@prefix vivo: . @prefix edm: . @prefix ns0: . @prefix dcterms: . @prefix skos: . vivo:departmentOrSchool "Science, Faculty of"@en, "Earth, Ocean and Atmospheric Sciences, Department of"@en ; edm:dataProvider "DSpace"@en ; ns0:degreeCampus "UBCV"@en ; dcterms:creator "Kushnir, Alexandra Roma Larisa"@en ; dcterms:issued "2012-09-28T18:49:50Z"@en, "2012"@en ; vivo:relatedDegree "Master of Science - MSc"@en ; ns0:degreeGrantor "University of British Columbia"@en ; dcterms:description """The role of dolomite on the strength and evolution of calcite-dolomite fold and thrust belts is largely unknown. Field investigations indicate that, under upper- to mid-crustal conditions, strain in natural systems is localized in calcite, resulting in a ductile response, while dolomite deforms in a brittle manner. The effect of dolomite on limestone rheology, and the potential for strain localization in composites have not yet been fully quantified. I conducted 11 constant displacement rate (3x10⁻⁴ and 10⁻⁴ s⁻¹), high confining pressure (300 MPa), and high temperature (750°C and 800°C) torsion experiments to address the role of dolomite on the strength of calcite-dolomite composites. Starting materials were formed by hot isostatic pressing mixtures of dolomite and calcite powders (given as Dm%: Dm25, Dm35, Dm51, and Dm75) and were deformed up to a maximum shear strain of ~5. Mechanical data show a considerable increase in yield strength with increasing dolomite content. Microstructural analysis shows that dolomite grains <~50 μm are characterized by diffuse and poorly defined grain boundaries; in Dm25 and Dm35, high aspect ratio dolomite grains are aligned into a foliation. Dolomite grains >~50 μm are characterized by well-defined grain boundaries and cleavage-controlled fracture. Electron backscatter diffraction (EBSD) shows no crystallographic preferred orientation (CPO) development in dolomite, but optical microscopy confirms brittle deformation of dolomite grains by Mode I cracks, shear fractures, and subsequent grain size reduction. Calcite grains are internally strain-free, equiaxed to tabular in shape, and characterized by triple-junction grain boundaries. EBSD confirms a distinct CPO of calcite c-axes perpendicular to the direction of maximum stretching. The microstructure of calcite aggregates suggests grain boundary sliding, accommodated by diffusion and dislocation glide, which accommodates high shear strains without significant change in grains shape and size. Dolomite is essentially undeformed in run products with less than 35% dolomite; calcite accommodates most of the displacement in these experiments. In contrast, for dolomite contents greater than 51%, dolomite accommodates displacement by brittle processes. My experiments provide insights into the processes controlling rheology within bimodal calcite-dolomite systems, suggesting that a minimum dolomite-content exists (between 35% and 51%) above which dolomite significantly influences composite strength."""@en ; edm:aggregatedCHO "https://circle.library.ubc.ca/rest/handle/2429/43299?expand=metadata"@en ; skos:note """AN EXPERIMENTAL INVESTIGATION OF THE MECHANICAL BEHAVIOUR OF SYNTHETIC CALCITE-DOLOMITE COMPOSITES by Alexandra Roma Larisa Kushnir B.Sc. The University of British Columbia, 2008 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in The Faculty of Graduate Studies (Geological Sciences) THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver) September 2012 © Alexandra Roma Larisa Kushnir, 2012 ii Abstract The role of dolomite on the strength and evolution of calcite-dolomite fold and thrust belts is largely unknown. Field investigations indicate that, under upper- to mid-crustal conditions, strain in natural systems is localized in calcite, resulting in a ductile response, while dolomite deforms in a brittle manner. The effect of dolomite on limestone rheology, and the potential for strain localization in composites have not yet been fully quantified. I conducted 11 constant displacement rate (3x10-4 and 10-4 s-1), high confining pressure (300 MPa), and high temperature (750°C and 800°C) torsion experiments to address the role of dolomite on the strength of calcite-dolomite composites. Starting materials were formed by hot isostatic pressing mixtures of dolomite and calcite powders (given as Dm%: Dm25, Dm35, Dm51, and Dm75) and were deformed up to a maximum shear strain of ~5. Mechanical data show a considerable increase in yield strength with increasing dolomite content. Microstructural analysis shows that dolomite grains <~50 µm are characterized by diffuse and poorly defined grain boundaries; in Dm25 and Dm35, high aspect ratio dolomite grains are aligned into a foliation. Dolomite grains >~50 µm are characterized by well-defined grain boundaries and cleavage-controlled fracture. Electron backscatter diffraction (EBSD) shows no crystallographic preferred orientation (CPO) development in dolomite, but optical microscopy confirms brittle deformation of dolomite grains by Mode I cracks, shear fractures, and subsequent grain size reduction. Calcite grains are internally strain-free, equiaxed to tabular in shape, and characterized by triple-junction grain boundaries. EBSD confirms a distinct CPO of calcite c-axes perpendicular to the direction of maximum stretching. The microstructure of calcite aggregates suggests grain boundary sliding, accommodated by diffusion and dislocation glide, which accommodates high shear strains without significant change in grains shape and size. Dolomite is essentially undeformed in run products with less than 35% dolomite; calcite accommodates most of the displacement in these experiments. In contrast, for dolomite contents greater than 51%, dolomite accommodates displacement by brittle processes. iii My experiments provide insights into the processes controlling rheology within bimodal calcite-dolomite systems, suggesting that a minimum dolomite-content exists (between 35% and 51%) above which dolomite significantly influences composite strength. iv Preface The work presented in this thesis is, in part, a collaboration between the Centre for the Experimental Study of the Lithosphere (CESL) at the University of British Columbia (UBC) and the Experimental Rock Deformation Laboratory (ERDL) at the Swiss Federal Institute of Technology in Zürich (ETH- Zürich). The starting powders were mixed and hot isostatically pressed at ETH- Zürich by Dr. L.A. Kennedy and Dr. P. Benson. I characterized the starting material by thin section, scanning electron microscope (SEM), electron backscatter diffraction (EBSD), and X-ray diffraction (XRD) methods. I performed the torsion experiments at ETH- Zürich under the supervision of Dr. P. Benson and Dr. S. Misra. Additionally, I was responsible for characterization of the deformed materials by thin section, SEM, EBSD, XRD, and microprobe methods. v Table of Contents   Abstract  ...................................................................................................................................................  ii   Preface  ....................................................................................................................................................  iv   Table  of  Contents  ..................................................................................................................................  v   List  of  Tables  ........................................................................................................................................  vii   List  of  Figures  ....................................................................................................................................  viii   Acknowledgements  .............................................................................................................................  x   Dedication  ..............................................................................................................................................  xi   Chapter  1:  Introduction  .....................................................................................................................  1   Chapter  2:  The  State  of  the  Art  .........................................................................................................  3   2.1  Calcite  and  Dolomite  ...............................................................................................................................  3   2.2  Deformation  Mechanisms  in  the  Earth’s  Crust  ..............................................................................  5  2.2.1  Brittle  Deformation  .............................................................................................................................................  5  2.2.2  The  Brittle-­‐Ductile  Transition  and  Ductile  Deformation  ....................................................................  7   2.3  Experimental  Rock  Deformation  ........................................................................................................  7  2.3.1  Calcite  Rheology  ...................................................................................................................................................  7  2.3.2  Dolomite  Rheology  ...........................................................................................................................................  13   2.4  Deformation  in  Bimineralic  Crystalline  Rocks  ...........................................................................  15   2.5  Decarbonation  .......................................................................................................................................  16   Chapter  3:  Experimental  Methods  ...............................................................................................  18   3.1  Deformation  Apparatus  and  Techniques  ......................................................................................  18   3.2  Sample  Assembly  ..................................................................................................................................  23   3.3  Microstructural  and  Textural  Analyses  .........................................................................................  26   3.4  X-­‐ray  Diffraction  ....................................................................................................................................  26   3.5  Microprobe  ..............................................................................................................................................  27   Chapter  4:  Starting  Material  Preparation  and  Characterization  .......................................  28   4.1  Sample  Preparation  .............................................................................................................................  28  4.1.1  Starting  Powders  ...............................................................................................................................................  28  4.1.2  Hot  Isostatic  Pressing  (HIP)  .........................................................................................................................  29  4.1.3  Chemistry  .............................................................................................................................................................  29  4.1.4  Porosity  .................................................................................................................................................................  30  4.1.5  Sample  Assembly  Preparation  ....................................................................................................................  32   4.2  Microstructure  .......................................................................................................................................  32   4.3  Textures  and  Fabrics  ...........................................................................................................................  39   Chapter  5:  Results  .............................................................................................................................  43   5.1  Sample  Decarbonation  ........................................................................................................................  43   5.2  Mechanical  Results  ...............................................................................................................................  43  5.2.1  Strain  Rate  Stepping  Experiment  ...............................................................................................................  45  5.2.2  Yield  Experiments  .............................................................................................................................................  48  5.2.3  High  Strain  Experiments  ................................................................................................................................  48  5.2.4  High  Temperature  and  Low  Strain  Rate  Experiments  ......................................................................  49   5.3  Microstructure  .......................................................................................................................................  51  5.3.1  Yield  Experiments  .............................................................................................................................................  51   vi 5.3.2  High  Strain  Experiments  ................................................................................................................................  54  5.3.3  High  Temperature  Experiments  .................................................................................................................  59   5.4  Texture  Analyses  ...................................................................................................................................  59  5.4.1  ! = !  .......................................................................................................................................................................  59  5.4.2  Yield  Experiments  .............................................................................................................................................  