the thrust fault architecture in the external sierras (new)

A Thrust system in the External Sierras: Evolution of South Central

Pyrenees

Isaac Kenyon

Figure: http://upload.wikimedia.org/wikipedia/commons/3/33/Pyrenees_Catalonia.jpg

Location of the Western External Sierras. Types of thrust faults of the Western External

Sierras and how they form i.e. Decollment mechanisms.

Geological history of the South Central Pyrenees. Relation of the Western External Sierras and the

regional context of the Alpine Orogeny.

Topics

Location of the Western External Sierras

Figure: http://su-thermochronology.syr.edu/_images/pyreneesmap3.jpg

Figure: Minh Nguyen (PANO_20140606_152833 ) photo from the highest peak of my mapping area

Thrust faults - Are reverse faults but with a low taper angle and have a hanging wall block above a very low angle thrust.

Decollment – Is a gliding plane between two rock masses. AKA (basal detachment fault).

Back thrusts – A thrust fault which has an opposite vergence to that of the main thrust system or thrust belt.

Definitions

Mechanically weak layers slip in strata allowing the development of stepped thrusts.

Decollment in the Pyrenees occurs from mechanically weak basements i.e. Shales and evaporites (my area).

Decollment? How does it relate to Pyrenean orogeny

(Vidal-Royo, Koyi and Muñoz, 2009)

Figure: http://upload.wikimedia.org/wikipedia/commons/thumb/3/31/Decollement_in_a_compressional_setting.pdf/page1-1280px-Decollement_in_a_compressional_setting.pdf.jpg

It’s a deformational structure associated with compressional settings (fold-and-thrust belts).

Triassic Evaporites

Figure from mapping: Minh Nguyen photo: IMG_20140604_145331

Models of decollment

Model 1 - (Meigs and Burbank, 1997)

Model 2 - (Vidal-Royo, Koyi and Muñoz, 2009)

Fold and thrust development Critical-taper wedge model.

The thrust belt revolves around the critical taper angle between basal decollment and the surface slope.

Model implies that internal deformation is modulated by changes in the surface slope and in material properties within and at the base of the wedge.

Model depicts the ductile frictional contrasts of the basal decollment of structures through thin-skinned shortening tectonics (a style of thrusting in which sedimentary cover is entirely removed from underlying basement).

Models summary Comparison

Model 1 - (Meigs and Burbank, 1997) Model 2 - (Vidal-Royo, Koyi and Muñoz, 2009)

Issue: not sufficient resolution of data.

Limited applicability to fold and thrust belts due to mechanical and deformational incompatibilities between the geological record and the model.

Model depends on the mechanical behaviour of evaporites and it’s interaction with the overlying overburden.

High frictional domain (dashed lines represent sand)

Low frictional domain (black areas shows the ductile layer

Source: Meigs and Burbank, 1997)

Duplex thrusts (Antiformal stack duplex) – Where a series of thrusts connects both with a floor thrust below and a roof thrust above i.e. Back thrust.

Form in the hanging walls of the thrust system. Anticlines are related to folding at the tip of basal

decollment. It develops as a result of thrusting to accommodate

deformation i.e. fault-propagation folds

Duplex thrust systems during the Middle Eocene

(Vidal-Royo, Koyi and Muñoz, 2009)

Source: http://www.diggles.com/pgs/2008/Thrust_Belt_plays.jpg

Source: (McClay, 1991)

Duplex thrust – my fair copy map

A thrust fault which has an opposite vergence to that of the main thrust system

The back thrusts in my area formed a tectonic wedge (a body of rock that has moved between a pair of oppositely vergent thrusts).

The triangle zone in the South of my area is a wedge in which a third, foreland-south vergent thrust completes a triangle in cross section.

Back thrusts

Figure taken from: http://www.diggles.com/pgs/2008/Thrust_Belt_plays.jpg

Figure taken from: (McClay, 1991)

Example triangle zone from my fair copy map.

Roof thrusts – When a back thrust cuts off the top of original thrust vergence.

The upper thrust surface bounds a duplex. It can be smooth/folded by movement on underlying thrusts of the duplex.

Roof thrust

Figure taken from: http://www.diggles.com/pgs/2008/Thrust_Belt_plays.jpg

Figure taken from: (McClay, 1991)

(McClay, 1991)

Example of the Duplex, Back and Roof thrusts in my area – my own cross-section.

Geological/Structural History of the Pyrenees

Figure: http://all-geo.org/highlyallochthonous/wp-content/uploads/2010/07/Cretmap.jpg

Let the Journey Begin!

Figure: http://upload.wikimedia.org/wikipedia/commons/thumb/b/b6/Iberian_Tectonic_EN.svg/300px-Iberian_Tectonic_EN.svg.png

Geological time periods of interest

Starting here

Ending here

Figure: Shows the change from the rifting of Africa from Eurasia after the break up from Pangaea to compression and the movement of Africa towards Iberia and Eurasia. This is where the thrust faults start to develop early Cretaceous.

