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David Healy - One of the best experts on this subject based on the ideXlab platform.
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Resolution of impact-related Microstructures in lunar zircon: A shock-Deformation mechanism map
Meteoritics & Planetary Science, 2011Co-Authors: Nicholas E. Timms, Steven M. Reddy, David Healy, Alexander A. Nemchin, Marion Grange, Robert T. Pidgeon, Robert D. HartAbstract:Abstract– The Microstructures of lunar zircon grains from breccia samples 72215, 73215, 73235, and 76295 collected during the Apollo 17 mission have been characterized via optical microscopy, cathodoluminescence imaging, and electron backscatter diffraction mapping. These zircon grains preserve Deformation Microstructures that show a wide range in style and complexity. Planar Deformation features (PDFs) are documented in lunar zircon for the first time, and occur along {001}, {110}, and {112}, typically with 0.1–25 μm spacing. The widest PDFs associated with {112} contain microtwin lamellae with 65°/ misorientation relationships. Deformation bands parallel to {100} planes and irregular low-angle ( misorientation axes. This geometry is consistent with a dislocation glide system with {010} during dislocation creep. Nonplanar fractures, recrystallized domains with sharp, irregular interfaces, and localized annealing textures along fractures are also observed. No occurrences of reidite were detected. Shock-Deformation Microstructures in zircon are explained in terms of elastic anisotropy of zircon. PDFs form along a limited number of specific {hkl} planes that are perpendicular to directions of high Young’s modulus, suggesting that PDFs are likely to be planes of longitudinal lattice damage. Twinned {112} PDFs also contain directions of high shear modulus. A conceptual model is proposed for the development of different Deformation Microstructures during an impact event. This “shock-Deformation mechanism map” is used to explain the relative timing, conditions, and complexity relationships between impact-related Deformation Microstructures in zircon.
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relationship among titanium rare earth elements u pb ages and Deformation Microstructures in zircon implications for ti in zircon thermometry
Chemical Geology, 2011Co-Authors: Nicholas E. Timms, Steven M. Reddy, Peter D. Kinny, Katy Evans, Chris Clark, David HealyAbstract:Abstract A zircon grain in an orthopyroxene–garnet–phlogopite–zircon–rutile-bearing xenolith from Udachnaya, Siberia, preserves a pattern of crystallographic misorientation and subgrain microstructure associated with crystal–plastic Deformation. The zircon grain records significant variations in titanium (Ti) from 2.6 to 30 ppm that corresponds to a difference in calculated Ti-in-zircon temperatures of over several hundred degrees Celsius. The highest Ti concentration is measured at subgrain centres (30 ppm), and Ti is variably depleted at low-angle boundaries (down to 2.6 ppm). Variations in cathodoluminescence coincide with the Deformation microstructure and indicate localised, differential enrichment of rare earth elements (REE) at low-angle boundaries. Variable enrichment of U and Th and systematic increase of Th/U from 1.61 to 3.52 occurs at low-angle boundaries. Individual SHRIMP-derived U–Pb ages from more deformed zones (mean age of 1799 ± 40, n = 22) are systematically younger than subgrain cores (mean age of 1851 ± 65 Ma, n = 7), and indicate that open system behaviour of Ti–Th–U occurred shortly after zircon growth, prior to the accumulation of significant radiogenic Pb. Modelling of trace-element diffusion distances for geologically reasonable thermal histories indicates that the observed variations are ~ 5 orders of magnitude greater than can be accounted for by volume diffusion. The data are best explained by enhanced diffusion of U, Th and Ti along Deformation-related fast-diffusion pathways, such as dislocations and low-angle (
