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  • 1. Balic-Zunic, Tonci
    et al.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Katerinopoulou, Anna
    Schmith, Johan Haagen
    Full analysis of feldspar texture and crystal structure by combining X-ray and electron techniques2013In: American Mineralogist, ISSN 0003-004X, E-ISSN 1945-3027, Vol. 98, no 1, p. 41-52Article in journal (Refereed)
    Abstract [en]

    Feldspar crystals typically show a range of exsolution and polysynthetic twinning textures that can present problems for their full characterization, but at the same time give important information about their genesis. We present an integrated procedure for the micro-texture analysis, twin law identification plus crystal structure refinement of all components in a feldspar intergrowth. This procedure was applied to perthitic intergrowths in feldspars from two different pegmatites in the Larvik plutonic complex in the southern part of the Oslo region, Norway. It revealed that the two starting high-temperature (HT) feldspars had similar global chemical compositions but underwent significantly different cooling histories, with cooling times probably differing by over an order of magnitude. Powder X-ray diffraction with Rietveld refinement was used for a preliminary identification of the mineral components and concluding quantitative phase analysis. Electron microprobe analysis was used to bracket the chemical compositions of the constituents. Electron backscatter diffraction was used to reveal the texture of the samples, twin laws and spatial distribution and crystallographic orientation of the crystal domains. Single-grain X-ray diffraction recorded by an area detector was applied for a simultaneous integration of reflection intensities for all crystallographic domains with different orientations and severe diffraction overlaps. The crystal structures were refined using the program JANA2006 that allows a simultaneous calculation for structurally different components. Combined results of various methods helped improve accuracy and resolve ambiguities that arise from the application of a single technique. The approach is widely applicable to the study of mineral intergrowths and bridges an existing gap in the routinely accessible data on the structural characteristics of rock constituents.

  • 2.
    Bergman, Helena
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    The recognition of multiple magmatic events and pre-existing deformation zones in metamorphic rocks as illustrated by CL signatures and numerical modelling: examples from the Ballachulish contact aureole, Scotland2012In: International journal of earth sciences, ISSN 1437-3254, E-ISSN 1437-3262, Vol. 101, no 5, p. 1127-1148Article in journal (Refereed)
    Abstract [en]

    The combination of cathodoluminescence (CL) analysis, temperature and temperature-time calculations, and microstructural numerical modelling offers the possibility to derive the time-resolved evolution of a metamorphic rock. This combination of techniques is applied to a natural laboratory, namely the Ballachulish contact aureole, Scotland. Analysis of the Appin Quartzite reveals that the aureole was produced by two distinct magmatic events and infiltrated by associated fluids. Developing microstructures allow us to divide the aureole into three distinct regions. Region A (0-400 m, 663A degrees C < T (max) < 714A degrees C) exhibits a three-stage grain boundary migration (GBM) evolution associated with heating, fluid I and fluid II. GBM in region B (400-700 m, 630A degrees C < T (max) < 663A degrees C) is associated with fluid II only. Region C (> 700 m of contact, T (max) < 630A degrees C) is characterised by healed intragranular cracks. The combination of CL signature analysis and numerical modelling enables us to recognise whether grain size increase occurred mainly by surface energy-driven grain growth (GG) or strain-induced grain boundary migration (SIGBM). GG and SIGBM result in either straight bands strongly associated with present-day boundaries or highly curved irregular bands that often fill entire grains, respectively. At a temperature of similar to 620A degrees C, evidence for GBM is observed in the initially dry, largely undeformed quartzite samples. At this temperature, evidence for GG is sparse, whereas at similar to 663A degrees C, CL signatures typical for GG are commonplace. The grain boundary network approached energy equilibrium in samples that were at least 5 ka above 620A degrees C.

  • 3.
    Borthwick, V.E.
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Complex temperature dependent behaviour revealed by in-situ heating experiments on single crystals of deformed halite: New ways to recognize and evaluate annealing in geological materials2010In: Journal of Structural Geology, ISSN 0191-8141, E-ISSN 1873-1201, Vol. 32, no 7, p. 982-996Article in journal (Refereed)
    Abstract [en]

    The dynamics of substructures, which encompass all structures present at the subgrain-scale, were investigated by static, in-situ annealingexperiments. Deformed, single crystalhalite was annealed inside a scanning electron microscope at temperatures between 280 and 470 °C. Electron backscatter diffraction maps provided detailed information about crystallographic orientation changes. Three temperature dependent regimes were distinguished based on boundary misorientation changes. In regime I (280–300 °C) some low angle boundaries (LABs), i.e. with 1°–15° misorientation, increase in misorientation angle, while others decrease. In regime II (∼300 °C) all LABs undergo a decrease in misorientation angle. Regime III (>300 °C) is defined by enhancement of the subgrain structure as remaining LABs increase and some undergo a rotation axis change. Throughout regimes I and II, new LABs develop, subdividing subgrains. LABs could be divided into four categories based on annealingbehaviour, orientation and morphology. We suggest that these observations can be directly related to the mobility and activation temperature of climb of two dislocation groups introduced during deformation. Therefore, with in-depth investigation of a substructure with known deformation geometry, we can infer ratios of dislocation types and their post-deformation and post-annealing location. These can potentially be used to estimate the post-deformational annealing temperature in crystalline materials.

  • 4.
    Borthwick, Verity E.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Schmidt, S.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Gundlach, C.
    Quantification of mineral behavior in four dimensions: grain boundary and substructure dynamics in salt2012In: Geochemistry Geophysics Geosystems, ISSN 1525-2027, E-ISSN 1525-2027, Vol. 13, p. Q05005-Article in journal (Refereed)
    Abstract [en]

    Here we present the first four dimensional (time and three dimensional space resolved) experiment on a strongly deformed geological material. Results show that even complicated microstructures with large continuous and discontinuous changes in crystallographic orientation can be resolved quantitatively. The details that can be resolved are unprecedented and therefore the presented technique promises to become influential in a wide range of geoscientific investigations. Grain and subgrain scale processes are fundamental to mineral deformation and associated Earth Dynamics, and time resolved observation of these processes is vital for establishing an in-depth understanding of the latter. However, until recently, in situ experiments were restricted to observations of two dimensional surfaces. We compared experimental results from two dynamic, in situ annealing experiments on a single halite crystal; a 2D experiment conducted inside the scanning electron microscope and a 3D X-ray diffraction experiment. This allowed us to evaluate the possible effects of the free surface on grain and subgrain processes. The extent to which surface effects cause experimental artifacts in 2D studies has long been questioned. Our study shows that, although the nature of recovery processes are the same, the area swept by subgrain boundaries is up to 5 times larger in the volume than observed on the surface. We suggest this discrepancy is due to enhanced drag force on subgrain boundaries by thermal surface grooving. Our results show that while it is problematic to derive absolute mobilities from 2D experiments, derived relative mobilities between boundaries with different misorientation angles can be used.