Rifting to Compression

Image: http://geology.gsapubs.org/content/36/11/839/F4.large.jpg

Late Cretaceous (65Ma)

Bernd Andeweg, 2002

Africa

Iberia

Eurasia

•Not all models correspond to a simple plate tectonic reality.

Pyrenean fold belt

Figure: http://www.igc.cat/web/en/mapageol_atles_evoluciopaleo.html

There was a 150km separation between Iberia and Europe during this time (Andeweg, 2002).

Most of Iberia was below sea level (subtle eustatic sea level changes caused significant shifts in the position of the coastline.

Late Cretaceous (65Ma)Beach deposits

Source:IMG_20140523_121540 Minh Nguyen

Palaeocene-Eocene (54Ma)

Bernd Andeweg, 2002

Africa

Iberia

Eurasia


Figure: http://d1jqu7g1y74ds1.cloudfront.net/wp-content/uploads/2010/11/Geologic-time-scale.jpg

Clockwise rotation of Iberia, with partial subduction under Eurasia (Andeweg, 2002) with large scale deformation.

Rapid convergence between Iberia and Africa.

Palaeocene-Eocene (55Ma)

Iberia

Eurasia

Betics

Africa

Sardinia

Bernd Andeweg, 2002

Southward thrust sheet emplacement from rapid convergence of Africa and Eurasia (Andeweg, 2002).

Inversion of previously rifted Mesozoic basins.

Introduction of marine foreland deposits.

Development of the Ebro basin. Deposits of limestone platforms

due to marine transgressions.

Palaeocene-Eocene (55Ma) Western External Sierras Tectonics

Figures: mapping Minh Nguyen (A) IMG_20140523_155047(B) IMG_20140529_123447(C) Thin section photo supplied by the

department

B

CA

Transgression

Middle Eocene (42Ma)

Bernd Andeweg, 2002

Africa

Iberia

Eurasia


Pyrenean suture becomes a compressional active plate margin (Andeweg, 2002).

Southward thrusting creates the first important relief of the Pyrenees.

Ebro foreland basin is deep marine and turbiditic at this point and is widening to the cope with advancing load.

The sediments derived are shelf and slope marls and sandstones.

Middle Eocene (42Ma)

Source: IMG_20140528_113104 Minh Nguyen

Late Eocene (36Ma)

Bernd Andeweg, 2002

Africa

Iberia

Eurasia

Ebro Basin


Peak collision of the Pyrenees Folding of a syncline separates the Pyrenean foreland basin from marine

waters (Andeweg, 2002). Eastern Ebro basin is now closed from the worlds oceans (endoheric). Lacustrine centre and alluvial fan building on the margins of the basin occurs. Basement detachment faults become reactivated.

Late Eocene (36Ma)

Figure taken from: http://claymin.geoscienceworld.org/content/47/3/303/F2.large.jpg

Early Oligocene (30Ma)

Bernd Andeweg, 2002


Africa

Iberia

Eurasia


Pyrenees is further deformed and uplifted

Syn-sedimentary continental deposition and molasse (alluvial) sedimentation

Influx of terrestrial sandstone, marine shale and rapid exhumation.

Early Oligocene (30Ma)

(Andeweg, 2002)

Figure taken from: http://upload.wikimedia.org/wikipedia/commons/3/37/Uureg_Nuur.jpg

Late Oligocene (27Ma)

Bernd Andeweg, 2002

Africa

Iberia

Eurasia


External Sierras fully develops

End of the sedimentation cycle and start of erosion

Ebro basin begins to fill with conglomerates, passing into fluvial/lacustrine sediments (siltstones and sandstones).

Late Oligocene (27Ma)

Figure taken from: http://www.reditec.org/en/sortida_geotectonica

The External Sierras

Oligocene-Miocene (24Ma)

Bernd Andeweg, 2002

Africa

Iberia

Eurasia


Convergence between Eurasia (containing Iberia) and Africa begins to slow down. Sedimentary break in the plate boundary reorganisation. Limited activity along the plate boundary (axial zone). External Sierras stops developing in the west SE verged thrusting terminates (25Ma) A shift to major denudation (erosion) Passive margin

Oligo-Miocene (24Ma)

(Andeweg, 2002)Figure taken from: http://gent.uab.cat/ateixell/en/content/field-seminar

Many of the thrust faults in the Pyrenees are roll over thrust anticline faults.

Can be ideal for trapping hydrocarbons as the anticlines plunge create a 4-way dip closure effect. (Possibility?)

Impermeable evaporites (strong competent, and crystalline)

The marine sediments and limestones etc. would act as reservoirs and source rocks for the area.

Thrust Fault Hydrocarbon traps (Petroleum Potential)

Figure: taken from the Geology of Petroleum module from Moodle Lecture 7 - Pete Burgess

Impermeable

Source: IMG_20140602_142651 Minh Nguyen

Lets Summarise!

