ORCID Profile
0000-0001-7723-8170
Current Organisation
University of Leeds
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Geology | Structural Geology | Igneous and Metamorphic Petrology | Geodynamics | Inorganic Geochemistry
Expanding Knowledge in the Earth Sciences | Oil and Gas Exploration | Mineral Resources (excl. Energy Resources) not elsewhere classified | Precious (Noble) Metal Ore Exploration |
Publisher: Elsevier BV
Date: 02-2017
Publisher: Informa UK Limited
Date: 27-02-2019
Publisher: Elsevier BV
Date: 04-2014
Publisher: Elsevier BV
Date: 12-2006
Publisher: MyJove Corporation
Date: 04-2017
DOI: 10.3791/55506
Publisher: Elsevier BV
Date: 03-2017
Publisher: Mineralogical Society of America
Date: 20-12-2012
DOI: 10.2138/AM.2013.4179
Publisher: Trans Tech Publications, Ltd.
Date: 08-2014
DOI: 10.4028/WWW.SCIENTIFIC.NET/AMR.996.969
Abstract: Three natural polycrystalline diamond s les have been investigated non-destructively in their raw as-discovered forms. The s les originate from different locations in the world and possibly have different mechanisms of formation. The study reveals that the stones are primarily composed of cubic diamond with varying amounts of impurities that emanate from their excessive porosities and entrapped environmental contamination from the areas they were formed and subsequently discovered. Residual stress analyses with X-ray and neutron diffraction techniques of the diamond phase in the interior regions of the diamonds revealed low stress values.
Publisher: Geological Society of America
Date: 13-04-2020
DOI: 10.1130/G47126.1
Abstract: Localized rheological weakening is required to initiate and sustain intracontinental orogenesis, but the reasons for weakening remain debated. The intracontinental Alice Springs orogen dominates the lithospheric architecture of central Australia and involved prolonged (450–300 Ma) but episodic mountain building. The mid-crustal core of the orogen is exposed at its eastern margin, where field relationships and microstructures demonstrate that deformation was accommodated in biotite-rich shear zones. Rheological weakening was caused by localized melt-present deformation coupled with melt-induced reaction softening. This interpretation is supported by the coeval and episodic nature of melt-present deformation, igneous activity, and sediment shed from the developing orogen. This study identifies localized melt availability as an important ingredient enabling intracontinental orogenesis.
Publisher: Elsevier BV
Date: 05-2017
Publisher: American Geophysical Union (AGU)
Date: 09-2016
DOI: 10.1002/2015GC006236
Publisher: Wiley
Date: 18-11-2022
DOI: 10.1111/JMG.12698
Abstract: Melt migration through high‐strain zones in the crust fundamentally influences their rheological behaviour and is important for the transfer of fluids to upper crustal regions. The inference of former melt‐present deformation, based on field observations, may be h ered if the high‐strain zone experience a low time‐integrated melt flux or high melt volume expulsion during deformation. In these cases, typical macro‐scale field evidence of former melt presence limits interpretations. In this contribution, we investigate igneous field evidence ranging from obvious to cryptic in the Gough Dam shear zone (central Australia), a 2‐ to 4‐km‐wide high‐strain zone shown to have acted as a significant melt pathway during the Alice Springs Orogeny. Within bands of the high‐strain zone, granitic lenses are easily discernible in the field and are inferred to have formed during melt present deformation. Related coarse K‐feldspar is observed in biotite‐rich ( vol%) schist (glimmerite) as either isolated grains, forming trails (sub)parallel to the main foliation, or in aggregates with subordinate quartz. Detailed characterization of the granitic lenses shows that pockets of phenocrysts may be entrained in the shear zone. If melt expulsion and melt‐rock interaction is severe, isolated K‐feldspar grains in glimmerite may form. These grains exhibit (i) partially preserved crystal faces (ii) a lack of internal grain deformation (iii) reaction textures preferentially formed along the main crystallographic axes showing dissolution of K‐feldspar and precipitation of dominantly biotite (iv) low‐strain domains between multiple K‐feldspar grains being inferred to enclose crystallized melt pockets, with some apparently isolated grains showing connectivity in three dimensions and (v) a weak quartz and K‐feldspar crystallographic preferred orientation. These observations suggest an igneous phenocrystic origin for the isolated K‐feldspar grains hosted in glimmerite, which is consistent with the observed REE concentration patterns with positive Eu anomaly. We propose that the K‐feldspar phenocrysts are early‐formed crystals that were entrained into the glimmerite rocks as reactive melt migrated through the actively deformatting high‐strain zone. Previously entrained K‐feldspar phenocrysts were trapped during the collapse of the melt pathway when melt flux‐related fluid pressure waned while confining pressure and tectonic stress were still significant. The active deformation facilitated expulsion or loss of the melt phase but retainment and trapping of phenocrysts. Hence, the presence of isolated or ‘trains’ of K‐feldspar phenocrysts is a cryptic signature of syndeformational melt transfer. If melt transfer occurs in an open chemical system, phenocrysts will be entrained within the reaction product of melt‐rock interaction. We suggest that these so‐called trapped phenocrysts are a viable indicator of former syntectonic melt passage through rocks.