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Relationship among titanium, rare earth elements, U–Pb ages and Deformation Microstructures in zircon: Implications for Ti-in-zircon thermometry
Chemical Geology, 2010Co-Authors: Nicholas E. Timms, Steven M. Reddy, Peter D. Kinny, Katy Evans, Chris Clark, David HealyAbstract:Abstract A zircon grain in an orthopyroxene–garnet–phlogopite–zircon–rutile-bearing xenolith from Udachnaya, Siberia, preserves a pattern of crystallographic misorientation and subgrain microstructure associated with crystal–plastic Deformation. The zircon grain records significant variations in titanium (Ti) from 2.6 to 30 ppm that corresponds to a difference in calculated Ti-in-zircon temperatures of over several hundred degrees Celsius. The highest Ti concentration is measured at subgrain centres (30 ppm), and Ti is variably depleted at low-angle boundaries (down to 2.6 ppm). Variations in cathodoluminescence coincide with the Deformation microstructure and indicate localised, differential enrichment of rare earth elements (REE) at low-angle boundaries. Variable enrichment of U and Th and systematic increase of Th/U from 1.61 to 3.52 occurs at low-angle boundaries. Individual SHRIMP-derived U–Pb ages from more deformed zones (mean age of 1799 ± 40, n = 22) are systematically younger than subgrain cores (mean age of 1851 ± 65 Ma, n = 7), and indicate that open system behaviour of Ti–Th–U occurred shortly after zircon growth, prior to the accumulation of significant radiogenic Pb. Modelling of trace-element diffusion distances for geologically reasonable thermal histories indicates that the observed variations are ~ 5 orders of magnitude greater than can be accounted for by volume diffusion. The data are best explained by enhanced diffusion of U, Th and Ti along Deformation-related fast-diffusion pathways, such as dislocations and low-angle (
Nicholas E. Timms - One of the best experts on this subject based on the ideXlab platform.
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Resolution of impact-related Microstructures in lunar zircon: A shock-Deformation mechanism map
Meteoritics & Planetary Science, 2011Co-Authors: Nicholas E. Timms, Steven M. Reddy, David Healy, Alexander A. Nemchin, Marion Grange, Robert T. Pidgeon, Robert D. HartAbstract:Abstract– The Microstructures of lunar zircon grains from breccia samples 72215, 73215, 73235, and 76295 collected during the Apollo 17 mission have been characterized via optical microscopy, cathodoluminescence imaging, and electron backscatter diffraction mapping. These zircon grains preserve Deformation Microstructures that show a wide range in style and complexity. Planar Deformation features (PDFs) are documented in lunar zircon for the first time, and occur along {001}, {110}, and {112}, typically with 0.1–25 μm spacing. The widest PDFs associated with {112} contain microtwin lamellae with 65°/ misorientation relationships. Deformation bands parallel to {100} planes and irregular low-angle ( misorientation axes. This geometry is consistent with a dislocation glide system with {010} during dislocation creep. Nonplanar fractures, recrystallized domains with sharp, irregular interfaces, and localized annealing textures along fractures are also observed. No occurrences of reidite were detected. Shock-Deformation Microstructures in zircon are explained in terms of elastic anisotropy of zircon. PDFs form along a limited number of specific {hkl} planes that are perpendicular to directions of high Young’s modulus, suggesting that PDFs are likely to be planes of longitudinal lattice damage. Twinned {112} PDFs also contain directions of high shear modulus. A conceptual model is proposed for the development of different Deformation Microstructures during an impact event. This “shock-Deformation mechanism map” is used to explain the relative timing, conditions, and complexity relationships between impact-related Deformation Microstructures in zircon.