59  5.4.3  High  Strain  Experiments  ................................................................................................................................  60  5.4.4  High  Temperature  Experiment  ...................................................................................................................  60  5.4.5  Calcite  Clumps  ....................................................................................................................................................  61   5.5  Chemical  Changes  Attending  Deformation  ..................................................................................  73  5.5.1  Energy-­‐dispersive  X-­‐ray  Spectroscopy  ....................................................................................................  73  5.5.2  Microprobe  ..........................................................................................................................................................  73   Chapter  6:  Discussion  ......................................................................................................................  76   6.1  Overview  of  Results  ..............................................................................................................................  76  6.1.1  Mechanical  Data  .................................................................................................................................................  76  6.1.2  Microstructure  and  Texture:  Calcite  .........................................................................................................  78  6.1.3  Microstructure  and  Texture:  Dolomite  ....................................................................................................  78   6.2  Deformation  Mechanisms  ..................................................................................................................  79  6.2.1  Dislocation  Creep  with  Dynamic  Recrystallization  ............................................................................  79  6.2.2  Superplastic  Flow  and  Calcite  ......................................................................................................................  79  6.2.3  Calcite  Clumps:  Analogues  for  Veins  in  Nature?  ..................................................................................  81  6.2.4  The  Role  of  Dolomite:  Brittle  and  Ductile  Behaviour  ........................................................................  81   6.3  Application  to  Natural  Systems  ........................................................................................................  85   6.4  Summary  ..................................................................................................................................................  85   Chapter  7:  Conclusions  ....................................................................................................................  87   Bibliography  .......................................................................................................................................  89   Appendix  A:  Matlab  Code  ................................................................................................................  94   A.1  Grain  Size  Analysis  ...............................................................................................................................  94   A.2  Paterson  Deformation  Analysis  .......................................................................................................  94  A.2.1  Torsion_data_processing_n_factor.m  .......................................................................................................  94  A.2.2  Torsion_load_data.m  .......................................................................................................................................  95  A.2.3  Torsion.m  .............................................................................................................................................................  96   A.3  Microprobe  Analysis  ............................................................................................................................  97   Appendix  B:  X-­‐ray  Diffractograms  ...............................................................................................  99   B.1  Starting  Powders  ................................................................................................................................  100   B.2  Hot  Isostatic  Pressing  Product  .......................................................................................................  101   B.3  Deformed  Run  Product  .....................................................................................................................  103   Appendix  C:  Microprobe  Data  .....................................................................................................  104   vii List of Tables Table 2.1 Identified glide planes in calcite and conditions for activation of slip and twinning along them…………………………………………………………………9 Table 2.2 Identified glide planes in dolomite and conditions for activation of slip and twinning along them………………………………………………………………15 Table 4.1 HIP conditions and properties of HIP product………………………………………30 Table 5.1 List of deformation experiments performed…………………………………………45 Table 5.2 List of sample slices used for microstructural analysis………...……………………51 viii List of Figures Figure 2.1 Hexagonal structure shared by calcite and dolomite…………………………………..4 Figure 2.2 Deformation of a circle by simple shear………………………………………………6 Figure 2.3 Stress-strain relationships for Wombeyan marble…………………………………….6 Figure 2.4 Brittle and ductile fabrics for sinistral shear systems……………………………..….11 Figure 2.5 Stereographic projection showing important slip and twinning planes for calcite and dolomite………………………………………………………………………….…11 Figure 2.6 Deformation map for Solnhofen limestone………………………………………….12 Figure 2.7 Deformation map for dolomite………………………………………………………14 Figure 2.8 Thermal dissociation of confined dolomite………………………………………….17 Figure 3.1 Schematic of the Paterson deformation rig with torsion actuator……………...........21 Figure 3.2 Schematic of sample geometry………………………………………………...…….22 Figure 3.3 Relationship between stress exponent (n) and shear stress………………………….22 Figure 3.4 Torsion rig sample assemblies……………………………………………………….24 Figure 3.5 Schematic diagram of the three principal thin section cuts of a rock deformed by torsion……………………………………………………………………………………25 Figure 4.1 Volume percent grain size distributions of starting material powders………….……31 Figure 4.2 Backscatter electron (BSE) images of Dm25 starting material…………..…………..34 Figure 4.3 Backscatter electron (BSE) images of Dm35 starting material………..……………..35 Figure 4.4 Backscatter electron (BSE) images of Dm51 starting material……………..………..36 Figure 4.5 Backscatter electron (BSE) images of Dm75 starting material………………………37 Figure 4.6 Backscatter electron images of a pure calcite clump in Dm25 starting material….....38 Figure 4.7 Electron backscatter diffraction (EBSD) analysis of Dm25 starting material……….40 Figure 4.8 Electron backscatter diffraction (EBSD) analysis of Dm75 starting material……….41 Figure 4.9 Area fraction grain size distributions of hot isostatically pressed starting materials...42 Figure 5.1 Thermal dissociation equilibrium of confined dolomite………………………..……44 Figure 5.2 Strain rate-steeping experiment, P1529 (Dm35)…………………………….……….47 Figure 5.3 Mechanical data for all experiments…………………………………………………50 Figure 5.4 Scanning electron microscopy (SEM) images of yield experiments……………..….52 Figure 5.5 Optical and scanning electron microscopy (SEM) images of deformed materials…..53 Figure 5.6 High strain deformed material: Dm25 (P1527)………………………………...…….55 Figure 5.7 High strain deformed material: Dm75 (P1538)…………………………..…………..56 ix Figure 5.8 Dm51 deformed at high temperature (P1534)………………………………………..57 Figure 5.9 Electron backscatter diffraction (EBSD) analysis of 0-strain: Dm25…………...…...62 Figure 5.10 Electron backscatter diffraction (EBSD) analysis of 0-strain: Dm75…………...….63 Figure 5.11 Electron backscatter diffraction (EBSD) analysis of yield experiment: Dm51…….64 Figure 5.12 Electron backscatter diffraction (EBSD) analysis of yield experiment: Dm75….…65 Figure 5.13 Electron backscatter diffraction (EBSD) analysis of yield experiment: Dm75…….66 Figure 5.14 Electron backscatter diffraction (EBSD) analysis of high strain experiment: Dm25………………………………………………………………………………….…67 Figure 5.15 Electron backscatter diffraction (EBSD) analysis of high strain experiment: Dm35…………………………………………………………………………………….68 Figure 5.16 Electron backscatter diffraction (EBSD) analysis of high strain experiment: Dm75…………………………………………………………………………………….69 Figure 5.17 Area fraction grain size distributions of high strain experiments………………..…70 Figure 5.18 Electron backscatter diffraction (EBSD) analysis of high temperature experiment: Dm51………………………………………………………………………………...…..71 Figure 5.19 Crystallographic preferred orientation (CPO) development near calcite clumps…..72 Figure 5.20 Energy-dispersive X-ray spectroscopy (EDS) maps of magnesium concentration for experiment P1527 (Dm25)…………………………………………....74 Figure 5.21 Microprobe analysis maps for high strain experiments P1527 (Dm25) and P1538 (Dm75)…………………………………………………………………………………...75 Figure 6.1 Evolution of crystallographic preferred orientation (CPO) with strain………………77 Figure 6.2 Comparison of study data with the reported deformation behaviour of Solnhofen limestone…………………………………………………………………………………83 Figure 6.3 Comparison of study data with the reported deformation behaviour of Madoc dolomite………………………………………………………………………………….84 Figure 6.4 Field examples of coexistant micrite and dolomite, Toscana Strata of the Apennines in the Gulf of La Spezia………………………………………………………….…...…86 x Acknowledgements I sincerely thank Dr. L.A. Kennedy for constantly challenging me to ask penetrating questions and guiding me in the pursuit of answers. It has truly been a pleasure discussing science. I offer my enduring gratitude to Prof. J.K. Russell for always having an open door and for saying it like it is. The guidance and opportunities he has given me have truly been one of the most rewarding aspects of my degree. I thank Dr. C. Sinclair for his eternal enthusiasm and lively discussions. To J. Kabel and G. LeFebvre, I owe many thanks for their support and unwavering patience in guiding me through my exhaustive hours of EBSD analysis. To Dr. R. Bruijn, Dr. P. Benson, and Dr. S. Misra, I am grateful for their advice and assistance during the experimental program at ETH-Zürich. The learning curve was steep and the challenge was invigorating. To my lab family: M. Campbell, D. Woodell, S. Kolzenburg, L. Hilchie, B. Friedlander, C. Ryane, L. Porritt, A. Ryan, and J. Welles. You have made the last two years an utter pleasure and the end of this period of time is most bittersweet. Your endless support and humour have kept me going. To M. Heap for keeping me from losing my enthusiasm and always being just a phone call away. My funding was provided by the Alexander Graham Bell Canada Graduate Scholarship (CGS) from the National Sciences and Engineering Research Council of Canada xi Dedication For my parents, without whom very little of what I have achieved would have been possible. 1 Chapter 1: Introduction Approximately 20% of the sedimentary rock in the Earth’s crust is limestone. Calcite (CaCO3) is the major constituent of limestone (i.e. rock containing > 95% wt% calcite), however, calcite is commonly partially or completely replaced by dolomite (MgCa(CO3)2) through the enrichment of magnesium ions, a process called dolomitization. The deformation mechanisms and rheology of calcite aggregates have been explored extensively (Barnhoorn et al., 2003, 2005a; Bruijn et al., 2010; Casey et al., 1997; De Bresser et al., 2005; Kennedy and Logan, 1997; Kern and Wenk, 1983; Leiss and Molli, 2002; Molli et al., 2011; Oesterling et al., 2006; Paterson and Olgaard, 2000; Pieri et al., 2000a; Pieri et al., 2000b; Rutter et al., 1993; Rutter, 1972, 1995; Schmid et al., 1977; Schmid et al., 1987; Schmid et al., 1980; Walker et al., 1990). The rheology of dolomite is not well defined under crustal conditions (Austin and Kennedy, 2005; Austin et al., 2005; Barber et al., 1994; Davis et al., 2008; Delle Piane et al., 2007; Delle Piane et al., 2008; Leiss and Barber, 1998; Newman and Mitra, 1994). Calcite and dolomite commonly occur together and behave quite differently when involved in crustal-scale deformation (Erikson, 1994; Woodward et al., 1988). Dolomitic rocks, in particular, play an important structural role in controlling the strength of thrust faults and nappes. For example, the varying degree of dolomitization within rocks of the Naukluft Nappe Complex and Naukluft Thrust, central Namibia, likely played a significant role in their structural evolution (Miller et al., 2008; Viola et al., 2006). Ductile deformation occurs within calcite- mylonites, whereas the basal Naukluft Fault is localised along a pre-existing massive, dolomite layer through both brittle and ductile reworking (Miller et al., 2008). Dolomite within continental low-angle normal faults, such as the Zuccale Fault in Italy (Smith et al., 2007), is responsible for their profound and long-term weakness (Collettini et al., 2009). Additionally, dissolution of calcite is, in part, responsible for devastating earthquakes in active fault systems (e.g. Fucino Fault System of the Central Apennines; Carcaillet et al. (2008)). Despite the structural and chemical similarities of calcite and dolomite, dolomitic rocks (i.e., rocks containing > 95% wt.% of dolomite) are apparently stronger than their calcite-rich counterparts (i.e. limestone) at low temperatures (< 700°C). At high temperatures (> 700°C), fine-grained dolomite rocks weaken significantly compared to similar experiments on calcite rocks (Delle Piane et al., 2009a). To date, the influence of dolomite content on the strength of limestone under both ambient and high temperature conditions is not well constrained in the laboratory. 