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Guoyin Shen - One of the best experts on this subject based on the ideXlab platform.
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single crystal synchrotron x ray diffraction study of wustite and Magnesiowustite at lower mantle pressures
Journal of Synchrotron Radiation, 2005Co-Authors: Steven D Jacobsen, Guoyin Shen, Vitali B Prakapenka, Jung-fu Lin, Ho-kwang Mao, Ross J Angel, Przemyslaw Dera, Russell J. HemleyAbstract:This study demonstrates the use of monochromatic synchrotron X-ray radiation of 40 keV for high-precision equation-of-state studies on sets of single crystals analysed individually in the same diamond-anvil pressure cell. Angle-dispersive zone-axis diffraction patterns were obtained from crystals of wustite-Fe0.93O and Magnesiowustite-(Mg0.73Fe0.27)O to 51 GPa in a hydrostatic helium pressure medium. The rhombohedral phase of Fe0.93O was observed above 23 GPa, and its isothermal bulk modulus (K0) was determined to be 134 (±4) GPa, assuming K′ = 4. The rhombohedral phase of Fe0.93O is more compressible than B1-structured Fe0.93O, with K0 = 146 (±2) GPa. Magnesiowustite-(Mg0.73Fe0.27)O remains cubic over the experimental pressure range, and has a bulk modulus of 154 (±3) GPa with K′ = 4.0 (±0.1).
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in situ observation of texture development in olivine ringwoodite Magnesiowustite and silicate perovskite at high pressure
Earth and Planetary Science Letters, 2004Co-Authors: Hansrudolf Wenk, I Lonardeli, J Pehl, James M Devine, Vitali B Prakapenka, Guoyin ShenAbstract:Magnesium silicates are the dominant minerals in the earth’s mantle. Their preferred orientation is important for understanding the rheology and seismic anisotropy in the deep earth. Here we report results of radial synchrotron diffraction diamond anvil cell (DAC) experiments on San Carlos olivine, axially compressed to 50 GPa. Experiments were performed at room temperature, except for brief laser heating to induce phase transformations. High stresses and development of preferred orientation were observed in diffraction images. Quantitative texture information was obtained by analyzing the images with the Rietveld method. With increasing pressure (between 9 and 43 GPa) olivine develops a texture with [001] axes perpendicular to the compression direction that is compatible with {hk0}[001] pencil glide. Ringwoodite (between 20 and 50 GPa) develops weak preferred orientation with {011} lattice planes perpendicular to the compression direction. After the phase transformation, perovskite and magnesiowqstite display transformation textures that are then modified by continuing deformation. Magnesiowqstite has a weak h111i maximum parallel to the compression direction that changes towards h001i with increasing deformation. Perovskite, transforming from olivine, has a pronounced (100) transformation texture and with increasing deformation a {012} maximum develops. The transformation texture is probably produced by mechanical {110} twinning and nucleation in orientations that minimize elastic strain energy. The deformation texture of perovskite is due to slip. D 2004 Elsevier B.V. All rights reserved.
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in situ observation of texture development in olivine ringwoodite Magnesiowustite and silicate perovskite at high pressure
Earth and Planetary Science Letters, 2004Co-Authors: Hansrudolf Wenk, I Lonardeli, J Pehl, James M Devine, Vitali B Prakapenka, Guoyin ShenAbstract:Magnesium silicates are the dominant minerals in the earth’s mantle. Their preferred orientation is important for understanding the rheology and seismic anisotropy in the deep earth. Here we report results of radial synchrotron diffraction diamond anvil cell (DAC) experiments on San Carlos olivine, axially compressed to 50 GPa. Experiments were performed at room temperature, except for brief laser heating to induce phase transformations. High stresses and development of preferred orientation were observed in diffraction images. Quantitative texture information was obtained by analyzing the images with the Rietveld method. With increasing pressure (between 9 and 43 GPa) olivine develops a texture with [001] axes perpendicular to the compression direction that is compatible with {hk0}[001] pencil glide. Ringwoodite (between 20 and 50 GPa) develops weak preferred orientation with {011} lattice planes perpendicular to the compression direction. After the phase transformation, perovskite and magnesiowqstite display transformation textures that are then modified by continuing deformation. Magnesiowqstite has a weak h111i maximum parallel to the compression direction that changes towards h001i with increasing deformation. Perovskite, transforming from olivine, has a pronounced (100) transformation texture and with increasing deformation a {012} maximum develops. The transformation texture is probably produced by mechanical {110} twinning and nucleation in orientations that minimize elastic strain energy. The deformation texture of perovskite is due to slip. D 2004 Elsevier B.V. All rights reserved.