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relationship among titanium rare earth elements u pb ages and Deformation Microstructures in zircon implications for ti in zircon thermometry
Chemical Geology, 2011Co-Authors: Nicholas E. Timms, Steven M. Reddy, Peter D. Kinny, Katy Evans, Chris Clark, David HealyAbstract:Abstract A zircon grain in an orthopyroxene–garnet–phlogopite–zircon–rutile-bearing xenolith from Udachnaya, Siberia, preserves a pattern of crystallographic misorientation and subgrain microstructure associated with crystal–plastic Deformation. The zircon grain records significant variations in titanium (Ti) from 2.6 to 30 ppm that corresponds to a difference in calculated Ti-in-zircon temperatures of over several hundred degrees Celsius. The highest Ti concentration is measured at subgrain centres (30 ppm), and Ti is variably depleted at low-angle boundaries (down to 2.6 ppm). Variations in cathodoluminescence coincide with the Deformation microstructure and indicate localised, differential enrichment of rare earth elements (REE) at low-angle boundaries. Variable enrichment of U and Th and systematic increase of Th/U from 1.61 to 3.52 occurs at low-angle boundaries. Individual SHRIMP-derived U–Pb ages from more deformed zones (mean age of 1799 ± 40, n = 22) are systematically younger than subgrain cores (mean age of 1851 ± 65 Ma, n = 7), and indicate that open system behaviour of Ti–Th–U occurred shortly after zircon growth, prior to the accumulation of significant radiogenic Pb. Modelling of trace-element diffusion distances for geologically reasonable thermal histories indicates that the observed variations are ~ 5 orders of magnitude greater than can be accounted for by volume diffusion. The data are best explained by enhanced diffusion of U, Th and Ti along Deformation-related fast-diffusion pathways, such as dislocations and low-angle (
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Relationship among titanium, rare earth elements, U–Pb ages and Deformation Microstructures in zircon: Implications for Ti-in-zircon thermometry
Chemical Geology, 2010Co-Authors: Nicholas E. Timms, Steven M. Reddy, Peter D. Kinny, Katy Evans, Chris Clark, David HealyAbstract:Abstract A zircon grain in an orthopyroxene–garnet–phlogopite–zircon–rutile-bearing xenolith from Udachnaya, Siberia, preserves a pattern of crystallographic misorientation and subgrain microstructure associated with crystal–plastic Deformation. The zircon grain records significant variations in titanium (Ti) from 2.6 to 30 ppm that corresponds to a difference in calculated Ti-in-zircon temperatures of over several hundred degrees Celsius. The highest Ti concentration is measured at subgrain centres (30 ppm), and Ti is variably depleted at low-angle boundaries (down to 2.6 ppm). Variations in cathodoluminescence coincide with the Deformation microstructure and indicate localised, differential enrichment of rare earth elements (REE) at low-angle boundaries. Variable enrichment of U and Th and systematic increase of Th/U from 1.61 to 3.52 occurs at low-angle boundaries. Individual SHRIMP-derived U–Pb ages from more deformed zones (mean age of 1799 ± 40, n = 22) are systematically younger than subgrain cores (mean age of 1851 ± 65 Ma, n = 7), and indicate that open system behaviour of Ti–Th–U occurred shortly after zircon growth, prior to the accumulation of significant radiogenic Pb. Modelling of trace-element diffusion distances for geologically reasonable thermal histories indicates that the observed variations are ~ 5 orders of magnitude greater than can be accounted for by volume diffusion. The data are best explained by enhanced diffusion of U, Th and Ti along Deformation-related fast-diffusion pathways, such as dislocations and low-angle (
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Deformation related Microstructures in magmatic zircon and implications for diffusion
