Deformation Microstructures and Mechanisms in Minerals and Rocks

156 Pages·2000·39.469 MB·English

by  Tom Blenkinsop (auth.)

DEFORMATION MICROSTRUCTURES AND MECHANISMS IN MINERALS AND ROCKS
Deformation Microstructures and Mechanisms
in Minerals and Rocks
by
Tom Blenkinsop
Department ofGeology,
University of Zimbabwe, Harane Zimbabwe
KLUWER ACADEMIC PUBLISHERS
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Contents
Acknowledgements ix
Symbols, Abbreviations and Units xi
1 Introduction and Terminology 1
1.1 Introduction 1
1.2 Classifications ofdeformationmicrostructures andmechanisms 1
1.3 Deformation microstructures and mechanisms in the earth: Brittle-semibrittle-plastic transitions 3
1.4 The description of deformation: Scale, continuity, distribution, mechanism and mode 4
1.5 Ductility and the “brittle-ductile transition” 4
1.6 Character and classification of deformation zone rocks 5
1.7 Format and use of this book 5
2 Cataclasis 7
2.1 Introduction 7
2.2 Fundamental cataclastic deformation mechanisms 7
2.2.1 Microcracking 7
2.2.2 Frictional sliding 10
2.3 Microcracks 10
2.3.1 Classification,characteristics and observation 10
2.3.2 Microstructures and mechanisms 12
2.3.3 Impingement microcracks 12
2.3.4 Flaw-induced microcracks 13
2.3.5 Microfracturing of pre-existing flaws 13
2.3.6 Cleavage microcracks 13
2.3.7 Elastic mismatch microcracks 13
2.3.8 Plastic mismatch microcracks 14
2.3.9 Microfault-inducedmicrocracks: Microscopic feather fractures (mffs) 14
2.3.10 Thermally-induced microcracks 15
2.3.11 Phase transformation-induced microcracks 16
2.4 Microfaults 17
2.4.1 Characteristics 17
2.4.2 Mechanisms 17
2.5 Deformation bands 18
2.5.1 Characteristics and classification 18
2.5.2 Mechanisms 18
2.6 Distributed cataclasis and cataclastic flow 18
2.7 Gouge zone microstructures 19
2.8 Microfracture surface features 19
2.9 Crystallographic fabrics 22
2.10 Pre-lithification deformation microstructures and mechanisms 22
2.11 Pseudotachylites and frictional melting 22
2.11.1 Characteristics 22
2.11.2 Origin 22
2.11.3 Misidentification 23
v
vi CONTENTS
3 Diffusive MassTransferby Solution 24
3.1 Introduction 24
3.2 Fundamental deformationmechanismsofdiffusivemasstransferbysolution 24
3.3 Grain surface solutiontextures 25
3.4 Indenting,truncating andinterpenetratinggraincontacts 25
3.5 Strain caps 27
3.6 Microstylolites 27
3.6.1 Characteristics 27
3.6.2 Formation andpropagation 27
3.7 Diffusivemass transferandcleavage 28
3.7.1 Classification 28
3.7.2 Spaced cleavages 29
3.7.3 Continuouscleavage 30
3.8 Grain surface depositiontextures 30
3.9 Overgrowths, porosityreduction,pressure shadowsandfringes, andmica beards 32
3.9.1 Characteristics 32
3.9.2 Mechanisms 33
3.10 Grain shapefabrics 33
3.11 Fluid inclusion planes 33
3.12 Microveins 35
4 Intracrystalline Plasticity 39
4.1 Introduction 39
4.2 Fundamental mechanismsofintracrystallineplasticity 39
4.3 Deformationtwins 39
4.4 Undulatoryextinction 41
4.5 Intracrystalline deformationbands,
kink bandsandsubgrains: Recovery 41
4.6 Deformation lamellae 47
4.7 Grain shapefabricsandribbongrains 47
4.8 New grains,core andmantlestructure: Dynamicrecrystallization 47
4.9 Crystallographic fabrics 50
5 Diffusive Mass Transferand Phase Transformationsin the Solid State 52
