPa, 250MPa

and 460MPa for about 30 hours, resulting in a minor strain (<0.04%). EBSD scans were

obtained with a Zeiss Evo scanning electron microscope and TSL software at UC

Berkeley.

The EBSD maps show that DTBs are present in the starting material as well as in

experimentally stressed samples. Through a manual EBSD processing, the crystal lattice

orientation of grains free of DTBs and grains containing DTBs are identified. This

analysis aims to quantify the relationship of crystal lattice orientation and stress

orientation to initiate mechanical Dauphiné twinning.

Comparing pole figures of DTB-free grains of the reference sample with those of the

stressed samples show a significant different orientation distribution for the r and z poles.

The reference sample shows a maximum for r poles and a minimum for z poles, related to

the natural paleostress direction (before the stress experiment). All stressed samples show

a dominant maximum for r poles and a minimum for z poles in the axial stress direction. A

further detailed analysis of grains containing DTBs suggests a possibility to distinguish

between r (twinned part) and z (host part) domains in the grain.

The analysis of the crystal lattice orientation of grains containing, and especially of grains

free of DTBs, could be a significant instrument to reconstruct the paleostress state in

naturally stressed rocks.


97

Review on spheroidal weathering and associated fractures

Achyuta Ayan Misra

1, Soumyajit Mukherjee

2

1 Petroleum Exploration, Reliance Industries Ltd., Navi Mumbai 400 701, Maharashtra,

India. [email protected] 2 Department of Earth Sciences, Indian Institute of Technology Bombay, Powai, Mumbai

400 076, Maharashtra, India.

We review spheroidal weathering/ “corestone shell systems” and genesis of associated

fractures that are usually sub-circular/sub-lenticular in shape. Intact individual cores of

unweathered rock, sometimes twinned and/or pitted, 0.02 to 2 m in diameter consisting of

several zones of micro-crack densities, which transform temporally from ellipsoid to

sphere, are left behind. Such cores are surrounded by a shell of weathered rinds/rings.

Sometimes granular structureless rock materials are found in place of solid cores. Towards

the core, fractures are usually more circular. Spheroidal weathering has been noticed most

commonly in basalts where curved fractures are more close-spaced, and also in granites

with fewer and widely spaced fractures, dolerites, limestones, mudstones and sandstones.

Tectonic and atectonic joints/fractures, columnar joints in some cases and shear zones

augment chemical weathering by providing preferred flow path of (acidic) fluids. Water

absorption, chemical decay and brush fire affects the outermost part of rocks. However,

these processes and change in meteoric water shower/frost action cannot be the unique

mechanisms of spheroidal weathering since this phenomenon has also been reported from

shallow depth. In the later case, pneumatolysis (effect of hot fluids from depths to start the

weathering process) might be the trigger. Whether chemical alteration of rocks can

produce dilation in rock has been questioned, although dilation has been ascertained from

orientation pattern of deformed crystals in vesicles in the altered rim of some spheroids.

Volume change and subsequent spheroidal weathering might be possible also by

unloading/exhumation of sedimentary- and metamorphic rocks, but this does not possibly

apply to Deccan trap basalts in western India. Alternate rings in spheroidal weathering

could be enriched in Si, Al, K and Zr in certain zones and in Ca and Fe in other.

Concentration of Fe, Ca, Zr, Y, Rb, Al, Si and K may vary from one colour zone into the

other. This chemical constraint along with colour contrasts observed in some spheroidally

weathered igneous rocks possibly indicate that the Liesegang hypothesis of weathering

might hold true even in natural conditions where alternate Fe-rich and Fe-poor layers may

form around the core. Spheroids of the Deccan trap basalts in and around Mumbai are

certainly not tectonic inclusions nor are centers of cooling of lava. Mathematical models

of spheroidal weathering mechanism that simulated hyperbola like weathered surfaces

have not yet significantly included chemical constraints such as the the Liesegang

hypothesis.


98

The influence of initial damage on microcrack healing at hydrothermal

conditions

T. Mitchell

1, A. Anuar

1, P. Meredith

1 and P. Perez-Flores

2

1 Department of Earth Sciences, University College London, Gower Street, London,

WC1E 6BT

[email protected] 2 Departamento de Ingeniería Estructural y Geotécnica, Pontifical Catholic University of

Chile, Santiago, Región Metropolitana, Chile

Off-fault coseismic fracture damage at depth can be inferred from reductions of crustal

seismic velocity following large earthquakes. A growing body of geophysical evidence

exists for ‘healing’ processes occurring in the bulk following such earthquakes, inferred

from time-dependent increases in seismic velocity lasting from days to years. Surprisingly,

little is known about the controls on co-seismic microfracture damage healing rates. Here,

we present experimental and microstructural observations on the rates of microfracture

healing in terms of post-seismic recovery of seismic velocity, porosity and permeability,

as a function of varying initial damage. Preliminary results indicate that highly damaged

samples show up to three orders of magnitude reduction in permeability over several days

at temperatures and pressures commensurate with just 4km depth, combined with

significant decreases in porosity and increases in seismic velocity.



99

Review on Symmetric Structures in Ductile Shear Zones

Soumyajit Mukherjee

Department of Earth Sciences, Indian Institute of Technology Bombay, Powai, Mumbai

400 076, Maharashtra, India. [email protected]

Ductile shear zones may consist of symmetric augen, lenticular mineral fish, clasts with or

without mantles/wings/tails, lozenges, boudins, veins and folds in a wide range of rock

types. Symmetric augen, clasts, lozenges and boudinaged clasts can have a number of

shapes such as lenticular, sub-circular, euhedral, rectangular, rhombic, squarish etc. Augen

can have syntectonic or postectonic growth, can act as a porphyroblast or even a

porphyroclast, may have magmatic origin, and might be defined by more competent

minerals. More competent minerals such as hornblende over feldspar develop naked clasts

more feasibly. Separate analogue- and numerical modeling and microstructural

observations indicate that the degree of symmetry and geometry of clast and mantle

depends on (i) the flow pattern developed within the matrix; (ii) matrix rheology: whether

Newtonian or non-Newtonian; (iii) rheological contrast between the clasts and the matrix;

(iv) degree of slip of clasts within the matrix; (v) variation of rate of shear across shear

zone; (vi) deformation temperature; and (vii) shear intensity. For example, winged clasts

form when the mantle and the matrix are of nearly the same competency. Coiled mantles

develop in more viscous media. However, how all the seven constraints can govern the

shape asymmetry of clasts simultaneously is not known. Additionally, the mantle/wing

geometry is primarily controlled by (i) the initial aspect ratio of the clast; (ii) rate of fall of

clast size; (iii) ratio of simple- to pure shear; and (iv) relative rates of crystallization and

strain. Recrystallization of clasts can supply materials for mantle and help transform a

delta structure into a phi structure, and then into a sigma structure. A slow recrystallization

rate, on the other hand, can produce a theta structure. Pure shear can produce symmetric

pressure shadows, -fringes and augen. Lower curvature of tails can indicate a pure shear.

Symmetric lozenges form for certain angular relation between shear zone and planes of

anisotropy in rocks, and that between cross-cutting shear zones. Ductile shear sense might

still be deduced from symmetric clasts by noting either any quarter fold of matrix foliation

formed around clasts, or sigmoidal nature of the inclusion pattern (S-internal) inside them.

Extension of a non-Newtonian matrix with Non-Newtonian clasts embedded develops

symmetric necking around clasts. Asymmetry develops upon intense extension. Near

symmetric bone-shaped boudins might be produced by rotation of veins. Pure shear can

produce highly convex bulging symmetric boudins. False/pseudo boudins may be

symmetric and lenticular. Orthorhombic symmetric boudins produce by no slip of inter-

boudin surfaces. Unlike clasts, matrix rheology may not decide geometry of all kinds of

(foliation) boudins. Extensional stress parallel to foliation planes can develop symmetric

pinch and swell structures, and compressional stress symmetric folds. Parasitic folds of a

lower order fold not affected by ductile shear are symmetric Newtonian viscous layer

under pure shear within a non-Newtonian matrix may form symmetric folds. Post-tectonic

veins cutting across main foliations (primary shear C-planes) and do not give shear sense.

Natural examples of symmetric objects from Himalayan ductile shear zones show internal

foliations inside augen concordant with the matrix foliation. Symmetric lenticular objects

with high aspect ratios might indicate pronounced ductile shear and might have a previous

asymmetric shape. Tails of centrally pinched augen indicate a pure shear component,

whihc has been deduced from Greater Himalayan Crystallines by previous workers.


100

Topology of small-scale fault damage zones

Nærland, K.

1, Dimmen, V.

1, Rotevatn, A.

1, Kristensen, T.B.

1, Nixon, C.W.

1, Peacock,

D.C.P.1, Bastesen, E.

2

1

Department of Earth Science, University of Bergen, Allégaten 41, 5007 Bergen, Norway.