There is a wealth of geological data in the Western external Sierras to study thrust fault geometry in relation to the Alpine orogeny.

The Western External Sierras supports the types of thrusting: duplex, roof and back thrusts.

My work reflects on a combination of both models as proof that not all work.

Different lithologies (mechanically speaking have variations in tectonic stresses which produce different thrust fault mechanisms).

Models are useful in a small context, geology is never small. The thrust fault geometry has a part to play in the depositional

environment of the Pyrenees Places similar Future work

Conclusion

Field photos – Minh Nguyen – Samsung phone RHUL logo – https://www.royalholloway.ac.uk/iQuad/graphics/cER/Primary/RHULMasterlogoCMYK-Cropped-550x275.jpg Wally - http://i.dailymail.co.uk/i/pix/2010/06/01/article-1283070-0622451D0000044D-804_306x598.jpg 4.bp.blogspot.com, (2015). [online] Available at: http://4.bp.blogspot.com/--mh-6Nft1iE/TlZ240s0MtI/AAAAAAAADE4/GL9HWfkr3n0/s1600/

SCHELLART_2002_Pyreenes_profile.jpg [Accessed 20 Feb. 2015]. All-geo.org, (2015). [online] Available at: http://all-geo.org/highlyallochthonous/wp-content/uploads/2010/07/Cretmap.jpg [Accessed 20 Feb. 2015]. Andeweg, B. (2002). Cenozoic tectonic evolution of the Iberian Peninsula. [S.l.: s.n.], pp.83 - 118. Anon, (2015). . Claymin.geoscienceworld.org, (2015). [online] Available at: http://claymin.geoscienceworld.org/content/47/3/303/F2.large.jpg [Accessed 20 Feb. 2015]. Diggles.com, (2015). [online] Available at: http://www.diggles.com/pgs/2008/Thrust_Belt_plays.jpg [Accessed 20 Feb. 2015]. Discoveringfossils.co.uk, (2015). [online] Available at: http://www.discoveringfossils.co.uk/eocenemap.jpg [Accessed 20 Feb. 2015]. Geology.gsapubs.org, (2015). [online] Available at: http://geology.gsapubs.org/content/36/11/839/F4.large.jpg [Accessed 20 Feb. 2015]. Igc.cat, (2015). Paleogeographical evolution. [online] Available at: http://www.igc.cat/web/en/mapageol_atles_evoluciopaleo.html [Accessed 20 Feb. 2015]. McClay, K. (1991). Glossary of thrust tectonic terms. Thrust Tectonics: London, Chapman & Hall, pp.419-433. Meigs, A. and Burbank, D. (1997). Growth of the South Pyrenean orogenic wedge. Tectonics, 16(2), pp.239-258. Reditec.org, (2015). Virtual field trip - Geotectonics | REDITEC. [online] Available at: http://www.reditec.org/en/sortida_geotectonica [Accessed 20 Feb.

2015]. Stampfli, G., Borel, G., Marchant, R. and Mosar, J. (2002). Western Alps geological constraints on western Tethyan reconstructions. Journal of the Virtual

Explorer, 08. Su-thermochronology.syr.edu, (2015). [online] Available at: http://su-thermochronology.syr.edu/_images/pyreneesmap3.jpg [Accessed 20 Feb. 2015]. Teixell, A., Arboleya, M., Julivert, M. and Charroud, M. (2003). Tectonic shortening and topography in the central High Atlas (Morocco). Tectonics, 22(5),

p.n/a-n/a. Upload.wikimedia.org, (2015). [online] Available at: http://upload.wikimedia.org/wikipedia/commons/thumb/9/92/Tectonic_map_Mediterranean_EN.svg/

400px-Tectonic_map_Mediterranean_EN.svg.png [Accessed 20 Feb. 2015]. Upload.wikimedia.org, (2015). [online] Available at: http://upload.wikimedia.org/wikipedia/commons/3/33/Pyrenees_Catalonia.jpg [Accessed 20 Feb. 2015]. Vergés, J., Fernàndez, M. and Martìnez, A. (2002). The Pyrenean orogen: pre-, syn-, and post-collisional evolution. Journal of the Virtual Explorer, 08. Vidal-Royo, O., Koyi, H. and Muñoz, J. (2009). Formation of orogen-perpendicular thrusts due to mechanical contrasts in the basal décollement in the

Central External Sierras (Southern Pyrenees, Spain). Journal of Structural Geology, 31(5), pp.523-539.

References

http://i.dailymail.co.uk/i/pix/2010/06/01/article-1283070-0622451D0000044D-804_306x598.jpg

Thank you for listening!

Feel free to ask any questions

Figure: Minh Nguyen (IMG_20140530_120304)

the thrust fault architecture in the external sierras (new)

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