Publisher: Geological Society of America
Date: 20-12-2018
DOI: 10.1130/G39584.1
Publisher: Elsevier BV
Date: 08-2020
Publisher: Oxford University Press (OUP)
Date: 02-2018
Publisher: Copernicus GmbH
Date: 02-09-2015
Abstract: Abstract. The flow properties of middle crustal rocks are commonly represented by viscous flow. Ex les of pinch and swell structures found in a high strain zone at St. Anne Point (Fiordland, New Zealand) and Wongwibinda (N.S.W., Australia) suggest pinch and swell structures may be initiated by brittle failure of the more competent layer in conjunction with subsequent material softening. On this basis we develop a numerical model where Mohr–Coulomb constitutive strain localising behaviour is utilised to initiate pinch and swell structure development. Results show that pinch and swell structures develop in a competent layer in both Newtonian and non-Newtonian flow, provided the competent layer has sufficient viscosity contrast and can localise strain to form shear bands. The flow regime and strain localising characteristics of the surrounding country rock appear not to impact pinch and swell structure formation. The degree of material softening after the initial strain localising behaviour is shown to impact pinch and swell characteristics, while extensive material softening causes the formation of thick necks between swells by limiting the focused localisation of strain into shear bands. To aid analysis of the structures and help derive the flow properties of rocks in the field, we define three stages of pinch and swell development and offer suggestions for measurements to be made in the field. Our study suggests that Mohr–Coulomb strain localising behaviour combined with viscous flow is a viable alternative representation of the heterogeneous rheological behaviour of rocks seen in the middle crust. This type of mid-crustal rheological behaviour can have significant influence on the localisation of strain at all scales. For ex le, inclusion of Mohr–Coulomb strain localising behaviour with viscous flow in just some mid-crustal layers within a crustal-scale model can result in significant strain localisation, extending from the upper crust into the middle crust. This localisation also influences the development of near-surface structures.
Publisher: Informa UK Limited
Date: 09-10-2023
Publisher: Oxford University Press (OUP)
Date: 20-02-2016
Publisher: Wiley
Date: 08-06-2015
DOI: 10.1111/JMG.12132
Publisher: Trans Tech Publications, Ltd.
Date: 04-2012
DOI: 10.4028/WWW.SCIENTIFIC.NET/MSF.715-716.461
Abstract: n-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 s le of deformed single crystal halite was heated to between 260-400 °C. Before and after heating a volume of 500 by 500 by 300 μm was mapped using a planar beam, which was translated over the s le 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 °C. Additional small syn-heating maps over a constrained s le 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 s le 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 sub ision 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.
Publisher: American Geophysical Union (AGU)
Date: 10-2013
DOI: 10.1002/GGGE.20246
Publisher: Elsevier BV
Date: 09-2018
Publisher: Geological Society of America
Date: 27-09-2018
DOI: 10.1130/G45359.1
Publisher: Springer Science and Business Media LLC
Date: 12-10-2017
DOI: 10.1038/S41598-017-13221-6
Abstract: The metamorphic conditions and mechanisms required to induce foundering in deep arc crust are assessed using an ex le of representative lower crust in SW New Zealand. Composite plutons of Cretaceous monzodiorite and gabbro were emplaced at ~1.2 and 1.8 GPa are parts of the Western Fiordland Orthogneiss (WFO) ex les of the plutons are tectonically juxtaposed along a structure that excised ~25 km of crust. The 1.8 GPa Breaksea Orthogneiss includes suitably dense minor components (e.g. eclogite) capable of foundering at peak conditions. As the eclogite facies boundary has a positive dP/dT , cooling from supra-solidus conditions ( T 950 ºC) at high- P should be accompanied by omphacite and garnet growth. However, a high monzodioritic proportion and inefficient metamorphism in the Breaksea Orthogneiss resulted in its positive buoyancy and preservation. Metamorphic inefficiency and compositional relationships in the 1.2 GPa Malaspina Pluton meant it was never likely to have developed densities sufficiently high to founder. These relationships suggest that the deep arc crust must have primarily involved significant igneous accumulation of garnet–clinopyroxene (in proportions %). Crustal dismemberment with or without the development of extensional shear zones is proposed to have induced foundering of excised cumulate material at P 1.2 GPa.
Publisher: Copernicus GmbH
Date: 28-10-2022
Abstract: Abstract. Ice fabrics – the distribution of crystal orientations in a polycrystal – are key for understanding and predicting ice flow dynamics. Despite their importance, the characteristics and evolution of fabrics produced outside of the deformation regimes of pure and simple shear flow has largely been neglected, yet they are a common occurrence within ice sheets. Here, we use a recently developed numerical model (SpecCAF) to classify all fabrics produced over a continuous spectrum of incompressible two-dimensional deformation regimes and temperatures. The model has been shown to accurately predict ice fabrics produced in experiments, where the ice has been deformed in either uniaxial compression or simple shear. Here we use the model to reveal fabrics produced in regimes intermediate to pure and simple shear, as well as those that are more rotational than simple shear. We find that intermediate deformation regimes between pure and simple shear result in a smooth transition between a fabric characterised by a girdle and a secondary cluster pattern. Highly rotational deformation regimes are revealed to produce a weak girdle fabric. Furthermore, we provide regime diagrams to help constrain deformation conditions of measured ice fabrics. We also obtain predictions for the strain scales over which fabric evolution takes place at any given temperature. The use of our model in large-scale ice flow models and for interpreting fabrics observed in ice cores and seismic anisotropy provides new tools supporting the community in predicting and interpreting ice flow in a changing climate.