5.1 Introduction 52
5.2 Fundamental deformationmechanisms ofsolidstate diffusivemasstransferandphasetransformations 52
5.3 Grain shapefabricsandribbon grains 52
5.4 Foam texture, static and secondary recrystallization 54
5.5 Decussate texture 54
5.6 Porphyroblasts and inclusion trails 54
5.6.1 Characteristics 54
5.6.2 Growthmechanisms 55
5.6.3 Relationship todeformation 55
5.7 Reaction rims, relictminerals, coronasand symplectites 57
5.8 Chemical zoning 57
5.9 Solid state phase transformationmicrostructures 57
5.10 Superplasticity 57
6 Magmatic and Sub-magmatic Deformation 59
6.1 Introduction 59
6.2 Fundamental deformationmechanisms andmicrostructuresin rocks containing melt 59
6.2.1 Magmatic flow 59
6.2.2 Sub-magmatic flow 60
6.2.3 Magmatic andsub-magmatic flowandrheology 60
6.3 Mesoscopic evidencefor magmaticand sub-magmatic flow 60
6.4 Magmatic microstructures 62
6.4.1 Grainshapefabrics 62
6.4.2 Crystallographicfabrics 62
6.5 Sub-magmaticmicrostructures 62
6.5.1 Grain shapefabrics 62
CONTENTS vii
6.5.2 Intracrystallineplasticity 62
6.5.3 Diffusivemass transfer 63
6.5.4 Cataclasis 63
6.6 Other microstructures 63
6.7 Non-magmaticdeformation 63
7 Microstructural Shear Sense Criteria 65
7.1 Introduction 65
7.2 Curved foliation 66
7.3 Oblique foliationsandshapepreferred orientations 66
7.4 Porphyroclast systems 67
7.4.1 Characteristics and classification 67
7.4.2 Mechanisms offormation 68
7.4.3 Stair-step direction: and tails 69
7.4.4 Faces ofa tail 69
7.4.5 Deflectionand embaymentsof tails 69
7.5 S-,C-and 70
7.5.1 Characteristics andclassification 70
7.5.2 Formation andevolution 72
7.5.3 Curvature ofS-foliation 73
7.5.4 Shear onC-or 73
7.6 Pressure shadowsandfringes 73
7.6.1 Kinematics ofpressure shadowsandfringesin shear zones 73
7.6.2 Geometry ofthelastincrementofgrowth 73
7.6.3 Shape 73
7.7 Mica fish 74
7.8 Porphyroblast internalfoliations 75
7.9 Crystallographicfabrics 75
7.10 Asymmetricmicroboudins 76
7.11 Asymmetric microfoldsandrollingstructures 77
7.12 Shearsense criteria inrockscontaining melt 77
7.12.1 Magmaticshearzones 77
7.12.2 Oblique grainshapefabrics 78
7.12.3 Tiling andimbrication 78
7.12.4 S-C fabrics 78
7.12.5 Sub-magmaticmicrofractures 78
7.13 Shearsense criteria forfaults 79
7.13.1 Shearsense observations onfaults 79
7.13.2 Displaced grainfragments 79
7.13.3 Risers andslickenfibres 79
7.13.4 Gouges 79
7.13.5 Jogs andbends 79
8 Shock-induced microstructures and shock metamorphism 80
8.1 Introduction 80
8.2 Shockmechanisms 80
8.3 Microfractures 80
8.4 Planar DeformationFeatures (PDFs) 81
8.5 Mosaicism 82
8.6 Diaplectic glass 83
8.7 High pressurepolymorphsofquartz -Coesite and stishovite 83
8.8 Lechatelierite 83
8.9 Tectites, microtectites andspherules 84
8.10 Shock barometryandthermometry 85
8.11 Calibration ofshockpressuresfrommicrostructures 85
8.11.1 Calibration ofshockpressuresfromoptical propertiesofquartz 87
8.11.2 Problems ofshockbarometry 87
8.12 Diagnosticimpactmicrostructures 88
viii CONTENTS
9 From Microstructuresto Mountains: Deformation Microstructures, Mechanismsand Tetonics 90
9.1 Introduction 90
9.2 Failure criteria 90
9.2.1 Coulomb andMohrfailurecriteria 90
9.2.2 Griffithfailurecriteria 90
9.3 Pore fluid pressure and faulting 91
9.4 Fracture mechanicsand failurecriteria 91