[email protected] 2

Centre for Integrated Petroleum Research, University of Bergen, Allégaten 41, 5007

Bergen, Norway

Characterisation of fault and fracture populations generally uses their geometric

properties, such as length, aperture, orientation and intensity. Such data, however, give us

little information about the relationships between the different faults and fractures that

form a network. Although individual faults and fractures are well understood, their

arrangement as a network (topology) and the resulting effect on fluid flow and transport

within fractured media is less clear.

By characterising the topology of fault and fracture systems we can better describe

the relationships between faults and fractures in a network and assess their connectivity.

The topology of a fracture and fault network can be considered in terms of nodes and

branches between nodes. The nodes represent the isolated tips of faults/fractures (I-nodes)

and their intersecting relationships (abutting/splaying Y-nodes and crossing X-nodes).

Branches are defined by the different nodes as each end and can be divided into isolated

branches (I-I), partly connected branches (I-C) and fully connected branches (C-C).

Simple number counts of the different nodes and branches in the field can lead to an array

of topological parameters that can be used to describe the degree of connectivity within a

network.

In this study, we investigate the topology of different fault damage zones affecting

carbonate rocks (Miocene, Malta). We compare the topological characteristics of damage

zones associated with fault tips, fault splays and relay zones. Three questions are

addressed in this study. (i) What are the topological differences between different types of

fault damage zones? (ii) Are specific damage zone types associated with a characteristic

topological signature? (iii) What does the use of topology add to improve fault damage

zone characterisation?

The results show that the proportions of I-nodes and I-I branches are higher, and

therefore connectivity is lower, in fault tip zones than in relay zones and fault splay zones.

The damage associated with fault splays and relays show similarities in topology that

could be related to similarities in their evolution, in the sense that they both reflect

interaction of at least two faults.


101

Using structural reconstructions to constrain volcanic passive margin

evolution; a case study from the Orange Basin, offshore SW Africa

James Norcliffe

1, Douglas Paton

1, Estelle Mortimer

1, Andrew McCaig

1

1 School of Earth and Environment, University of Leeds, Leeds, UK

[email protected]

On volcanic passive margins, the transition from continental rifting to seafloor spreading

is marked by the eruption of continental flood basalts. On seismic reflection profiles these

are imaged as seaward dipping reflectors (SDRs). SDR distribution provides insight into

the relative roles of mantle temperature and rift history during continental breakup.

However, on the SW African margin, a lack of well data has lead to uncertainty in seismic

interpretations.

This study uses recently acquired 2D seismic reflection data from the Orange Basin to

assess margin evolution. Uncertainty is reduced through structural analysis and

reconstructions: Initially, the SDRs are differentiated from the syn-rift, then the

geodynamic implications of SDR emplacement are addressed.

The syn-rift stratigraphy is confined in a wide (> 80 km) basin; the magnitude of faulting

is unclear due to a loss of resolution with depth. SDRs were emplaced outboard of the

underlying basin and emplacement was marked by a rapid narrowing of the deformation

zone (to a width of < 25 km). SDRs show downdip thickening and an upwards swallowing

of dips; this indicates synchronous emplacement and tilting. This process also leads to the

tilting of the underlying syn-rift. We interpret the seaward dips as resulting from loading-

related subsidence.

Hence, in the absence of well data, structural reconstructions can be used to constrain

margin evolution. The narrowing of the deformation zone during SDR emplacement

represents the transition from distributed continental stretching to localised seafloor

spreading. Therefore, SDR formation represents a distinct tectonic event.


102

Last interglacial marine terraces reveal extreme surface uplift rates in

the Iranian Makran

R. Normand

1, G. Simpson

1 and A. Bahroudi

2

1Department of Earth Sciences, University of Geneva, Rue des Maraichers 13, CH-1205

Genève. ([email protected]) 2Exploration department, School of Mining Engineering, University of Tehran, Northern

Kargar avn, P.O. Box 11365-4563, Tehran

We have studied and dated a sequence of uplifted marine terraces exposed along the

coastal margin of the aseismic western segment of the Makran subduction zone. The

terraces contain marine shell material that we have dated using the 14

C technique. All of

the studied terraces were formed during late Marine Isotopic Stage 3 (MIS3). The highest

terrace culminates at 220m a.s.l. and has an age of ca. 32000 yrs.B.P.. Considering that the

terrace formed at a time when the sea level was considerably lower than today (probably

ca. -80m), a maximum surface uplift rate close to 9 mm/yr during the late Quaternary is

inferred. This exceeds most subduction zone surface uplift rates by a factor of at least

three. Lack of evidences towards sustained (long term) uplift tends to indicate that,

although extremely rapid, this deformation is short lived and probably very local. The

terraces are cut by numerous trench-parallel normal faults, with late Quaternary offsets of

up to 60 m. These faults are thought to result from gravitational collapse following uplift

linked to motion on main plate boundary thrust. Although the reason why the Makran

experiences anomalously high surface uplift rates is presently unknown, the significant

vertical motions and recent normal fault activity are in opposition with the apparently

aseismic nature of this subduction zone.


103

Landscape maturity and fold growth timing in the Kirkuk Embayment,

northern Iraq

Ahmed Obaid

1 and Mark B. Allen

1

1Department of Earth Sciences, University of Durham, Durham, DH1 3LE.

[email protected]; [email protected]

The Kirkuk Embayment (KE) is located in the southwestern part of the Zagros fold–and-

thrust belt (ZFTB) of Iraq. Like fold-and-thrust belts worldwide, the Zagros is

conventionally understood to have grown sequentially from the hinterland towards the

foreland, i.e. from northeast to southwest, either in a series of tectonic pulses or a more

continuous progression. Here we use landscape maturity analysis to understand the

development of anticlines in the KE. DEM-based geomorphic indices Hypsometric

Integral (HI), Surface Roughness (SR) and their mathematical combination Surface Index

(SI) have been applied to quantify landscape maturity. Topographic position Index (TPI)

has also been used to investigate the effect of deformation on the landscape.

The results reveal new ideas regarding the sequence of anticline growth within the KE.

The growth sequence is not classical ‘piggy back’ thrusting; the maturity indices are

highest for the QaraChauq anticline in the center of the Embayment, then the

Makhool/Himreen anticlne to the south and lastly, the Kirkuk anticline to the north. This

pattern fits the exhumation record, which is loosely constrained by the level of exposed

stratigraphy within the fold cores: QaraChauq exposes the oldest strata of the three main

folds considered.

The favoured hypotheses for the order of fold growth are either i) the folds have grown at

different time and out of sequence (QaraChauq first, the Makhool/Himreen, and Kirkuk

last), or, ii) the growth occurred with different rate of exhumation but at broadly the same

time. There are few constraints from available data on syn-tectonic sedimentation patterns,

but it may be that fold growth across much of the Embayment began within a limited

timeframe in the late Miocene – Pliocene(?), during the deposition of the Bakhtiari

Formation. Another possible hypothesis is that the folds have grown in sequence towards

the foreland with different rates of exhumation, but we consider this less likely. TPI

analysis combined with analysis of Lesser Zab River longitudinal profiles shows new

antiforms in a region where they have not been described before. TPI could be used in the

discovery of anticlines of importance in the oil exploration of the region.




104

Structure and Cretaceous evolution of the multiphase East Røst Fault

Zone, Lofoten Margin, Northern Norway

Ordemann, M.

1, Henstra, G.

1, Rotevatn, A.

1, Ravnås, R.

2, Kristensen, T.

1


2 Norske Shell, Tankvegen 1, 4056 Stavanger


The growth and geometry of basins and fault systems in multiphase rifts are less

well understood than in provinces with a single phase of extension. This study will focus

on the geometry and growth of the East Røst Fault Zone (ERFZ), which bounds the North

Træna Basin, and is located along the Lofoten segment of the Norwegian passive margin.

The ERFZ is a long-lived basin-bounding fault located in a province that underwent

multiphase extension throughout the Paleozoic to Mesozoic; break-up, and opening of the

North Atlantic and formation of the Norwegian passive margin occurred subsequently in

the early Cenozoic. In this study, we investigate the Cretaceous evolution of this fault

system, which is particularly poorly understood. To do this, we investigate 3D reflection

seismic and shallow stratigraphic core data.

The North Træna Basin (NTB) is bounded by the ERFZ to the west, and the

Vesterdjupet Fault Zone (VFZ) to the east. The ERFZ is an NE-trending, E-dipping

normal fault zone, composed of two large fault segments with a NE-SW orientation, and

separates the North Træna Basin (NTB) from the Utrøst Ridge. The larger fault segments

are linked via smaller, NNE-SSW orientated segments. The studied lengt of the fault is c.

15 km, from a total length of c. 50 km.

To understand the evolution of the fault complex, we analyze the displacement

distribution along the fault as well as the distribution of syn-tectonic growth strata.

Preliminary results indicate that i) selective reactivation of pre-existing faults

characterized the accommodation of middle Cretaceous extension, and ii) that the ERFZ

behaved as a single, kinematically coherent fault during the studied interval, although its

segments were soft-linked at the surface.