Contributions to Mineralogy and Petrology, 2009Co-Authors: Steven M. Reddy, Nicholas E. Timms, Patrick Joseph Hamilton, Helen R SmythAbstract:An undeformed glomeroporphyritic andesite from the Sunda Arc of Java, Indonesia, contains zoned plagioclase and amphibole glomerocrysts in a fine-grained groundmass and records a complex history of adcumulate formation and subsequent magmatic disaggregation. A suite of xenocrystic zircon records Proterozoic and Archaean dates whilst a discrete population of zoned, euhedral, igneous zircon yields a SHRIMP U-Pb crystallisation age of 9.3 ± 0.2 Ma. Quantitative microstructural analysis of zircon by electron backscatter diffraction (EBSD) shows no Deformation in the inherited xenocrysts, but intragrain orientation variations of up to 30° in 80% of the young zircon population. These variations are typically accommodated by both progressive crystallographic bending and discrete low angle boundaries that overprint compositional growth zoning. Dispersion of crystallographic orientations are dominantly by rotation about an axis parallel to the zircon c-axis [001], which is coincident with the dominant orientation of misorientation axes of adjacent analysis points in EBSD maps. Less common misorientation axes account for minor components of crystallographic dispersion. These observations are consistent with zircon Deformation by dislocation creep and the formation of tilt and twist boundaries associated with the operation of {100} and {010} slip systems. The restriction of Deformation Microstructures to large glomerocrysts and the young magmatic zircon population, and the absence of Deformation within the host igneous rock and inherited zircon grains, indicate that zircon Deformation took place within a low-melt fraction (<5% melt), mid-lower crustal cumulate prior to fragmentation during magmatic disaggregation and entrainment of xenocrystic zircons during magmatic decompression. Tectonic stresses within the compressional Sunda Arc at the time of magmatism are considered to be the probable driver for low-strain Deformation of the cumulate in the late stages of initial crystallisation. These results provide the first evidence of crystal plastic dislocation creep in zircon associated with magmatic crystallisation and indicate that the development of crystal-plastic Microstructures in zircon is not restricted to high-strain rocks. Such Microstructures have previously been shown to enhance bulk diffusion of trace elements (U, Th and REE) in zircon. The development of Deformation Microstructures, and therefore multiple diffusion pathways in zircon in the magmatic environment, has significant implications for the interpretation of geochemical data from igneous zircon and the trace element budgets of melts due to the potential enhancement of bulk diffusion and dissolution rates.
Steven M. Reddy - One of the best experts on this subject based on the ideXlab platform.
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Resolution of impact-related Microstructures in lunar zircon: A shock-Deformation mechanism map
Meteoritics & Planetary Science, 2011Co-Authors: Nicholas E. Timms, Steven M. Reddy, David Healy, Alexander A. Nemchin, Marion Grange, Robert T. Pidgeon, Robert D. HartAbstract:Abstract– The Microstructures of lunar zircon grains from breccia samples 72215, 73215, 73235, and 76295 collected during the Apollo 17 mission have been characterized via optical microscopy, cathodoluminescence imaging, and electron backscatter diffraction mapping. These zircon grains preserve Deformation Microstructures that show a wide range in style and complexity. Planar Deformation features (PDFs) are documented in lunar zircon for the first time, and occur along {001}, {110}, and {112}, typically with 0.1–25 μm spacing. The widest PDFs associated with {112} contain microtwin lamellae with 65°/ misorientation relationships. Deformation bands parallel to {100} planes and irregular low-angle ( misorientation axes. This geometry is consistent with a dislocation glide system with {010} during dislocation creep. Nonplanar fractures, recrystallized domains with sharp, irregular interfaces, and localized annealing textures along fractures are also observed. No occurrences of reidite were detected. Shock-Deformation Microstructures in zircon are explained in terms of elastic anisotropy of zircon. PDFs form along a limited number of specific {hkl} planes that are perpendicular to directions of high Young’s modulus, suggesting that PDFs are likely to be planes of longitudinal lattice damage. Twinned {112} PDFs also contain directions of high shear modulus. A conceptual model is proposed for the development of different Deformation Microstructures during an impact event. This “shock-Deformation mechanism map” is used to explain the relative timing, conditions, and complexity relationships between impact-related Deformation Microstructures in zircon.