9.5 Frictional sliding laws 91
9.5.1 Byerlee’s law 91
9.5.2 Rate andstatedependentfrictionalsliding 92
9.6 Flowlaws 92
9.6.1 Diffusivemasstransfer:Grain sizesensitivecreep 92
9.6.2 Intracrystalline plasticity 93
9.6.3 Empirical flowlawsfromexperimental data 94
9.7 Polymineralic deformation 94
9.8 Deformationmechanismmaps 97
9.9 Lithosphericstrengthenvelopes 97
9.10 Palaeopiezometry 98
9.10.1 Methods andcalibration 98
9.10.2 Recrystallized grain size 98
9.10.3 Subgrain size 100
9.10.4 Dislocationdensity 100
9.10.5 Twinning -differentialstress 100
9.10.6 Deformationlamellae 101
9.10.7 Principal stress orientations from deformationlamellae 103
9.10.8 Principal stressorientations andstrainsfromtwins 103
9.10.9 Generalproblemswith palaeopiezometers 104
9.11 Geothermobarometry 104
9.11.1 Methods andcalibration 104
9.11.2 Calcitetwin morphology 104
9.11.3 Suturedquartzgrainboundaries 105
9.11.4 Subgrain boundaryorientation inquartz 105
References 107
Index 127
Color Plate Section 133
Acknowledgements
Most of the photomicrographs weredeveloped and printed by Cuthbert Banda, whose assistance, with that of other members
of the staff of the Geology Department, University of Zimbabwe, was invaluable. James Preen guided the preparation of the
TEX version of the text. Faith Samkange and Maxwell Matongo were able research assistants, supported by the University of
ZimbabweResearch Board. The following are thanked for contributing photomicrographs or thin sections: P. Dirks (Plates
11, 30, 31, 32, 33, 35, 44), R. Fernandes (Fig. 2.9), H. Frimmel (Plate 18), S. Kamo (Figs. 8.4 - 8.6), H. Leroux (Figs. 8.2,
8.3), J.E.J. Martini (Figs. 8.7, 8.8), U. Reimold (Plate 46), J. Stowe (Plate 22), D. Van Der Wal and M. Drury (Fig. 4.2).
Plates 1 - 4 and Figs. 2.5, 2.18, 2.19, 3.18 of core material from the Cajon Pass drillhole were made at the Institute for Crustal
Studies, University of California, Santa Barbara, as part of research on deformation mechanisms with R. Sibson, supported
by the National Science Foundation, U.S.A., under grant DAR-84-10924. The assistance of the technical staff at U.C.S.B. is
gratefully acknowledged. Some research for this book was supported by the IUGS Commission on Tectonics, COMTEC.
Detailed reviews of chapters from the following are greatly appreciated: P. Dirks, R. Hanson, H. Jelsma, W. Means, A.
Ord, M. Paterson, U. Reimold, E.H. Rutter, A. Schmid Mumm.
Fig. 8.2 was reproduced from Leroux et al. (1994), and Fig. 8.7, 8.8 from Martini (1991), all with kind permission of
Elsevier Science - NL Sara Burgerhartstraat 25, 1055 KV Amsterdam, The Netherlands. Fig. 8.4 was reproduced from Krogh
et al. (1996) with kind permission from the American Geophysical Union. Fig. 9.5 was reproduced from Burkhard(1993),
and Fig. 7.20 from Goldstein (1988), both with kindpermission from Elsevier Science Ltd. The Boulevard, Langford Lane,
Kidlington OX5 1GB, U.K. Figs. 9.6, 9.7 were reproduced from Kruhl and Nega (1996), with kind permission from Springer
Verlag. Full details of these publications are given in the references.
ix
Symbols, Abbreviations and Units
Numbers in brackets give the chapters and sections where the symbols are used. Units are given if they are referred to in the
text.