2 In this study, synthetic hot isostatically pressed (HIP) calcite-dolomite (Cc-Dm) composites are deformed in a torsion apparatus under elevated temperature and confining pressure to determine the rheological behaviour of the composites and to evaluate the effect of dolomite content on rock strength. The composites are composed of 25 %, 35%, 51%, and 75% coarse-grained dolomite with the remainder being fine-grained calcite. The experimental campaign comprises a total of 12 rock deformation experiments; the conditions of experimentation are temperatures, T, of 750°C and 800°C, confining pressure, Pc, of 300 MPa, and total shear strains between 0.16 and 5.5. These experiments directly address variations in the mechanical behaviour of composite materials as a function of composition and grain size. I show that with increasing dolomite content, these synthetic composites demonstrate a two-fold increase in mechanical strength. Previous studies (see Delle Piane et al., 2009) of similar ilk demonstrate that dolomite can decrease in yield strength when relatively small proportions of dolomite are of the same grain size as the surrounding calcite. In this study I explore the implications of composition and grain size on strain localization in calcite-dolomite composites. The results of this study can be applied to the rheological behaviour of dolomite-rich limestones in foreland fold and thrust belts (e.g. Canadian Rockies, Apennines, Italy). 3 Chapter 2: The State of the Art 2.1 Calcite and Dolomite Subtle differences in crystal structure set calcite and dolomite apart both in physical properties and in available mechanisms of deformation. Calcite (CaCO3) is hexagonal (!3! symmetry) with interlayers of Ca and triangular CO3 perpendicular to the crystal c-axis (see Figure 2.1A). The density of calcite is 2.71 g/cm3. Dolomite (CaMg(CO3)2) is hexagonal (!3 symmetry) with Ca, Mg, and triangular CO3 layers interlayered perpendicular to the c-axis (see Figure 2.1B). The density of dolomite is 2.88 g/cm3. The fundamental structural difference between calcite and dolomite is the introduction of Mg layers in the dolomite, resulting in lower structural symmetry. The two cations occupy specific structural positions and, therefore, there is no implied solid solution between CaCO3 and MgCO3 at low temperatures. For temperatures in excess of 1000°C, a complete solid solution exists between calcite and dolomite. The solid-solid mineral reaction between calcite and dolomite is a complex process. Chemical interactions between calcite and dolomite phases have been well documented, especially for the establishment of geothermometry techniques (Goldsmith and Newton, 1969). Significantly, deformation-enhanced chemical exchange has been noted in calcite-dolomite (Cc- Dm) composites deformed to high strains, complicating the geothermometry of naturally deformed systems (Delle Piane et al., 2009a). -a3 a2 a1 c c a2 a1 -a3 c c -a3 a2 a1 B A Figure 2.1 Hexagonal structure shared by calcite and dolomite. Green rhombohedron is the primi- tive, acute rhombohedron of both minerals. The red parallelogram is subject to three-fold rotation to produce the hexagonal structure. A. Calcite. B. Dolomite. Red dots are Ca, green dots are Mg, and the blue triangles sit in the CO3 position. 4 5 2.2 Deformation Mechanisms in the Earth’s Crust Stress (σ; shear stress: τ) is the force on an area divided by its area and generally reported in the earth sciences in units of MPa. Strain is a unitless measure of the change in shape of a material under stress. For example, absolute axial strain of a given material is given by ! = !!! , where L is the starting length of material and ΔL is the change in length during deformation (Middleton and Wilcock, 1994). Shear strain, !, is calculated in non-coaxial deformation regimes by ! = tan! for small !, where ! is the angular shear (Figure 2.2) (Middleton and Wilcock, 1994). In the crust, the mode of deformation depends on a wide range of strain rates, temperatures, and confining pressures. Deformation can be broadly described as either brittle or ductile. These terms describe the macroscopic deformation behaviour of a material and are not mechanism specific. I discuss these failure modes broadly in the following sections. 2.2.1 Brittle Deformation Brittle deformation refers to macroscopic deformation of a material that loses its ability to support load, see Figure 2.3A (Rutter, 1986). This type of deformation typically occurs at low pressure-temperature conditions. Catastrophic failure is accommodated by the coalescence of microfractures (formed by dilatant microcracking) along a macroscopic shear plane (Paterson and Wong, 2005). ab ψ x z s = γz γ = tanψ Figure 2.2 Deformation of a circle by simple shear. x and z are the directions of maximum stretching and shortening, respectively of the original circle. Shear strain is calculated γ = tanψ, where ψ is the angular shear. a b Figure 2.3 Stress-strain relationships for Wombeyan marble deforming by A. brittle failure and B. ductile processes. This schematic shows the eect of conning pressure on the brittle-ductile transition in Wombeyan marble (Paterson and Wong, 1977). 0 0.01 0.02 0.03 0.04 0 100 200 Absolute Strain D i er en tia l S tr es s (σ 1-σ 3)/ M Pa σ3 = 3.5 MPa σ3 = 35 MPa B A 6 7 2.2.2 The Brittle-Ductile Transition and Ductile Deformation Ductile deformation refers to macroscopic deformation of a material that does not lose its ability to support load (see Figure 2.3B). The transition between brittle and ductile behaviour can be facilitated by increases in temperature or pressure, decreases in strain rate, or changes in the material properties (e.g. composition) of the material deformed. The geometry of fabrics in brittle and ductile shear systems is similar, however, the mechanisms of deformation giving rise to the fabrics are different (see Figure 2.4). A number of operative deformation mechanisms (including dilatant microcraking and cataclasis) contribute to ductility, making ductility a complicated material behaviour. Possible ductile mechanisms include: pressure solution, mechanical twinning, dislocation glide, dislocation creep, diffusion creep, and grain boundary sliding. An extensive description of these mechanisms can be found in Passchier and Trouw (2005). 2.3 Experimental Rock Deformation A number of experimental apparatuses have been designed to study the deformation of the crust. Uniaxial and triaxial compression apparatuses can only access strains up to a maximum of approximately 5-10%. However, the crust can behave in a ductile manner to very large strains, which are only replicated experimentally through non-coaxial experimental configurations such as the torsion rig (Paterson and Olgaard, 2000). Torsion experimental studies typically target large, high strain systems such as orogenic development. 2.3.1 Calcite Rheology Given the relative ease of deforming carbonates and their global profusion in continental tectonics, the mechanical behaviour of carbonate rocks has been extensively studied. The body of knowledge on the ductile deformation of calcite is especially exhaustive in the field (Kennedy and Logan, 1997; Leiss and Molli, 2002; Molli et al., 2011; Oesterling et al., 2006), in single crystals (De Bresser and Spiers, 1990, 1993; De Bresser and Spiers, 1997; Handin et al., 1967), in compression (De Bresser et al., 2005; Kern and Wenk, 1983; Rutter et al., 1993; Rutter, 1972, 1995; Schmid et al., 1977; Schmid et al., 1987; Schmid et al., 1980; Walker et al., 1990), and in torsion (Barnhoorn et al., 2003, 2005a; Bruijn et al., 2010; Casey et al., 1997; Oesterling et al., 2006; Paterson and Olgaard, 2000; Pieri et al., 2000a; Pieri et al., 2000b) Intracrystalline deformation (dislocation glide and creep) is dominated by the movement of dislocations along specific glide planes. Dominant glide planes in calcite have been identified 8 by means of single crystal deformation experiments and are summarized in Table 2.1. These glide planes are stereographically presented in Figure 2.5A. Of particular interest to this study is the behaviour of fine-grained calcite at high temperature and low strain rates. Depending on stress, strain rate, and grain size, calcite deforms at high temperatures and low strain rates by either linear viscous creep (involving the movement of point defects and grain boundary sliding) or dislocation creep (involving the movement of dislocations) (De Bresser and Spiers, 1990, 1993; Herwegh et al., 2003; Rutter et al., 1994; Schmid, 1976; Schmid et al., 1980; Walker et al., 1990). Grain-size sensitive flow, or diffusion creep, dominates the deformation of calcite rocks for grain sizes less than 10-40 µm (Brodie and Rutter, 2000). Intracrystalline deformation (i.e. dislocation creep dominated; the rate controlling step is diffusion assisted) is dominant in fine-grained calcites at high to moderate strain rates and high to moderate differential stresses (regimes 1 and 2, see Figure 2.6) (Schmid et al., 1977). The behaviour of calcite under these conditions is best described by an exponential stress dependence (regime 1) or power-law creep (regime 2)(Schmid et al., 1977). In the context of rock deformation, superplastic flow resides in regime 3 of Figure 2.6 and is strongly grain size dependent; strain increases with a decrease in grain size for any given stress. Grain boundary sliding is the dominant deformation mechanism assisting deformation in this field. 9 Table 2.1 Identified glide planes in calcite and conditions for activation of slip and twinning along them. Modified from De Bresser and Spiers (1997) and Wenk et al. (1983). System ! T Pc τ Reference (s-1) (°C) (MPa) (MPa) Slip ! 0001 1210 2.5x10-4 800 500 ? Griggs et al. (1960) 2.5x10-4 300 500 ? Turner and Orozco (1976) 3x10-5 600-800 unconf. ? De Bresser and Spiers (1993) ! 1210 2021 ? 300, 500 500 ? Paterson and Turner (1970) 3.3x10-7 300 500 ? Turner and Heard (1965) !! 1012 1011 3x10-4 – 3x10-8 550-800 unconf.? 18 Turner et al. (1954); Spiers and Wenk (1980); De Bresser and Spiers (1990); De Bresser and Spiers (1997) !! 1012 2201 0221 2.5x10-4 20 500 ? Turner et al. (1954) 2.5x10-4 600-800 500 ? Griggs et al. (1960) !! 1012 2201 0221 2.5x10-5 575-650 unconf. ? Spiers and Wenk (1980) !! 1012 1011 3x10-5 600-800 unconf. ? De Bresser and Spiers (1993) !! 1012 0221 10-4 25-800 210-16.5 Turner et al. (1954) !! 1014 2021 ? 300 500 ? Weiss and Turner (1972) 1x10-4 460-550 unconf. ? Braillon and Serughetti (1976) 2.5x10-5 350-650 unconf. ? Spiers and Wenk (1980) 3x10-4 – 3x10-8 550-800 unconf. ? De Bresser and Spiers (1993) 10-5 600 ? >16 Spiers and Wenk (1980) 10 System ! T Pc τ Reference (s-1) (°C) (MPa) (MPa) !! 1014 2021 10-1 10-7 300-500 300-500 64-18 30-13 Turner et al. (1954) !! 1014 2021 2.5x10-4 20-400 300-1000 ? Turner et al. (1954) 2.5x10-4 300-00 500 ? Griggs et al. (1960) 4x10-1 3x10-7 25-500 500 ? Turner and Heard (1965) 3x10-5 300-800 unconf. ? De Bresser and Spiers (1993) Twinning !! 1018 4041 2.5x10-4 20-300 500-100 11.5-6.5 8.0-8.5 Turner et al. (1954) 2.5x10-4 300-800 500 ? Griggs et al. (1960) !! 1014 2021 ? 20 300 > 12 Borg and Handin (1967) ? 300 500 ? Weiss and Turner (1972) !! 1012 1011 ? 300? 500 ? Paterson and Turner (1970) C S Y R’ R Figure 2.4 Brittle fabric (Riedel shear, A) and ductile fabric (S-C fabric, B) for sinistral shear systems. The geometry of fabrics is similar for both shear systems, however, the mechanisms of deformation giving rise to the fabrics are dierent. A represents shallow level fault zones while B represents deeper level fault zones. A B P C’ +a3 +a2 +a1 c e1 e2 e3 r1 r2r3 f1 f2 f3 +a3 +a2 +a1 c r1 r2r3 f1 f2 f3 Figure 2.5 Stereographic projection (upper hemisphere equal angle) showing important slip and twinning planes for A. calcite (modied from De Bresser and Spiers, 1997), and B. dolomite (modied from Barber and Wenk, 2001). A B 11 0 2 4 6 8−1 −0.5 0 0.5 1 1.5 2 2.5 −log10 Strain rate (s −1) lo g 1 0 D iff er en tia l s tre ss (M Pa ) Regime 1 Regime 2 Regime 3 600˚C 700˚C 900˚C 800˚C Figure 2.6 Log-log plot of the dierential stress vs. strain rate for compression deformation experiments on Solnhofen limestone (Schmid et al., 1977). Regime 1: Exponential relationship between strain rate and stress; Regime 2: Power-law creep; Regime 3: Superplasticity. Regimes 1 and 2 are characterized in the microstructure by dislocaiton glide and/or creep. Regime 3 is characterized in the microstructure by grain boundary sliding. 12 13 2.3.2 Dolomite Rheology Dolomite rheology is not well understood. Studies have included deformation investigation in the field (Leiss and Barber, 1998; Newman and Mitra, 1994), in single crystals (Barber et al., 1981; Barber and Wenk, 2001; Higgs and Handin, 1959; Turner et al., 1954), in compression (Austin and Kennedy, 2005; Austin et al., 2005; Barber et al., 1994; Davis et al., 2008), and in torsion (Delle Piane et al., 2007; Delle Piane et al., 2008). Field observations suggest that dolomite is stronger than calcite; dolomite is frequently observed fractured and adjacent to calcite, which has undergone extensive internal strain (Erikson, 1994; Woodward et al., 1988). Under similar test conditions, dolomite rock is stronger and less ductile than calcite limestone (Griggs et al., 1951, 1953; Handin and Fairburn, 1955; Higgs and Handin, 1959). Dominant dolomite slip systems are summarized in Table 2.2 and plotted in Figure 2.5B. The role of grain size sensitive deformation mechanisms in fine-grained dolomite has been recently investigated (Davis et al., 2008; Delle Piane et al., 2007; Delle Piane et al., 2008). Mechanical and microstructural evidence suggests that fine-grained dolomites (<40 µm) deform in a linear viscous manner accommodated by diffusion creep associated with grain boundary sliding (Delle Piane et al., 2008). Low to moderate temperature deformation is assisted by basal slip, while at moderate to high temperatures deformation twinning is active (Delle Piane et al., 2008). Fine-grained dolomite deforms by diffusion creep at strengths more comparable to fine- grained calcite. Coarse-grained dolomites show significant strength compared to analogous calcite grain sizes, emphasizing the critical nature of grain size in determining the rheology contrast between calcite and dolomite. Coarse-grained dolomite is stronger than calcite in the crystal plastic and dislocation creep fields (Davis et al., 2008). Figure 2.7 is a deformation map for coarse-grained dolomite (grain size = 100 µm) showing the dislocation creep, diffusion creep, and twinning fields. The shaded grey region shows the field for fine-grained dolomite experiments performed by Davis et al. (2008). Crystal Plasticity and Twinning Dislocation Creep Diusion Creep 100 300 500 700 900 1000 100 10 1 0.1 -1 σ1 -σ 3 ( M Pa ) T (˚C) 10-14 s-1 10-10 s-1 10-8 s-1 10-6 s-1 10-5 s-1 10-14 s-1 Figure 2.7 Deformation map for dolomite of grain size d = 100 μm. Temperature is normalized by a melting temperature for dolomite of 1100˚C. The stress-temperature eld for synthetic dolomite experi- ments is shown by the shaded box, (Davis et al., 2008). 