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relationship among titanium rare earth elements u pb ages and Deformation Microstructures in zircon implications for ti in zircon thermometry
Chemical Geology, 2011Co-Authors: Nicholas E. Timms, Steven M. Reddy, Peter D. Kinny, Katy Evans, Chris Clark, David HealyAbstract:Abstract A zircon grain in an orthopyroxene–garnet–phlogopite–zircon–rutile-bearing xenolith from Udachnaya, Siberia, preserves a pattern of crystallographic misorientation and subgrain microstructure associated with crystal–plastic Deformation. The zircon grain records significant variations in titanium (Ti) from 2.6 to 30 ppm that corresponds to a difference in calculated Ti-in-zircon temperatures of over several hundred degrees Celsius. The highest Ti concentration is measured at subgrain centres (30 ppm), and Ti is variably depleted at low-angle boundaries (down to 2.6 ppm). Variations in cathodoluminescence coincide with the Deformation microstructure and indicate localised, differential enrichment of rare earth elements (REE) at low-angle boundaries. Variable enrichment of U and Th and systematic increase of Th/U from 1.61 to 3.52 occurs at low-angle boundaries. Individual SHRIMP-derived U–Pb ages from more deformed zones (mean age of 1799 ± 40, n = 22) are systematically younger than subgrain cores (mean age of 1851 ± 65 Ma, n = 7), and indicate that open system behaviour of Ti–Th–U occurred shortly after zircon growth, prior to the accumulation of significant radiogenic Pb. Modelling of trace-element diffusion distances for geologically reasonable thermal histories indicates that the observed variations are ~ 5 orders of magnitude greater than can be accounted for by volume diffusion. The data are best explained by enhanced diffusion of U, Th and Ti along Deformation-related fast-diffusion pathways, such as dislocations and low-angle (
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Relationship among titanium, rare earth elements, U–Pb ages and Deformation Microstructures in zircon: Implications for Ti-in-zircon thermometry
Chemical Geology, 2010Co-Authors: Nicholas E. Timms, Steven M. Reddy, Peter D. Kinny, Katy Evans, Chris Clark, David HealyAbstract:Abstract A zircon grain in an orthopyroxene–garnet–phlogopite–zircon–rutile-bearing xenolith from Udachnaya, Siberia, preserves a pattern of crystallographic misorientation and subgrain microstructure associated with crystal–plastic Deformation. The zircon grain records significant variations in titanium (Ti) from 2.6 to 30 ppm that corresponds to a difference in calculated Ti-in-zircon temperatures of over several hundred degrees Celsius. The highest Ti concentration is measured at subgrain centres (30 ppm), and Ti is variably depleted at low-angle boundaries (down to 2.6 ppm). Variations in cathodoluminescence coincide with the Deformation microstructure and indicate localised, differential enrichment of rare earth elements (REE) at low-angle boundaries. Variable enrichment of U and Th and systematic increase of Th/U from 1.61 to 3.52 occurs at low-angle boundaries. Individual SHRIMP-derived U–Pb ages from more deformed zones (mean age of 1799 ± 40, n = 22) are systematically younger than subgrain cores (mean age of 1851 ± 65 Ma, n = 7), and indicate that open system behaviour of Ti–Th–U occurred shortly after zircon growth, prior to the accumulation of significant radiogenic Pb. Modelling of trace-element diffusion distances for geologically reasonable thermal histories indicates that the observed variations are ~ 5 orders of magnitude greater than can be accounted for by volume diffusion. The data are best explained by enhanced diffusion of U, Th and Ti along Deformation-related fast-diffusion pathways, such as dislocations and low-angle (
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Deformation related Microstructures in magmatic zircon and implications for diffusion