This study showcases the growth and evolution of a polyphasal extensional fault

system and broadens the understanding of the Mesozoic evolution of the Norwegian

passive margin.


105

What is the structure of the North Anatolian Fault below the Moho?

E. Papaleo, D. G. Cornwell, N. Rawlinson

School of Geosciences, University of Aberdeen, Aberdeen, UK.

[email protected]

The deep structure of the North Anatolian Fault Zone (NAFZ) is poorly understood.

Various models for the possible structure of global deep transcurrent faults, from very

narrow zones of localised deformation that cross-cut entirely the lithosphere, to faults that

exhibit broad zones of ductile deformation beneath the upper crustal layer, have been

postulated. GPS studies following the 1999 Izmit and Duzce events suggest that the North

Anatolian Fault might be rooted in the upper mantle rather than in the crust, however, no

definite evidence exists about the structure of the fault at depth.

With a length of 1500 km, the NAFZ is a major continental strike-slip fault. Seismicity

along the fault includes regular high-magnitude events; from historical records it is

thought that the fault periodically exhibits a series of migrating earthquakes that move

along the fault activating its different segments. Currently a new sequence of events is

taking place: it started in 1939 with the Erzincan earthquake and it is moving westwards;

the last two events being the Izmit and Duzce events, both in 1999. This poses a risk to the

city of Istanbul, situated close to one of the two strands in which the fault splays before

reaching the Sea of Marmara. Therefore it is of great importance to obtain more detailed

information on the structure of the westernmost part of the North Anatolian Fault.

Previous studies are not in agreement on the velocity structure beneath the NAFZ, so to

better constrain the structure of the fault zone at depth a dense array of seismometers was

deployed close to the city of Izmit, where the fault last ruptured. Using teleseismic

tomography, a technique that allows velocity variations to be imaged using arrival times

from earthquakes very far from the area of interest, it will be possible to image the fault

signature in the lower crust and upper mantle. Moreover, the very tight spacing of the

deployed array will ensure the resolution of features smaller than ~7 km, providing images

of unprecedented detail.

From the results new important information on the fault structure below the Moho can be

gained. In fact the mechanical conditions and deformation mechanisms in a fault zone can

vary over short distance scales - internally and externally to the shear zone. With the

present work it will be possible to obtain a very detailed image of the shear zone, allowing

us not only to detect if any of the fault strands cut through the entire crust and reaches the

upper mantle, but also how the width of the shear zone varies with depth.


106

Titanite petrochronology of ore-controlling shear zones: Insights from

the Sudbury mining camp (Sudbury, ON)

Kostas Papapavlou1, James Darling

1, Craig Storey

1, Peter Lightfoot

2, Desmond Moser

3 &

Stephanie Lasalle1

1 School of Earth and Environmental Sciences, University of Portsmouth, UK

2 Vale Technology Development (Canada) Limited, Brownfield exploration, Copper cliff,

Ontario, Canada 3 University of Western Ontario, London, Ontario, Canada

Deformed impact structures are unique sites to understand the development of both

orogenic and syn-impact exogenic fabrics. In the Sudbury impact structure (Canada, ON),

the main manifestation of strain localization is a network of greenschist to amphibolite

facies ductile shear zones, the South Range Shear Zone. The timing of operation, orogenic

affinity, and deformation path of the structures that comprise this network of crustal-scale

shear zones remain ambiguous. Texturally controlled age dating of these ore-controlling

shear zones will provide new insights on the timing of their operation/reworking. The two

structures under investigation are an outcrop-scale mylonitic zone (Six shaft shear zone)

exposed at the 5400 level of the Creighton mine and a chlorite-rich mylonitic zone (Cliff

lake shear zone) that transects the Sudbury igneous complex. The Six shaft shear zone is

a biotite-rich mylonitic zone characterised by a strong dip-slip component that exhibits

different monoclinic symmetry shear sense indicators (e.g. sigmoids, mica fish,

asymmetric winged porphyroclasts) with consistent top-to-the-SW, reverse, sense of

shear. The Cliff lake shear zone is a reverse sense structure with diagnostic features of low

grade mylonites that defines the southern boundary of the South Range Shear Zone

(SRSZ). Detailed imaging and quantitative textural analysis of shear-hosted accessory

phases using micro and nano-beam techniques (SEM/BSE, EBSD) revealed: (a) titanite

grains with metasomatic features (e.g. patchy zoning and ilmenite cores), (b)

recrystallized, ribbon-shaped, titanite grains with high-angle sub-grain boundaries (>10˚)

and extreme intra-grain lattice misorientations (100˚), and (c) syn-kinematic, patchily

zoned titanites that developed sigmoids and mineral fish microstructures. Preliminary U-

Pb isochron age dating of accessory phases from both structures, using laser ablation-

inductively coupled plasma-mass-spectrometry (LA-ICP-MS), yielded an age of 1672±53

Ma (2σ) for the titanite population and 1629±38 Ma (2σ) for the allanite population.

Overall, microstructural data from metasomatic titanites that locally underwent intense

crystal-plastic deformation indicate that pulses of fluid flow and strain accumulation

alternate during the operation of these high-strain zones. Moreover, the new age data

strongly suggest that the operation of the studied shear zones is associated with the

Mazatzalian-Labradorian (1.65-1.70 Ga) tectonothermal event.


107

Dynamic growth and linkage of extensional faults in detached half-

grabens

L. Pérez-Díaz

1 and J. Adam

2


London, Egham, UK. [email protected]


London, Egham, UK.

The localisation, growth and linkage of extensional faults control (a) the complex fault

kinematics, (b) strain partitioning and (c) subsidence patterns in detached half-grabens.

We study the kinematic evolution of these half graben systems with scaled analogue

experiments. Full-field 2D-3D digital image correlation techniques have been used to

monitor incremental and total displacements and strains.

Fault nucleation and growth depend critically on the original thickness of the prekinematic

overburden. Fault nucleation in thin prekinematic sediment packages is nearly

instantaneous. In thick prekinematic layers discrete fault segments localise in high-strain

zones and faults evolve by vertical and lateral fault segment linkage and frequent

reactivation of inactive segments. This results in a complex and variable kinematic pattern

of secondary faults and strain partitioning in the hangingwall of the half-graben structure.

Synkinematic sedimentation has a dramatic effect on fault kinematics because the

additional sediment loading increases normal stresses and consequently the strength of the

underlying prekinematic strata and shear zones. This can cause deactivation of deep-seated

secondary faults of the hangingwall and strain localisation in graben-bounding faults.

Heterogeneous fault displacement gradients and subsidence patterns in graben structures

are the result of the interaction of newly-formed fault segments (within the synkinematic

layers) with pre-existing deeper faults.

The rheology and mechanical strength of frictional basal detachment layers together with

the thickness of the prekinematic layer controls the geometry and curvature of graben-

bounding faults during early nucleation. In contrast, viscous detachment layers enable

finite fault block rotation with minimal internal deformation of hangingwall blocks. In late

stages, rotational fault blocks may subside and founder to the base of the ductile layer

triggering new secondary faults in the fault blocks.

The high-resolution 2D-3D displacement data and strain maps provide insights into the

nucleation and growth pattern of faults in half-grabens under variable geological boundary

conditions. The quantitative information obtained challenges conventional views on

structural modelling of extensional fault systems and provides a more realistic framework

on which to carry out fault analysis and basin modelling in extensional half-graben

systems.


108

Get the ‘Maximum’ out of it:

Maximum Likelihood Estimators for Fracture Attributes

R. E. Rizzo*, D. Healy*, L. De Siena*‚ and A. Awdal‡

* Department of Geology and Petroleum Geology, School of Geosciences, King’s College,

University of Aberdeen, UK. [email protected] ‡ GeoScience Limited, Falmouth, UK

The acquisition of fracture data is usually based on measurements from outcrops, core

samples, and borehole data. Each of these sources has their intrinsic issues which can affect

the quality of the data set in different ways. However, they all share a common problem: it is

only possible to acquire a finite data set, meaning that to expand the data set statistical

techniques have to be applied. Fractures are frequently characterised geometrically in terms of

length, density and aperture. These geometrical attributes are often well described by certain

statistical distributions, e.g. lognormal, power-law or exponential [4]. Interpretation of

measurements to estimate a statistical distribution for a data set can be problematic; a blind

application of analytical techniques and lack of rigour in evaluating the suitability of a

distribution can result in inaccurate and even a meaningless estimate of the distribution

parameters [5].

The main objective of this work is to use a more robust statistical approach to obtain more

useful data from outcrop analogues. A common way to show that a certain data set follows a

specific statistical distribution is to construct a cumulative distribution function by simple rank

ordering of the data; a least-squares linear regression is then applied to this function. However,

this method - in most cases - is actually a poor way of proceeding and generates several

problems when it is applied [6]. In order to establish the best statistical distribution for fracture

attributes, we apply Maximum Likelihood Estimators for determining the distribution

parameters of power-law, lognormal, and exponential distributions. These methods are shown

to be more powerful and more reliable, because they suffer neither subjective biases, nor

biases related to the precision of parameter estimation.