14 15 Table 2.2 Identified glide planes in dolomite and conditions for activation of slip and twinning along them. Modified from Wenk et al. (1983). System !   (s-1) T (°C) τ (MPa) Reference Slip ! 0001 2110 10-5 25-700 50-130 Barber et al. (1981); Barber and Wenk (2001) !! 1012 2201 10-5 25-700 170-100 Barber et al. (1981) !! 1014 1210 10-5 > 500 Barber et al. (1981) Twinning ! 1012 1011 10-5 250-600 90-1000 Barber et al. (1981) 2.4 Deformation in Bimineralic Crystalline Rocks Deformation of bimineralic rocks has been addressed in a variety of studies including studies of calcite-anhydrite (in compression: Bruhn and Casey (1997); Bruhn et al. (1999); in torsion: Barnhoorn et al. (2005b)), calcite-muscovite (in torsion: Delle Piane et al. (2009b)), calcite-halite (in torsion: Jordan (1988)), calcite-quartz (in compression: Siddiqi (1997); in torsion: Rybacki et al. (2003)), and calcite-dolomite composites (in torsion: Delle Piane et al. (2009a)). Local heterogeneities of phase distribution can lead to strain localization in originally homogeneous material. Chemical reactions and ion exchange are common between unlike phases and encourage stain localization in poly-mineralic rocks (Olgaard, 1990). However, dragging and pinning at grain boundary contacts by secondary phases (e.g. pores, different mineral phases) inhibits grain boundary mobility (Olgaard, 1990). Strain localization has been associated with a change in deformation mechanism of the ‘weak’ phase (e.g. anhydrite in the calcite-anhydrite system, Barnhoorn et al. (2005b)) from dislocation creep to diffusion creep and/or grain boundary sliding. In fine-grained calcite-dolomite composites, strain localization and foliation development is attributed to grain boundary sliding and diffusion processes accommodated by dislocation activity in dolomite (Delle Piane et al., 2009a). Strong phases do not significantly assist deformation and, therefore, material strength increases with the addition of a strong phase (Rybacki et al., 2003). 16 2.5 Decarbonation High temperatures can facilitate intense mineralogical, chemical, and textural modifications of carbonate rock, leaving it acutely altered, fractured, and thus weakened (Chen et al., 2009; Homand-Etienne and Troalen, 1984; Mao et al., 2009). Calcite dissociates at high temperature according to the reaction (Samtani et al., 2002): CaCO3(s) → CaO(s) + CO2(g). (1) The thermal decomposition of calcite produces lime (CaO) and CO2 gas. The thermal decomposition of dolomite differs slightly: it is a two-stage process involving the reaction (Maitra et al., 2005; McIntosh et al., 1990): CaMg(CO3)2(s) → CaCO3(s) + MgO(s) + CO2(g). (2) The solid calcite products of equation (2) then break down as per reaction equation (1) and the net dolomite decomposition reaction can be rewritten: CaMg(CO3)2(s) → MgO(s) + CaO(s) + 2 CO2(g). (3) Previous studies show that the onset of decarbonation in dolomite occurs at lower temperatures than in calcite (between 600°C and 850°C) (Gunasekaren and Anbalagan, 2007). In unvented experimental setups, an infinitesmial decarbonation reaction occurs when the system is taken out of the stability field for Cc and Dm (Figure 2.8). This fills any pore space with CO2, imparting a pore fluid pressure on the system and reducing the effective confinement of samples. T (˚C) P( CO 2) (M Pa ) MgCa(CO3)2 MgO+CaCO3+CO2 300 400 500 600 700 800 900 200 150 100 50 0 Figure 2.8 From Davis et al., 2008. Thermal dissociation equilibrium of conned dolomite (Goldsmit and Newton, 1959). Dissociation begins at 560˚C. Unvented, jacketed samples containing dolomite taken to ambient temperatures above this dissociation threshold dissociate and generate a CO2 pore uid pressure as indicated by the curve. CaCO3 + MgCa(CO3)2 Stability eld 17 18 Chapter 3: Experimental Methods To model the behaviour of rock deformation experimentally, rocks are typically collected from nature and cored to dimensions that can be deformed within the constraints of current laboratory technology. The experimentalist attempts to deform material under feasible crustal pressure, temperature, pore fluid, and strain rate conditions, but realistic strain rates are generally sacrificed in the interest of producing mechanical results in a timely manner (i.e. not on typical geological timescales). Traditionally, rock mechanics testing has employed coaxial deformation of rock cores in uniaxial or triaxial compression experiments. The geometric limitations of such apparatuses limit total absolute strain to << 1 - typically maxima of 0.05 - 0.1. With the advent of the torsion actuator (Paterson and Olgaard, 2000), high-temperature rock deformation experiments can be performed to very high values of total strain - strains in excess of 50. This apparatus, therefore, allows the experimentalist to more closely simulate conditions in the Earth for at least two reasons. Firstly, natural systems are active for hundreds of millions of years, resulting in absolute strains in excess of 1. Secondly, the geometry of torsion experiments is more physically comparable to non-coaxial movement along fault surfaces. An additional benefit is that the geometry of torsion experiments (explained below) results in a deformed sample that captures the entire range of strain, from 0 to the final strain. This allows for detailed microstructural investigations of the strain evolution in a single sample. The Paterson rig with torsion actuator is used in this experimental program in order to assess high strain in a non-coaxial system and thereby provide better quantification of the textural development of calcite-dolomite composites. Ultimately, this elucidates the role of increasing dolomite content on the mechanical behaviour and strength of calcite limestones. 3.1 Deformation Apparatus and Techniques I performed all experiments in this study in an internally heated, argon-confining medium, triaxial deformation apparatus with torsion actuator (the Paterson rig), described by Paterson and Olgaard (2000) (Figure 3.1). The Paterson rig is capable of deforming samples in torsion under the following temperature (T), confining pressure (Pc), shear strain rate (!), and internal torque (M) conditions: 0℃ < ! < 1350℃, 0  !"# < !! < 500  !"#, 5×10!!  !!! 3 in regime 2 (!~4.7 for Solnhofen limestone) and 1 > ! > 3 in 46 regime 3 (!~1.7 for Solnhofen limestone) (Schmid et al., 1977). As mentioned in Chapter 2, regimes 1 and 2 are microstructurally characterized by intracrystalline deformation; regime 3 is characterized by superplastic flow (grain boundary sliding accommodated by diffusion creep and/or dislocation glide). 1 1.5 2 2.5 3 3.5 4−16 −14 −12 −10 −8 −6 −4 −2 Ln Torque Ln S he ar S tra in R at e n=2 Figure 5.2 Log-log plot of shear strain rate vs. torque for the strain rate stepping experiment (P1529; Dm35). Conditions: T=750˚C; Pc = 300 MPa. The red line is the line of best t through the mechanical data. The slope this line is the n-value for the given composition (n=2). n-values of 1 and 3 are shown for comparison. n=3 n=1 47 48 A Dm35 sample was deformed in a strain rate stepping experiment, and from the procedure outlined in Chapter 3, n is empirically determined to be 2 (Figure 5.2). n = 2 was used to process all the mechanical data gathered in this study. 5.2.2 Yield Experiments Yield experiments were performed for Dm75 (P1525) and Dm51 (P1528), at a confining pressure of 300 MPa and temperature of 750°C using a strain rate of 3x10-4 s-1. Experiments were terminated after the mechanical yield point on the load-displacement curve so that the microstructure created during the first moments of inelastic deformation could be assessed. Yield shear stress is greater for Dm75 (~70 MPa) than for Dm51 (~48 MPa) (Figure 5.3A). I chose the yield point for all experiments to be the first deviation from the elastic portion of the deformation curve. The mechanical yield for both experiments occurs at !~0.025, suggesting that the slope of the elastic portion of both curves is the same. Following elastic deformation, both curves see a pronounced roll-over between 0.025 < ! < 0.075. Dm75 continued to strain harden until the experiment ended. Dm51 exhibited some strain hardening after roll-over but this is subtle and the curve is sub-horizontal. Both experiments were terminated by rapid decompression of the sample due to breaking of the iron jackets. This is a result of the inherent strength of the Dm51 and Dm75 materials with a diameter of 15 mm; the internal torque measured during deformation is proportional to the cube of the sample diameter (! ∝ !!) (see Chapter 3, equation 2). Therefore, for the same shear stress, cores of smaller diameter can be deformed to lower internal torques, and are therefore more easily deformed. 5.2.3 High Strain Experiments High strain experiments were conducted for all four compositions (experiments P1524, P1527, P1537, and P1538) at T=750°C, Pc=300 MPa, and ! = 3×10!!!!!. The maximum shear strain in each experiment exceeded ! = 5 (Figure 5.3B). Due to a heating coil malfunction within the sample furnace, the heating history during experiment P1537 (Dm51) is not confidently known beyond !~2; only the mechanical data up until the furnace malfunction is used. P1537 was not used for microstructural analysis because of its variable heating history. Yield strength of the synthetic composite samples increases with increasing dolomite content (Figure 5.3B). Dm25 and Dm35 are mechanically similar, both reaching a peak yield strength of ~79 MPa. Mechanical steady-state (~79 MPa) is established in both samples at γ < 0.1, with limited strain hardening in Dm25 at γ ~ 3.75. With increasing dolomite content, there is 49 a significant increase in strength; Dm51 and Dm75 have peak yield strengths of ~140 MPa and ~178 MPa, respectively. Dm51 reaches a tenuous steady-state at τ~130 MPa and γ~0.4. In particular, the evolution of the mechanical behaviour of the Dm75 sample is dynamic, with dramatic strain weakening after yield to a shear strain of !~1. Strain hardening and weakening are observed between 3 < ! < 4; this change in shear stress is considered to be real as there were no noted technical problems during the experiment. 5.2.4 High Temperature and Low Strain Rate Experiments High temperature and low strain rate experiments were performed on the high dolomite content materials with the aim of reducing the strength of the materials to prevent rupturing of the jackets. A high temperature experiment was performed on Dm51 which was deformed at T=800°C, Pc = 300 MPa, and ! = 3×10!!!!! (P1534). At these conditions it was possible to deform Dm51 with a diameter of 15 mm. The mechanical data (Figure 5.3C) show a yield stress of ~67 MPa and a shear stress vs. shear strain curve similar to that of Dm25 shown in Figure 5.2B. Temporary mechanical steady state (τ~66 MPa) is achieved immediately after the yield point, followed by limited strain hardening beginning at !~2.75 to a maximum shear strain of τ~69 MPa and strain weakening at !~3.7. The experiment was halted by a catastrophic Mode I crack through the sample and jacket leading to rapid decompression. XRD analysis detected no decarbonation products and therefore the microstructure has been analyzed to investigate the microstructural response of the sample over large strains. Low strain rate experiments confirm that yield shear stress increases with increasing dolomite content (Figure 5.3D). Dm75 (P1533) was terminated by a jacket puncture due to the inherent strength of the Dm75 material. Dm51 (P1523) was deformed to !~1.9 and showed continued strain hardening after a yield stress of ~28 MPa to a maximum shear stress of ~36 MPa. Figure 5.3 Mechanical data for all the experiments performed in this study. Pc = 300MPa for all experi- ments. See table 5.1 for experimental conditions. A. Yield experiments: P1525 (Dm75) and P1528 (Dm51). B. High strain experiments: P1524 (Dm35), P1527 (Dm25), P1537 (Dm51), and P1538 (Dm75). C. High temperature experiment: P1534 (Dm51). D. Low strain rate experiments: P1523 (Dm51), P1533 (Dm75), and P1543 (Dm35). 0 0.05 0.1 0.15 0.2 0.25−20 0 20 40 60 80 100 120 140 Shear strain Sh ea r s tre ss (M Pa ) Dm-75 Dm-51 0 1 2 3 4 5 6−50 0 50 100 150 200 Shear strain Sh ea r s tre ss (M Pa ) Dm-35 Dm-75 Dm-25Dm-51 0 1 2 3 4 5−10 0 10 20 30 40 50 60 70 Shear strain Sh ea r s tre ss (M Pa ) 0 0.5 1 1.5 2−20 0 20 40 60 80 100 Shear strain Sh ea r s tre ss (M Pa ) Dm-75 Dm-35 Dm-51 A B C D Dm-51 Conditions: T = 800˚C; Strain rate = 3x10-4 s-1 Conditions: T = 800˚C; Strain rate = 1x10-4 s-1 Conditions: T = 750˚C; Strain rate = 3x10-4 s-1 Conditions: T = 750˚C; Strain rate = 3x10-4 s-1 Yield Experiments High Strain Experiments High Temperature Experiment Low Strain Rate Experiments 50 51 5.3 Microstructure Six representative deformed samples were prepared for microstructural analysis (see Table 5.2). Table 5.2 List of sample slices used for microstructural analysis. Approximate shear strains for each slice are estimates based on the distance from the centre of the sample. All experiments were deformed using ! = 3×10!!  !!!. See Chapter 3 for a description of sample preparation. Dolomite Content Sample number Pc T Approx. γ (%) (MPa) (°C) 25% P1527_1 300 750   5.5 25% P1527_2 300 750 2.25 25% P1527_3 300 750 0 35% P1524_1 300 750 5 35% P1524_2 300 750 2.5 51% P1528_1 300 750 0.21 51% P1534_1 300 800 4.25 51% P1534_2 300 800 2.1 75% P1538_1 300 750 5.5 75% P1538_2 300 750 2.25 75% P1538_3 300 750 0 75% P1525_1 300 750 0.16 5.3.1 Yield Experiments Yield experiments were performed on Dm51 and Dm75 and pure calcite clumps are absent. Like the starting material compositions, the yield experiment microstructure is populated by equiaxed calcite with generally straight grain boundaries. Calcite grains are closely packed with triple junction grain boundaries (Figures 5.4). Dolomite grains are homogeneously distributed throughout both samples (Figures 5.4A and B). Dolomite grains are angular to subangular and are fractured; straight fractures appear to follow cleavage planes but curved fractures also exist. Fractures do not continue into the calcite matrix. Intergranular porosity is greatest at dolomite-calcite interfaces. There is no foliation evident in these samples in BSE imaging and all high aspect ratio dolomite grains are randomly oriented and do not define a fabric. 20 μm 100 μm A B CFigure 5.4 Scanning electron microscope (SEM) images of yield experiments. Dolomite (Dm) is dark grey and calcite (Cc) is the light grey matrix. Dolomite grains are angular to subangular, and no rigid body rotation has taken place. See Table 5.1 for experimental conditions. Arrows indicate shear direction and the x-z coordinate systems show the orientation of the kinematic plane: x is the direction of maximum stretching and z is the direction of maximum shortening. A. Dm75 (P1525). Note Dm-Dm contacts. B. Dm51 (P1528). x z x z Dm Cc 52 2mm2.5mm 1.5mm Figure 5.5 Deformed material. Dolomite is the larger, cream-coloured phase. Calcite is the dark matrix. Arrows indicate shear direction and the x-z coordinate systems show the orienta- tion of the kinematic plane: x is the direction of maximum stretching and z is the direction of maximum shortening. A, B, and C. Core scans of Dm25 (P1527), Dm35 (P1524), and Dm75 (P1538), respectively, deformed to γ~5. Conditions: Pc=300 MPa, T=750˚C, and shear strain rate 3x10-4. Foliation is dened in A and B by elongate calcite clumps. Shear strain is calcu- lated by γ=tanψ, as shown in A. The dark lines in C are cracks in the thin section glass and not experimentally induced. D. Plane polarized image of Dm25 run product. Foliation is delin- eated by c-slip surfaces and elongate pyrite grains. Dolomite grains are organized along foliation and are not obviously rounded. E. Plane polarized image of Dm75 run product. Foliation is delineated by elongate pyrite and phyllosilicates. Dolomite is obviously rounded, but not well organized along foliation. BA C D x z c-slip pyrite x z E 500 μmphyllosilicate pyrite ψ 500 μm crack in thin section x z x z x z 53 54 5.3.2 High Strain Experiments Low dolomite content (Dm25 and Dm35): Core scans of Dm25, Dm35, and Dm75 samples deformed to high strain are shown in Figures 5.5A, 5.5B, and 5.5C. A bulk foliation is observed in Dm25 and Dm35, delineated by elongate, macroscopic zones of fine-grained calcite (Figure 5.5A and 5.5B). Dolomite grains are not obviously reduced in size or rounded, compared to the starting material (Figure 5.5D and 5.5E). Optical microscopy images of Dm25 show a reorganization of the calcite matrix along foliation, highlighted by elongate pyrites and dark, narrow bands along foliation, which appear to be c-slip surfaces (Figure 5.5D): surfaces of relatively higher shear strain. The calcite clumps identified in the starting material are sheared into thin bands (ellipses) of pure calcite with aspect ratios ranging from 0.2:4.5 and 0.4:7.5 (Figure 5.5A and5.5B). Assuming that these clumps were originally circular in cross section and that there was no loss of volume during deformation, the angular strain can be calculated ! = !"#$, where ! is the angle between the sample long axis and the long axis of the rotated clump (Figure 5.5A). These clumps record shear strains of 4 and 5.7 for Dm25 and Dm35, respectively. The calcite grains comprising the layers are equiaxed, with straight grain boundaries exhibiting triple junctions. Compositional layering of the samples is defined by these thin layers of pure calcite, alternating with composite mixtures (Figure 5.6A). Calcite layers are inclined along the direction of maximum stretching, while the surrounding dolomite-calcite material foliation is less inclined, resulting in two foliations (Figure 5.6B). This results in deflected foliations throughout Dm25 and Dm35 samples. Within the Dm-Cc bulk matrix, calcite grains are closely packed with straight grain boundaries forming triple junctions (Figure 5.6C). Grain boundaries are most defined approximately parallel to the direction of maximum stretching (Figure 5.6C), suggesting some grain elongation. Contributing to the foliation is the rigid body rotation of high aspect ratio dolomite grains (aspect ratios > 1; Figure 5.6B and 5.6D). Dolomite grains do not appear to have sustained any additional brittle fracture, as fracture density is qualitatively the same as in the starting material. While there is observed rigid body rotation, there does not appear to be significant rounding of grains above ~100 µm. Dolomite grains <100 µm show some rounding (Figure 5.6D). Accessory minerals, in particular pyrite and phyllosilicates, act as strain markers. Pyrite is significantly elongated and boudinaged throughout Dm25 and Dm35 samples and defines foliation along with c-slip surfaces and elongate calcite clumps. xz A Figure 5.6 High strain deformed material: Dm25; P1527; γ~5; 750˚C; 3x10-4 s-1. A. Deformed Cc clumps, circles are sheared to ellipses (dashed line). C-slip surfaces are along present near these features (white arrow). Plane polarized optical photograph. B. Deected foliation from bulk Cc-Dm into more deformed pure-Cc band. Dashed white line delineates the bulk foliation within the sample. Dashed orange line delineates the orientation of the boundaries of the pure-Cc band. C. Closely packed, equiaxed to tabular Cc-grains. Grain boundaries form triple junctions and are generally straight. Note signicant isolated porosity. D. Dm35 (P1524). Localized porosity developing at boundaries of coarse grained dolomite, along foliation. 20 μm D x z 200 μm 20 μm C x z x z B 55 200 μm x z C 20 μm Dx z Figure 5.7 High strain deformed material: Dm75. P1538; γ~5; 750˚C; 3x10-4 s-1. A and B. Plain polarized light (ppl) optical images. A. Evidence of brittle fracture during deformation. C-slip surfaces are traced by white lines. Mode I cracks in dolomite are identied by the black arrow. The white ellipse highlights a dolomite grain that has fragmented by shear. B. Evidence of ductile deformation. The white line dened the local foliation developed within the calcite matrix. The foliation is deected around large dolomite grains that cannot be incorporated into the foliation. A deformed pyrite is identied by the white ellipse. C. SEM image showing patchy foliation development in Dm75, (see the centre of the image where a narrow ow band occurs). The opaque mineral in top left hand corner (white) has been boudined and deformed around the more rigid dolomite grain. D. Closely packed, equiaxed to elongate cc-grains. Grain boundaries form triple junctions and are generally straight. Straight calcite grain boundaries and high aspect ratio dolomite grains dene foliation. Stretched, boudined phyllosilicate, centre-top. x z A Bx z 200 μm 200 μm 56 200 μm A x z x z 20 μm Figure 5.8 Dm51 deformed at high temperature; P1534; γ~4; 800˚C; 3x10-4 s-1. A. Foliation dened by dolomite grains with high aspect ratios (i.e. aspect ratios >1). Foliation deected around a coarse grained, fractured dolomite. Dashed white line shows foliation. B. Closely packed, equiaxed to tabular cc-grains. Grain boundaries form triple junctions and are gener- ally straight. Straight grain boundaries are oriented along foliation. Note signicant isolated porosity (small, black features) in A and B. A B porosity 57 58 While porosity is prevalent at calcite grain boundaries, porosity is visibly reduced with respect to the starting material. Porosity is more homogeneously distributed at triple junctions in the calcite matrix than in the starting material. Intracrystalline porosity (both pores and fractures) in dolomite remains largely unchanged and there is no evidence of fracture healing. Locally, there are regions of higher porosity within the calcite matrix aligned along foliation (Figure 5.5E and 5.5F). These regions form in pressure shadow-like geometries on the peripheries of some dolomite grains > 70 µm (Figure 5.6D). High dolomite content (Dm75): There is a poorly defined foliation in Dm75 defined by crude variation in grain size and fine-grained, high aspect ratio dolomite. On the sample scale, foliation is highlighted by deformed phyllosilicates and pyrites (Figure 5.5E). Dolomite grains are visibly rounded at this scale. There is evidence of brittle fracture in Dm75 including discontinuous slip surfaces sub-parallel to the shear zone boundary (as in Dm25; Figure 5.7A), Mode I cracks in individual dolomite grains (Figure 5.7A), and R1 Riedel shear fractures resulting in grain size reduction of dolomite (Figure 5.7A). However, narrow bands of deformed calcite deflected around more rigid dolomite attest to ductile deformation in the calcite aggregates (Figure 5.7B, 5.7C). Similar to Dm25 and Dm35, calcite grains are locally equiaxed to elongate, bounded by straight grain boundaries, which meet neighbouring calcite grains at triple junctions (Figure 5.7D). Straight grain boundaries are oriented along foliation. In particular, in narrow regions between dolomite grains, calcite grain boundaries are oriented parallel to the dolomite grain boundaries, irrespective of the global direction of maximum stretching (Figure 5.7D). While there are Mode I fractures and brittle deformation of dolomite, no fractures are observed propagating from dolomite and into the calcite matrix. Locally, a lineation is defined by reorientation of dolomite <20 µm. In particular, local foliation only incorporates dolomite grains <20 µm and wraps around coarser dolomite grains (Figure 5.7B and 5.7C), resulting in ribbons of foliation surrounding areas of coarse-grained dolomite (Figure 5.7C). Twinning is noted in some dolomite grains but this is relict from the starting material. When present, accessory pyrite and phyllosilicates, derived from the Badshot marble, are stretched and boudinaged reflecting the extension associated with shear strain (Figure 5.7D, centre-top). Intergranular porosity still exists but appears significantly reduced compared to the starting material. In contrast to low dolomite samples, there do not appear to be regions of localized porosity forming along foliation. 59 5.3.3 High Temperature Experiments At high temperature (800°C), calcite grains are closely packed and equiaxed to elongated. Straight grain boundaries parallel to the direction of shear are more defined than grain boundaries outside of this orientation. No local calcite clumps exist and there is no observed compositional banding. Foliation is more easily identified in the Dm51 than in the Dm75 sample deformed at 750°C due to the higher fraction of calcite. Bulk foliation is defined by high aspect ratio dolomite grains of all scales rotated into the direction of maximum elongation. Dolomite grains <50 µm define local foliation and are deflected around coarse-grained dolomite (Figure 5.8A). Dolomite grains < 50 µm are rounded. Intercrystalline porosity is present (Figure 5.8B), but as with deformed samples of Dm25, Dm35, and Dm75, it is reduced when compared to the starting material. Porosity is greatest at dolomite grain boundaries, but local concentrations of porosity along foliation are absent. 5.4 Texture Analyses 5.4.1 ! = ! Shear strain equal to 0 strain sample cuts of the deformed Dm25 (P1527) and Dm35 (P1524) samples were examined (see Figure 3.5). These sections intersect the centre of the deformed cores where there is zero rotation and therefore no shear strain (Paterson and Olgaard, 2000). However, these sections were exposed to the same experimental pressure and temperature conditions. In both the Dm25 (Figure 5.9) and Dm75 (Figure 5.10) there is a diffuse to poorly developed c-axis CPO developed in calcite grains. This may have developed during cold pressing of the starting powders (as suggested by Figures 4.7 and 4.8), or it is possible that the ! = 0 slices were offset from the sample centres and therefore record some strain. 5.4.2 Yield Experiments Yield experiments (Dm75 and Dm51) show non-existent to weak CPO development of the c-axis in calcite. CPO of the c-axis in calcite is diffuse for Dm51 (Figure 5.11), but locally developed for Dm75 (compare Figures 5.12B and 5.13B). The EBSD analysis of these deformed samples show little to no intracrystalline textural development (e.g. no twinning, no dislocation glide); in this regard (e.g., EBSD results) they are similar to the undeformed material. Calcite 60 grains are equiaxed and lack intracrystalline deformation. Similarly, dolomite grains show little intracrystalline deformation and porosity remains isolated and concentrated at grain boundaries. 5.4.3 High Strain Experiments All compositions taken to high strain at 750°C (Dm25, Dm35, and Dm75) show well- defined activation of the c-axis and a-axis slip systems in calcite (Figures 5.14B, 5.15B, and 5.16B). All stereonets have been corrected for the inclination of foliation to the shear boundary, and therefore all stereonets are displayed in the true kinematic plane of the sample. The c-axes girdles are well defined and symmetric along the direction of maximum shortening (the z-axis in the kinematic plane), indicating basal slip activation. With increasing dolomite content, the stereonet patterns become more diffuse, but remain well defined. In all cases, the c-axis system patterns are most pronounced, followed by the a-axis, r-axis, and f-axis systems. As in the c-axis system, the a-axis girdles are well defined but are symmetric about the direction of maximum stretching (x-axis). Two-dimensional grain size distributions from P1527 (Dm25) and P1538 (Dm75) (Figure 5.17) suggest possible calcite grain growth in Dm25 (from 5.5 to 7.5 µm) and possible calcite grain size reduction (from 4.5 to 3.5 µm) in Dm75. These changes in grain size are considered to be too small to have been mechanically induced and I conclude that there is neither grain growth nor grain size reduction in the deformed samples. None of the high strain experiments display a significant activation of any of the dolomite slip systems. This is confirmed by the absence of undulose extinction in optical thin section. Inverse pole maps for experiment P1538 (large strain, Dm75; Figure 5.16C) show minor undulosity in coarse dolomite grains, but most grains are composed of one even colour indicating no intracrystalline deformation. All deformed samples show shape preferred orientation (SPO), indicating rigid body rotation of high aspect ratio dolomite grains. As described above, this foliation development becomes difficult to identify in Dm75, but is nonetheless present. SPO demonstrates that in low dolomite content samples Dm25 (Figure 5.14) and Dm35 (Figure 5.15), high aspect ratio dolomite grains have become oriented with their long axes parallel to the direction of maximum stretching. 