Contributions to Mineralogy and Petrology, 2009Co-Authors: Steven M. Reddy, Nicholas E. Timms, Patrick Joseph Hamilton, Helen R SmythAbstract:An undeformed glomeroporphyritic andesite from the Sunda Arc of Java, Indonesia, contains zoned plagioclase and amphibole glomerocrysts in a fine-grained groundmass and records a complex history of adcumulate formation and subsequent magmatic disaggregation. A suite of xenocrystic zircon records Proterozoic and Archaean dates whilst a discrete population of zoned, euhedral, igneous zircon yields a SHRIMP U-Pb crystallisation age of 9.3 ± 0.2 Ma. Quantitative microstructural analysis of zircon by electron backscatter diffraction (EBSD) shows no Deformation in the inherited xenocrysts, but intragrain orientation variations of up to 30° in 80% of the young zircon population. These variations are typically accommodated by both progressive crystallographic bending and discrete low angle boundaries that overprint compositional growth zoning. Dispersion of crystallographic orientations are dominantly by rotation about an axis parallel to the zircon c-axis [001], which is coincident with the dominant orientation of misorientation axes of adjacent analysis points in EBSD maps. Less common misorientation axes account for minor components of crystallographic dispersion. These observations are consistent with zircon Deformation by dislocation creep and the formation of tilt and twist boundaries associated with the operation of {100} and {010} slip systems. The restriction of Deformation Microstructures to large glomerocrysts and the young magmatic zircon population, and the absence of Deformation within the host igneous rock and inherited zircon grains, indicate that zircon Deformation took place within a low-melt fraction (<5% melt), mid-lower crustal cumulate prior to fragmentation during magmatic disaggregation and entrainment of xenocrystic zircons during magmatic decompression. Tectonic stresses within the compressional Sunda Arc at the time of magmatism are considered to be the probable driver for low-strain Deformation of the cumulate in the late stages of initial crystallisation. These results provide the first evidence of crystal plastic dislocation creep in zircon associated with magmatic crystallisation and indicate that the development of crystal-plastic Microstructures in zircon is not restricted to high-strain rocks. Such Microstructures have previously been shown to enhance bulk diffusion of trace elements (U, Th and REE) in zircon. The development of Deformation Microstructures, and therefore multiple diffusion pathways in zircon in the magmatic environment, has significant implications for the interpretation of geochemical data from igneous zircon and the trace element budgets of melts due to the potential enhancement of bulk diffusion and dissolution rates.
Haemyeong Jung - One of the best experts on this subject based on the ideXlab platform.
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Experimental study on the Deformation Microstructures and crystallographic preferred orientation of glaucophane and epidote in deformed epidote blueschist at high pressure
2021Co-Authors: Yong Park, Sejin Jung, Haemyeong JungAbstract:<p>To understand the crystallographic preferred orientation (CPO) of glaucophane and epidote and Deformation Microstructures at the top of a subducting slab in a warm subduction zone, Deformation experiments of epidote blueschist were conducted in simple shear by using a modified Griggs apparatus. Deformation experiments were performed under high pressure (0.9&#8211;1.5 GPa), temperature (400&#8211;500 &#176;C), shear strain (&#947;) in the range of 0.4&#8211;4.5, and shear strain rate of 1.5&#215;10<sup>-5</sup>&#8211;1.8&#215;10<sup>-4</sup> s<sup>-1</sup>. After experiments, CPO of minerals were determined by electron back-scattered diffraction (EBSD) technique, and Microstructures of deformed minerals were observed by transmission electron microscopy (TEM). At low shear strain (&#947; &#8804; 1), the [001] axes of glaucophane were in subparallel alignment to shear direction, and the (010) poles were sub-normally aligned to the shear plane. At high shear strain (&#947; > 2), the [001] axes of glaucophane were in subparallel alignment to shear direction, and the [100] axes were sub-normally aligned to the shear plane. At a shear strain between 2 < &#947; < 4, the (010) poles of epidote were in subparallel alignment to shear direction, and the [100] axes were sub-normally aligned to the shear plane. At a high shear strain where &#947; > 4, the alignment of the (010) epidote poles had altered from subparallel to subnormal to the shear plane, while the [001] axes were in subparallel alignment to the shear direction. TEM observations and EBSD mapping revealed that the CPO of glaucophane was developed by dislocation creep, somewhat affected by the cataclastic flow at high shear strain. On the other hand, the CPO development of epidote is considered to have been affected by dislocation creep under a shear strain of 2 < &#947; < 4 but is highly affected by cataclastic flow with rigid body rotation under a high shear strain (&#947; > 4). Our experimental results indicate that the magnitude of shear strain and rheological contrast between component minerals plays an important role on the formation of CPOs of glaucophane and epidote.</p>