Publisher: American Geophysical Union (AGU)
Date: 10-2012
DOI: 10.1029/2012GC004250
Publisher: Copernicus GmbH
Date: 26-04-2021
DOI: 10.5194/TC-2021-118
Abstract: Abstract. Ice fabrics are key for understanding and predicting ice flow dynamics. Despite its importance, the characteristics and evolution of ice fabrics beyond pure and simple shear flow has largely been neglected. However, 80 % of the flow of ice in Antarctica is outside the regimes of pure and simple shear. We use a new validated numerical model (SpecCAF), which has been shown to accurately reproduce experimentally observed fabrics in both compression and simple shear, to explore the fabrics produced between pure and simple shear, as well as those that are highly rotational. We present a definitive classification of all fabric patterns. We find that intermediate deformations between pure and simple shear result in a smooth transition between a fabric characterised by a cone-shape and a secondary cluster pattern. Highly-rotational fabrics are found to produce a weak girdle fabric. In addition we obtain complete predictions for the strain required for any fabric under a 2D deformation to reach steady state at any given temperature. Use of our data in current ice flow models as well as for ice core fabric and seismic anisotropy interpretation will enhance the communities' ability to predict future ice flow in a changing climate.
Publisher: Wiley
Date: 19-02-2004
DOI: 10.1111/J.0022-2720.2004.01304.X
Abstract: The combination of subgrain- and grain-scale microstructural data collected during in-situ heating experiments and numerical simulations of equivalent microstructural development offers an innovative and powerful tool in the advancement of the understanding of microstructural processes. We present a system that fully integrates subgrain- to grain-scale crystallographic data obtained during in-situ observations during heating experiments in a scanning electron microscope and the two-dimensional hybrid numerical modelling system Elle. Such a system offers the unique opportunity to test and verify theories for microstructural development, as predictions made by numerical simulations can be directly coupled to appropriate physical experiments and, conversely, theoretical explanations of experimental observations should be testable with numerical simulations. Discrepancies between data obtained with both techniques suggest the need for an in-depth investigation and thus open up new avenues of theory development, modification and verification. In addition, because in numerical models it is possible to select the processes modelled, the effect of in idual processes on the microstructural development of a specific material can be quantified. To illustrate the potential and methodology of the so-called EBSD2Elle system, two in-situ experiments and their equivalent numerical experiments are presented. These are static heating experiments of (a) an annealed Ni-foil coupled with a front tracking model for grain growth and (b) a cold deformed rock salt with kinetic Monte Carlo simulations for subgrain growth.
Publisher: Elsevier BV
Date: 07-2015
Publisher: Wiley
Date: 29-05-2019
DOI: 10.1111/JMG.12488
Abstract: Melt must transfer through the lower crust, yet the field signatures and mechanisms involved in such transfer zones (excluding dykes) are still poorly understood. We report field and microstructural evidence of a deformation‐assisted melt transfer zone that developed in the lower crustal magmatic arc environment of Fiordland, New Zealand. A 30–40 m wide hornblende‐rich body comprising hornblende ± clinozoisite and/or garnet exhibits 'igneous‐like' features and is hosted within a metamorphic, two‐pyroxene–pargasite gabbroic gneiss (GG). Previous studies have interpreted the hornblende‐rich body as an igneous cumulate or a mass transfer zone. We present field and microstructural characteristics supporting the later and indicating the body has formed by deformation‐assisted, channelized, reactive porous melt flow. The host granulite facies GG contains distinctive rectilinear dykes and garnet reaction zones (GRZ) from earlier in the geological history these form important reaction and strain markers. Field observations show that the mineral assemblages and microstructures of the GG and GRZ are progressively modified with proximity to the hornblende‐rich body. At the same time, GRZ bend systematically into the hornblende‐rich body on each side of the unit, showing apparent sinistral shearing. Within the hornblende‐rich body itself, microstructures and electron back‐scatter diffraction mapping show evidence of the former presence of melt including observations consistent with melt crystallization within pore spaces, elongate pseudomorphs of melt films along grain boundaries, minerals with low dihedral angles as small as ° and up to °, and interconnected 3D melt pseudomorph networks. Reaction microstructures with highly irregular contact boundaries are observed at the field and thin‐section scale in remnant islands of original rock and replaced grains, respectively. We infer that the hornblende‐rich body was formed by modification of the host GG in situ due to reaction between an externally derived, reactive, hydrous gabbroic to intermediate melt percolating via porous melt flow through an actively deforming zone. Extensive melt–rock interaction and metasomatism occurred via coupled dissolution–precipitation, triggered by chemical disequilibrium between the host rock and the fluxing melt. As a result, the host plagioclase and pyroxene became unstable and were reacted and dissolved into the melt, while hornblende and to a lesser extent clinozoisite and garnet grew replacing the unstable phases. Our study shows that hornblendite rocks commonly observed within deep crustal sections, and attributed to cumulate fractionation processes, may instead delineate areas of deformation‐assisted, channelized reactive porous melt flow formed by melt‐mediated coupled dissolution–precipitation replacement reactions.