The application of Maximum Likelihood Estimators can have important consequences,

especially when we aim to predict the tendency of fracture attributes towards smaller and

larger scales than those observed, in order to build consistent, useable models from

outcrop observations.

4 Bonnet et al. “Scaling of fracture system in geological media”. Reviews of Geophysics 39.3 (2001) 5 Berkowitz “Characterizing flow and transport on fractured geological media: A Review” Advances in water resources

25.8 (2002) 6 Clauset et al. “Power law distribution in empirical data” in SIAM review 51.4 (2009)


109

Figure 4: Topographic map of the Altiplano-

Puna Plateau with the locations of Quaternary

volcanic centres (black dots) and thrust

earthquake epicentres (white dots).

Plate controls on the location of arc volcanoes

E. Scott, M. Allen, K. McCaffrey, C. Macpherson, J. Davidson, Chris Saville

Department of Earth Sciences, Durham University, Durham, UK.

[email protected]

Arc volcanoes have immense scientific and societal importance, for example as sites of

generation of new crust, sources of CO2 flux into the atmosphere, and locations of

damaging eruptions. Such volcanoes are ultimately related to melting of the mantle wedge

above subduction zones, and so their locations on the Earth’s surface are assumed to relate

to sub-lithospheric, i.e. sub-plate, processes. However, recent work has identified linear,

en echelon belts of volcanoes in the Sunda Arc, Indonesia, suggesting that magma ascent

through the arc lithosphere is influenced by the structures within it and therefore by the

regional stress field.

In this poster, we aim to test this hypothesis in the

volcanic belts of the South American Andes. We

carry out spatial analysis of Quaternary arc

volcanoes, and volcanic structures identified using

SRTM data, in the Northern, Central and Southern-

Austral Volcanic Zones using the Hough Transform

technique, which objectively recognises and

quantifies continental scale linear arrays of volcanic

centres. Large scale linear arrays of volcanic

centres are well developed in the Southern-Austral

Volcanic Zone, but appear to break down in the

high Altiplano-Puna Plateau where there is a more

widespread distribution of volcanism.

Furthermore, we have found that volcanic centres

in the Altiplano-Puna Plateau, South America are

found to be at or above a critical elevation contour

(3500 m above sea level), which also defines the

cut off for seismogenic thrusting (figure 1). Normal

faults are also only found above the critical

elevation contour. This apparent correlation

between volcanism and elevation implies that the

location of volcanoes relates to the precise state of

stress in the crust. However, many implications of

this relationship still remain unexplored, including

the precise state of stress at the critical elevation

contour and to what degree the plateau effect can

modify the emplacement of melt.


110

Tectono-magmatic interaction at the Boset volcanic complex in the

Main Ethiopian Rift

M. Siegburg

1, T.M. Gernon

1, J. Bull

1, D. Keir

1, C.W. Nixon

2, R.N. Taylor

1 and B. Abebe

3

1Ocean and Earth Science, University Southampton, UK, [email protected]

2Department of Earth Science, University Bergen, Norway

3Department of Earth Science, Addis Ababa University, Ethiopia

The East African rift system provides important insights into the interaction of tectonism

and magmatism during continental break. Pre-existing fractures within the rift system may

provide pathways for rising magma, and consequently influence the orientation of craters

and cones at the surface. Alternatively, ascending pressurised melts and / or pressure

variation within sub-volcanic magma plumbing systems may initiate new fractures within

the local stress field. The relative role of these will be examined at the Boset volcanic

complex, the largest stratovolcano in the Main Ethiopian Rift.

The Boset volcanic complex covers an area of 600 km²-, and, although it is surrounded by

major population centres, with up to 4 million people within 100 km radius, little is known

about the past history of tectonic or magmatic activity. Boset comprises the northern

Berichia stratovolcano and the southern Gudda caldera which both lie along a NNE-SSW

fissure. The overall fracture system comprises mainly rift-related extensional faults,

striking NNE-SSW with individual faults having displacement of up to 50 m. On top of

the Gudda caldera as well as north of Berichia volcano, several cones and craters are

oriented along the continuation of the fissure.

Here, a 2-m resolution digital elevation model derived from a NERC ARSF LIDAR

survey, together with satellite images and field observations will be presented, along with

an analysis of structural and magmatic features.

The tectonic mapping includes fracture distribution, directions, displacements and relative

age relations of fractures compared to lava flows. We use these constraints to characterise

the development of rifting at the Boset volcanic complex in the MER. Further analyses of

orientations and distributions of fissures, craters and cones may indicate the magmatic

interaction within the rifting system through time. Structural mapping results are

supported by petrological and geochemical analyses of lava flows from the Boset volcanic

complex.

This study emphasizes the importance of structural mapping in an active continental rift to

understand the tectonic and magmatic development in the past and outline potential

tectonic and volcanic hazards for the future.


111

Fault zone evolution and fluid circulation within active extensional faults

in carbonate rocks

L. Smeraglia

1, F. Berra

2, A. Billi

3, C. Boschi

4, E. Carminati

1,3, and C. Doglioni

1,3

1Department of Earth Sciences, Sapienza University of Rome, Italy.

[email protected] 2Department of Earth Sciences, University of Milan, Italy.

3National Research Council, IGAG, Rome, Italy

4National Research Council, IGG, Pisa, Italy

Structural and geochemical methods applied to the seismically-active extensional Tre

Monti Fault (central Apennines, Italy) were used to develop a conceptual evolutionary

model of seismic faulting with fluid involvement for shallow (≤ 3 km depth) extensional

faults in carbonate rocks.

The relative chronology of these structures was reconstructed through cross-cutting

relationships and cathodoluminescence analyses. C- and O-isotope data from different

generations of fault-related mineralizations show a shift from marine- to meteoric-derived

fluid circulation during exhumation from 3 to ≤1 km depths and concurrent fluid cooling

from ~68 to <35 °C. Between ~3 km and ~1 km depths, impermeable barriers within the

sedimentary sequence created a semi-closed hydrological system, where marine-derived

fluids circulated within the fault zone at temperatures between 60° and 75°C without any

mixing with meteoric-derived fluids. During fault zone exhumation at depths ≤ 1 km and

temperatures <35 °C, the hydrological circulation became open and meteoric-derived

fluids progressively infiltrated and circulated within the fault zone. The presence of low-

permeability clayey layers in the sedimentary sequence contributed to control the type of

fluids infiltrating into the fault zone.

These results can foster the comprehension of fault-related fluid circulation within

seismogenic faults at shallow depths in carbonate rocks of other fold-thrust belts involved

in post-collisional seismogenic extensional tectonics.


112

The Impact of Fault Zone Architecture in Modelling the Fluid

Overpressure Driven Faulting and Seismicity of the Colfiorito Seismic

Sequence

T. Snell

1, N. De Paola

1, J. van Hunen

1, and S.Nielsen

1

1Department of Earth Sciences, Durham University, Durham, UK.

[email protected]

The mainshocks of the 1997-98 Colfiorito seismic sequence nucleated at 6km depth

within the Triassic Evaporites. It has been proposed that the maishocks and their

aftershock sequenece was driven by supercritical CO2 overpressures, measured in two

deep boreholes drilled in the epicentral area. Here, we present a numerical invesitigation

about the effects of overpressured supercritical CO2 on earthquake nucleation processes,

using natural fault zone architecture in Triassic Evaporites rocks and laboratory derived

permeability values as modelling input parameters.

Outcropping faults in Triassic evaporites in the Umbria-Marche Apennines, analogous to

the nucleation site for the Colfiorito seismic sequence, exhibit lithologically

heterogeneous and anisotropic fault zones comprising: a fault core made of an inner

domain, where most of the shear displacement is accommodated, encompassed within an

outer domain of foliated fault rocks; a damage zone, where the intensity of fracturing

decreases as one moves away from the fault core and towards the intact protolith rocks.

The inner fault core is characterized by fault gouges, cataclastites, often showing the

development of very fine-grained ultracataclastites associated with thin, a few millimetres,

slip zones of localized slip. Fault-parallel foliated cataclasites are the dominat fault rocks

in the outer fault core. Distributed extensional/shear fractures and subsidiary faults are the

dominant structures in the damage zone.

Fluid flow from high pressure reservoirs in the damage zone have been modelled across

the fault core, using its internal architecture and the mechanical and permeability values

measured during laboratory experiments from previous studies.

A finite difference method is used with a time dependent solver to solve a nonlinear Darcy

flow model with a pore pressure and stress dependent permeability.

A comparison of the time evolution of pore pressure fields is attempted for a fault

assuming both a homogenous and a heterogeneous structure. Predictions of the fault

patches undergoing failureand the effective stresses acting upon them are made and used

to calculate earthquake nucleation length.

The inclusion of heterogeneous fault zone architecture within numerical simulation can

be shown to alter the predictions of the length of the interseismic period, by producing

failure patches which exhibit unstable behaviour more readily.