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Analysis of electron backscattered diffraction (EBSD) mapping of geological materials: precautions for reliably collecting and interpreting data on petro-fabric and seismic anisotropy
Geosciences Journal, 2020Co-Authors: Munjae Park, Haemyeong JungAbstract:Automated electron backscattered diffraction (EBSD) data yield abundant information on the lattice-preferred orientations (LPOs) and Deformation Microstructures and mechanisms of minerals in a rock, which aid in our understanding of the tectonic conditions and history of a region. Additionally, this information allows us to interpret seismic anisotropies in the crust and mantle. However, great care must be taken in the collection and production of crystallographic orientation data via automated EBSD to more precisely interpret LPOs, Deformation Microstructures, and seismic anisotropies because petro-fabrics can be different depending on sampling methods such as all-points-per-grain (whole) data and one-point-per-grain (one orientation per grain) data. Here, we report a detailed comparison of the crystallographic orientation data produced using both all-points-per-grain and one-point-per-grain techniques to analyze eclogites from the Yuka terrane in the North Qaidam ultrahigh-pressure metamorphic belt of northwestern China. By comparing eclogite crystallographic orientations between different sampling methods, we found that there was no marked difference in the LPOs, fabric strengths (J-index and M-index), and seismic anisotropies for relatively small mineral grains (e.g., garnet and omphacite). However, there were large differences in the LPOs, fabric strengths, and seismic anisotropies of relatively large minerals grains (e.g., amphibole). This result can be attributed to the acquisition method of crystallographic orientation data, which can influence the LPO, fabric strength, and seismic anisotropy of minerals and rocks. Therefore, the pole figures of minerals should be constructed from one point per grain data in order to avoid the oversampling of large grains for samples with highly heterogenous grain size distributions, as well as to permit the comparison of crystallographic orientations obtained using different tools and in other studies.
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Lattice Preferred Orientation and Deformation Microstructures of Glaucophane and Epidote in Experimentally Deformed Epidote Blueschist at High Pressure
Minerals, 2020Co-Authors: Yong Park, Sejin Jung, Haemyeong JungAbstract:To understand the lattice preferred orientation (LPO) and Deformation Microstructures at the top of a subducting slab in a warm subduction zone, Deformation experiments of epidote blueschist were conducted in simple shear under high pressure (0.9–1.5 GPa) and temperature (400–500 °C). At low shear strain (γ ≤ 1), the [001] axes of glaucophane were in subparallel alignment with the shear direction, and the (010) poles were subnormally aligned with the shear plane. At high shear strain (γ > 2), the [001] axes of glaucophane were in subparallel alignment with the shear direction, and the [100] axes were subnormally aligned with the shear plane. At a shear strain between 2< γ <4, the (010) poles of epidote were in subparallel alignment with the shear direction, and the [100] axes were subnormally aligned with the shear plane. At a shear strain where γ > 4, the alignment of the (010) epidote poles had altered from subparallel to subnormal to the shear plane, while the [001] axes were in subparallel alignment with the shear direction. The experimental results indicate that the magnitude of shear strain and rheological contrast between component minerals plays an important role in the formation of LPOs for glaucophane and epidote.
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Relationships Between Eclogite‐Facies Mineral Assemblages, Deformation Microstructures, and Seismic Properties in the Yuka Terrane, North Qaidam Ultrahigh‐Pressure Metamorphic Belt, NW China
Journal of Geophysical Research: Solid Earth, 2019Co-Authors: Munjae Park, Haemyeong JungAbstract:To understand the relationships between eclogite-facies mineral assemblages, Deformation Microstructures, and the seismic properties of subducting oceanic crust, eclogites from the Yuka terrane, No...