  • 5.
    Borthwick, Verity
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry. geologi.
    piazolo, sandra
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry. geologi.
    Experimental observations of substructure dynamics:2007In: European Mineral Sciences Intiative: 1st EuroMinSci Conference, 2007, p. 53-Conference paper (Other academic)
  • 6.
    Borthwick, Verity
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry. geologi.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry. geologi.
    Experimental observations of substructure dynamics: deviations from current models?2007In: Rendiconti della Societa Geologica Italiana, 2007, p. 42-Conference paper (Other academic)
  • 7.
    Borthwick, Verity
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Post-deformational annealing at the subgrain scale: Temperature dependent behaviour revealed by in-situ heating experiments on deformed single crystal halite2010In: Journal of Structural Geology, ISSN 0191-8141, E-ISSN 1873-1201, Vol. 32, no 7, p. 982-996Article in journal (Refereed)
    Abstract [en]

    The dynamics of substructures, which encompass all structures present at the subgrain-scale, were investigated by static, in-situ annealing experiments. Deformed, single crystal halite was annealed inside a scanning electron microscope at temperatures between 280-470 ºC. Electron backscatter diffraction maps provided detailed information about crystallographic orientation changes. Three temperature dependent regimes were distinguished based on boundary misorientation changes. In regime I (280-300 ºC) some low angle boundaries (LABs), i.e. with 1º-15º misorientation, increase in misorientation angle, while others decrease. In regime II (~300 ºC) all LABs undergo a decrease in misorientation angle. Regime III (>300 ºC) is defined by enhancement of the subgrain structure as remaining LABs increase and some undergo a rotation axis change. Throughout regimes I and II, new LABs develop, subdividing subgrains. LABs could be divided into four categories based on annealing behaviour, orientation and morphology. We suggest that these observations can be directly related to the mobility and activation temperature of climb of two dislocation groups introduced during deformation. Therefore, with in-depth investigation of a substructure with known deformation geometry, we can infer ratios of dislocation types and their post-deformation and post-annealing location. These can potentially be used to estimate the post-deformational annealing temperature in crystalline materials.

  • 8.
    Borthwick, Verity
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Two distinct annealing phases observed during in-situ experiments2008In: The second EuroMinSci Conference, 2008Conference paper (Other academic)
    Abstract [en]

    The behaviour of substructures during annealing of deformed single-crystal halite has been investigated by in-situ heating experiments in the SEM. Electron Backscatter Diffraction (EBSD) maps were taken before and after each heating stage, providing information about the crystallographic orientation and misorientation of the sample surface. Two differing samples were used in a number of experiments. Both samples were deformed at a temperature of 450 ºC with GP1a deformed to ~0.180 strain, at a strain rate of ~6*10-6s-1 and TL1 deformed to 0.165 strain, at a strain rate of 6.9*10-6s-1 with a longer cooling phase. The samples were heated to temperatures between 280- 450 ºC with an arbitrary increase in temperature at each heating stage. The length of each heating stage varied from 30 minutes to six hours.

    Substructural observations can be divided into two phases of stored energy reduction:

    (a) Smoothing of crystallographic variations:

    (a1) slight overall decrease in misorientation with variations between some

    subgrains (SGs) decreasing

    (a2) decrease in the misorientation within individual SGs,

    (a3) SGs with a remaining high internal misorientation subdividing into plateaus of

    like misorientation

    (a4) decrease in misorientation and/or dissipation of many subgrain boundaries

    (SGBs <15º)

    (b) SGB development:

    (b1) increase in the misorientation of many SGB segments

    (b2) SG coarsening by movement of SGBs

    Phase (a) was primarily observed in sample GP1a but similar behaviour took place in TL1 at lower temperatures. Phase (b) was only observed in sample TL1, at heating temperatures above ~400 ºC with occasional marked movement (over distances of ~20µm) apparent.

    Results suggest that two distinct annealing phases are operating to achieve energy reduction of the whole system. The first recovery phase (a) focuses on an overall smoothing of the sample, primarily via decrease in internal misorientation of subgrains and the variation between them. During this phase, annihilation of dislocations occurs as dislocations of unlike signs migrate along lattice planes. SGB segments either decrease in misorientation, some dissipating with dislocation annihilation or remain fixed. The differences observed between the samples during (a) may be attributed to a longer cooling time for TL1 after deformation which led to it attaining an advanced stage of recovery. During the movement phase (b) most SGBs are distinct and begin to increase in misorientation as remaining dislocations in the system are added to them, facilitated by increased temperatures. In TL1, phase (a) continues to a minor extent during phase (b) with (a4) taking place to some degree. Stored energy is further reduced by coarsening of SGs via movement of SGB segments.

  • 9.
    Borthwick, Verity
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Evans, Lynn
    Griera, Albert
    Bons, Paul
    Numerical simulation coupled with in-situ annealing experiments: A new model for recoveryManuscript (preprint) (Other academic)
    Abstract [en]

    A new, deterministic model for recovery integrated with the microstructural modelling platform Elle is presented here. Experimental data collected from 2D in-situ annealing experiments were used to develop and verify the simulation. The model is based on the change of strain energy related to misorientation when a virtual rotation is applied to a crystallite (i.e. physical data point). Boundary energies are calculated using the Read-Shockley relationship. The axes of rotation were selected based on the deformation geometry and potentially activated slip systems. Crystallographic rotation was applied in the case where largest reduction of energy was observed. The effect of parameters such as rotation mobility, neighbourhood size, critical misorientation and specific energy calculation method were systematically investigated. Simulations reproduced many aspects of the experiments and showed that processes were highly dependent on dislocation type and increase of long-range effects with temperature. The results suggest that dislocations remain independent entities for longer than expected, even in an organised subgrain boundary. The model could not, however, retain higher angle boundaries and always resulted in a general shift of boundary distributions towards lower angles. We suggest that the classic interpretation of boundary energies does not entirely work for misorientations that lie in the less defined part of the Read-Shockley relationship.

  • 10.
    Borthwick, Verity
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Pennock, Gill
    Utrecht University, Department of Earth Sciences.
    Bons, Paul
    University of Tübingen, Institute für Geowissenschaften.
    Evans, Lynn
    The University of Melbourne, Department of Earth Sciences.
    Peach, Colin
    Utrecht Univeristy, Department of Earth Sciences.
    How to recognise post-deformational annealing at the subgrain scale: In-situ annealing experiments and numerical simulation.2009In: Geophysical Research Abstracts, 2009Conference paper (Other academic)
    Abstract [en]

    Recognising post-deformational annealing is key to interpreting rheological adjustments after deformation. The focus of this study is to use coupled in-situ experimental techniques with numerical simulation to increase understanding of substructure dynamics in a geological material, and as a consequence recognise microstructures formed during post-deformational annealing.

    In-situ annealing experiments have been conducted in the Scanning Electron Microscope, using Electron Backscatter Diffraction (EBSD) to collect information about the crystallographic orientation of the surface. A single crystal of halite, pre-deformed under uniaxial compression at temperatures of ~450 ºC with a strain rate of 6.9x10-6s-1, and to a final strain of 0.165, was examined. Different temperature time-paths were investigated with temperatures between 280-470 ºC and durations of heating between 30 min and 6 h. EBSD maps were taken before, during and after heating. Behaviour during annealing was found to be temperature dependent and could be divided into three main phases of development. Subgrain boundaries could be divided into five categories based on behaviour during annealing, morphology and orientation. Observations could be directly linked to the variable mobility of two groups of dislocations introduced during deformation, as well as temperature control on dislocation glide and climb. We infer that the dislocation budget throughout annealing changed significantly, with respect to both ratio of dislocation types, as well as their location in the substructure. We thus suggest that by investigating the dislocation budget of a system with known deformation geometry the temperature of annealing can potentially be established.

    In conjunction with experimentation, development of a numerical model for the processes occurring during annealing has also been undertaken. The experiments were directly compared to the simulation in order to improve the model. A first attempt at modelling the behaviour in the experiments applied a phase field method of gradient reduction. While the model did reproduce some of the results from the experiments, including the subdivision of subgrains into areas of like orientation, it did not realistically replicate other features. To combat the limitations presented by this method a new model is being developed, focusing on new techniques in dislocation density and burgers vector calculation. Information from the experimental results will be used in the development of the code. Once this model is able to reproduce behaviour observed in the experiments it can be used to model the substructure dynamics at a variety of conditions and within other materials.