113

Predicting fault permeability at depth: data pooling from multiple field

sites

Silvia Sosio de Rosa

1*, Zoe Shipton

1, Rebecca Lunn

1, Yannick Kremer

1

1Department of Civil and Environmental Engineering, Strathclyde University, Glasgow, UK.

*[email protected]

Understanding fault sealing and permeability is key for evaluating subsurface structural

integrity of reservoir formations and hydrocarbon and CO2 migration pathways. Fault

zones are highly complex structures, with properties that are variable within a single fault

and between faults in similar lithologies. This presents considerable challenges to

predicting fault sealing and permeability at depth. Existing fault seal evaluation tools (e.g.

Shale Gouge Ratio) are only reliable in limited circumstances and do not quantify their

inherent uncertainty.

The hydraulic behaviour of faults at depth is determined by the three dimensional fault

zone architecture and by the petrophysical properties of the fault rocks. The focus of this

study is the permeability of fault rocks in siliciclastic sequences of the upper crust, and in

particular the permeability, composition and internal structure of clay-rich gouges.

The review of published literature on fault rock permeability highlights the heterogeneity

of fault rocks, which show a very wide range of permeability values both between

different fault rocks and within the same fault rock types. For instance, the clay-rich

gouges display a range of 9 orders of magnitude, from 10-7

mD to 102 mD. There is a

general trend of decreasing permeability with increasing confining pressure, but no clear

relationship with host rock, fault zone thickness or mineralogical composition of clay;

fault zones present a high dergee of comlpexity.

The mesoscale heterogeneity of fault zones has been observed as well at the microscale

during the microstructural analysis of several fault rock samples from the Moab Fault

(Utah). The two main fault rock studied are the altered sandstone from the damage zone

and the clay-rich gouge from the inner foliated fault gouge. Evidences of fluid flow:

• Hydrocarbon staining along slip surfaces in the fault gouge and along fractures and

slip surfaces in the altered sandstone from the damage zone

• Bleaching of red hematite grain rims in the sandstone, associated with oil stains

• Highly variable degree of calcite cementation in the altered sandstone

• Variable amount of authigenic clays both as grain replacement and interstitial in

the altered sandstone and in the sandstone lenses inside of the clay gouge.

Future work will involve industry data collection from a range of tectonic and lithological

settings (ongoing), field work in faulted sand-shale sequences in Miri (Malaysia), and the

development of a statistical analysis method using industry and field data.



114

Sill emplacement controlled by stress state rather than host layering

Tara Stephens

1, RJ Walker

1, D. Healy

2, RW England

1, KJW McCaffrey

3

[email protected]

1 Department of Geology, University of Leicester, Leicester, LE1 7RH, UK

2 School of Geosciences, King’s College, University of Aberdeen, Aberdeen, AB24 3UE,

UK 3

Department of Earth Sciences, Durham University, Durham, DH1 3LE, UK

Igneous sill complexes represent a significant volumetric contribution to upper crustal

magma systems, and can play an important role in petroleum system maturation and gas

generation in sedimentary basins. Although vertical igneous dikes are typically assumed

as being the dominant sub-volcanic supply route for effusive volcanism, recent studies

have shown that sills can act as major transport networks. Despite their significance, the

causes of sill formation, particularly in terms of the transition from dikes to sills, remains

ambiguous. A level of neutral buoyancy and mechanical stratigraphy have long been

argued as causing dike to sill transition, but natural examples show that sills can occupy

broad depth/elevation ranges within the stratigraphy, and often form at a low angle to host

rock layering.

Here, we focus on the Loch Scridain sills, Isle of Mull, which are gently inclined, NW and

SE dipping intrusions emplaced into sub-vertically-foliated Moine metasedimentary rocks,

and younger sub-horizontal basalt lavas. Sills hosted in the Moine units show similar dips

to those in the lavas above, suggesting that mechanical layering is not a control on sill

emplacement. Detailed field observations in the Moine metasedimentary rocks revealed

the presence of sub-horizontal and sub-vertical fracture networks within the host rock,

which predate sill emplacement. Sill margins show steps parallel to the sub-vertical

foliation, and sub-vertical fractures, but neither structure is intruded. Sub-horizontal

fractures are intruded locally, forming tapered sill tips. This geometric reactivation is

consistent with sub-horizontal compression, and vertical extension, during sill

emplacement.

Mechanical modelling shows that intrusion may be aided by the development of oriented

microcracks related to the compressional stress state, particularly at a local scale around

pre-existing faults where the high density of existing microcracks will facilitate failure at

lower magnitudes of fluid overpressure. Importantly, this model for emplacement of

horizontal intrusions does not require host rock mechanical layering, and hence can be

applied to horizontal intrusions within non-layered, or vertically-layered, media.



115

Investigating the dynamic response of a Granitoid rock mass to reservoir

draining at Grimsel Test Site, Switzerland, as an analogue for Glacial

Retreat

Stillings, M.D., Kinali, M., Lunn R.J., Lord, R., Pytharouli, S., Shipton, Z.K.

Department of Civil and Environmental Engineering, University of Strathclyde


The drainage and refilling of a surface water reservoir beside the Grimsel Test Site (GTS)

underground rock laboratory in Switzerland, has provided a unique opportunity to study

in-situ rock mechanical, hydraulic and chemical interactions under large-scale stress

changes. The reservoir was drained in October/November 2014 to enable dam

maintenance and extension of the regional hydropower tunnel system. Reservoir drainage

will have caused rapid unloading of the rock mass. The GTS sits ~37m below the top of

the reservoir and ~200-600m away laterally within the mountainside on the eastern bank

of the reservoir. For reference, previous research at Strathclyde in similar bedrock showed

that oscillations in surface reservoir depth of only 3-6m could produce microseismicity of

magnitude up to 2 (Pytharouli et al., GRL, 2011, doi: 10.1029/2010GL045875). Gradual

refilling of the reservoir via natural snowmelt and runoff commenced in February 2015.

Research at Strathclyde, funded by Radioactive Waste Management Ltd., have been

investigating mechanical-chemical-hydraulic coupling within the rock mass as an

analogue for glacial unloading and loading of a future Geological Disposal Facility. We

hypothesise that reservoir unloading and reloading will cause microseismic events due to

slip on fractures within the surrounding rock mass. These events will open new pathways

for fluid flow, expose fresh mineral surfaces and may release previously trapped pore

waters. We have deployed three 3-component and 6 single-component micro-

seismometers within the GTS and surrounding hydropower tunnel network. In parallel, we

have implemented a groundwater sampling program, using boreholes within the GTS, for

temporal determination of geochemistry and flow rate. Preliminary data analyses show

groundwater anomalies during unloading, as well as the detection of microseismic events.



116

Uncertainty in seismic depth conversion and structural validation

Y. Totake

1,2, R. Butler

1, C. Bond

1

1

Department of Geology and Petroleum Geology, University of Aberdeen, Aberdeen, UK.

[email protected] 2

Technical Resources Unit, INPEX CORPORATION, Tokyo, Japan

Validation techniques in structural geology are often used to test reliability of seismic

interpretations. This is because seismic interpretation is essentially an uncertain product

based on imperfect datasets, with limits in data resolution and spatial extent. Structural

validation is completed on depth sections, which are converted from seismic time-based

data using velocities derived from well checkshot survey, seismic velocity analysis (e.g

NMO correction), or even estimates when velocity data is missing. Depth conversion

choices critically control the final depth image and hence structural geometry of

interpretations. However, as with the interpretation of seismic reflection, in most

published cases, uncertainty in depth conversion and its influence on structural validation

are rarely examined.

Here we explore how structural validation techniques respond to different versions of

depth interpretations converted by different velocities. We use a seismic time-based image

of a fold-thrust structure in the deepwater Niger Delta to interpret, and convert to depth

using three different velocity models: constant velocity (VM1); a single layer having

initial velocity v0 at layer top with vertical velocity gradient k (VM2); and three layers

having each v0-k set (VM3) below seabed. Forward modelling, inverse trishear modelling

(Cardozo and Brandenburg, 2014) and area-depth-strain (ADS) methods (Groshong et al.

2012) are applied to test the structural geometry of the depth-converted interpretations.

We find all versions of interpretation, regardless of the velocity model used for depth

conversion, can ‘pass’ both forward modelling and inverse trishear modelling. Multiple

sets of model parameters ‘fit’ the interpreted structures for these two validation

approaches. On the other hand, only velocity model VM3 ‘passes’ the ADS validation

method, with the detachment level interpreted concordant with the depth estimated from

excess area analysis, based on interpreted horizons.

These results show that 1) the range of parameters available in both forward modelling

and inverse trishear modelling ensure ‘fit’ with a broader range of depth-converted

products than the ADS method, and 2) the model parameters that ‘fit’ interpreted

structures are not always unique. In other words, interpretations ‘validated’ by both these

two techniques still have a range of uncertainty which may be narrowed by the ADS

method. Although we must note the ADS method is only effective if seismic data quality

allows the detachment layer to be recognised. Combining ADS methods with other

structural validation techniques helps reduce uncertainty in the geological model.