Publisher: Elsevier BV
Date: 11-2016
Publisher: Informa UK Limited
Date: 02-02-2020
Publisher: Mineralogical Society of America
Date: 2019
DOI: 10.2138/AM-2019-6503
Publisher: Elsevier BV
Date: 09-2016
Publisher: Elsevier BV
Date: 12-2014
Publisher: Geological Society of London
Date: 09-12-2013
DOI: 10.1144/SP394.11
Publisher: Springer Science and Business Media LLC
Date: 12-02-2016
DOI: 10.1038/NCOMMS10490
Abstract: Trace elements diffuse negligible distances through the pristine crystal lattice in minerals: this is a fundamental assumption when using them to decipher geological processes. For ex le, the reliable use of the mineral zircon (ZrSiO 4 ) as a U-Th-Pb geochronometer and trace element monitor requires minimal radiogenic isotope and trace element mobility. Here, using atom probe tomography, we document the effects of crystal–plastic deformation on atomic-scale elemental distributions in zircon revealing sub-micrometre-scale mechanisms of trace element mobility. Dislocations that move through the lattice accumulate U and other trace elements. Pipe diffusion along dislocation arrays connected to a chemical or structural sink results in continuous removal of selected elements (for ex le, Pb), even after deformation has ceased. However, in disconnected dislocations, trace elements remain locked. Our findings have important implications for the use of zircon as a geochronometer, and highlight the importance of deformation on trace element redistribution in minerals and engineering materials.
Publisher: Mineralogical Society of America
Date: 07-2015
DOI: 10.2138/AM-2015-5044
Publisher: Elsevier BV
Date: 11-2017
Publisher: CSIRO Publishing
Date: 2015
DOI: 10.1071/RS15011
Abstract: Major polar ice sheets and ice caps experience cycles of variable flow during different glacial periods and as a response to past warming. The rate and localisation of deformation inside an ice body controls the evolution of ice microstructure and crystallographic fabric. This is critical for interpreting proxy signals for climate change, with deformation overprinting and disrupting stratigraphy deep under ice caps due to the nature of the flow. The final crystallographic fabric in polar ice sheets provides a record of deformation history, which in turn controls the flow properties of ice during further deformation and affects geophysical sensing of ice sheets. For ex le, identification of layering in ice sheets, using seismic or ice radar techniques, is attributed to grain size changes and fabric variations. Such information has been used to provide information on climate state and its changes over time, and as the Fourth Intergovernmental Panel on Climate Change (IPCC) Report (Solomon et al. 2007) points out there is currently still a lack of understanding of internal ice-sheet dynamics. To answer this we have recently conducted experiments at the Australian Nuclear Science and Technology Organisation (ANSTO) to collect fully quantitative microstructural data from polycrystalline heavy water (D2O) ice deformed in a dynamic regime. The ice and temperature (–7°C) chosen for this study is used as a direct analogue for deforming natural-water ice as it offers a unique opportunity to link grain size and texture evolution in natural ice at –10°C. Results show a dynamic system where steady-state rheology is not necessarily coupled to microstructural and crystallographic fabric stability. This link needs to be taken into account to improve ice-mass-deformation modelling critical for climate change predictions.
Publisher: Elsevier BV
Date: 11-2017
Publisher: Copernicus GmbH
Date: 23-03-2020
DOI: 10.5194/EGUSPHERE-EGU2020-12862
Abstract: & & & span& The studied outcrop, located within the Bergen arcs of southwestern Norway, preserves the hydration of an anorthositic granulite at hibolite-facies conditions. The hibolite-facies hydration is expressed as both a statically hydrated hibolite and a shear zone rock, defined by the interlayering of hibolite with leucocratic domains. Within the outcrop, quartz-filled fractures and their associated hibolite alteration haloes crosscut the granulite. These fractures are relicts of the initial fluid infiltration event. The fracture assemblage (quartz + plagioclase + zoisite + kyanite & #177 muscovite & #177 biotite) is equivalent to that occurring locally within leucocratic domains of the shear zone. Due to the textural and compositional similarities between quartz-filled fractures and leucocratic domains, the compositional layering of the shear zone rock may be directly linked to fracturing during initial fluid infiltration. Mass-balance calculations indicate quartz-filled fractures and compositional differentiation of the shear zone form by internal fractionation rather than partial melting or precipitation of minerals from an eternally derived fluid. This inferred fluid connectivity combined with the enhanced local dissolution indicates the presence of a continuously replenished fluid along fracture pathways. The overall conclusion is that the mass transfer processes that result in metamorphic differentiation of the shear zone lithologies are dependent on both continuous fluid flux and heterogeneous strain distribution. & /span& & &
Publisher: Elsevier BV
Date: 04-2018
Publisher: Elsevier BV
Date: 08-2019
Publisher: American Geophysical Union (AGU)
Date: 09-2016
DOI: 10.1002/2016GC006471
Publisher: Elsevier BV
Date: 11-2005
Publisher: Springer Science and Business Media LLC
Date: 22-08-2016
DOI: 10.1038/SREP31369
Abstract: Geochemical signatures throughout the layered Earth require significant mass transfer through the lower crust, yet geological pathways are under-recognized. Elongate bodies of basic to ultrabasic rocks are ubiquitous in exposures of the lower crust. Ultrabasic hornblendite bodies hosted within granulite facies gabbroic gneiss of the Pembroke Valley, Fiordland, New Zealand, are typical occurrences usually reported as igneous cumulate hornblendite. Their igneous features contrast with the metamorphic character of their host gabbroic gneiss. Both rock types have a common parent field relationships are consistent with modification of host gabbroic gneiss into hornblendite. This precludes any interpretation involving cumulate processes in forming the hornblendite these bodies are imposter cumulates. Instead, replacement of the host gabbroic gneiss formed hornblendite as a result of channeled high melt flux through the lower crust. High melt/rock ratios and disequilibrium between the migrating magma (granodiorite) and its host gabbroic gneiss induced dissolution (grain-scale magmatic assimilation) of gneiss and crystallization of mainly hornblende from the migrating magma. The extent of this reaction-replacement mechanism indicates that such hornblendite bodies delineate significant melt conduits. Accordingly, many of the ubiquitous basic to ultrabasic elongate bodies of the lower crust likely map the ‘missing’ mass transfer zones.