  • 11.
    Borthwick, Verity
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Pennock, Gill
    Peach, Colin
    Substructure dynamics: Complex temperature dependent behaviour revealed by in-situ heating experiments2008In: : , Stockholm, 2008, p. 28-Conference paper (Other academic)
    Abstract [en]

    1. Introduction and methods

    Static in-situ annealing of deformed single-crystal halite shows that three distinct temperature dependent stages of dislocation rearrangement result in an overall decrease in the crystallographic variation of the sample.

    Substructure dynamics have been investigated in “real-time” by in-situ heating experiments conducted in the SEM. Electron Backscatter Diffraction (EBSD) maps were taken before, during and after each heating stage, to collect detailed information about the crystallographic orientation and misorientation of the sample substructure. Samples were pre-deformed under uniaxial compression at a temperature of ~450 ºC to strains of 0.165, at a strain rate of 6.9*10-6s-1. Samples were then annealed within an SEM in several heating stages at temperatures between 280-470 ºC, with an arbitrary increase in temperature at each heating stage (see fig. 1b). The length of each heating stage varied from 30 minutes to six hours. The setup of the heating stage and an orientation contrast image of the areas of the crystal analysed are shown in fig. 1.

    2. Results

    Behaviour during annealing of halite can be divided into three distinct phases based on the low-angle boundary (LAB <15º) behaviour and overall changes in the substructure. LABs were divided into five categories based on their morphology, orientation and behaviour. Fig 2 shows a schematic of the boundary types and a table detailing their important features.

    Characteristic behaviour of the annealing phases (see fig. 3):

    Annealing phase one 280-300 ºC

    a) Type 1 and 2 LABs: increase in the misorientation

    b) Type 3 and 4 LABs: decrease in the misorientation

    c) Type 5: boundary movement with an average velocity of 0.085µm/min

    d) subdivision of some subgrains into plateaus of like orientation

    Annealing phase two ~300 ºC

    a) All LAB types: decrease in the misorientation

    b) Type 5: significant decrease in boundary velocity to an average of 0.032µm/min

    c) continued subdivision of subgrains and formation of new LABs at plateau borders

    Annealing phase three >300 ºC

    a) All LAB types: increase in misorientation of remaining LABs

    b) Type 5: increase in boundary movement to an average velocity of 0.169µm/min

    c) no new plateau formation occurs

    3. Substructural evolution during annealing

    We suggest that annealing behaviour is both temperature dependent and varies according to which boundary is examined. Fig. 4 shows a diagram of inferred behaviour occurring during annealing. At lower temperatures (T<300 ºC) annihilation of dislocations in the subgrain interior and at the boundary site for LABs aligned with the harder slip system occurs, resulting in a decrease in misorientation. Concurrently, dislocations are added into the boundaries in preferred alignment, which then increase in misorientation. In areas where there are no dislocations of opposite sign, annihilation is not possible and dislocations of like sign begin to align. Consequently, next to these aligned dislocations plateaus of like orientation form. Phase two (T ~300 ºC) marks a switch in behaviour for type 1 and 2 LABs, which begin to decrease as dislocations annihilate at the boundaries. As temperature increases the length scale on which dislocations are attracted to boundaries extends and previously trapped dislocations begin to move. New tilt boundaries form at borders of plateau regions as more dislocations are added. At T>300 ºC changes are dominated by LAB development, where remaining dislocations move towards boundaries as the range of attraction increases further. The cumulation of these processes results in an overall decrease in the crystallographic variation of the sample and thus a significant decrease in the stored energy of the system.

  • 12.
    Borthwick, Verity
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Schmidt, Søren
    Denmarks Technical University, Materials Research Department.
    Gundlach, Carsten
    Lund University, MaxLab.
    Pennock, Gill
    Utrecht University, Department of Earth Sciences.
    Peach, Colin
    Utrecht University, Department of Earth Sciences.
    Substructure dynamics in halite: Comparison of 2D in-situ annealing experiments with 3D X-ray diffraction annealing2009In: Deformation Mechanisms, Rheology and Tectonics 2009, 2009Conference paper (Other academic)
    Abstract [en]

    The understanding of substructural behaviour during post-deformational annealing is key to interpreting rheological adjustments during tectonic change, and the processes which cause them. The focus of this study is to use in-situ experimental techniques to increase understanding of substructure dynamics in geological materials. 2D in-situ annealing experiments have been conducted in the scanning electron microscope, using electron backscatter diffraction (EBSD) to collect information about the crystallographic orientation of the surface. A single crystal of halite, pre-deformed under uniaxial compression at temperatures of ~450 ºC with a strain rate of 6.9x10-6s-1, and to a final strain of 0.165, was examined. Different temperature time-paths were investigated with temperatures between 280-470 ºC and durations of heating between 30 min and 6 h. EBSD maps were taken before, during and after heating. Behaviour during annealing was found to be temperature dependent and could be divided into three main phases of development. Subgrain boundaries could be divided into five categories based on behaviour during annealing, morphology and orientation. Annealing behaviour could be directly related to preferential activation of one set of slip systems due to the chosen aspect ratio of the crystal.

    While the 2D experiments provided valuable information, it is impossible to rule out the potential influence surface effects may have on annealing behaviour. In order to verify the results of these experiments, a 3D X-ray diffraction experiment was conducted at the synchrotron in Grenoble, France. The experiment followed a similar heating procedure as that for the 2D experiments and was performed on the same sample. This newly developed technique allows non-destructive internal examination of the crystal. Data was collected before, during and after each heating stage. During heating crystallographic information was collected within a limited rotation threshold (12-30º) in order to illuminate one or two subgrains and allow us to follow their progress. Comparison of the shape and strength of intensity spots has allowed us to draw some early conclusions from the data without a full crystallographic analysis. Preliminary results suggest that similar processes may be occurring as those observed in the 2D experiments, including spots becoming more distinct as well as some spots rotating away from the bulk of the subgrain indicating some subdivision and potential polygonisation. We can thus suggest that some of the behaviour exhibited in the 3D experiment is similar to that from the 2D experiment. Full crystallographic analysis of large maps taken after heating will allow us to examine the behaviour of the substructure in more detail and potentially rule out surface effects from the 2D experiments.

  • 13.
    Borthwick, Verity
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Schmidt, Søren
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Gundlach, Carsten
    Griera, Albert
    Bons, Paul
    Jessell, Mark
    The application of in-situ 3D X-ray Diffraction in annealing experiments: First interpretation of substructure development in deformed NaCl2010In: Recrystallization and Grain Growth: Proceedings of the fourth Joint International Conference of Recrystallization and Grain Growth, 2010Conference paper (Refereed)
    Abstract [en]

    In-situ 3D X-ray diffraction (3DXRD) annealing experiments were conducted at the ID-11 beamline at the European Synchrotron Radiation Facility in Grenoble. This allowed us to non-destructively document and subsequently analyse the development of substructures during heating, without the influence of surface effects. A sample of deformed single crystal halite was heated to between 260-400 ºC. Before and after heating a volume of 500 by 500 by 300 mm was mapped using a planar beam, which was translated over the sample volume at intervals of 5-10 µm in the vertical dimension. In the following we present partially reconstructed orientation maps over one layer before and after heating for 240min at 260 ºC. Additional small syn-heating “maps” over a constrained sample rotation of 12-30º. The purpose of this was to illuminate a few reflections from 1 or 2 subgrains and follow their evolution during heating.