References Cardozo, N., Brandenburg, J.P., 2014. Kinematic modeling of folding above listric propagating

thrusts. J. Struct. Geol. 60, 1–12.

Groshong, R.H., Withjack, M.O., Schlische, R.W., Hidayah, T.N., 2012. Bed length does not remain constant during deformation: Recognition and why it matters. J. Struct. Geol. 41, 86–97.


117

Palaeoseismological history of the Gyrtoni Fault (Thessaly, Central

Greece). Preliminary results and problems. I.M. Tsodoulos

1,2, S. Pavlides

3,4, I. Koukouvelas

5,6, R. Caputo

6,4, A. Chatzipetros

3,4, A.

Belesis4, E. Kremastas

3, G. Papathanasiou

3, S. Valkaniotis

3,4, K. Ioannides

1,2,

K. Stamoulis1,2

, C. Gallousi1,2

, and C. Papachristodoulou1,2

1 Department of Physics, University of Ioannina, GR-45110 Ioannina, Greece.

2 Archaeometry Center, University of Ioannina, GR-45110 Ioannina, Greece.

3 Department of Geology, Aristotle University of Thessaloniki, Earthquake Geology

(http://eqgeogr.weebly.com/) GR-54124 Thessaloniki, Greece. 4 Research and Teaching Center for Earthquake Geology, Tyrnavos, Greece.

5 Department of Geology, University of Patras, GR-26500, Greece.

6 Department of Physics & Earth Sciences, University of Ferrara, I-44122 Ferrara, Italy.

The Gyrtoni Fault (GF) is a south-dipping normal fault that defines the northeastern

boundary of the Middle-Late Quaternary Tyrnavos Basin (Thessaly plain, Central Greece)

and is located at a distance of ~13 km from the city of Larissa, one of the largest cities of

Greece. The understanding of the seismic history of this tectonic structure in terms of slip

rate on fault, recurrence interval and date of past earthquakes, elapsed time from the last

seismic event, is of great importance. The study of the recent tectonic activity of the fault,

was previously based on morphotectonic mapping, remote sensing analyses and electrical

resistivity tomography. However, in order to understand its Holocene earthquake history,

two paleoseismological trenches were excavated along the Gyrtoni Fault. Twenty five

fluvial-colluvial sediment and pottery samples from both the footwall and the hanging

wall were collected and investigated. Optically Stimulated Luminescence (OSL) dating

has been applied to chemically purified coarse grain quartz using the single-aliquot

regenerative-dose (SAR) protocol. Investigations of luminescence characteristics using

various tests confirmed the suitability of the material for OSL dating using the SAR

protocol. The estimated OSL ages are internally consistent and agree well with the

available stratigraphical data, archaeological evidence and radiocarbon dates.

The recognition of the past faulting events was based on sedimentological and

crosscutting relationships exposed in the fault zone. The stratigraphic sequences exposed

by the trenches have been displaced and dragged by the main fault and its secondary

splays in the down throw fault block. The most recent displacement event (E1) and the

penultimate event (E2) were recognized on the presence of filled fissures created on the

base of the fault palaeo-scarp during surface faulting. The palaeoseismological analysis of

the two trenches indicates evidence of at least three surface faulting events in the time

span between 5.59 ± 0.13 ka and 1.42 ± 0.06 ka BP. A fourth, earlier faulting event is also

possible, with a minimum age of 5.59 ± 0.13 ka. The observed vertical displacement per

event of 0.50 – 0.60 m corresponds to a Mw 6.5 earthquake. This implies that GF may

display a “characteristic earthquake” behavior. An average fault slip rate of 0.41 ± 0.01

mm/a and a mean recurrence interval of 1.39 ± 0.14 ka for earthquakes were estimated.

Since the seismic history of the Gyrtoni Fault was not previously known, our new data

allow to expand the existing knowledge on the Holocene tectono-stratigraphy of this

structure and consequently the seismic history of the fault. Accordingly, as the return

period from the most recent event (minimum age 1.42 ± 0.06 ka) has expired or it is close

to be, the possibility for reactivation of this seismogenic source in the near future seems to

be relatively high.


118

Enormous volumes of pseudotachylites on Barra, Outer Hebrides

B. Vogt1 and Z. K. Shipton

1



The term ‘pseudotachylite’ is nowadays used as a synonym for ‘friction melt rock’ (e.g.

Kirkpatrick and Rowe, 2013; BGS rock classification scheme). A literature-based dataset

of pseudotachylite characteristics indicates that pseudotachylite thicknesses (i.e. width)

most frequently range from millimeters to a few decimeters (Sibson and Toy, 2006).

However, theoretical considerations show that melt production by friction is limited to

pseudotachylite micro-faults, i.e. a maximum of a few centimeters in thickness (McKenzie

and Brune, 1972; Sibson, 1975; Melosh, 2005). The formation process for thicker

pseudotachilytes (pseudotachylitic breccias) remains debateable (e.g. Melosh, 2005).

Despite this, there is rising interest in using the structural characteristics of

pseudotachylites to constrain earthquake source parameters. The Outer Hebrides are

almost a type locality for tectonic pseudotachylites following Sibson's seminal work in the

region (Sibson, 1975). The pseudotachylitic breccias (Sibson’s ‘quasi-conglomerate’)

have gained little attention since, and we feel it is timely to revisit these famous outcrops

to shed light on the formation processes of thick pseudotachylites, i.e. pseudotachylitic

breccias. Our study is concerned with the extent and structural characterization of

pseudotachylitic breccias on Barra, one of the southerly islands of the Outer Hebrides.

The pseudotachylitic breccias in Barra often occur in subhorizontal zones over

several tens of meters (possibly several hundreds) in length, with the pseudotachylites

themselves several meters (up to 15m) thick. The host rock fragments (Lewisian Gneiss)

inside the breccia are up to 1m in diameter. Locally, pseudotachylite matrix (‘melt’)

constitutes as much as over 30% of the rock. Between these zones, pseudotachylite micro-

faults often form networks. We have estimated the total pseudotachylite matrix (excluding

host rock fragments) for the mapped area (1km2), and find it is as high as 3%. Structural

analyses on meso (1m–mm) and micro (≤mm) scales find a prevailingly brittle behaviour

of the host rock, as shown by curved fractures, dilational fractures, and fracture sets

resembling indentation fracture systems. A pervasive micro-fracture network controls, at

least locally, the orientation of pseudotachylite veins. Crosscutting relationships are

absent, suggesting that the breccias have formed during a single event.

The estimated melt volume and the observed meso-scale structures closely

resemble the pseudotachylitic breccias from the Vredefort impact structure rather than the

demonstrably fault-related pseudotachylites from the Alps (e.g. Di Toro et al., 2005) and

Sierra Nevada (e.g. Kirkpartick and Shipton, 2009) that have recently been used to

constrain earthquake source parameters.

References:

Di Toro, G., et al. (2005). Can pseudotachylytes be used to infer earthquake source parameters? An example of limitations in the study of exhumed faults. Tectonophysics, 402(1-4):3-20. – Kirkpatrick, J.D. and Rowe, C.D. (2013). Disappearing ink: How

pseudotachylytes are lost from the rock record. JSG, 52(1):183–198. – Kirkpatrick, J.D. and Shipton, Z.K. (2009). Geologic evidence

for multiple slip weakening mechanisms during seismic slip in crystalline rock. JGR 114(B12). – McKenzie, D. and Brune, J.N. (1972). Melting on Fault Planes During Large Earthquakes. Geophys. J Royal Astronom. Soc, 29:65–78. – Melosh, H.J. (2005). The Mechanics

of Pseudotachylite Formation in Impact Events. In Koeberl, C. and Henkel, H., eds, Impact Tectonics, Springer. – Sibson, R. (1975).

Generation of Pseudotachylyte by Ancient Seismic Faulting. Geophys. J Internat., 43:775–794. – Sibson, R. and Toy, V. (2006). The

habitat of fault-generated pseudotachylyte: Presence vs. absence of friction-melt. In Geophys. Monograph Series: Earthquakes:

Radiated Energy and the Physics of Faulting, p153–166. AGU.


119

The Cenzonic tectonic evolution and genetic mechanism of Liaodong Bay

Depression, East China

G. Wang1,2

, Z. Wu1, X. Zhang

1 and T. Mitchell

2

1School of Geosciences, China University of Petrolem, Qingdao, China.


Liaodong bay depression (LBD) is located in north part of Bohai bay area, the biggest marine

oil and gas exploration potential area in China. And from west to east, it has Liaoxi sag,

Liaoxi uplift, Liaozhong sag, Liaodong uplift and Liaodong sag five secondary structure units.