Publisher: Elsevier BV
Date: 11-2016
Publisher: Copernicus GmbH
Date: 04-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-12078
Abstract: & & Antarctic ice flow shows deviation from the deformation regimes of pure and simple shear. By analysing the vorticity number from surface velocity data it is found that approximately 80% of the flow is outside these regimes. These deformations are both between pure and simple shear, as well as highly rotational, highlighting the need for fabric predictions away from the commonly studied regimes of pure and simple shear.& & / & & & We use the numerical scheme SpecCAF, which has been shown to accurately reproduce experimentally observed fabrics with no free parameters, to study ice fabrics in such general deformations. By exploring the parameter space of temperature and vorticity number, we present a definitive classification of fabrics patterns which arise, and construct a universal regime diagram for ice fabrics under general two-dimensional deformation. We find that intermediate deformations see a smooth transition between a cone-shape fabric and a secondary cluster. We present the first investigation of the fabrics produced in highly rotational deformations, which produce a weak girdle fabric with the axis aligned to the vorticity axis. We also show that across deformation and temperature space fabrics only reach a true steady-state above strains of 200%, and there is significant variation in this across the parameter space. & & / &
Publisher: Copernicus GmbH
Date: 23-03-2020
DOI: 10.5194/EGUSPHERE-EGU2020-12939
Abstract: & & & span& Metamorphic differentiation, resulting in the segregation of minerals into compositional bands, is a common feature of metamorphic rocks. Considering the ubiquitous nature of compositionally layered metamorphic rocks, the processes that are responsible for metamorphic differentiation have received very little attention. The studied outcrop, located within the Bergen arcs of southwestern Norway, preserves the hydration of an anorthositic granulite at hibolite-facies conditions. The hibolite-facies hydration is expressed as both a statically hydrated hibolite and a shear zone rock, defined by the interlayering of hibolite with leucocratic domains. Detailed petrography, quantitative mineral chemistry and bulk rock analyses are applied to investigate compositional variation with assemblage microstructure. Within the outcrop, quartz-filled fractures and their associated hibolite alteration haloes, are observed crosscutting the granulite. These fractures are demonstrated to be relict of the initial fluid infiltration event. The fracture assemblage (quartz + plagioclase + zoisite + kyanite & #177 muscovite & #177 biotite) is equivalent to that occurring locally within leucocratic domains of the shear zone. Due to the textural and compositional similarities between quartz-filled fractures and leucocratic domains, the compositional layering of the shear zone rock may be directly linked to fracturing during initial fluid infiltration. & /span& & & & & & span& & & & & & & & & & & & Mass-balance and thermodynamic calculations indicate quartz-filled fractures and compositional differentiation of the shear zone form by internal fractionation rather than partial melting or precipitation of minerals from an eternally derived fluid. The process of internal fractionation within the shear zone is attributed to enhanced dissolution along fracture pathways, resulting in the loss of MgO, Fe& sub& & /sub& O& sub& & /sub& and K& sub& & /sub& O within leucocratic domains. These elements, being more mobile in the fluid, are then transported and ultimately either precipitated in hibolite lithologies or escape with the fluid, resulting in an overall volume loss in the shear zone. This inferred fluid connectivity combined with the enhanced local dissolution indicates the presence of a continuously replenished fluid along fracture pathways, leading to the overall conclusion that the mass transfer processes that result in metamorphic differentiation of the shear zone lithologies are dependent on both continuous fluid flux and heterogeneous strain distribution. & /span& & &
Publisher: Elsevier BV
Date: 07-2016
Publisher: Cambridge University Press (CUP)
Date: 27-12-2018
DOI: 10.1017/JOG.2018.100
Abstract: This contribution discusses results obtained from 3-D neutron diffraction and 2-D fabric analyser in situ deformation experiments on laboratory-prepared polycrystalline deuterated ice and ice containing a second phase. The two-phase s les used in the experiments are composed of an ice matrix with (1) air bubbles, (2) rigid, rhombohedral-shaped calcite and (3) rheologically soft, platy graphite. S les were tested at 10°C below the melting point of deuterated ice at ambient pressures, and two strain rates of 1 × 10 −5 s −1 (fast) and 2.5 × 10 −6 s −1 (medium). Nature and distribution of the second phase controlled the rheological behaviour of the ice by pinning grain boundary migration. Peak stresses increased with the presence of second-phase particles and during fast strain rate cycles. Ice-only s les exhibit well-developed crystallographic preferred orientations (CPOs) and dynamically recrystallized microstructures, typifying deformation via dislocation creep, where the CPO intensity is influenced in part by the strain rate. CPOs are accompanied by a concentration of [ c ]-axes in cones about the compression axis, coinciding with increasing activity of prismatic- a slip activity. Ice with second phases, deformed in a relatively slower strain rate regime, exhibit greater grain boundary migration and stronger CPO intensities than s les deformed at higher strain rates or strain rate cycles.