5.4.4 High Temperature Experiment At high temperature (experiment P1534), Dm51 shows a well-developed CPO in calcite along the c-axis perpendicular to foliation, suggesting the activation of basal slip (Figure 5.18B). 61 As with the high strain experiments carried out at 750°C, a defined CPO along the a-axis is also developed. The r- and f- patterns are diffuse and show no CPO development along those slip system. 5.4.5 Calcite Clumps For low dolomite content samples (i.e. Dm25 and Dm35), the pure calcite layers (an artifact of the sample preparation, see Figure 4.6) have the strongest crystallographic preferred orientations. This is illustrated in Figure 5.19 (a compilation of four EBSD scans across a calcite layer). It is clear that the calcite layer has a more defined CPO than the surrounding calcite- dolomite composite (Figure 5.19B). Figure 5.19C shows a region scanned ~600 µm away from the calcite layer. The stereographic projections of the calcite slip systems are identical to the general observations above. Figure 5.19D is of an area adjacent to the calcite band margin (~100 µm away from the calcite band), which still contains dolomite grains. The calcite is evidently more texturally evolved than that found apart from the band; the calcite slip system girdles are more defined and asymmetric, indicating the sense of shear. Finally, Figure 5.19E lies within the calcite band. The slip system girdles are well defined and asymmetrical with respect to the maximum shortening direction. In particular, the c-axis girdle is oriented such that it indicates the sinistral shear sense used in the experiments. Calcite Dolomite A B C SZB z SZB z SZB z 20 μm 20 μm 40 μm40 μm 25%-Dm - Experiment P1527 Conditions: T = 750˚C Strain rate: 0 s-1 γ = 0 SZB SZB z z zz SZB SZB z z zz Figure 5.9 EBSD analaysis of 0-strain, Dm25. A. Experimental conditions; Pc = 300 MPa. Low magnication BSE image, with inset of the EBSD scan area to scale. The sample is oriented such that the shear zone boundary (SZB) (i.e. the top and bottom of the deformed samples) is horizontal and the z is the direction of axial load in the deformation rig. This convention diers from the coordinate system used in deformed samples as the sample has not been strained. B. Calcite: Inverse pole gure (top); upper hemisphere contoured stereoplots (bottom) for the c, r, a, and f slip systems, clockwise from top left. C. Dolomite: Inverse pole gure (top); upper hemisphere contoured stereoplots (bottom) for the c, r, a, and f slip systems, clockwise from top left. Blackened portions of the IPFs are components of dierent phases, not indexed. See text for details. 62 Calcite Dolomite A B C 20 μm 100 μm 40 μm 40 μm x x x x z z zz x x x x z z zz SZB z SZB z SZB z 75%-Dm - Experiment P1538 Conditions: T = 750˚C Strain rate: 0 s-1 γ = 0 Figure 5.10 EBSD analaysis of 0-strain, Dm75. A. Experimental conditions; Pc = 300 MPa. Low magnication BSE image, with inset of the EBSD scan area to scale. The sample is oriented such that the shear zone bound- ary (SZB) (i.e. the top and bottom of the deformed samples) is horizontal and the z is the direction of axial load in the deformation rig. This convention diers from the coordinate system used in deformed samples as the sample has not been strained. B. Calcite: Inverse pole gure (top); upper hemisphere contoured stereo- plots (bottom) for the c, r, a, and f slip systems, clockwise from top left. C. Dolomite: Inverse pole gure (top); upper hemisphere contoured stereoplots (bottom) for the c, r, a, and f slip systems, clockwise from top left. Blackened portions of the IPFs are components of dierent phases, not indexed. See text for details. 63 xz x z Calcite Dolomite A B C x z x z 20 μm100 μm 70 μm70 μm x x x x z z zz x x x x z z zz 51%-Dm - Experiment P1528 Conditions: T = 750˚C Strain rate: 3x10-4 s-1 γ = 0.21 Figure 5.11 EBSD analaysis of yield experiments, Dm51. A. Experimental conditions; Pc = 300 MPa. Low magnication BSE image, with inset of the EBSD scan area to scale. The cooridante system refers to the orientation of the kinematic plane, where x is the direction of maximum stretching and z is the direction of maximum shortening. B. Calcite: Inverse pole gure (top); upper hemisphere contoured stereoplots (bottom) for the c, r, a, and f slip systems, clockwise from top left. C. Dolomite: Inverse pole gure (top); upper hemi- sphere contoured stereoplots (bottom) for the c, r, a, and f slip systems, clockwise from top left. Blackened portions of the IPFs are components of dierent phases, not indexed. See text for details. 64 xz Calcite Dolomite A B C 100 μm 100 μm 200 μm200 μm x x x x z z zz x x x x z z zz x z x z 75%-Dm - Experiment P1525 Conditions: T = 750˚C Strain rate: 3x10-4 s-1 γ = 0.16 Figure 5.12 EBSD analysis of yield experiment, Dm75. A. Experimental conditions; Pc = 300 MPa. Low magni- cation BSE image, with inset of the EBSD scan area to scale. The coordinate system refers to the orientation of the kinematic plane, where x is the direction of maximum stretching and z is the direction of maximum shortening. B. Calcite: Inverse pole gure (top); upper hemisphere contoured stereoplots (bottom) for the c, r, a, and f slip systems, clockwise from top left. C. Dolomite: Inverse pole gure (top); upper hemisphere contoured stereoplots (bottom) for the c, r, a, and f slip systems, clockwise from top left. Blackened portions of the IPFs are components of dierent phases, not indexed. See text for details. 65 xz Calcite Dolomite A B C x z 20 μm 20 μm 45 μm x x x x z z zz x x x x z z zz x z 45 μm Figure 5.13 EBSD analysis of yield experiment, Dm75. A. Experimental conditions; Pc = 300 MPa. Low magni- cation BSE image, with inset of the EBSD scan area to scale. The coordinate system refers to the orientation of the kinematic plane, where x is the direction of maximum stretching and z is the direction of maximum shortening. B. Calcite: Inverse pole gure (top); upper hemisphere contoured stereoplots (bottom) for the c, r, a, and f slip systems, clockwise from top left. C. Dolomite: Inverse pole gure (top); upper hemisphere contoured stereoplots (bottom) for the c, r, a, and f slip systems, clockwise from top left. Blackened portions of the IPFs are components of dierent phases, not indexed. See text for details. 75%-Dm - Experiment P1525 Conditions: T = 750˚C Strain rate: 3x10-4 s-1 γ = 0.16 66 xz Calcite Dolomite x z x z A B C 100 μm 100 μm 100 μm100 μm x x x x z z zz x x x x z z zz 25%-Dm - Experiment P1527 Conditions: T = 750˚C Strain rate: 3x10-4 s-1 γ ~ 5 Figure 5.14 EBSD analysis of high strain experiment, Dm25. A. Experimental conditions; Pc = 300 MPa. Low magnication BSE image, with inset of the EBSD scan area to scale. The coordinate system refers to the orientation of the kinematic plane, where x is the direction of maximum stretching and z is the direction of maximum shortening. B. Calcite: Inverse pole gure (top); upper hemisphere contoured stereoplots (bottom) for the c, r, a, and f slip systems, clockwise from top left. C. Dolomite: Inverse pole gure (top); upper hemisphere contoured stereoplots (bottom) for the c, r, a, and f slip systems, clockwise from top left. Blackened portions of the IPFs are components of dierent phases, not indexed. See text for details. 67 xz x z Calcite Dolomite A B C 100 μm x x x x z z zz x x x x z z zz x z x z 100 μm 100 μm 100 μm 35%-Dm - Experiment P1524 Conditions: T = 750˚C Strain rate: 3x10-4 s-1 γ ~ 5 Figure 5.15 EBSD analysis of high strain experiment, Dm35. A. Experimental conditions; Pc = 300 MPa. Low magnication BSE image, with inset of the EBSD scan area to scale. The coordinate system refers to the orientation of the kinematic plane, where x is the direction of maximum stretching and z is the direction of maximum shortening. B. Calcite: Inverse pole gure (top); upper hemisphere contoured stereoplots (bottom) for the c, r, a, and f slip systems, clockwise from top left. C. Dolomite: Inverse pole gure (top); upper hemisphere contoured stereoplots (bottom) for the c, r, a, and f slip systems, clockwise from top left. Blackened portions of the IPFs are components of dierent phases, not indexed. See text for details. z 68 xz Calcite Dolomite A B C x x x x z z zz x x x x z z zz x z x z 100 μm100 μm 200 μm200 μm 75%-Dm - Experiment P1538 Conditions: T = 750˚C Strain rate: 3x10-4 s-1 γ ~ 5 Figure 5.16 EBSD analysis of high strain experiment, Dm75. A. Experimental conditions; Pc = 300 MPa. Low magnication BSE image, with inset of the EBSD scan area to scale. The coordinate system refers to the orientation of the kinematic plane, where x is the direction of maximum stretching and z is the direction of maximum shortening. B. Calcite: Inverse pole gure (top); upper hemisphere contoured stereoplots (bottom) for the c, r, a, and f slip systems, clockwise from top left. C. Dolomite: Inverse pole gure (top); upper hemi- sphere contoured stereoplots (bottom) for the c, r, a, and f slip systems, clockwise from top left. Blackened portions of the IPFs are components of dierent phases, not indexed. See text for details. 69 100 101 102 103 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Grain Size (�m) Ar ea F ra ct io n Dm−25 Dm−75 100 101 102 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 Grain Size (�m) Ar ea F ra ct io n Dm−25 Dm−75A B μ μ Figure 5.17 Area fraction grain size distributions of high strain experiments. A. Grain size distri- butions of calcite for Dm25 (P1527) and Dm75 (P1538). B. Grain size distributions of dolomite for Dm25 (P1527) and Dm75 (P1538). 70 xz Calcite Dolomite A B C x z x z 100 μm100 μm 20 μm100 μm x x x x z z zz x x x x z z zz 51%-Dm - Experiment P1534 Conditions: T = 800˚C Strain rate: 3x10-4 s-1 γ ~ 4 Figure 5.18 EBSD analysis of high temperature experiment, Dm51. A. Experimental conditions; Pc = 300 MPa. Low magnication BSE image, with inset of the EBSD scan area to scale. The coordinate system refers to the orientation of the kinematic plane, where x is the direction of maximum stretching and z is the direction of maximum shortening. B. Calcite: Inverse pole gure (top); upper hemisphere contoured stereoplots (bottom) for the c, r, a, and f slip systems, clockwise from top left. C. Dolomite: Inverse pole gure (top); upper hemisphere contoured stereoplots (bottom) for the c, r, a, and f slip systems, clockwise from top left. Blackened portions of the IPFs are components of dierent phases, not indexed. See text for details. 71 100um B C D E A Figure 5.19 Crystallographic preferred orientation development near calcite clumps. A. BSE image of Dm25 sample deformed to γ~5.5 (see Table 5.1; P1527). A deformed calcite aggre- gate is outlined in red. B. IPF and upper hemisphere stereonet projection of the major slip systems in calcite across the deformed calcite band. C. IPF and steronet projection of calcite in a region removed from the calcite band. D. IPF and stereonet projections of a region adjacent to the calcite band, but including dolomite grains. E. IPF and stereonet projection of a region within the calcite band. EDC B 70 μm 50 μm 200 μm 100 μm 25%-Dm γ~5.5 x z x x x x z z zz x x x x z z zz x x x x z z zz x x x x z z zz 72 73 5.5 Chemical Changes Attending Deformation 5.5.1 Energy-dispersive X-ray Spectroscopy Energy-dispersive X-ray spectroscopy (EDS) analysis used to assist EBSD analysis of the calcite and dolomite phases highlights slight changes in composition with increasing strain. In particular, the Mg content of calcite increases with increasing strain. This is most pronounced in calcite grains proximal to dolomite phases. Figure 5.20 demonstrates the evolution of magnesium transfer from γ=0 to the largest strains for Dm-25 (!~5.5). Magnesium is restricted to dolomite grains at γ=0. With increasing strain magnesium becomes more easily mobilized and is observed in calcite proximal to dolomite grains. 5.5.2 Microprobe I performed microprobe analysis on Dm25 and Dm75 samples deformed to high strain (experiments P1527 and P1538) to confirm EDX observations of Mg2+ migration from dolomite to calcite during deformation (Figure 5.21). Microprobe analysis confirms a depletion of Mg2+ in fine-grained dolomite proximal to calcite in Dm25, however, calcite removed from dolomite grain boundaries is not enriched (yellow points). Mg-enrichment of calcite is pervasive in Dm75, owing to the abundance of dolomite throughout the system. Mg-enrichment is observed throughout the sample, regardless of proximity to thin ribbons of plastically deformed calcite. γ~0 γ~5.5γ~2.25 x z x z 100 μm 200 μm 200 μm 0 186 0 201 0 144 Figure 5.20 Energy-dispersive X-ray spectroscopy (EDS) maps of magnesium concentration for experiment P1527. Dm25 deformed in torsion at Pc=300MPa, T=750˚C, and strain rate 3*x0-4 s-1. Dark green grains are dolomite. The calcite matrix contains very little magnesium and, therefore, is light green. For γ=0, there is little magnesium contained within the matrix. With increasing strain, Mg concentrations increase in the matrix. This only occurs in regions of the sample with locally signicant dolomite content. With increasing strain, Mg becomes more concentrated along the developing foliation of the sample. 