microstructures, textures and material properties of ...•greenschists facies metamorphism during...
TRANSCRIPT
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Paolo Conti
Samos Training School, 26-30 August 2013
Microstructures, textures and material properties
of marble rocks
, Italy
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• Marble behaviour• Crystal structure of minerals and rocks• Rock fabrics• Marble deterioration• Mechanical properties• Natural examples
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Contents
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Marbles: different behaviour
3(from Shushakova et al., 2010)(Ephesus, Turkey)
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Marbles: different behaviour
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panels
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Marbles: different behaviour
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Marbles
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Same composition (≃100 % CaCO3)
Different behaviour due to:• anisotropic physical properties of calcite crystals• texture of rocks• microstructure of rocks
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Anisotropic physical properties:Crystal structure of rocks
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Anisotropic physical properties: strength
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crystal“weak”bond
“strong”bond
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Anisotropic physical properties: strength
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crystal“weak”bond
“strong”bond
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Anisotropic physical properties:thermal expansion
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Increasing temperature: stretch of bond length “weak”
bond
“strong”bond
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Anisotropic physical properties:thermal expansion
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(Winkler, 1994)
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Anisotropic physical properties:natural texture
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crystallographicdirection
(a) (b) (c) (d) (e)
strong crystallographicpreferred orientation
weak crystallographicpreferred orientation
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Anisotropic physical properties: shapes
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(Ruedrich et al., 2011)
Along grain buondaries, weatering: micro-karst, breakouts, coloration, formation of crusts, biological colonization, granular desintegration, peeling, moisture expansion, etc.Superficial disintregration - loss of cohesion (dilatancy) - total decay of the material
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Anisotropic physical properties: shapes
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straight grain boundaries
lobate grain boundaries
“slide” “locked”
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Anisotropic physical properties: shapes
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shape preferred orientation of crystals
no shape preferred orientation of crystals
(anisotropic volume increase)
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Developement of microstructures (movies)
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dynamic(syn-tectonic)
recrystallization
staticrecrystallization
(annealing)
Octachloropropane (organic material)Means et al. (1994) J. Struct. Geol.,16, 403-418
before:no shape preferred orientation, straight grain boundaries
before:shape preferred orientation, lobate grain boundaries
http://www.atmos.albany.edu/geology/webpages/wdmovies/wdmoviep.html
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Anisotropic physical properties
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(a) (b) (c) (d) (e)
•no shape preferred orientation of grains
•no crystallographic preferred orientation
•no shape preferred orientation of grains
•crystallographic preferred orientation
•shape preferred orientation of grains
•no crystallographic preferred orientation
•shape preferred orientation of grains
•crystallographic preferred orientation
crystallographic preferred orientation of crystals = texture of rockshape preferred orientation of crystals = microstructure of rock
(texture + microstructure = fabric)
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In marbles...
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limited informations from outcrop studies only
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Microstructures in marbles“ultra” thin section (
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Microstructures in marbles
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(Carmignani, Conti, et al., 2007)
Carrara marble (Italy)
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Microstructures in marbles: measure
(Molli, Conti et al., 2007)
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Textures in marbles: measure
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(same color, same crystallographic orientation)
(Molli, Conti et al., 2007)
CIP analysis(Heilbronner Panozzo R. & Pauli C. (1993) - Integrated spatial and orientation analysis of quartz c-axis by computer-aided microscopy. Journal of Structural Geology, 13, 369–382.)
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In marble rocks ...
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• Physical properties of rock linked with texture and microstructure;
• Laboratory studies yield informations about rock texture and microstructure and therefore inferences about physical properties;
• Development of texture and microstructure related to geological history of rock;
• Field geology and laboratory studies allow to estimate the microstucture and texture expected in an area.
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Microstructure, texture and geological evolution
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tracce dei profilia
foliazione D1
SW
SW
NE
NE
direzione di trasporto D1direzione di trasporto D2
C
V
cataclasiti
!!
N
Carrara
Massa
Arni
Vinca
M. Sumbra
Pietrasanta
Unità di Massa
Complesso metamorfico delle Alpi Apuane
Basamento paleozoico
dolomia (Trias)
marmi e marmidolomitici (Lias)
calcari selciferi, diaspri, scisti sericitici,“pseudomacigno” (Dogger-Oligocene)
“Autoctono” Auct.
C
TV
A
C : Sinclinale di CarraraV : Anticlinale di VincaA : Sinclinale di M. AltissimoT : Anticlinale di M.Tambura
T
Stazzema
Vagli
Roma
Pisa
Genova
5 km0
a
b
c
d
m 0
anticlinali esinclinali D1antiformi D2
Depositi quaternari
Unità liguri e Falda Toscana
e
0 m
A
V T
1000
cb
a
d
e
500
m 0
500
m 0
Carrara marble,Alpi Apuane, Italian Northern Apennines
•Alpi Apuane tectonic window
•Jurassic limestones: marbles
•greenschists facies metamorphism during Tertiary
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Microstructure, texture and geological evolution
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1) subduction, main thrusting, folding 2) metamorphism
3) later thrusting4) extension, exhumation, normal faulting
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Conclusions
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• marbles usually are NOT homogeneous rocks;• marbles are thermally sensitive rocks because calcite
anisotropic behaviour, damages at low temperature;• studies on microstructures and textures in marbles
are performed at thin section scale (or even at smaller scale)
• regional and field geology investigations important to link microstructures with tectonic features in the field;
• investigating microstructure and texture in rocks is an appropriate tool for:‣better set recovery and preservations of marble
artifacts;‣ inferences about marble behaviour;‣evaluation of marble quality.
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... evaluation of marble quality ...
• Amoco Corporation Building, Chicago, USA• Bowing of external marble panels: replacement
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w w w. g e o t e c n o l o g i e . u n i s i . i t / c o n t i
Slides, handouts, papers:
cont i@unis i . i t