Publisher: Wiley
Date: 25-11-2019
DOI: 10.1111/JMG.12514
Publisher: American Geophysical Union (AGU)
Date: 06-2022
DOI: 10.1029/2021JE007080
Abstract: The Martian nakhlite meteorites, which represent multiple events that belong to a single magma source region represent a key opportunity to study the evolution of Martian petrogenesis. Here 16 of the 26 identified nakhlite specimens are studied using coupled electron backscatter diffraction (EBSD) and emplacement end‐member calculations. EBSD was used to determine shape preferred orientation of contained augite (high Ca‐clinopyroxene) phenocrysts by considering their crystallographic preferred orientation (CPO). Parameters derived from EBSD, and energy dispersive X‐ray spectroscopy spectra were used in basic emplacement models to assess their dominant mechanism against three end‐member scenarios: thermal diffusion, crystal settling, and crystal convection. Results from CPO analyses indicate low intensity weak‐moderate CPO. In all s les, a consistent foliation within the axes of augite are observed typically coupled with a weaker lineation CPO in one of the other crystallographic axes. These CPO results agree best with crystal settling being the dominant emplacement mechanism for the nakhlites. Modeled crystal settling results identify two distinguishable groups outside of the model's resolution indicating the presence of secondary emplacement mechanisms. Comparison of the two identified groups against CPO, geochemical, and age parameters indicate random variability between in idual meteorites. Therefore, coupled CPO and emplacement modeling results identify an overarching characteristic of a dominant crystal settling emplacement mechanism for the nakhlite source volcano despite exhibiting random variation with each discharge through time.
Publisher: Trans Tech Publications, Ltd.
Date: 04-2012
DOI: 10.4028/WWW.SCIENTIFIC.NET/MSF.715-716.502
Abstract: The understanding of the dynamics of substructures during deformation and annealing is fundamental in our ability to predict microstructural and physical properties such as rheological behaviour of crystalline materials. Here, we present an overview of new insights into substructure dynamics through a combination of in-situ heating experiments, detailed Electron Backscatter Diffraction (EBSD) analysis and numerical modelling.
Publisher: Informa UK Limited
Date: 27-01-2020
Publisher: American Geophysical Union (AGU)
Date: 12-2019
DOI: 10.1029/2019GC008633
Publisher: Elsevier BV
Date: 02-2021
Publisher: American Geophysical Union (AGU)
Date: 06-2022
DOI: 10.1029/2021JE007082
Abstract: Deformation is a near ubiquitous process that is observed within nearly all naturally forming rocks. Electron backscatter diffraction (EBSD) is a technique that enables slip‐systems (a form of plastic deformation) to be inferred from intracrystalline misorientations at a comparable scale to the representative CPO analysis (≥300 crystals for the nakhlites). Extensive laboratory and studies on naturally occurring s les have identified preferential mantle condition extrinsic parameters for specific slip‐system signatures within olivine and clinopyroxene. Intracrystalline misorientation patterns for olivine and augite (high Ca‐clinopyroxene) for 16 different Martian nakhlite meteorites (21 sections) were analyzed and assessed against these known parameters. Investigation of high and low deformation regions within the nakhlites revealed a shift in intracrystalline misorientation patterns for 10 of the 21 sections. Interpreted as both shock (high deformations) and emplacement (low deformation) signatures, the observed variations in deformation patterns for the two main regimes of deformation indicate heterogeneous s ling of the nakhlite source crater. Our findings indicate that shock deformation is prevalent throughout the nakhlites, and that great care needs to be taken when interpreting intracrystalline misorientations of crystals within apparent lower deformation regions.
Publisher: Elsevier BV
Date: 08-2019
Publisher: Wiley
Date: 19-03-2019
DOI: 10.1111/JMG.12473
Abstract: The Breaksea Orthogneiss in Fiordland, New Zealand preserves water‐poor intermediate and mafic igneous rocks that were partially recrystallized to omphacite granulite and eclogite, respectively, at P ≈ 1.8 GP a and T ≈ 850°C. Metamorphic reaction consumed plagioclase and produced grossular‐rich garnet, jadeite‐rich omphacite, clinozoisite and kyanite. The extent of metamorphic reaction, identified by major and trace element composition and microstructural features, is patchy on the grain and outcrop scale. Domains of re‐equilibration coincide with areas that exhibit higher strain suggesting a causal link between crystal plastic strain and metamorphic reaction. Quantitative orientation analysis ( EBSD ) identifies gradual and stepped changes in crystal lattice orientations of igneous phenocrysts that are surrounded by homophase areas of neoblasts, characterized by high grain boundary to volume ratios and little to no internal lattice distortion. The narrow, peripheral compositional modification of less deformed garnet and omphacite phenocrysts reflects limited lattice diffusion in areas that lacked three‐dimensional networks of interconnected low‐angle boundaries. Low‐angle boundaries acted as elemental pathways (pipe diffusion) that enhanced in‐grain element diffusion. The scale of pipe diffusion is pronounced in garnet relatively to clinopyroxene. Strain‐induced mineral transformation largely controlled the extent of high‐ T metamorphic reaction under relatively fluid‐poor conditions.