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Stability of magnesiowüstite in Earth's lower mantle
Proceedings of the National Academy of Sciences of the United States of America, 2003Co-Authors: Jung-fu Lin, James M Devine, Dion L. Heinz, Ho-kwang Mao, Russell J. Hemley, Guoyin ShenAbstract:Magnesiowustite [(Mg,Fe)O] is the second most abundant mineral of Earth's lower mantle. Understanding its stability under lower mantle conditions is crucial for interpreting the physical and chemical properties of the whole Earth. Previous studies in an externally heated diamond anvil cell suggested that Magnesiowustites decompose into two components, Fe-rich and Mg-rich Magnesiowustites at 86 GPa and 1,000 K. Here we report an in situ study of two Magnesiowustites [(Mg0.39,Fe0.61)O and (Mg0.25,Fe0.75)O] at pressures and temperatures that overlap with mantle conditions, using a laser-heated diamond anvil cell combined with synchrotron x-ray diffraction. Our results show that addition of Mg in wustite (FeO) can stabilize the rock-salt structure to much higher pressures and temperatures. In contrast to the previous studies, our results indicate that Mg-rich Magnesiowustite is stable in the rock-salt structure in the lower mantle. The physical and chemical properties of Magnesiowustite should change gradually and continuously in the lower mantle, suggesting that it does not make a significant contribution to seismic-wave heterogeneity of the lower mantle. Stable Mg-rich Magnesiowustite in lowermost mantle can destabilize FeO in the core–mantle boundary region and remove FeO from the outer core.
Jung-fu Lin - One of the best experts on this subject based on the ideXlab platform.
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high spin low spin transition in Magnesiowustite mg0 75 fe0 25 o at high pressures under hydrostatic conditions
Jetp Letters, 2010Co-Authors: Jung-fu Lin, I S Lyubutin, A G Gavriliuk, K V Frolov, I A TroyanAbstract:The spin states of Fe2+ ions in (Mg0.75,Fe0.25)O Magnesiowustite crystals at hydrostatic pressures up to 90 GPa created in a diamond-anvil cell with helium as a pressure-transmitting medium have been investi-gated by transmission and synchrotron Mossbauer spectroscopy at room temperature. An electron transition from the high-spin (HS) state to the low-spin (LS) state (HS-LS crossover) has been observed in the pressure range of 55–70 GPa. The true HS-LS transition occurs in a narrow pressure range and the extension of the electron transition to ∼15 GPa is attributed to the effect of the nearest environment and to thermal fluctuations between the high-spin and low-spin states at finite temperatures. It has been found that the lowest pressure at which the electron HS-LS transition can occur in the Mg1 − x Fe x system is 50–55 GPa.
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pressure induced electronic spin transition of iron in Magnesiowustite mg fe o
Physical Review B, 2006Co-Authors: Jung-fu Lin, Viktor V Struzhkin, Steven D Jacobsen, Paul Chow, W Sturhahn, A G Gavriliuk, Choongshik YooAbstract:An electronic transition of iron in magnesiowuestite has been studied with synchrotron Moessbauer and X-ray emission spectroscopies under high pressures. Synchrotron Moessbauer studies show that the quadrupole splitting disappears and the isomer shift drops significantly across the spin-paring transition of iron in (Mg{sub 0.75},Fe{sub 0.25})O between 62 and 70 GPa, whereas X-ray emission spectroscopy of the Fe-K{sub {beta}} fluorescence lines in dilute (Mg{sub 0.95},Fe{sub 0.05})O also confirms that a high-spin to low-spin transition occurs between 46 GPa and 55 GPa. Based upon current results and percolation theory, we reexamine the high-pressure phase diagram of (Mg,Fe)O and find that iron-iron exchange interaction plays an important role in stabilizing the high-spin state of iron in FeO-rich (Mg,Fe)O.