    Preliminary results show that significant changes occurred within the sample volume, for which, surface effects can be excluded. Results show a number of processes, including: i) change in subgrain boundary misorientation angle and ii) subgrain subdivision into areas of similar lattice orientation with new subgrain boundary formation. These results demonstrate that 3DXRD coupled with in-situ heating is a successful non-destructive technique for examining real-time post-deformational annealing in strongly deformed crystalline materials with complicated microstructures.

  • 14.
    Brander, Linus
    et al.
    Department of Earth Sciences, University of Gothenburg.
    Svahnberg, Henrik
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Brittle-plastic deformation in initially dry rocks at fluid present conditions: Transient behavior of feldspar at mid crustal levelsManuscript (preprint) (Other academic)
  • 15. Brander, Linus
    et al.
    Svahnberg, Henrik
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Brittle-plastic deformation in initially dry rocks at fluid-present conditions: transient behaviour of feldspar at mid-crustal levels2012In: Contributions to Mineralogy and Petrology, ISSN 0010-7999, E-ISSN 1432-0967, Vol. 163, no 3, p. 403-425Article in journal (Refereed)
    Abstract [en]

    We present detailed microstructural and chemical analyses from an initially dry anorthositic rock deformed during wet amphibolite facies conditions. Three different domains representing the microstructural variation of the deformed samples are investigated in detail in terms of fracture morphology and mode, grain characteristics and chemistry of present phases. Results show transient deformational behaviour where a close interaction between brittle, plastic and fluid-assisted deformation mechanisms can be observed. Our analysis allows us to describe the succession, interrelationships and effects of active mechanisms with progressively increasing strain in three so-called stages. In Stage 1, initial fracturing along cleavage planes promoted fluid influx that caused fragmentation and chemical reactions, producing fine-grained mineral assemblages in the fractures. Deformation twins and dislocations developed in clast pieces due to stress relaxation. Passive rotation of conjugate fracture sets and interconnection of intracrystalline fractures formed micro-shear-zones, constituting Stage 2. Microstructures and grain relationships indicate the activity and fluctuation between fracturing, dissolution-precipitation creep, grain boundary sliding and locally dislocation creep, reflecting the transient behaviour of brittle and plastic deformation mechanisms. Further rotation and widening of fractures into overall foliation parallel shear-bands (Stage 3) promoted strain partitioning into these areas through increased fluid influx, influence of fluid-assisted grain boundary sliding, phase mixing and presence of weak phases such as white mica. We suggest that local differences in fluid availability, volume fraction of weak phases produced by fluid present metamorphic reactions coupled with volume increase and local variations in stress concentration induced transient brittle-plastic behaviour. The studied shear-zone represents an example of the transformation of a rigid dry rock to a soft wet rock during deformation through syntectonic fracturing.

  • 16. Ebner, M.
    et al.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Koehn, D.
    Initiation of and distributed deformation at and around stylolite interfaces: Insights from detailed microstructural analysis.2009Conference paper (Refereed)
  • 17. Ebner, Marcus
    et al.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Renard, Francois
    Koehn, Daniel
    Stylolite interfaces and surrounding matrix material: Nature and role of heterogeneities in roughness and microstructural development2010In: Journal of Structural Geology, ISSN 0191-8141, E-ISSN 1873-1201, Vol. 32, no 8, p. 1070-1084Article in journal (Refereed)
    Abstract [en]

    Rough pressure solution interfaces, like stylolites, are one of the most evident features of localized slow deformation in rocks of the upper crust. There is a general consensus that the development of these rough structures is a result of localized, stress enhanced, dissolution of material along a fluid filled interface, but little is known on the initiation of this roughness. The aim of this article is to reveal the role of heterogeneities initially present in the host-rock on roughness initiation. This should give insights on whether stylolite roughness is generated by a stress-induced instability or by the presence of disorder in the material (i.e. quenched noise). We use a microstructural approach based on SEM/EBSD analysis combined with orientation contrast (OC) image analysis of stylolites in limestones. We found that the stylolite roughness is induced by heterogeneities in the host rock (clay particles and detrital quartz grains in our case). In addition, close to mature stylolite interfaces matrix modifications occur, which can be attributed to the compaction along the stylolite. The grain size decreases by 15-25% and a pre-existing shape- and lattice-preferred orientation (SPO, LPO) are significantly modified in the vicinity of the stylolite. The results presented here imply that localized pressure solution along stylolites is not necessarily restricted to the actual interface but influences the adjacent matrix. The heterogeneity data might serve as a quantitative basis for elaborate numerical models of localized compaction.

  • 18.
    Godinho, Jose R. A.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences. Oak Ridge National Laboratory, United States.
    Putnis, Christine V.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geological Sciences. Macquarie University, Australia.
    Direct Observations of the Dissolution of Fluorite Surfaces with Different Orientations2014In: Crystal Growth & Design, ISSN 1528-7483, E-ISSN 1528-7505, Vol. 14, no 1, p. 69-77Article in journal (Refereed)
    Abstract [en]

    Atomic force microscopy has been used to observe the surface dynamics during dissolution of polished fluorite surfaces with different orientations. These surfaces, with an initially high density of atomic scale defects, showed fast changes during the first seconds in contact with a solution. Different types of structures developed on each surface, depending on its initial orientation and solution composition. These structures dissolved slower than the main surface persisting for at least 67.5 days of continuous dissolution. A new interpretation of traditional kinetic and thermodynamic models of dissolution applied to surfaces with a high density of steps is proposed to explain the observations. The new model includes the following: (a) fast initial dissolution at defect sites, (b) formation of a fluid boundary layer at the mineral solution interface enriched in the dissolving ions, and (c) precipitation of more stable fluorite structures nucleated at surface defects. This model highlights the importance of considering surface defects and crystal orientation for advancing our understanding of processes happening at the mineral solution interface and for developing more accurate kinetic dissolution and crystal growth models essential in Earth and material sciences.

  • 19.
    Godinho, José R. A.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Evins, L. Z.
    Effect of surface orientation on dissolution rates and topography of caf22012In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 86, p. 392-403Article in journal (Refereed)
    Abstract [en]

    This paper reports how during dissolution differences in surface chemistry affect the evolution of topography of CaF2 pellets with a microstructure similar to UO2 spent nuclear fuel. 3D confocal profilometry and atomic force microscopy were used to quantify retreat rates and analyze topography changes on surfaces with different orientations as dissolution proceeds up to 468 h. A NaClO4 (0.05 M) solution with pH 3.6 which was far from equilibrium relative to CaF2 was used. Measured dissolution rates depend directly on the orientation of the exposed planes. The {111} is the most stable plane with a dissolution rate of (1.2 +/- 0.8) x 10(-9) mol m(-2) s(-1), and {112} the least stable plane with a dissolution rate 33 times faster that {111}. Surfaces that expose both Ca and F atoms in the same plane dissolve faster. Dissolution rates were found to be correlated to surface orientation which is characterized by a specific surface chemistry and therefore related to surface energy. It is proposed that every surface is characterized by the relative proportions of the three reference planes {111}, {100} and {110}, and by the high energy sites at their interceptions. Based on the different dissolution rates observed we propose a dissolution model to explain changes of topography during dissolution. Surfaces with slower dissolution rate, and inferred lower surface energy, tend to form while dissolution proceeds leading to an increase of roughness and surface area. This adjustment of the surface suggests that dissolution rates during early stages of dissolution are different from the later stages. The time-dependency of this dynamic system needs to be taken into consideration when predicting long-term dissolution rates.