Publisher: Wiley
Date: 07-12-2016
DOI: 10.1111/JMG.12231
Publisher: American Geophysical Union (AGU)
Date: 12-2018
DOI: 10.1029/2018TC005106
Abstract: The accommodation of intraplate stresses in preexisting weak regions of plate interiors is here investigated using thin viscous sheet numerical models. The intraplate stresses are governed by multicomponent and multidirectional stresses originating at plate boundaries. The modeled scenarios mimic plate boundary conditions during the intraplate Alice Springs Orogeny (ASO), central Australia, and include (1) a northwest‐southeast zone of weak lithosphere within strong continental blocks to the north and southand (2) a principal south directed stress condition at the northern boundary that causes minor clockwise rotation of the northern block. Alternative tectonic environments are investigated in additional models that include (1) secondary compressional or extensional stresses acting at the eastern boundary, representing the temporally variable stress conditions during the Tasmanides Orogeny, and (2) an eastern wedge‐shaped zone of rheologically weak lithosphere, mirroring rift fill of the Irindina subbasin. Our results highlight that a low angle between major crustal features (e.g., orogenic elongation and preexisting regional structures) and the principal transmitted stresses is highly relevant in the concentration of elevated levels of differential stress and subsequent localization of deformation in plate interiors. Secondary stresses orthogonal to the principal acting stresses may introduce effects that explain the episodic orogenic activity in the case of the ASO. The combination of secondary extensional stresses at the eastern boundary of Australia and weak lithosphere of the preexisting Irindina subbasin strongly influences the observed spatial strain intensity, localization, and kinematics of deformation during the ASO.
Publisher: Trans Tech Publications, Ltd.
Date: 04-2012
DOI: 10.4028/WWW.SCIENTIFIC.NET/MSF.715-716.62
Abstract: Misorientation can be calculated over large datasets and a theme of this paper is the usefulness of examining the results statistically. Comparing the statistics of misorientations calculated from neighbouring pixels (or grains) with those calculated from pairs of pixels (or grains) selected at random helps to indicate deformation and recrystallisation mechanisms. Taking boundary length into account provides a link to grain boundary energy, and boundary length versus misorientation data should be used to examine how boundaries with different misorientations evolve through time. Time lapse misorientation maps indicate how orientation changes through time at particular points in a microstructure during in situ experiments. The size of areas which have changed orientation by particular amounts can be linked to boundary length and boundary migration velocities. When dealing with different phases, the statistics of angular relationships, akin to intraphase misorientation analysis, can indicate orientation relationships in the absence of prior knowledge, which is advantageous in investigating the plethora of minerals that make up the Earth.
Publisher: Copernicus GmbH
Date: 15-05-2023
DOI: 10.5194/EGUSPHERE-EGU23-15396
Abstract: Oxide mineral phases within high-grade metamorphic rocks are often largely ignored compared to silicate minerals, except for when constraining the redox state of a s le. It is becoming increasingly apparent that unusual concentrations of oxide phases (e.g. magnetite, ilmenite and spinel) are more common in granulite facies metamorphic rocks that previously thought. However, the mechanism of their formation remains poorly constrained. For ex le, it is currently unclear what process or combination of processes result in high (over 50% oxide concentration in a s le in some cases) concentrations. There is an ongoing debate if a single process can be applied across all protoliths, with the goal that these assemblages could be used to pinpoint particular crustal process(es). A number of mechanisms have been suggested to form such extreme concentrations of oxides within metamorphic rocks. These include melt fluxing in a deformation zone (Ghatak et al., 2022), partial melt loss (Morrissey et al., 2016), deformation related metamorphic reactions and protolith composition or a combination thereof. Within a collection of high grade metapelites from Rogaland, SW Norway, we see variations in mineralogy, including changes in orthopyroxene and cordierite content with oxide concentrations, variations in grain size, variable layering as well as variable signature of the amount of deformation. Using a combination of microstructures, EBSD, EDS, XCT and other& data we will assess and illustrate the processes behind the generation of high oxide concentrations within metapelites and what this could mean for crustal processes during high-grade metamorphism.& Ghatak, H., Gardner, R. L., Daczko, N. R., Piazolo, S., & Milan, L. (2022). Oxide enrichment by syntectonic melt-rock interaction. Lithos, 414& #8211 , 106617. 0.1016/J.LITHOS.2022.106617Morrissey, L. J., Hand, M., Lane, K., Kelsey, D. E., & Dutch, R. A. (2016). Upgrading iron-ore deposits by melt loss during granulite facies metamorphism. Ore Geology Reviews, 74, 101& #8211 . ttp://0.1016/j.oregeorev.2015.11.012
Publisher: Geological Society of London
Date: 2002
Publisher: Springer Science and Business Media LLC
Date: 2010
Publisher: Springer Science and Business Media LLC
Date: 13-11-2015
DOI: 10.1038/SREP16484
Abstract: Investigations of the Mantle Transition Zone (MTZ 410–660 km deep) by deformation experiments and geophysical methods suggest that the MTZ has distinct rheological properties, but their exact cause is still unclear due to the lack of natural s les. Here we present the first direct evidence for crystal-plastic deformation by dislocation creep in the MTZ using a chromitite from the Luobusa peridotite (E. Tibet). Chromite grains show exsolution of diopside and SiO 2 , suggesting previous equilibration in the MTZ. Electron backscattered diffraction (EBSD) analysis reveals that olivine grains co-existing with exsolved phases inside chromite grains and occurring on chromite grain boundaries have a single pronounced crystallographic preferred orientation (CPO). This suggests that olivine preserves the CPO of a high-pressure polymorph (wadsleyite) before the high-pressure polymorph of chromite began to invert and exsolve. Chromite also shows a significant CPO. Thus, the fine-grained high-pressure phases were deformed by dislocation creep in the MTZ. Grain growth in inverted chromite produced an equilibrated microstructure during exhumation to the surface, masking at first sight its MTZ deformation history. These unique observations provide a window into the deep Earth and constraints for interpreting geophysical signals and their geodynamic implications in a geologically robust context.