Based on detailed interpretation of abundant 2D and 3D seismic data, regional magnetic and

gravimetric analysis and previous geological dynamics research results, this paper discussed

the Cenozoic evolution and mechanism of LBD. And the magnetic and gravimetric data

showed a deep crust-scale fault located only in the east part of LBD, and right under the NNE

Tanlu fault (TLF), which extends upwards under the combined action of plate collision and

mantle upwelling and control the development of LBD. And from Paleocene to Eocene was

the rift stage of LBD. At early Paleocene, due to the slowdown of 340°subduction of Pacific

plate (PP) towards Eurasian plate(EP), the NE trending mantle upwelling zone beneath TLF

and under Liaozhong Sag occurred, which indured a series of NNE-NE-trending, W-dipping

basin-controlling faults form, and only a few secondary faults evenly distribution in LBD and

were also in NE trending. They all displayed slab-like faults in profiles, but the faults in

Liaoxi Sag had a gentler dip angles than that of Liaozhong Sag. Due to the disappearance of

Kula plate, from middle Eocene, the subduction direction of PP changed to 305°and

decelerated further, meanwhile, Indian Ocean Plate (IOP) collided NE towards EP, and their

combined effect made mantle upwell more intensely, the basin-controlling faults in LBD

became longer and more NE secondary faults developed but mainly in Liaoxi Sag. And south

part of Liaodong fault began to develop, which not only indicated initial formtion of the

Liaodong uplift and Liaodong sag, also the development of the whole framework of LBD. In

profile, basin-controlling faults extended upwards further and faults displayed gentle listric in

Liaoxi Sag, but showed sharp slab-like in east sags. And the whole Oligocene was strike-slip

and extensional stage. At the end of Eocene, subduction direction of PP changed to 285°along with the distanct eastwards compression of IOP, TLF began to dextral strike slipped

strongly, while owing to the increase of the subduction speed of PP, extension induced by

mantle upwelling began to become weaker. So LBD suffered from both strike slip and

extension. As the branches of TLF, most basin-controlling faults in east LBD developed

flower or flower-like structures and in the plane, along with massive newly-formed subparallel

E-W trending secondary faults, many strike-slip associated structures, such as pull-apart

basins, pop-up structures, duplexes, imbricate fans, transfer zones developed at releasing or

restraining bends, stepovers and tails of TLF, besides, some mud and magma diapir also

dveleoped in Liaodong sag. But not the case in Liaoxi sag, the basin-controlling faults still

gently developed, and secondary faults were still mainly NE trending, though at late

Oligocene, some supparall E-W secondary fualts did form along its basin controlling faults.

Then after Oligocene, LBD entered depression stage, with the back arc spreading of Japan Sea

and further accelerating subduction of PP, mantle upwelling stopped, LBD began thermal

subsidence and only suffered from weak strike-slip. Almost all major faults stopped, only

massive en echelon minor faults developed.and mainly distributed in east part of LBD.


120

Discrete Fracture Network (DFN) modelling of a folded tight sandstone

reservoir analogue

H. Watkins

1, D. Healy

1, C. E. Bond

1 and R. W. H. Butler

1

1 Geology and Petroleum Geology, University of Aberdeen, UK

[email protected]

Fractured reservoir quality is controlled by the amount of secondary porosity and

permeability provided by fracture networks. These factors are controlled by fracture

connectivity, fill, intensity and orientation. We investigate whether it is possible to predict

fracture attribute variations using Discrete Fracture Network (DFN) modelling, and

assesses the practicality of the technique. Field fracture data is collected at various

structural positions on four Torridon Group sandstone anticlines in the Achnashellach

Culmination, Moine Thrust Belt. A 3D model of these anticlines is built using bedding

data and field observations. 3D restoration of the model is conducted to predict strain

distributions across the folds. From these strains, DFN modelling is undertaken to

generate fracture networks on each anticline. DFN model attributes are then compared

with field fracture data.

Field data suggests fracture attributes are consistent and predictable in high strain regions;

fracture connectivity is consistently high and field data compares well to modeled

fractures. Although fracture attributes are predictable, fractures are quartz-filled meaning

secondary porosity is very low and fractured reservoir quality would be poor. In low strain

regions, fracture attributes show significant variations over short distances, which may be

controlled by lithological variations rather than strain. This variability means fracture

patterns observed in the field cannot be adequately predicted using fracture modelling.

Although fractures are unpredictable they remain open at the surface, indicating these low

strain regions could have higher fractured reservoir potential than areas that have

undergone higher strain.


121

The age and character of magmatism in the Netoni Intrusive Complex,

Bird’s Head Peninsula, West Papua, Indonesia.

M. Webb

1, L. T. White

1, and B. M. Jost

1

1South East Asia Research Group, Department of Earth Sciences, Royal Holloway

University of London, UK. [email protected]

The Bird’s Head is the most northwestern peninsula on the island of New Guinea. It is

situated close to the Australian and Pacific/Caroline plate boundary and many consider

this to be a major east-west trending, strike-slip fault zone (the Sorong Fault Zone). The

Netoni Intrusive Complex represents a suite of granitoids (granite, granodiorite, quartz

diorite and diorite) and associated country rocks that are bisected by the Sorong Fault

Zone. Our knowledge of the age of the granitic intrusions is limited to a series of

previously reported K-Ar ages from float material (Bladon, 1988). The majority of these

ages range between the Triassic and Cretaceous (240-78 Ma), but several Neogene ages

were also reported (Bladon, 1988). The Netoni Intrusive Complex and Bird’s Head

peninsular as a whole has until now been relatively understudied due in part to its

remoteness and the dense vegetation limiting access. We present a detailed, integrated

study of the magmatic age and petrogenesis of the Netoni Intrusive Complex based on

new U-Pb LA-ICPMS data from zircons, whole-rock geochemistry, petrology and

microstructural studies.

Geochemically the granites are calc-alkalic to alkali-calcic, metaluminous to peraluminous

and were likely produced by arc magmatism. The U-Pb isotopic analyses of zircons from

the granitoids indicate that the Netoni Intrusive Complex crystallised in the Early to Late

Triassic. We found no evidence for any of the younger ages that were previously reported

(Bladon, 1988). The granites of the Netoni Intrusive Complex are also considerably more

deformed than previously stated (Pieters et al., 1983). They show evidence of both ductile

and brittle deformation as well as partial recrystallisation. The country rocks into which

the Netoni granitoids were observed to intrude consist of medium-high grade, multiply

deformed schists and gneisses. The final phase of deformation is potentially associated

with movement along the Sorong Fault Zone. These results have implications for our

understanding of the development of the Australian–Pacific plate boundary, the

emplacement style and history of the Netoni Intrusive Complex and large scale

deformation events across the Bird’s Head.

Bladon, G. M. (1988). Preliminary geological report. Catalogue, appraisal and

significance of K-Ar isotopic ages determined for igneous and metamorphic rocks in Irian

Jaya. Indonesia-Australia Geological Mapping Project, 79pp.

Pieters, P.E., Pigram, C.J., Trail, D.S., Dow, D.B., Ratman, N., Sukamto, R. (1983). The

stratigraphy of western Irian Jaya. Indonesian Petroleum Association, Proceedings 12th

Annual Convention, Jakarta, 229–262.


122

Workflows and techniques for building a 3D model in Move: a case

study from North Arran

S. B. Willan

1

1Midland Valley Exploration Ltd., 2 West Regent St., Glasgow, UK.

[email protected]

The Isle of Arran, Scotland, is dominated by the North Arran Granite (NAG), a near-

circular intrusion emplaced during the opening of the North Atlantic around 60 Ma.

Surrounding the north and west of the granite are late Precambrian age metasedimentary

rocks belonging to the Dalradian Supergroup. These were intially folded during the

Grampian Orogeny to form the NE-SW striking Aberfoyle Synform, but have since been

deflected and refolded into a rim syncline (Catacol Synform) that runs parallel to the

margin of the NAG. To the south and east of the granite, exposures of Old Red Sandstone

and Carboniferous strata have been displaced along numerous faults reactivated during

granite emplacement.

This poster demonstrates how Midland Valley’s Move™ software was used to build a 3D

model of North Arran, and explores the benefits of modelling for subsurface

interpretation. Data gathering exercises were carried out and maps collected from a

number of sources from which, a combination of interpretations were digitized in Move.

On examining the interpretations, it was deduced that minor faults in the structurally

complex area to the east would be excluded, to avoid ‘over-cluttering’ the model. The 3D

model was then built using outcrop traces and dip data by integrating a number of

geometric and geostatistical methods in Move. The NAG was constructed first, as this was

the dominant structure. This was carried out using published gravity profiles and depth

estimates. The trace of each gravity profile was digitized as a cross-section and a 3D

surface was interpolated using the Kriging algorithm in the Create Surface tool in Move.