74 100 μm 20 μm 2 A B Figure 5.21 Microprobe analysis maps. Data from Table A.D1 is plotted as follows: yellow points represent Cc (0.90 1) are rotated such that their long axes help to define a foliation. In dolomite-poor run products, dolomite grains show no change in grain size, nor is there any qualitative increase in crack density within the grains. These observations indicate that brittle deformation (e.g. microcracking and shear fracturing) has not accommodated significant strain. Rounding of dolomite grains <~ 50 µm in diameter is observed in all dolomite-poor deformed samples. In contrast, Dm75 run products contain abundant Mode I cracks and shear fractures within dolomite. All dolomite grains are visibly sub-rounded to rounded and some dolomite grains are offset by R1 Riedel shears, resulting in grain size reduction. There is no well-developed CPO in dolomite from deformed samples, nor is there pervasive undulose extinction, although Dm75 shows minor undulose extinction in coarse dolomite. Therefore, dolomite did not accommodate strain by intracrystalline plasticity. 79 Diffusion processes were active, as indicated by the movement of Mg2+ from dolomite to calcite. Mg2+ enrichment in calcite is localized around rounded dolomite grains < ~50 µm suggesting solid-state diffusive processes must be operative. 6.2 Deformation Mechanisms 6.2.1 Dislocation Creep with Dynamic Recrystallization The development of crystallographic preferred orientations (CPOs) in geologic materials requires intracrystalline deformation and is expected to develop under a) low homologous temperatures (T/Tm, where Tm is the absolute melting temperature of the phase) and/or high strain rates, or b) conditions where recrystallization is dominant (Wenk et al., 1990). The microstructure associated with a CPO typically shows evidence of extensive undulose extinction, subgrain development, and the generation of dynamically recrystallized grains. My experiments operated at high homologous temperatures for calcite and moderate strain rates. The calcite matrices comprise small, equidimensional, polygonal, strain-free calcite grains, which are not typically associated with dislocation creep. Additionally, there is no evidence of dynamic recrystallization; grain size distributions of the starting and deformed materials show no change in calcite grain size. Thus, microstructural observations suggest that steady state was not achieved in my experiments by dislocation creep and associated dynamic recrystallization. Rather, the microstructures are indicative of those formed by grain boundary sliding processes (Schmid et al., 1977). However, intracrystalline deformation mechanisms (i.e. dislocation glide +/- climb or cross slip) must be active in calcite to generate slip on the calcite slip systems, as shown by EBSD data (Rutter et al., 1994; Schmid et al., 1987). Despite this, there is no evidence to suggest that these mechanisms are dominant. The mechanical and microstructural evidence suggests superplastic flow accommodated by intracrystalline plasticity as the dominant deformation behaviour, as discussed in the following section. 6.2.2 Superplastic Flow and Calcite Superplasticity, or superplastic flow, is a metallurgic term that refers to exceptional ductility in tensile tests, where elongation exceeds 1000% without necking and subsequent failure (Langdon, 2006). It is a grain size sensitive mechanism – that is, it favours small grain sizes. Superplasticity is characterized by nearly Newtonian flow (n = 1) and is observed for temperatures >0.5 the homologous temperature. Superplasticity is characterized by n-values 80 between 1 and 3 for constitutive equations of the form ! ∝ !!, and microstructurally, grains are equiaxed, polygonal, strain free, and generally less than 10 microns in diameter. Superplasticity does not specify a deformation mechanism, but rather refers to a macroscopic behavior. Grain boundary sliding (GBS) is a dominant mechanism in superplastic flow (Edington et al., 1976; Schmid et al., 1977). Grain boundary sliding refers to the movement of grains at or in the vicinity of their interfaces in response to an external stress (Langdon, 2006). It cannot accommodate displacement on its own because of irregularities in the grain boundaries and, especially, at the junctions where more than two grains meet (Schmid et al., 1977). Typically, GBS occurs with 1) the diffusion of material as required for accommodation (including grain boundary diffusion; Ashby and Verrall (1973)); or 2) plastic deformation of grains (i.e. glide of dislocations; Mukherjee (1975)). Grain boundary sliding accommodated by dislocation creep or glide is known as Rachinger sliding (Langdon, 2006). Rashinger sliding requires grain sizes below 10 µm and temperature greater than 0.5T/Tm. This process results in strain free, equiaxed grains with a developed CPO due to dislocation creep accommodating deformation in polycrystalline materials. Grain boundary sliding accommodated by diffusion, either grain boundary diffusion or intragranular diffusion, is known as Lifshitz sliding (Langdon, 2006). This process results in elongate grains due to mass transfer from areas of high stress to areas of low stress. Grain boundary sliding also encourages chemical exchange between phases, since neighbouring grains are constantly moving past one another (Herwegh et al., 2003). The microstructure of calcite in all run products in this study supports superplastic flow of calcite aggregates. Grain boundary diffusion is required to explain the subtle elongation of calcite grains and the solid-state diffusion processes that accommodate Mg2+ movement from dolomite into calcite. Dislocation glide is required to explain the well-developed CPO of c- and a-slip. There is scarce work published on the deformation behaviour of Cc-Dm composites. Delle Piane et al. (2009a) used the same torsion rig and experimental conditions (i.e. Pc, T, strain rate) used in this study to deform Cc-Dm mixtures with ~ 9 %-Dm and 38 %-Dm. The major difference between the two studies, is that dolomite and calcite in Delle Piane et al. (2009a) have grain sizes of ~ 10 µm. Delle Piane et al. (2009) report near-Newtonian creep at 700°C with a stress exponent of n~1.7 and peak shear stresses of ~90 MPa and ~140 MPa for 9%-Dm and 38%-Dm, respectively. Both calcite and dolomite phases have strong c-axis preferred orientation 81 inclined to the shear direction. Shape preferred orientation was not found to be significantly dependent on strain. Individual grains are internally strain free and grain boundaries are straight and aligned. They interpret that grain boundary sliding and diffusion processes were dominant and accommodated, in part, by dislocation activity. Thus, at fine grain sizes, calcite and dolomite have similar strengths when deforming by superplastic flow. The Delle Piane et al. (2009a) experiments support the observations of diffusion creep in fine-grained dolomite in this study. 6.2.3 Calcite Clumps: Analogues for Veins in Nature? Compositionally homogeneous calcite bands accumulated the same calculated shear strain as the surrounding Cc-Dm host. However, EBSD analysis showing stronger CPOs in these regions and the presence of deflected foliations suggest strain partitioning. Strain partitioning may occur because compositionally homogeneous regions are more easily deformed as grain boundary pinning is not encouraged (Olgaard, 1990), resulting in maintaining the initial compositional zoning of the samples. Areas rich in dolomite possibly accommodated less displacement (i.e. are less sheared) than monomineralic layers of calcite. While these calcite regions are artifacts of the sample preparation, they provide an interesting analog for calcite veins in nature that are observed to absorb more strain than surrounding material (Kennedy and White, 2001). Low chemical potential gradients between single phase grains inhibit diffusion processes, leading to the activation of dislocation glide and, ultimately, back-stressing from the pileup of dislocations at grain boundaries, resulting in a population of strain free grains with similar CPO. This effect is more pronounced in pure calcite regions of Dm25 and Dm35 because the chemical potential gradients between grains are such that diffusion processes are curtailed (Kennedy and White, 2001). 6.2.4 The Role of Dolomite: Brittle and Ductile Behaviour Small quantities of Mg2+ in calcite limit grain growth, thereby keeping grain size sensitive diffusion creep and grain boundary sliding operative during deformation (Herwegh et al. (2003). Herwegh et al. (2003) found that calcite grain size is inversely proportional to Mg- content, resulting in an extrinsic control on strength as calcite grain growth is inhibited. In my experiments, Mg2+ migration from dolomite to calcite confirms that diffusion creep processes occurred during deformation, and this may have contributed to the maintenance of small grain size throughout the duration of the experiments. With respect to quartz-calcite composites, the addition of quartz significantly increases the flow stress needed for steady state deformation 82 (Rybacki et al., 2003). That study suggests that the incorporation of Si into the dislocation cores of calcite is responsible for the increase in flow strength of calcite. It is unknown if a similar driving force exists in the Cc-Dm system, though this cannot be excluded due to the evidence for Mg2+ migration during deformation. In samples containing < 51% dolomite, the coarse grained dolomite grains show no evidence of extensive brittle deformation or intracrystalline deformation. Finer grained dolomite (< 50 µm) that have aspect ratios >1 are rotated into the foliation, indicating their active role as rotating rigid bodies. Although the calcite deforms by superplastic flow and accommodates most strain, these composite rocks are stronger than 100% calcite of the same grain size and deformed under similar experimental conditions, see Figure 6.2 (Schmid et al., 1987). I speculate that although the dolomite grains are not deformed, the distributed presence of these rigid bodies acts to create anastomosing, connected networks of calcite grains. In effect, the dispersed dolomite grains provide local resistance to grain boundary sliding and this resistance results in an increase in the flow stress necessary for steady state deformation. Strength increases with Dm51, yet only minor brittle deformation of dolomite is observed. However, there is a marked increase in strength in Dm75. In Dm75, dolomite forms connected grain networks that support most of the load. I interpret that the high yield stress of Dm75 is a result of Dm-Dm contact initially supporting the load. Subsequent reorganization of Dm-Dm contacts by Mode I and shear fractures leads to weakening and the establishment of flow networks in the fine-grained calcite. Steady state is only achieved when the calcite and fine- grained dolomite establish a grain boundary network for grain boundary sliding to occur. The increase in shear stress at high strain may result from the inhibition of these flow networks and brittle deformation of dolomite. The re-establishment of the calcite networks leads to the final strain weakening (refer to Figure 6.1D). Similar behaviour is proposed in the strong phase of other multi-phase systems (e.g. quartz-calcite; Rybacki et al. (2003)). Dm75 composites are weaker than 100% dolomite deformed under similar conditions (Figure 6.3), attesting to the role of the calcite networks in weakening the rocks. Thus, with increasing dolomite content, the composites are stronger. There are two distinctly different types of deformation mechanisms occurring in parallel (or in series, it is difficult to assess) during shearing: brittle failure of dolomite by Mode I cracks, shear fractures, and subsequent grain size reduction (all of which are pressure-dependent mechanisms) and superplastic flow of calcite (which is more temperature- and grain size-dependent). 0 2 4 6 8−1 −0.5 0 0.5 1 1.5 2 2.5 −log10 Strain rate (s −1) lo g 1 0 D iff er en tia l s tre ss (M Pa ) Regime 1 Regime 2 Regime 3 600˚C 700˚C 900˚C 800˚C Figure 6.2 Comparison of study data with the reported deforma- tion behaviour of Solnhofen limestone. Log-log plot of the dier- ential stress vs. strain rate for compression deformation experi- ments on Solnhofen limestone (Schmid et al., 1977). Regime 1: Exponential relationship between strain rate and stress; Regime 2: Power-law creep; Regime 3: Superplasticity. Regimes 1 and 2 are characterized in the microstructure by dislocation glide and/or dislocation creep. Regime 3 is characterized in the microstructure by grain boundary sliding. Red stars indicate data from this study. With increasing dierential stress, these stars represent the peak strengths of Dm25, Dm35, Dm51, and Dm75. The green and blue stars indicate the peak stress for Solnhofen limestone deformed by torsion to high strains at 700˚C and 800˚C, respectively (Schmid et al., 1987). 83 Figure 6.3 Comparison of study data with reported deformation behav- iour of Madoc dolomite. Deformation map for 100 μm dolomite. The stress-temperature eld for synthetic dolomite experiments is shown by the shaded box. (Davis et al., 2008). Experiment P1538 (Dm75, taken to high strain) is plotted as a red star and lies in the diusion creep eld. The green star represents the dierential stress of Madoc dolomite (grain size = 240 μm) at 700˚C (Davis et al., 2008). Crystal Plasticity and Twinning Dislocation Creep Diusion Creep 100 300 500 700 900 1000 100 10 1 0.1 -1 σ1 -σ 3 ( M Pa ) T (˚C) 10-14 s-1 10-10 s-1 10-8 s-1 10-6 s-1 10-5 s-1 10-14 s-1 84 85 My data suggest that for dolomite contents below a minimum of 35%, dolomite does not actively deform, but its presence is rate-controlling given the strength of the composites compared to micritic limestone (Figure 6.1). Only when dolomite is present in sufficient quantities (>51 %) to inhibit the flow of calcite and/or restrict calcite flow to narrow, localized bands does brittle fracture of dolomite grains become mechanically significant in accommodating strain. 