Publisher: American Association for the Advancement of Science (AAAS)
Date: 06-09-2019
Abstract: Evidence for impact-generated water on Mars ~633 Ma ago predicts two craters at the nakhlite meteorite’s ejection site.
Publisher: Oxford University Press (OUP)
Date: 30-01-2017
DOI: 10.1017/S1431927616012745
Abstract: The application of atom probe tomography to the study of minerals is a rapidly growing area. Picosecond-pulsed, ultraviolet laser (UV-355 nm) assisted atom probe tomography has been used to analyze trace element mobility within dislocations and low-angle boundaries in plastically deformed specimens of the nonconductive mineral zircon (ZrSiO 4 ), a key material to date the earth’s geological events. Here we discuss important experimental aspects inherent in the atom probe tomography investigation of this important mineral, providing insights into the challenges in atom probe tomography characterization of minerals as a whole. We studied the influence of atom probe tomography analysis parameters on features of the mass spectra, such as the thermal tail, as well as the overall data quality. Three zircon s les with different uranium and lead content were analyzed, and particular attention was paid to ion identification in the mass spectra and detection limits of the key trace elements, lead and uranium. We also discuss the correlative use of electron backscattered diffraction in a scanning electron microscope to map the deformation in the zircon grains, and the combined use of transmission Kikuchi diffraction and focused ion beam s le preparation to assist preparation of the final atom probe tip.
Publisher: Elsevier BV
Date: 04-2017
Publisher: Elsevier BV
Date: 11-2012
Publisher: Elsevier BV
Date: 02-2015
Publisher: Copernicus GmbH
Date: 27-03-2022
DOI: 10.5194/EGUSPHERE-EGU22-3743
Abstract: & & Accurately predicting ice crystal fabrics is key to understanding the processes and deformation in ice-sheets. Here we use SpecCAF, a continuum fabric evolution model validated against laboratory experiments, to predict the fabric evolution with an active ice stream. This is done by predicting the fabrics at the East Greenland Ice core Project (EGRIP) site. We do this using satellite data and inferred particle paths, combined with the shallow ice approximation (with basal slip) to infer a leading order approximation for the deformation through the ice sheet. We find that SpecCAF is able to predict the patterns observed at EGRIP - a girdle/horizontal maxima fabric perpendicular to the flow direction. By reducing the rate of rotational recrystallization in the model we are also able to predict the fabric strength at EGRIP. This suggests the effect of rotational recrystallization on the fabric may be primarily strain-rate/stress dependent. These results show SpecCAF can be applied to real-world conditions and provide insights into the deformation and basal-conditions of the ice sheet. As the model only considers deformation and recrystallization through dislocation creep, the results imply that - for the ice stream modelled - no other process is significantly influencing both the produced ice fabric and the deformation. We find that the model gives best results for full slip at the base of the ice sheet, implying that the level of sliding at the base of the ice sheet in the North Greenland Ice stream may be very high. The methodology used here can be extended to other ice core locations in Greenland and Antarctica.& &
Publisher: Elsevier BV
Date: 08-2019
Publisher: Wiley
Date: 18-11-2016
DOI: 10.1111/JMG.12229
Publisher: Wiley
Date: 25-06-2018
DOI: 10.1111/JMG.12427
Publisher: Springer Science and Business Media LLC
Date: 27-01-2017
DOI: 10.1038/NCOMMS14032
Abstract: Deformation microstructures are widely used for reconstructing tectono-metamorphic events recorded in rocks. In crustal settings deformation is often accompanied and/or succeeded by fluid infiltration and dissolution–precipitation reactions. However, the microstructural consequences of dissolution–precipitation in minerals have not been investigated experimentally. Here we conducted experiments where KBr crystals were reacted with a saturated KCl-H 2 O fluid. The results show that reaction products, formed in the absence of deformation, inherit the general crystallographic orientation from their parents, but also display a development of new microstructures that are typical in deformed minerals, such as apparent bending of crystal lattices and new subgrain domains, separated by low-angle and, in some cases, high-angle boundaries. Our work suggests that fluid-mediated dissolution–precipitation reactions can lead to a development of potentially misleading microstructures. We propose a set of criteria that may help in distinguishing such microstructures from the ones that are created by crystal-plastic deformation.
Publisher: American Geophysical Union (AGU)
Date: 2018
DOI: 10.1002/2017TC004638
Publisher: Schweizerbart
Date: 12-06-2013
Publisher: Springer Science and Business Media LLC
Date: 26-04-2001
Location: United Kingdom of Great Britain and Northern Ireland
Start Date: 2012
End Date: 01-2017
Amount: $815,859.00
Funder: Australian Research Council
View Funded ActivityStart Date: 07-2022
End Date: 07-2025
Amount: $413,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 2012
End Date: 03-2016
Amount: $230,000.00
Funder: Australian Research Council
View Funded Activity