The faults that surround the NAG were extruded from their outcrop trace at a constant dip

with the 3D Dip Domain (ribbon) method and Carboniferous strata were constructed using

the Extrusion method, where changes in dip were modelled on a projection curve. For the

structurally complex Dalradian metasedimentary rocks, a workflow was adapted in which

the fold geometries were digitized on multiple cross-sections using projected dip data as

the template. The geo-referencing of each 2D cross-section allowed for fold geometries to

be interpolated from 2D to 3D using the Kriging and Spline Curve algortihms. As the

Spline Curve algorithm is suitable for modelling recumbent folds, it was also used to

construct the Aberfoyle Synform.

By using legacy data to create a 3D model of North Arran, the concentric change in

deformation style around the NAG (from ductile in the West to brittle in the East) is

highlighted. 3D model building is an important means of testing hypotheses on the

structure and evolution of an area, and may also reveal gaps in knowledge and areas of

uncertainty. It is an effective way of visualizing and communicating the results of

subsurface interpretations, and has many applications across academia and industry. This

model reveals the high level of uncertainty around the two transition zones between the

Aberfoyle and Catacol synforms, which suggests that these areas would benefit from

further field mapping.


123

Fracture analysis of deformation structures associated with the Trachyte

Mesa intrusion, Henry Mountains, Utah: implications for reservoir

connectivity and fluid flow around sill intrusions

Penelope I.R. Wilson

1, Ken J.W. McCaffrey

2, Robert. W. Wilson

3, Ian Jarvis

1 and David

J. Sanderson4

1 Department of Geography and Geology, Kingston University London, Kingston upon

Thames KT1 2EE, UK.

[email protected] 2Department of Earth Sciences, Durham University, Durham DH13LE, UK.

3BP Exploration, Chertsey Road, Sunbury-on-Thames TW16 7LN, UK.

4Department of Engineering and the Environment, University of Southampton,

Southampton, SO17 1BJ

Shallow level intrusions are a common feature of many basins currently being explored

for hydrocarbon potential. However the sub-seismic structure and reservoir scale

implications of igneous intrusions are poorly understood. The Trachyte Mesa intrusion is a

small (~1.5 km2), NE–SW trending satellite intrusion to the Mount Hillers intrusive

complex in the Henry Mountains, Utah. It is emplaced within the highly porous, aeolian

Entrada Sandstone Formation producing a network of deformation bands with conjugate

sets of NE–SW striking deformation bands trending parallel to the intrusion margins. A

small study of the fracture network has been carried out at 6 sample stations along a ~100

m long, NW–SE trending transect across the north-western lateral intrusion margin.

Following the methodology of Sanderson and Nixon (2015), the network was

characterized by a series of nodes and branches, from which the frequency, density

(intensity), spacing, characteristic length, and dimensionless intensity of the deformation

band traces and branches were determined. These quantitative geometric and topological

measures are supplemented with petrological, porosity and microstructural analyses.

Results show a marked increase in deformation band intensity and significant porosity

reduction with proximity to the intrusion. The deformation bands are likely to impede

fluid flow, forming barriers and baffles within a reservoir. A corresponding increase in Y-

and X- nodes highlights the significant increase in deformation band connectivity, which

in turn will significantly reduce the permeability of the sandstone. This study indicates

that fluid flow in deformed host rocks around igneous bodies may vary significantly from

that in the undeformed host rock. Therefore, a better understanding of the variability of

deformation structures, and their association with intrusion geometry, will have important

implications for hydrocarbon reservoir deliverability and CO2 sequestration.


Useful information


Locating Gustave Tuck lecture theatre in UCL Gustave Tuck lecture theatre is located on the third floor of the South Junction of UCL (D4). Head towards the grand Wilkins Building (the one with the big dome; D3) and turn right (do not climb the stairs) – see next page for detailed map. There will be a door way leading into the South Cloisters building, ignore this and take the second door which will be in the far right-hand corner. Upon entering this door turn right and walk through a second set of doors keeping to the right again (note: turning left will lead to south cloisters where posters and registration desk is). There will be a staircase in front of you with signs leading to the Gustave Tuck lecture theatre. Walk up the stairs (two flights), and the lecture theatre will be on your right-hand side.


Detailed map of main UCL quad area


Ice-breaker drinks and posters Date: Wednesday, January 6 Time: From 6:30 pm (following on from the final talk session on Day 1) Venue: Jeremy Bentham Room and South Cloisters, UCL A free drinks and nibbles reception will be held in the Jeremy Bentham Room (location highlighted on the campus map on the previous page) following the first afternoon of the conference, giving delegates an opportunity to network and socialise. Come along and have a beer, wine or soft drink and good conversation with friends old and new! Posters will be displayed in the south cloisters in UCL which is easily accessible from the Jeremy Bentham room is delegates would like to have wander and look at posters with their drinks.


Conference Dinner and River Cruise Date: Thursday, January 7 Time: Boarding from 7:30 pm, boat departs from pier at 7:45 pm Event: Thames Riverboat Cruise with food, drinks and entertainment! Cost: £40

Promises to be an evening to remember!

Event details Time: 7:30 pm (don’t be late or the boat will depart without you!) ’til midnight! Meeting Location: The Viscountess boat, Waterloo Pier / London Eye Event includes: 3 course buffet dinner, TSG annual speeches and prize ceremony, and a disco The TSG 2016 conference dinner will be held on the Viscountess Thames River Cruise party boat. The Viscountess is a middle-sized, traditional style Thames Boat with bags of character. The boat has two internal floors, a lower deck with tables and seating, and a teak floored upper deck, perfect for dancing the night away. It features a good outside space – great for clear dry nights (remember to bring a warm coat!).


On arrival, guests will be greeted with canopes and drinks. Later on, whilst cruising along the River Thames and admiring the stunning views on all sides, guests will be served a tasty, buffet-style, main dinner and dessert. Some wine and soft drinks will be provided, and there is also a cash-only bar on board the boat. Entertainment will include the traditional TSG annual speeches and a disco on the upper deck, so get on your dancing shoes! For those wanting to enjoy the view and music in a more relaxed setting, there is seating on the lower deck, perfect for chatting over a drink with friends.


Location of Waterloo Pier / London Eye Pier The pier is located directly in front of the London Eye big wheel, and is easily accessible from Waterloo station. From UCL, you can take the Northern Line direct from either Warren street or Goodge street to Waterloo. If the weather is nice, it is also a relatively easy 30 minute walk from UCL (1.5 miles) via the Waterloo bridge. A good way to see some of london!


Eating options around UCL London has lots of choice for eating out. Below is a list of restaurants close to UCL that might be useful.

Pied à Terre (Michelin starred French ) 34 Charlotte St., London W1P 2NH Tel.: (+44) (0) 20 7636 1178 8 minutes walk from UCL The Ivy (eclectic ) 1-5 West St., London WC2H 9NQ Tel.: (+44) (0) 20 7836 4751 17 minutes walk from UCL Sardo (Sardinian ) 45 Grafton Way, London W1T 5LA Tel.: (+44) (0) 20 7387 2521 3 minutes walk from UCL Fino (Spanish ) 33 Charlotte St., London W1T 1RR Tel.: (+44) (0) 20 7813 8010 9 minutes walk from UCL Pescatori (Italian seafood ) 57 Charlotte St., London W1T 4PD Tel.: (+44) (0) 20 7580 3289 9 minutes walk from UCL Bertorelli (Italian ) 19-23 Charlotte St., London W1T 1RL Tel.: (+44) (0) 20 7636 4174 10 minutes walk from UCL Dhaka Brasserie (Indian ) The Fitzrovia, Goodge St., London W1T 2NL Tel.: (+44) (0) 20 7436 9767 8 minutes walk from UCL Navarro's (Spanish ) 67 Charlotte St., London W1T 4PF Tel.: (+44) (0) 20 7637 7713 7 minutes walk from UCL Busaba Eathai (Thai ) 44 Floral St., London WC2E 9DA Tel.: (+44) (0) 20 7299 7900 20 minutes walk from UCL Prezzo (Italian ) 98 Tottenham Court Road, London W1T 4TR Tel.: (+44) (0) 20 7436 5355 3 minutes walk from UCL Ask! Italian ( Italian) 48 Grafton Way, London W1T 5DATel.: (+44) (0) 20 7388 8108 3 minutes walk from UCL Ragam ( Indian) 57 Cleveland St., London W1T 4JN Tel.: (+44) (0) 20 7636 9098 9 minutes walk from UCL Wagamama ( Japanese) 4 Streatham St., London WC1A 1JB Tel.: (+44) (0) 20 7323 9223 12 minutes from UCL

1. Connect to the UCLGuest Wireless Network.

3. Click on the link to the Self Servicepage; enter your information in thefields provided. Enter the event code.

4. Click ‘Generate Account’.

5.Your username and password will be displayed on the screen; these details willalso be sent to your e-mail address. Make a note of your username (your emailaddress) and password as you will need them each time you log into UCLGuest(the system will not remember your login details). The details will be valid for2 weeks as indicated by the expiry date; if the event code is valid for longer than 2weeks you can generate another account once your current one has expired.

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Registering with an Event Code

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Event code: TSG2016

6th 8th january @ university college london · 2016-01-13 · microtectonics workshop with cees...

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