6.3 Application to Natural Systems Calcite and dolomite coexist in many fault systems (e.g. the Apennines, Italy and the Canadian Rocky Mountains, Canada). Generally, at greenschist facies and lower conditions, dolomite is coarser grained and is found within variably dolomitized fine-grained micritic limestones (Figure 6.4). Only recently has a global interest in the role of dolomite on the mechanical behaviour of these systems arisen, particularly with respect to fault strength. The Portoro horizon in the Gulf of La Spezia (Isola Palmaria), Italy, is composed of a micritic limestone that has been partially dolomitized and crosscut by calcite and dolomite grains (Figure 6.4). Dolomitized layers impede propagation of deformation into the protolith, and deformation is restricted to the micritic mylonite (Taini, 2003). I conclude from this study that coarse grained dolomite in a micritic calcite matrix has a profound effect on the strength of composite materials, even at low concentrations (i.e. 25%- Dm). The strengths of low-dolomite (Dm25 and Dm35) samples in this study are far stronger than 100% micritic calcite, since dolomite grains inhibit the superplastic flow of calcite aggregates. In natural systems, this may result in the locking of high-dolomite content faults, and stress being transferred to other faults with minimal dolomite content. 6.4 Summary Strain localization in this study results from the contribution of different deformation mechanisms in calcite and dolomite. In particular, grain boundary sliding assisted by dislocation and diffusion creep are the primary mechanisms accommodating strain in the low dolomite content Cc-Dm composites; brittle deformation processes become increasingly important with increasing dolomite content. Figure 6.4 Field examples of coexistant micrite and dolomite, Toscana Strata of the Apennines in the Gulf of La Spezia. Dark, ne grained bands are micrite. Dolomite is light coloured. The dolomite is relatively coarse- grained (between 60 μm and 150 μm). Dolomotization is irregular. (Taini, 2003). 20 cm 86 87 Chapter 7: Conclusions In this study strain localization in calcite-dolomite (Cc-Dm) composites is established by the operation of different deformation mechanisms in calcite and dolomite. This disparate behaviour is fundamentally related to dolomite grain size, where fine-grained calcite and dolomite deform by grain boundary sliding assisted by diffusion and dislocation creep and coarse grained dolomite deforms by brittle processes. In this system, especially in high dolomite content samples (Dm75), grain boundary sliding of fine-grained calcite and dolomite is periodically inhibited by clusters of coarse-grained dolomite contact; this leads to strain hardening. Upon fracture and reorganization of dolomite grains, grain boundary sliding networks in calcite are re-established and the rocks experience strain weakening as displacement is by calcite, rather than by brittle deformation of strong dolomite. Even with low Dm% content, the presence of dolomite grains acts to increase the strength of shear zones, presumably because the material must flow around rigid bodies. The main conclusions of this study are listed below: • Dolomite inherently changes the strength of carbonate composites – as dolomite content increases, the mechanical strength of the composites increases. o Peak yield strengths for Dm25 and Dm35 were ~79 MPa. o Peak yield strengths of ~140 MPa and ~178 MPa were observed for Dm51 and Dm75, respectively. • Calcite absorbs most of the deformation by grain boundary sliding assisted by dislocation and diffusion creep. • A stress exponent, n, (from the power law creep law: ! = !!!!!!!") of 2 was determined from a shear strain rate experiment conducted on Dm35; given the similar behaviour of Dm25 and Dm35, the n-value is assumed to be appropriate for both compositions. • The interplay between superplastic flow in calcite and brittle failure in dolomite means that any calculated stress exponent, n, for Dm75 is invalid as deformation of Dm75 requires both brittle and ductile deformation processes. • The mechanical data suggest that a mechanical threshold, defined by composition, exists in Cc-Dm composites. 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Geol., v. 96, p. 351- 361. 94 Appendix A: Matlab Code A.1 Grain Size Analysis %% Processes data from Mastersizer 2000 grain size analysis close all clear all %% load vol% grain size analysis file A = importdata('Kushnir_Calcite_Pure_for_Matlab.txt') %% assign grain size analysis data data_grains = A; bins = data_grains(1,:) %% converting from vol% to number% vol_percent_cc = mean(data_grains(2:end,:)); radius = bins/2; volume = (4/3)*pi*radius.^3; n = vol_percent_cc./volume; tot = sum(n); num_percent_cc = n/tot*100; %% plot vol% and num% save('Cc','vol_percent_cc','num_percent_cc') %plot(bins,vol_percent) % plotyy(bins,vol_percent,bins,num_percent) %axis([0 50 0 10]) A.2 Paterson Deformation Analysis A.2.1 Torsion_data_processing_n_factor.m %% Code loads strain rate stepping experiment and plots pre-defined strain %% rates and the internal torques of Dm35 once the sample has reached %% steady state at a given strain rate % Load torsion data and plot desired parts of curve. close all A = importdata('P1529_D_35_C_4_stepping_expt_only.txt','\\t') data = A.data; time = data(:,1); %Paterson time (seconds from start of day) time_real = (time-time(1))*86400; %convert to real time (s) time_hours = time_real./60./60; %convert to hours time_zero = time_hours - time_hours(6000); temp = data(:,2); %degC Pc = data(:,3); %MPa intForce= data(:,4); torsionPos = data(:,5); intTorque_un_zero = data(:,6); 95 intTorque = intTorque_un_zero - intTorque_un_zero(6300); extTorque = data(:,7); intAxialPos = data(:,8); extAxialPos = data(:,9); extForce = data(:,10); %% define constants w = 219; % revolutions/min d = 15.00; % diameter (mm) l = 10.00; % sample length (mm) %gammaDot = 3*10^-4; % sample shear rate (/s) - at outer edge of sample % strain rates gammaDot = [1*10^-5 5*10^-5 7*10^-5 1*10^-4 3*10^-4]; % time at which strain rates were set/changed Time = [0 46 126 151 169 186 226] ./ 60; %plot time vs. internal torque plot(time_zero(6000:20000),intTorque(6000:20000)) % internal torque recorded as steady state is reached at each strain rate Mint = [intTorque(2337) intTorque(8552) intTorque(9690) intTorque(10618) intTorque(12056)]; figure(2) plot(log(Mint),log(gammaDot),'.') %loglog(log(Mint),log(gammaDot),'.') %plot(log10(gammaDot),log10(Mint),'.') %% User must fit the log-log plot of strain rate vs. internal torque; the %% slope of the linear fit is the stress exponent, n. For Dm35, n=2. A.2.2 Torsion_load_data.m function [time_real,temp,Pc,intForce,torsionPos,intTorque,extTorque,intAxialPos,extAxi alPos,extForce] = torsion_load_data %% tosion_load_data.m - script for user-controlled loading of raw torsion %% data %% load RAW file [filename, pathname, filterindex] = uigetfile('*.*', 'Pick RAW file'); full_name = fullfile(pathname,filename); uiimport(full_name); display('Press any key to continue script.'); pause; data_tor = data; %% Assigning variables time = data_tor(:,1); %Paterson time (seconds from start of day) temp = data_tor(:,2); %degC Pc = data_tor(:,3); %MPa intForce= data_tor(:,4); torsionPos = data_tor(:,5); intTorque = data_tor(:,6); 96 extTorque = data_tor(:,7); intAxialPos = data_tor(:,8); extAxialPos = data_tor(:,9); extForce = data_tor(:,10); %% Converting Paterson time to real time in seconds from start of %% experiment time_real = (time-time(1))*86400; %convert to real time (s) A.2.3 Torsion.m function torsion(filename) %% function loads torsion raw data and converts internal torque to stress %% using a power-law creep equation from Paterson and Olgaard, 2000 %% load RAW file [time_real,temp,Pc,intForce,torsionPos,intTorque,extTorque,intAxialPos,extAxi alPos,extForce] = torsion_load_data %% load sample dimensions and experimental strain rate diam = input('Core diameter (in mm):'); d = diam/1000; %in m len = input('Core length (in mm):'); strnrt = input('Strain rate (in 1/s):'); tor = input('Sample diamter ~15mm? - 1 = yes; 2 = no'); %% convert time to hours, if you care time_hours = time_real./60./60; %convert to hours %% Define n for power law n = 2; % from stepping experiment... %% zero plot %plot(time_hours,intTorque) %[time_0,x,y] = selectdata('selectionmode','closest','verify','on') time_zero = time_real - time_real(1); intTorque_zero = intTorque - intTorque(1); plot(time_zero,intTorque_zero,'.r') %% Iron jacket correction from Barnhoorn PhD thesis 2003 (Appendix C) % parameters for iron jacket at 750C 3*10^-4 1/s % if tor == 1 % intJacketTorque = 2.8; % else % intJacketTorque = 1; % end %parameters for iron jacket at 750C 1*10^-4 1/s if tor == 1 intJacketTorque = 2.4; else 97 intJacketTorque = 0.9; end % parameters for iron jacket at 800C 3*10^-4 1/s % if tor == 1 % intJacketTorque = 1.4; % else % intJacketTorque = NaN; % end %jacket correction intTorque_corr = intTorque_zero - intJacketTorque; %% process for strain strain = strnrt*time_zero; shear_stress = (4*intTorque_corr*(3+(1/n))) ./ (pi * d^3); semilogy(strain, shear_stress) xlabel('Strain') ylabel('Shear Stress') save(filename,'strain','shear_stress') A.3 Microprobe Analysis %% Microprobe anaylsis for Mg content of carbonates %load datafile from Edith %% load RAW file [filename, pathname, filterindex] = uigetfile('*.*', 'Pick RAW file'); full_name = fullfile(pathname,filename); uiimport(full_name); display('Press any key to continue script.'); pause; %% data_micro = data; data_micro_oxide = data(:,[2 4:end]); % C O Mg Ca Mn Fe b = ones(length(data_micro_oxide),8); %% OxMolWeight = [44.00964 40.32 56.08 70.94 71.85]; % CO2 MgO CaO MnO FeO catNumPerOx = [1 1 1 1 1]; % CO2 MgO CaO MnO FeO anNumPerCat = [2 1 1 1 1]; % CO2 MgO CaO MnO FeO for i = 1 : length (data_micro_oxide); % calculate cation proportions catProp = data_micro_oxide(i,:) .* catNumPerOx ./ OxMolWeight; % cation norm (4) catNorm = catProp .* 4 ./ sum(catProp); % predicted anion total 98 anionTot = catNorm .* anNumPerCat; % anion sum anionSum = sum(anionTot); % sum of x-site cations catSum = sum(anionTot(2:end)); % Ca fraction xCa = catNorm(3) / catSum; %Mg fraction xMg = catNorm(2) / catSum; b(i,:) = [anionTot catSum xCa xMg]; end %% text = textdata(2:end,1); P1527 = b(3:44,:); P1538 = b(45:165,:); standards = b([1,2,166:169],:); figure(1) plot(standards(:,2),'g.') hold on plot(P1527(:,2),'b.') title('P1527 Mg Content') figure(2) plot(standards(:,2),'g.') hold on plot(P1538(:,2),'b.') title('P1538 Mg Content') %% save file save('Microprobe.txt','text','b','-ascii', '-tabs' ) 99 Appendix B: X-ray Diffractograms All XRD data are presented here, including the Rietveld analysis of the starting powders, Rietveld analysis of the starting HIP materials, and smear mount XRD of the deformed run products. All analyses confirm that decarbonation did not produce enough periclase (MgO) or lime (CaO) to be detected. 100 B.1 Starting Powders Dolomite Powder: 0.09% calcite; 99.76% dolomite Calcite Powder: 99.04% calcite; 0.87% dolomite 807876747270686664626058565452504846444240383634323028262422201816141210864 33,000 32,500 32,000 31,500 31,000 30,500 30,000 29,500 29,000 28,500 28,000 27,500 27,000 26,500 26,000 25,500 25,000 24,500 24,000 23,500 23,000 22,500 22,000 21,500 21,000 20,500 20,000 19,500 19,000 18,500 18,000 17,500 17,000 16,500 16,000 15,500 15,000 14,500 14,000 13,500 13,000 12,500 12,000 11,500 11,000 10,500 10,000 9,500 9,000 8,500 8,000 7,500 7,000 6,500 6,000 5,500 5,000 4,500 4,000 3,500 3,000 2,500 2,000 1,500 1,000 500 0 -500 -1,000 Calcite 0.09 % Dolomite 99.76 % Quartz 0.15 % 807876747270686664626058565452504846444240383634323028262422201816141210864 22,000 21,500 21,000 20,500 20,000 19,500 19,000 18,500 18,000 17,500 17,000 16,500 16,000 15,500 15,000 14,500 14,000 13,500 13,000 12,500 12,000 11,500 11,000 10,500 10,000 9,500 9,000 8,500 8,000 7,500 7,000 6,500 6,000 5,500 5,000 4,500 4,000 3,500 3,000 2,500 2,000 1,500 1,000 500 0 -500 Calcite 99.04 % Dolomite 0.87 % Quartz 0.10 % 101 B.2 Hot Isostatic Pressing Product 25%-Dolomite: 74.47% calcite; 25.53% dolomite 35% - Dolomite: 64.82% calcite; 35.18% dolomite 75706560555045403530252015105 10,000 5,000 0 AK_D_25_1_E.raw Calcite 74.47 % Dolomite 25.53 % 75706560555045403530252015105 10,000 5,000 0 AK_D35_2.raw_1 Calcite 64.82 % Dolomite 35.18 % 102 51% -Dolomite: 48.86% calcite; 51.50% dolomite 75% - Dolomite: 24.73% calcite; 75.54% dolomite 75706560555045403530252015105 5,000 0 AK_D50-C3.raw Calcite 48.86 % Dolomite 51.50 % 75706560555045403530252015105 10,000 5,000 0 AK_D75_A2.raw Calcite 24.73 % Dolomite 75.54 % 103 B.3 Deformed Run Product Y + 100.0 mm - D_75_3_A - File: D_75_3_A.raw - Start: 3.000 ° - End: 80.088 ° - Step: 0.039 ° - Step time: 114.4 s Y + 90.0 mm - D_75_1_A_1 - File: D_75_1_A_1.raw - Start: 3.000 ° - End: 80.088 ° - Step: 0.039 ° - Step time: 114.4 s Y + 80.0 mm - D_75_1_A - File: D_75_1_A.raw - Start: 3.000 ° - End: 80.088 ° - Step: 0.039 ° - Step time: 114.4 s Y + 70.0 mm - D_50_B_4_P1534 - File: D_50_B_4_P1534.raw - Start: 3.000 ° - End: 80.088 ° - Step: 0.039 ° - Step ti Y + 60.0 mm - D_50_3_B_3_P1528 - File: D_50_3_B_3_P1528.raw - Start: 3.000 ° - End: 80.088 ° - Step: 0.039 ° - St Y + 50.0 mm - D_50_3_B - File: D_50_3_B.raw - Start: 3.000 ° - End: 80.088 ° - Step: 0.039 ° - Step time: 114.4 s Y + 40.0 mm - D_35_C_1_P1524 - File: D_35_C_1_P1524.raw - Start: 3.000 ° - End: 80.088 ° - Step: 0.039 ° - Step ti Y + 30.0 mm - D_35_3_C - File: D_35_3_C.raw - Start: 3.000 ° - End: 80.088 ° - Step: 0.039 ° - Step time: 114.4 s Y + 20.0 mm - D_25_3_C_3_P1527 - File: D_25_3_C_3_P1527.raw - Start: 3.000 ° - End: 80.088 ° - Step: 0.039 ° - St Y + 10.0 mm - D_25_3_C - File: D_25_3_C.raw - Start: 3.000 ° - End: 80.088 ° - Step: 0.039 ° - Step time: 114.4 s BadShot - File: BadShot.raw - Start: 3.000 ° - End: 80.088 ° - Step: 0.039 ° - Step time: 71.5 s Li n (C ou nt s) 0 20000 2-Theta - Scale 3 10 20 30 40 50 60 70 80 104 Appendix C: Microprobe Data Microprobe analysis was performed on Dm25 and Dm75 deformed to high strain at 750°C (experiments P1527 and P1538). Figure C.1 is a map of all data points collected. Table C.1 gives xCa and xMg values at each point. 100 μm 20 μm 25 14 15 13 12 11 24 16 17 18 19 23 8 10 9 20 21 4 5 22 7 3 31 26 2 1 30 22 23 29 25 27 26 52 53 54 55 5756 30 31 1 50 51 46 45 43 47 44 32 11 2 3 45 6 24 8 1213 42 10 39 40 4849 3335 36 37 21 19 17 18 29 28 27 6 14 16 15 9 7 20 28 38 41 A B Figure C.1 Microprobe analysis maps. Data from Table C.1 is plotted as follows: yellow points represent Cc (0.90