  • 20.
    Godinho, José R. A.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences. Oak Ridge National Laboratory, USA.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geological Sciences. Macquarie University, Australia.
    Balic-Zunic, T.
    Importance of surface structure on dissolution of fluorite: Implications for surface dynamics and dissolution rates2014In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 126, p. 398-410Article in journal (Refereed)
    Abstract [en]

    Dissolution rates are usually calculated as a function of surface area, which is assumed to remain constant ignoring the changes occurring on the surface during dissolution. Here we present a study of how topography of natural fluorite surfaces with different orientation changes during up to 3200 h of dissolution. Results are analyzed in terms of changes in surface area, surface reactivity and dissolution rates. All surfaces studied present fast changes in topography during the initial 200 h of dissolution. The controlling factors that cause the development of topography are the stability of the step edges forming the initial surface and its inclination to the closest stable planes, which are specific for each surface orientation. During an initial dissolution regime dissolution rates decrease significantly, even though the total surface area increases. During a second dissolution regime, some surfaces continue to present significant changes in topography, while for others the topography tends to remain approximately constant. The observed variation of dissolution rates are attributed to a decrease of the density of step edges on the surface and the continuous increase in exposure of more stable surfaces. Calculations of dissolution rates, which assume that dissolution rates are directly proportional to surface area, are not valid for the type of surfaces studied. Instead, to develop accurate kinetic dissolution models and more realistic stochastic dissolution simulations the surface reactivity, determined by the relative stability of the planes and type of edges that constitute a surface needs to be considered. Significant differences between dissolution rates calculated based on surface area alone, and based on surface reactivity are expected for materials with the fluorite structure.

  • 21.
    Godinho, José R. A.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Stennett, Martin C.
    Hyatt, Neil C.
    Sintering of CaF2 pellets as nuclear fuel analog for surface stability experiments2011In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 419, no 1-3, p. 46-51Article in journal (Refereed)
    Abstract [en]

    To enable a detailed study of the influence of microstructure and surface properties on the stability of spent nuclear fuel, it is necessary to produce analogs that closely resemble nuclear fuel in terms of crystallography and microstructure. One such analog can be obtained by sintering CaF2 powder.

    This paper reports the microstructures obtained after sintering CaF2 powders at temperatures up to 1240 °C. Pellets with microstructure, density and pore structure similar to that of UO2 spent nuclear fuel pellets were obtained in the temperature range between 900 °C and 1000 °C. When CaF2 was sintered above 1100 °C the formation of CaO at the grain boundaries caused the disintegration of the pellet due to hydration occurring after sintering.

    First results from a novel set-up of dissolution experiments show that changes in roughness, dissolution rate and etch pit shape of fluorite surfaces are strongly dependent on the crystallographic orientation of the expose surface. Consequently, the differences observed for each orientation will affect the overall dissolution rate and will lead to uncertainties in the estimation of dissolution rates of spent nuclear fuel.

  • 22. Henkel, Herbert
    et al.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Worman, Anders
    Jing, Lanru
    A deep rock laboratory in the Dellen impact crater2010In: GFF, ISSN 1103-5897, E-ISSN 2000-0863, Vol. 132, no 1, p. 45-54Article in journal (Refereed)
    Abstract [en]

    The Deep Rock Lab is a platform to establish a comprehensive subsurface bedrock characterization approach, by integrating site characterization techniques applied from different disciplines of geo-mechanics, geochemistry, hydrogeology, structural geology, lithology and geophysics, with consideration of the effects of coupled geological processes of importance for the understanding of groundwater renewal, continental shield deformations, engineering issues related to geological disposal of nuclear waste and CO2, and geothermal energy retrieval in crystalline rocks. The approach will focus on the physics and chemistry of crystalline rocks and groundwater with down-the-hole measurements of relevant variables, using and developing more efficient geo-scientific site investigation techniques for deep boreholes at a chosen site, and develop more advanced down-the-hole measurements and numerical modelling methods with more advanced inversion algorithms to help integrate data interpretations and object representations. The goal is to develop this platform into a long-term research facility that can be readily used by the scientific community for both subsurface fundamental and engineering-oriented research. Such a platform will be especially important for the education of PhD students for generations to come. The integrated drilling and research facility is suggested to be located at the Dellen site. This site has an impact crater with a large range of expected physical property changes with depth, complex and multiple thermal processes that have affected the bedrock, a favorable infrastructure and local supporting activities, and a large body of existing geo-scientific data.

  • 23. Henkel, Herbert
    et al.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Wörman, Anders
    Jing, Lanru
    Proposal for a Deep Rock Laboratory in the Dellen Impact Crater.2010In: GFF, ISSN 1103-5897, E-ISSN 2000-0863, Vol. 132, no 1, p. 45-54Article in journal (Refereed)
    Abstract [en]

    The Deep Rock Lab is a platform to establish a comprehensive subsurface bedrock characterization approach, by integrating site characterization techniques applied from different disciplines of geo-mechanics, geochemistry, hydrogeology, structural geology, lithology and geophysics, with consideration of the effects of coupled geological processes of importance for the understanding of groundwater renewal, continental shield deformations, engineering issues related to geological disposal of nuclear waste and CO2, and geothermal energy retrieval in crystalline rocks. The approach will focus on the physics and chemistry of crystalline rocks and groundwater with down-the-hole measurements of relevant variables, using and developing more efficient geo-scientific site investigation techniques for deep boreholes at a chosen site, and develop more advanced down-the-hole measurements and numerical modelling methods with more advanced inversion algorithms to help integrate data interpretations and object representations. The goal is to develop this platform into a long-term research facility that can be readily used by the scientific community for both subsurface fundamental and engineering-oriented research. Such a platform will be especially important for the education of PhD students for generations to come. The integrated drilling and research facility is suggested to be located at the Dellen site. This site has an impact crater with a large range of expected physical property changes with depth, complex and multiple thermal processes that have affected the bedrock, a favorable infrastructure and local supporting activities, and a large body of existing geo-scientific data.

  • 24. Hoffmann, J. Elis
    et al.
    Svahnberg, Henrik
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Schersten, Anders
    Muenker, Carsten
    The geodynamic evolution of Mesoarchean anorthosite complexes inferred from the Naajat Kuuat Complex, southern West Greenland2012In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 196, p. 149-170Article in journal (Refereed)
    Abstract [en]

    Layered anorthosite complexes are typical components of Archean crustal domains. However, the geodynamic settings in which they were emplaced are still discussed as geological relationships are often ambiguous. Here we report major, trace element and high-precision high-field-strength-element (HFSE) data for the recently discovered well preserved Naajat Kuuat Anorthosite Complex from the inner Ameralik fjord region, southern West Greenland. The dataset is complemented by the first combined Hf-Nd isotope analyses for Archean layered anorthosite complexes and U-Pb zircon geochronology. The data contribute to the small database on Archean layered anorthosite complexes and are used to unravel the origin of these complexes and the tectonic regime involved. Fractional crystallisation of olivine, pyroxene, plagioclase and possibly amphibole controls major and trace element variations in the layered intrusion. There are two groups of amphibolites: (1) a group with primitive mantle normalized trace element patterns are similar to those of MORB-like basalts and (2) typical island-arc tholeiites (IAT), apparently indicating an island-arc setting. Lu-Hf regression lines yield an age of 2985 +/- 59 Ma (MSWD 4) within the error of the Sm-Nd regression age of 2929 110 Ma (MSWD 17). The initial epsilon Hf(2985) for the Naajat Kuuat rocks range from +1.6 to +5.8 and the initial epsilon Nd(2985) range from +0.4 to +3.9, either indicating variably depleted mantle sources or variable degrees of crustal contamination. In contrast to most mafic assemblages, ratios of Nb/Ta are highly variable (7.85 to 18.6), reflecting fractionation and accumulation of amphibole, ilmenite and pyroxene. The MORB-like parental liquids have the highest Nb/Ta of ca. 18, consistent with a mantle source overprinted by melt-like components from subducting oceanic crust with high Nb/Ta. The accumulation of plagioclase forming the anorthosites and the primary fractionation of amphibole as well as the occurrence of high-Al basalts within the Naajat Kuuat complex argue for hydrous parental liquids in support of an island-arc related setting. Zircon U-Pb geochronology from the anorthosite and adjacent tonalites reveal major tonalite intrusion into the complex at ca. 2802 Ma and a second regional event at ca. 2710 Ma, in accord with crustal heating due to micro-continent amalgamation and crustal thickening. Altogether, the geochemical data can be interpreted with a geodynamic model, where anorthosite-complex associated rocks intrude into tectonically thickened island-arc crust. Crustal thickening is possibly triggered by island-arc accretion, leading to the emplacement of TTG bodies that further thickened the crustal pile. Further collision and amalgamation with other proto-crustal assemblages might have led to enhanced crustal magmatism and granulite facies metamorphism.