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single crystal synchrotron x ray diffraction study of wustite and Magnesiowustite at lower mantle pressures
Journal of Synchrotron Radiation, 2005Co-Authors: Steven D Jacobsen, Guoyin Shen, Vitali B Prakapenka, Jung-fu Lin, Ho-kwang Mao, Ross J Angel, Przemyslaw Dera, Russell J. HemleyAbstract:This study demonstrates the use of monochromatic synchrotron X-ray radiation of 40 keV for high-precision equation-of-state studies on sets of single crystals analysed individually in the same diamond-anvil pressure cell. Angle-dispersive zone-axis diffraction patterns were obtained from crystals of wustite-Fe0.93O and Magnesiowustite-(Mg0.73Fe0.27)O to 51 GPa in a hydrostatic helium pressure medium. The rhombohedral phase of Fe0.93O was observed above 23 GPa, and its isothermal bulk modulus (K0) was determined to be 134 (±4) GPa, assuming K′ = 4. The rhombohedral phase of Fe0.93O is more compressible than B1-structured Fe0.93O, with K0 = 146 (±2) GPa. Magnesiowustite-(Mg0.73Fe0.27)O remains cubic over the experimental pressure range, and has a bulk modulus of 154 (±3) GPa with K′ = 4.0 (±0.1).
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spin transition of iron in Magnesiowustite in the earth s lower mantle
Nature, 2005Co-Authors: Jung-fu Lin, Ho-kwang Mao, Viktor V Struzhkin, Steven D Jacobsen, Paul Chow, Jennifer Kung, Haozhe Liu, Russell J. HemleyAbstract:Iron is the most abundant transition-metal element in the mantle and therefore plays an important role in the geochemistry and geodynamics of the Earth's interior. Pressure-induced electronic spin transitions of iron occur in Magnesiowustite, silicate perovskite and post-perovskite. Here we have studied the spin states of iron in Magnesiowustite and the isolated effects of the electronic transitions on the elasticity of Magnesiowustite with in situ X-ray emission spectroscopy and X-ray diffraction to pressures of the lowermost mantle. An observed high-spin to low-spin transition of iron in Magnesiowustite results in an abnormal compressional behaviour between the high-spin and the low-spin states. The high-pressure, low-spin state exhibits a much higher bulk modulus and bulk sound velocity than the low-pressure, high-spin state; the bulk modulus jumps by approximately 35 percent and bulk sound velocity increases by approximately 15 percent across the transition in (Mg0.83,Fe0.17)O. Although no significant density change is observed across the electronic transition, the jump in the sound velocities and the bulk modulus across the transition provides an additional explanation for the seismic wave heterogeneity in the lowermost mantle. The transition also affects current interpretations of the geophysical and geochemical models using extrapolated or calculated thermal equation-of-state data without considering the effects of the electronic transition.
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Stability of magnesiowüstite in Earth's lower mantle
Proceedings of the National Academy of Sciences of the United States of America, 2003Co-Authors: Jung-fu Lin, James M Devine, Dion L. Heinz, Ho-kwang Mao, Russell J. Hemley, Guoyin ShenAbstract:Magnesiowustite [(Mg,Fe)O] is the second most abundant mineral of Earth's lower mantle. Understanding its stability under lower mantle conditions is crucial for interpreting the physical and chemical properties of the whole Earth. Previous studies in an externally heated diamond anvil cell suggested that Magnesiowustites decompose into two components, Fe-rich and Mg-rich Magnesiowustites at 86 GPa and 1,000 K. Here we report an in situ study of two Magnesiowustites [(Mg0.39,Fe0.61)O and (Mg0.25,Fe0.75)O] at pressures and temperatures that overlap with mantle conditions, using a laser-heated diamond anvil cell combined with synchrotron x-ray diffraction. Our results show that addition of Mg in wustite (FeO) can stabilize the rock-salt structure to much higher pressures and temperatures. In contrast to the previous studies, our results indicate that Mg-rich Magnesiowustite is stable in the rock-salt structure in the lower mantle. The physical and chemical properties of Magnesiowustite should change gradually and continuously in the lower mantle, suggesting that it does not make a significant contribution to seismic-wave heterogeneity of the lower mantle. Stable Mg-rich Magnesiowustite in lowermost mantle can destabilize FeO in the core–mantle boundary region and remove FeO from the outer core.
Masaaki Miyahara - One of the best experts on this subject based on the ideXlab platform.