a Microcrack long axis (2.2.1), Rate and state variable friction law constant (9.3.2)
A Flow law constant, (9.4.1), or (9.4.3)
S to C-surface angle (7.5), Flow law constant (9.4.3), Effectivestress coefficient(9.2.3)
b Microcrack short axis (2.2.1), Flow law constant (9.4.3)
Burger’s vector (4.2, 9.8)
B Particle velocity/unitpotential gradient (3.2), Flow law constant (9.4.3)
c Microcrack or flaw length (2.2, 2.3, 2.4.2), concentration of particles (3.2)
Cohesion, MPa (9.2, 9.3), Reference state solubility, mole fraction (9.4.1)
Anglesdefiningexternal asymmetry of an LPO (7.9)
CL Cathodoluminescence (2, 3, 8)
CMF Critical melt fraction (6.2)
d Particle size (2.2.2), Flaw spacing (2.4.2), Grain size, m (9.4), mm (9.8)
Subgrain size, mm (9.8.3)
D Fractal dimension (2, 9.9.3)
Referencestate diffusion coefficient for Pressure solution creep, (9.4.1)
Reference state diffusioncoefficient for Nabarro-Herring, Coble creep, (9.4.1)
S to C- or angle (7.5), Grain boundarywidth, m (9.4)
DMT Diffusive masstransfer (1, 3, 5, 9)
Twinning density, (9.8.5)
E Young’s modulus(2.2)
Strain rate, strain rate at 0 K in the Dorn Law, (9.4)
f Volumefraction of phase in polymineralic flow law (9.5)
Crystalfraction,fraction at critical packing (6.2.1)
Microcrack extension force, Critical value (2.2)
GBM Grain boundary migration (4.8, 9.4, 9.8)
Surface tension force (2.2), Angle between flaw and (2.3.4)
G Fracture toughness(2.2)
Viscosity of suspension, Viscosity of pure melt (6.2.1)
ISA Instantaneousstretching axes (7.1, 7.7)
Twinning incidence (9.8.5)
J Diffusive flux (3.2)
Angle between flaw array and (2.4.2)
k Dislocation density palaeopiezometer constant (9.8.4)
Stress intensityfactors for mode I, II, and III opening (2.2)
Threshold, Critical stress intensityfactors(2.2)
kC Velocity of deforming crystal face, (9.4.1)
l Model microcrack length (2.3, 2.4.2), Dislocation density palaeopiezometer constant (9.8.4)
L Critical slip distance (9.3.2), Length of grain boundary (9.9)
LPO Lattice preferred orientation (4.9, 5.10)
LSE Lithospheric strength envelope (9.7)
m Grain size exponent in flow law (9.4, 9.5), Grain size palaeopiezometer constant (9.8.2)
Coefficient of friction (2, 9.2), Chemical potential (3.2), Shear modulus, GPa (9.8.3, 9.8.4)
Coefficient of internal friction(9.2)
n Power law exponent for flow laws (9.4, 9.5)
P Mean stress, Pa (3.2, 9.4)
PDF Planar deformation feature (7)
xi
xii SYMBOLS, ABBREVIATIONS ANDUNITS
Pore fluid pressure (3.2, 9.2.3)
PPL Plane polarized light
Flaw to microcrack angle (2.3.4, 2.4.2)
Activation enthalpy, pressure solution and grain boundary diffusion, (9.4)
Activation enthalpy for volume diffusion, and diffusion creep, (9.4)
r Length of stride in divider method (9.9.3)
R Gas constant, (9.4)
RF Reflectedlight
Density, (9.4.1), Dislocation density, (9.8.4)
Deformation lamellae spacing, mm (9.8.6)
S
S Molar entropy (3.2)
Cohesion, MPa (9.2)
Oblique foliation, Bands parallel to shear plane (7.3)
External, Internal foliations (5.6, 7.8)
SEM Scanning electron microscope
ST Sensitive tint plate
Differentialstress, Pa or MPa (9.4)
Maximum, intermediate, minimum principal stresses, Compression positive (2,3,5)
Remote stress for microcrack closure (9.2.2), Remote applied stress (2.2.1)
Normal stress (2,3, 9.2), Stress at 0 K in Dorn Law (9.4)
Temperature,0C and K, Melting temperature
Uniaxial tensile strength, MPa (9.2.2)
TEM Transmission electron microscope
Shear stress, MPa (2.2.2, 9.2, 9.3)
u Dislocation density exponent in dislocation density palaeopiezometer (9.8.4)
U Molar internal energy (3.2)
Subgrain size exponent in subgrain size palaeopiezometer (9.8.3)
V Microcrack velocity (2.2.1), Sliding velocity (9.3.2), Activation volume, (9.4.3)
Molar volume, (3.2, 9.4)
Maximum twin volume, % (9.8.5)
Thickness of a grain boundaryfluid (9.4.1), Grain size palaeopiezometer exponent (9.8.2)
Angles defining internal asymmetry of an LPO (7.9)
XP Crossed polarized light
State variable in dynamic frictional sliding law (9.3.2)
() Miller-Bravais indices of a crystal face
{} Miller-Bravais indices of a representative face of a form
< > Miller-Bravais indices of a crystal direction