  • 25. Howell, D.
    et al.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Dobson, D. P.
    Wood, I. G.
    Jones, A. P.
    Walte, N.
    Frost, D. J.
    Fisher, D.
    Griffin, W. L.
    Quantitative characterization of plastic deformation of single diamond crystals: A high pressure high temperature (HPHT) experimental deformation study combined with electron backscatter diffraction (EBSD)2012In: Diamond and related materials, ISSN 0925-9635, E-ISSN 1879-0062, Vol. 30, p. 20-30Article in journal (Refereed)
    Abstract [en]

    We report the results of a high-pressure high-temperature (HPHT) experimental investigation into the deformation of diamonds using the D-DIA apparatus. Electron backscatter diffraction (EBSD) data confirm that well-defined 300-700 nm wide {111} slip lamellae are in fact deformation micro-twins with a 60 degrees rotation around a < 111 > axis. Such twins formed at high confining pressures even without any apparatus-induced differential stress; mechanical anisotropy within the cell assembly was sufficient for their formation with very little subsequent lattice bending (<1 degrees per 100 mu m). When apparatus-induced differential stresses were applied to diamonds under HPHT conditions, deformation twin lamellae were generated, and continuous and discontinuous crystal lattice bending occurred (4-18 degrees per 100 mu m), including bending of the {111} twin lamellae. The (111) < 011 > slip system dominates as expected for the face-centred cubic (FCC) structure of diamond. Slip occurs on multiple {111} planes resulting in rotation around < 112 > axes. Deformation microstructure characteristics depend on the orientation of the principal stress axes and finite strain but are independent of confining pressure and nitrogen content. All of the uniaxially deformed samples took on a brown colour, irrespective of their initial nitrogen characteristics. This is in contrast to the two quasi-hydrostatic experiments, which retained their original colour (colourless for nitrogen free diamond, yellow for single substitutional nitrogen, Type lb diamond) despite the formation of (111) twin lamellae. Comparison of our experimental data with those from two natural brown diamonds from Finsch mine (South Africa) shows the same activation of the dominant slip system. However, no deformation twin lamellae are present in the natural samples. This difference may be due to the lower strain rates experienced by the natural samples investigated. Our study shows the applicability and potential of this type of analysis to the investigation of plastic deformation of diamonds under mantle conditions.

  • 26.
    Jaconelli, Paulina
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    The influence of original crystal orientation and habit on the activity of slip systems and deformation mechanisms: A case study from Sillimanite. Deformation mechanisms, Rheology and Tectonics, Liverpool2009Conference paper (Refereed)
  • 27. Jessell, Mark
    et al.
    Sibert, E
    Bons, Paul
    Evans, lynn
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Chapter 4.3 Simple experiments in deformation localization.2008In: Microdynamics simulation: SPRINGER book series "Lecture Notes in Earth Science 106", 2008, p. 225-230Chapter in book (Refereed)
  • 28. Keulen, Nynke
    et al.
    Schumacher, John C.
    Scherstén, Anders
    Kokfelt, Thomas F.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Reinterpretation of the Tre Brødre-Tasiusarsuaq Terraneboundary in the Buksefjorden area, Southern West-Greenland. Deformation mechanisms, Rheology and Tectonics, Liverpool2009Conference paper (Refereed)
  • 29. Mamtani, M.
    et al.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Greiling, R. O.
    Kontny, A.
    Hrouda, F.
    Magnetite fabric in a syntectonic granite – inferences from AARM and SEM-EBSD analysisIn: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266Article in journal (Refereed)
  • 30. Mamtani, Manish A.
    et al.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Greiling, Reinhard O.
    Kontny, Agnes
    Hrouda, Frantisek
    Process of magnetite fabric development during granite deformation2011In: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 308, no 1-2, p. 77-89Article in journal (Refereed)
    Abstract [en]

    This study evaluates the fabric defined by magnetite grains in a syntectonically deformed granite and deciphers the processes that led to magnetite fabric development. Anisotropy of anhysteretic remanence magnetization (AARM) analysis is performed in samples taken from different parts of the granite to establish that the magnetite grains define a fabric. Along with microstructural studies, the AARM data help conclude that this fabric is on account of shape preferred orientation (SPO) of the magnetite grains. The intensity of magnetite fabric (degree of anisotropy of the AARM ellipsoid) is higher in the southern parts as compared to the north, which is inferred to indicate a strain gradient. Electron back scattered diffraction (EBSD) analyses of magnetite grains were performed to determine if there are intracrystalline deformation features that could have influenced magnetite shape and SPO, and thus AARM data. Detailed crystallographic orientation data coupled with orientation contrast imaging did not reveal any subgrains and/or significant variations in crystallographic orientations within magnetite grains. Instead, grains exhibit fractures and are in places associated with quartz pressure fringes. Hence, neither the SPO nor the variation in the magnetite fabric intensity in the granite can be attributed to intracrysta Hine deformation of magnetite by dislocation creep. It is concluded that the magnetite grains were rheologically rigid and there was relative movement between the magnetite and the matrix minerals (quartz, feldspar and biotite). These matrix minerals actually define the fabric attractor and the magnetite grains passively rotated to align with it. Thus it is demonstrated that the magnetite fabric in the granite stems from rigid body movement rather than dislocation creep.

  • 31. Menegon, Luca
    et al.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Pennacchioni, Giorgio
    The effect of Dauphin, twinning on plastic strain in quartz2011In: Contributions to Mineralogy and Petrology, ISSN 0010-7999, E-ISSN 1432-0967, Vol. 161, no 4, p. 635-652Article in journal (Refereed)
    Abstract [en]

    We present an electron backscatter diffraction analysis of five quartz porphyroclasts in a greenschist facies (T = 300-400A degrees C) granitoid protomylonite from the Arolla unit of the NW Alps. Mechanical Dauphin, twinning developed pervasively during the incipient stage of deformation within two porphyroclasts oriented with a negative rhomb plane {z} almost orthogonal to the compression direction (z-twin orientation). Twinning was driven by the anisotropy in the elastic compliance of quartz and resulted in the alignment of the poles of the planes of the more compliant positive rhomb {r} nearly parallel to the compression direction (r-twin orientation). In contrast, we report the lack of twinning in two porphyroclasts already oriented with one of the {r} planes orthogonal to the compression direction. One twinned porphyroclast has been investigated with more detail. It shows the localization of much of the plastic strain into discrete r-twins as a consequence of the higher amount of elastic strain energy stored by r-twins in comparison to z-twins. The presence of Dauphin, twins induced a switch in the dominant active slip systems during plastic deformation, from basal < a > (regions without twinning) to {pi} and {pi'} < a > (pervasively twinned regions). Dynamic recrystallization is localized along an r-twin and occurred dominantly by progressive subgrain rotation, with a local component of bulging recrystallization. Part of the recrystallized grains underwent rigid-body rotation, approximately about the bulk vorticity axis, which accounts for the development of large misorientation angles. The recrystallized grain size piezometer for quartz yields differential stress of 100 MPa. The comparison of this palaeostress estimate with literature data suggests that mechanical Dauphin, twinning could have a potential use as palaeopiezometer in quartz-bearing rocks.