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relationships between eclogite facies mineral assemblages Deformation Microstructures and seismic properties in the yuka terrane north qaidam ultrahigh pressure metamorphic belt nw china
Journal of Geophysical Research, 2019Co-Authors: Munjae Park, Haemyeong JungAbstract:To understand the relationships between eclogite-facies mineral assemblages, Deformation Microstructures, and the seismic properties of subducting oceanic crust, eclogites from the Yuka terrane, No...
Chris Clark - One of the best experts on this subject based on the ideXlab platform.
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relationship among titanium rare earth elements u pb ages and Deformation Microstructures in zircon implications for ti in zircon thermometry
Chemical Geology, 2011Co-Authors: Nicholas E. Timms, Steven M. Reddy, Peter D. Kinny, Katy Evans, Chris Clark, David HealyAbstract:Abstract A zircon grain in an orthopyroxene–garnet–phlogopite–zircon–rutile-bearing xenolith from Udachnaya, Siberia, preserves a pattern of crystallographic misorientation and subgrain microstructure associated with crystal–plastic Deformation. The zircon grain records significant variations in titanium (Ti) from 2.6 to 30 ppm that corresponds to a difference in calculated Ti-in-zircon temperatures of over several hundred degrees Celsius. The highest Ti concentration is measured at subgrain centres (30 ppm), and Ti is variably depleted at low-angle boundaries (down to 2.6 ppm). Variations in cathodoluminescence coincide with the Deformation microstructure and indicate localised, differential enrichment of rare earth elements (REE) at low-angle boundaries. Variable enrichment of U and Th and systematic increase of Th/U from 1.61 to 3.52 occurs at low-angle boundaries. Individual SHRIMP-derived U–Pb ages from more deformed zones (mean age of 1799 ± 40, n = 22) are systematically younger than subgrain cores (mean age of 1851 ± 65 Ma, n = 7), and indicate that open system behaviour of Ti–Th–U occurred shortly after zircon growth, prior to the accumulation of significant radiogenic Pb. Modelling of trace-element diffusion distances for geologically reasonable thermal histories indicates that the observed variations are ~ 5 orders of magnitude greater than can be accounted for by volume diffusion. The data are best explained by enhanced diffusion of U, Th and Ti along Deformation-related fast-diffusion pathways, such as dislocations and low-angle (
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Relationship among titanium, rare earth elements, U–Pb ages and Deformation Microstructures in zircon: Implications for Ti-in-zircon thermometry
Chemical Geology, 2010Co-Authors: Nicholas E. Timms, Steven M. Reddy, Peter D. Kinny, Katy Evans, Chris Clark, David HealyAbstract:Abstract A zircon grain in an orthopyroxene–garnet–phlogopite–zircon–rutile-bearing xenolith from Udachnaya, Siberia, preserves a pattern of crystallographic misorientation and subgrain microstructure associated with crystal–plastic Deformation. The zircon grain records significant variations in titanium (Ti) from 2.6 to 30 ppm that corresponds to a difference in calculated Ti-in-zircon temperatures of over several hundred degrees Celsius. The highest Ti concentration is measured at subgrain centres (30 ppm), and Ti is variably depleted at low-angle boundaries (down to 2.6 ppm). Variations in cathodoluminescence coincide with the Deformation microstructure and indicate localised, differential enrichment of rare earth elements (REE) at low-angle boundaries. Variable enrichment of U and Th and systematic increase of Th/U from 1.61 to 3.52 occurs at low-angle boundaries. Individual SHRIMP-derived U–Pb ages from more deformed zones (mean age of 1799 ± 40, n = 22) are systematically younger than subgrain cores (mean age of 1851 ± 65 Ma, n = 7), and indicate that open system behaviour of Ti–Th–U occurred shortly after zircon growth, prior to the accumulation of significant radiogenic Pb. Modelling of trace-element diffusion distances for geologically reasonable thermal histories indicates that the observed variations are ~ 5 orders of magnitude greater than can be accounted for by volume diffusion. The data are best explained by enhanced diffusion of U, Th and Ti along Deformation-related fast-diffusion pathways, such as dislocations and low-angle (