  • 32. Menegon, Luca
    et al.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Pennacchioni, Giorgio
    The role of Dauphiné twinning in the initiation of dynamic recrystallization within quartz Porphyroclasts2009Conference paper (Refereed)
  • 33. Menegon, Lucy
    et al.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    The influence of Dauphiné twinning on activation of slip systems and incipient dynamic recrystallization in quartz. Deformation mechanisms, Rheology and Tectonics, Liverpool2009Conference paper (Refereed)
  • 34. Montagnat, M.
    et al.
    Blackford, J.R.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Griera, A.
    Lebensohn, R.
    Characterization and modelling of deformation heterogeneities in ice. Euromat2009, Glasgow.2009Conference paper (Refereed)
  • 35. Montagnat, Maurine
    et al.
    Blackford, Jane R.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Arnaud, Laurent
    Lebensohn, Ricardo A.
    Measurements and full-field predictions of deformation heterogeneities in ice2011In: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 305, no 1-2, p. 153-160Article in journal (Refereed)
    Abstract [en]

    We have made creep experiments on columnar grained ice and characterised the microstructure and intragranular misorientations over a range of length scales. A FFT full-field model was used to predict the deformation behaviour, using the experimentally characterised microstructure as the starting material. This is the first time this combination of techniques has been used to study the deformation of ice. The microstructure was characterised at the cm scale using an optical technique, the automatic ice texture analyser AITA and at the micron scale using electron backscattered diffraction EBSD. The crystallographic texture and intragranular misorientations were fully characterised by EBSD (3 angles). The deformed microstructure frequently showed straight subgrain boundaries often originating at triple points. These were identified as kink bands, and for the first time we have measured the precise misorientation of the kink bands and deduced the nature of the dislocations responsible for them. These dislocations have a basal edge nature and align in contiguous prismatic planes enabling deformation along the c-axis. In addition, non-uniform grain boundaries and regions of recrystallization were seen. We present coupling between fine scale characterization of intragranular misorientations, from experiments, and prediction of internal stresses that cause it. The model predicts the morphology of the observed local misorientations within the grains, however it over predicts the misorientation values. This is because the annealing and recrystallization mechanisms are not taken into account in the model. Ice is excellent as a model material for measuring, predicting and understanding deformation behaviour for polycrystalline materials. Specifically for ice this knowledge is needed to improve models of ice sheet dynamics that are important for climatic signal interpretation.

  • 36. Perdikouri, Christina
    et al.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geological Sciences. Macquarie University, Australia.
    Kasioptas, Argyrios
    Schmidt, Burkhard C.
    Putnis, Andrew
    Hydrothermal replacement of Aragonite by Calcite: interplay between replacement, fracturing and growth2013In: European journal of mineralogy, ISSN 0935-1221, E-ISSN 1617-4011, Vol. 25, no 2, p. 123-136Article in journal (Refereed)
    Abstract [en]

    The hydrothermal transformation of single aragonite crystals into polycrystalline calcite has been studied under hydrothermal conditions. The transformation involves a fluid-mediated replacement reaction, associated with fracturing of the initial aragonite crystal and growth of calcite throughout various parts of the reacted aragonite. The observed overall preservation of the crystal morphology is typical of an interface-coupled dissolution-reprecipitation mechanism Analysis of the crystallographic orientation of the product calcite using electron backscatter diffraction (EBSD) showed little to no link between the two phases under the studied conditions, with calcite crystallites exhibiting dominantly different crystallographic orientations compared to those of the aragonite and of neighbouring calcite domains. The complexity of the observed textures is mainly a result of the combination of fracturing of the crystal and initiation of nucleation and growth at different points of the exposed aragonite surface. Experiments performed with solutions enriched in O-18 as a tracer for oxygen exchange and monitored by Raman spectroscopy, showed that carbonate ions in the starting solution are mixed with carbonate from the dissolving aragonite, resulting in an O-18 concentration in the product calcite which depended on the local fluid transport through the fractures. As replacement processes among the CaCO3 phases are relevant to a wide range of applications, understanding the mechanisms is essential for the interpretation of observations of natural and/or experimental samples. This study describes the interplay between the replacement process, the fracturing of the crystal and growth of the new phase, calcite, and provides new insights into the mechanism of the aragonite to calcite transition. The combination of the two methods, EBSD and Raman spectroscopy, demonstrates the importance of local fluid composition and transport pathways in determining the isotope and element exchange in mineral replacement reactions.

  • 37. Peternell, M.
    et al.
    Hasalova, P.
    Wislon, C.J.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Schulmann, K.
    A comparative study of quartz EBSD and Fabric Analyser: crystallographic preferred orientation from the Thaya region, Czeck Republic2010In: Journal of Structural Geology, ISSN 0191-8141, E-ISSN 1873-1201, Vol. 32, no 6, p. 803-817Article in journal (Refereed)
    Abstract [en]

    Quartz crystallographic preferred orientations (CPO) from three distinct orthogneisses using both the Electron Back Scatter Diffraction (EBSD) and Fabric Analyser (FA) techniques reveal a clear trend from basal <a> and rhomb <a + c> slip for high P–T conditions (670 ± 20 °C/9 kbar), rhomb <a + c> and basal <a> slip for medium P–T (590 ± 15 °C/6 kbar) and a dominance of prism <a> slip for lower P–T conditions (<570 °C/4–5 kbar). The textural variations are interpreted in terms of a temperature field gradient and microscale strain partitioning controlled by a weak feldspar matrix that can locally invert the expected slip system sequences. Locally quartz CPOs are different within one thin section, and in comparison to bulk orientation measurements both, EBSD and the Fabric Analyser techniques are ideal to determine such textural heterogeneities. While the EBSD is a powerful technique to determine the full CPO, measurements from similar locations inside several quartz grains from the orthogneisses and an annealed and undeformed quartzite show that the FA is an accurate tool to determine CPOs of c-axis orientations in uniaxial materials. In a CPO focussed study the FA is a cheap alternative to EBSD as the analysis of whole thin section can be accomplished in a very short time, with minimal sample preparation. With the FA it is possible to evaluate the CPOs of several samples quickly with an accuracy that allows identification of the main slip systems and their homogeneity.

  • 38. Peternell, M.
    et al.
    Hasalová, Pavlína
    Wilson, Christopher J.L.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Schulmann, Karel
    A comparison of quartz EBSD and Fabric Analyser. Deformation mechanisms, Rheology and Tectonics, Liverpool2009Conference paper (Refereed)
  • 39. Peternell, Mark
    et al.
    Hasalova, Pavlina
    Wilson, Christopher J. L.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Schulmann, Karel
    Evaluating quartz crystallographic preferred orientations and the role of deformation partitioning using EBSD and fabric analyser techniques2010In: Journal of Structural Geology, ISSN 0191-8141, E-ISSN 1873-1201, Vol. 32, no 6, p. 803-817Article in journal (Refereed)
    Abstract [en]

    Quartz crystallographic preferred orientations (CPO) from three distinct orthogneisses using both the Electron Back Scatter Diffraction (EBSD) and Fabric Analyser (FA) techniques reveal a clear trend from basal < a > and rhomb < a + c > slip for high P-T conditions (670 +/- 20 degrees C/9 kbar), rhomb < a + c > and basal < a > slip for medium P-T (590 +/- 15 degrees C/6 kbar) and a dominance of prism < a > slip for lower P T conditions (<570 degrees C/4-5 kbar). The textural variations are interpreted in terms of a temperature field gradient and microscale strain partitioning controlled by a weak feldspar matrix that can locally invert the expected slip system sequences. Locally quartz CPUs are different within one thin section, and in comparison to bulk orientation measurements both, EBSD and the Fabric Analyser techniques are ideal to determine such textural heterogeneities. While the EBSD is a powerful technique to determine the full CPO, measurements from similar locations inside several quartz grains from the orthogneisses and an annealed and undeformed quartzite show that the FA is an accurate tool to determine CPUs of c-axis orientations in uniaxial materials. In a CPO focussed study the FA is a cheap alternative to EBSD as the analysis of whole thin section can be accomplished in a very short time, with minimal sample preparation. With the FA it is possible to evaluate the CPUs of several samples quickly with an accuracy that allows identification of the main slip systems and their homogeneity.

  • 40.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry. geologi.
    Annealing in experiment and nature2007In: Metamorphic Studies Group Meeting 2007: abstract volume, 2007, p. 2-Conference paper (Other academic)
  • 41.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Chapter 3.4 Nucleation and subgrain formation. In Koehn, Jessell, Bons: Microdynamics simulation.2008In: Microdynamics simulation: SPRINGER book series "Lecture Notes in Earth Science 106", Springer , 2008, p. 105-114Chapter in book (Refereed)
  • 42.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Chapter 4.2 Application of microdynamic simulation, involving coupling of two or more processes: Dynamic Recrystallization/Crystalline Plasticity.2008In: Microdynamic simulation: SPRINGER book series "Lecture Notes in Earth Science 106", springer , 2008, p. 215-224Chapter in book (Refereed)
  • 43.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Deformation of iron ore: An example of the use of Electron Backscatter Diffraction (EBSD) Analysis in the Mineral Sciences2008In: Nordic Geological Winter Meeting Abstract Volume, 2008Conference paper (Other academic)
  • 44.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Subgrain growth-Potts model. In Koehn, Jessell, Bons: Microdynamics simulation.2008In: SPRINGER book series "Lecture Notes in Earth Science 106, Springer , 2008, p. 97-104Chapter in book (Refereed)
  • 45.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Substructure characterization of experimentally and naturally deformed ice grains using cryo-EBSD2008In: Nordic EBSD Users Meeting, Syninge, Sweden, 2008Conference paper (Other academic)
  • 46.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Substructure dynamics in minerals and metals: new insights from experiemtns and numerical simulations2008In: Final EuroMinScI conference, Obernai, France, 2008Conference paper (Other academic)
  • 47.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry. geologi.
    Substructure dynamics in rocks and minerals2007In: European Mineral Sciences Intiative,: 1st EuroMinSci Conference, 2007, p. 23-Conference paper (Other academic)
  • 48.
    Piazolo, Sandra
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Austrheim, Hakon
    Whitehouse, Martin
    Brittle ductile microfabrics in naturally deformed zircon: deformation mechanisms and consequences for u pb dating2012In: American Mineralogist, ISSN 0003-004X, E-ISSN 1945-3027, Vol. 97, no 10, p. 1544-1563Article in journal (Refereed)
    Abstract [en]

    We present an electron backscatter diffraction, cathodoluminescence, and radiogenic U-Pb dating study of large zircon grains (0.8-1.5 mm) that show evidence of intracrystalline deformation, fracturing, grain size reduction and a large spread in U-Pb ages. The samples are from an amphibolite facies deformation zone within granulite facies anorthositic rocks (Bergen Arc, Norway). Large zircon grains show three main lattice distortion types: (I) distortions with rotations around < 001 > and an orientation change of similar to 0.3 degrees/mu m subparallel to (100); (II) highly distorted, half circular shaped zones located at grain edges with at least 0.8-1 degrees/mu m distortions; and (III) low-angle boundary networks forming deformation zones up to 100 mu m wide. Types II and III distortions exhibit significant disturbances of the otherwise homogeneous CL signature. Crystal plastic deformation with the slip system [010](100) resulted in type I distortions. Stress concentrations at grain contacts between rheologically hard grains caused localized crystal plastic deformation with minor amount of microfracturing forming type H distortions. Type Ill distortions formed by crystal plastic deformation often associated with inclusions using several slip systems. Distortions of types I and II show minor and moderate resetting of the original ca. 900 Ma zircon grains, respectively, due to enhanced pipe diffusion along dislocation walls. In type II distortions, accelerated lattice diffusion through the highly distorted crystal lattice, combined with exceptionally high boundary to volume ratio, caused significant chemical disturbance and age resetting to 410 Ma. Fine-grained aggregates contain grains with low internal deformation and an oscillatory zoned CL signature (Z-grains) or high internal deformation and a disturbed CL signature (D-grains). Z- and D-grains are interpreted to have formed by heterogeneous nucleation and growth, and fracturing along strain-hardened low-angle boundaries present within types I and II, respectively. Z-grains show a clustered chemical signature with a 437 +/- 11 Ma age interpreted to directly date the Caledonian amphibolite facies reworking.

  • 49.
    Piazolo, Sandra
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry. Geologi.
    Dave, Prior
    Marian, Holness
    Andreas, Harstad
    Annealing in a natural laboratory: an EBSD and Cl study of calcite and quartz growth from volumes of rock heated by a nearby melt intrusion2007In: Materials Science Forum, no 550, p. 333-338Article in journal (Refereed)
  • 50.
    Piazolo, Sandra
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Jessell, M. W.
    Bons, P. D.
    Evans, L.
    Becker, J. K.
    Numerical Simulations of microstructures using the Elle platform: A modern research and teaching tool.2010In: Journal of the Geological Society of India, ISSN 0016-7622, E-ISSN 0974-6889, Vol. 75, no 1, p. 110-127Article in journal (Refereed)
    Abstract [en]

    The last 20 years have seen a manifold increase in the application of numerical simulations in the earth sciences. This contribution aims to provide an overview of the possibilities of using numerical techniques, in particular the numerical simulation package Elle, as an aid in the training for microstructural interpretation in rocks. Three sets of experiments are described to illustrate the range of simulations currently possible, investigating the effects of grain growth, polyphase deformation and dynamic recrystallisation. Numerical simulations of static annealing of a pre-deformed natural sample show that Crystallographic Preferred Orientations can still be used for the interpretation of kinematic and deformation conditions, even after substantial postdeformational annealing. However, the grain network characteristics such as grain size, grain size distribution, boundary shapes and aspect ratios are rapidly altered during annealing, especially if the grains possessed highly contrasting internal strain energies. Experiments modelling two and three phase viscous deformation show that the rheology and microstructural evolution of a rock is largely determined by the linearity or non-linearity of viscous deformation; whereas the number of phases with differing viscosity is less important. Variations in strain in the same mineral phases can be used to infer flow properties. The spatial distribution of phases significantly influences the rheology at a specific point in time. During dynamic recrystallization the rates of the competing processes of grain size reduction and increase can have a systematic influence on the evolution of grain characteristics. Relatively high rates of grain size increasing processes result in larger grain sizes, lower aspect ratios, stabilization of grain size at lower strain and less strain localization. Numerical simulations can help to answer field related questions and to identify the number of significant active processes. They are also extremely useful as teaching tools as processes can easily be turned on or off, parameters can be changed and boundary conditions altered. Fortunately, numerical simulations have now matured to a point where users that do not want to spend time in coding a model can still perform and analyse numerical simulations.

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