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phase transition processes of olivine in the shocked martian meteorite tissint clues to origin of ringwoodite bridgmanite and Magnesiowustite bearing assemblages
Physics of the Earth and Planetary Interiors, 2016Co-Authors: Ahmed El Goresy, Shin Ozawa, Eiji Ohtani, Masaaki Miyahara, Philippe GilletAbstract:Abstract Tissint is a heavily shocked olivine-phyric shergottite. We investigated and documented several phase transformations and dissociation phenomena of olivine adjacent to and in many shock-induced melt-pockets of Tissint. Olivine grains entrained in the melt-pockets dissociated to equigranular Magnesiowustite + bridgmanite (latter now vitrified). With approaching to the boundaries between the melt-pockets and host-rocks of Tissint, some olivine grains entrained in the melt-pockets are incompletely dissociated. Spherulitic Magnesiowustite + bridgmanite assemblages occur in the incompletely dissociated olivine. Several residual olivine domains are retained at the center of spherulitic texture. With further approaching to the boundaries between the melt-pockets and host-rocks, some olivine grains entrained in the melt-pockets are segmented with a cellular-like texture, presumably induced by defect arrangement. Many fine-grained Magnesiowustite occurs around the individual “cells” of the segmented olivine grains. Considering the temperature gradient in the melt-pockets and the arrangement of dissociation and segmentation textures, olivine dissociation reaction was presumably initiated by the segmentation of olivine, subsequently followed by Magnesiowustite crystallization around the individual “cells” of the segmented olivine, and, by bridgmanite formation. Subsequently, spherulitic Magnesiowustite + bridgmanite assemblages occur around residual olivine domain, and finally, olivine completely dissociates to equigranular Magnesiowustite + bridgmanite assemblage. Olivine grains adjacent to the melt-pockets transform to randomly oriented polycrystalline ringwoodite assemblages. In rare case, ahrensite occurs in the more iron-rich portions of the olivine grains. With increasing distance from the melt-pockets, sets of ringwoodite lamellae occur in increasing abundance into the interior of the olivine grains. The lamellae consist of almost crystallographically oriented polycrystalline ringwoodite assemblages. The phase transitions from olivine to ringwoodite were presumably promoted by interface-controlled incoherent mechanism. The ringwoodite would be metastable phase which formed in the stability field where olivine dissociates into Magnesiowustite + bridgmanite.
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evidence for multiple dynamic events and subsequent decompression stage recorded in a shock vein
Earth and Planetary Science Letters, 2011Co-Authors: Masaaki Miyahara, Shin Ozawa, Eiji Ohtani, M Kimura, Toshiro Nagase, Masahiko Nishijima, Kenji HiragaAbstract:We investigated a shock vein of the Yamato 791384 L6 chondrite to clarify the nature and sequence of the dynamic processes that resulted from the shock events. The chondritic host-rock of Y-791384 mainly consists of olivine (Fa24–25), low-Ca pyroxene (Fs18–22), albitic feldspar (An9–10Ab84–86Or5–7), troilite and metallic Fe–Ni. The shock vein contains majorite (or majorite-pyropess) and Magnesiowustite (+ minor jadeite) as high-pressure polymorphs. Two different dynamic events were recorded in the shock vein. The majorite grain contained vitrified (Mg,Fe)SiO3-perovskite inclusions. The (Mg,Fe)SiO3-perovskite was crystallized from a chondritic melt, and is a remnant of a first dynamic event. The majorite and Magnesiowustite were also crystallized directly from a chondritic melt but induced by a second dynamic event. The pressure condition for the first and second dynamic events would be >~24 GPa and <~22 GPa, respectively. Pervasive feather-shaped olivine (Fa16) nucleated on the Magnesiowustite and majorite. This feather-shaped olivine is evidence for rapidly grown olivine from the melt related to the shock event. Phase relations deduced from high-pressure melting experiments of the Allende meteorite and peridotite indicate that the Magnesiowustite and majorite + olivine pair cannot coexist at equilibrium condition. The disequilibrium assemblage reflects a decompression stage. These features demonstrate the complexity of events during a natural dynamic process.
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natural dissociation of olivine to mg fe sio3 perovskite and Magnesiowustite in a shocked martian meteorite
Proceedings of the National Academy of Sciences of the United States of America, 2011Co-Authors: Masaaki Miyahara, Ahmed El Goresy, Shin Ozawa, Eiji Ohtani, Toshiro Nagase, Kenji Hiraga, Naohisa Hirao, Makoto Kimura, Takeshi Sakai, Yasuo OhishiAbstract:We report evidence for the natural dissociation of olivine in a shergottite at high-pressure and high-temperature conditions induced by a dynamic event on Mars. Olivine (Fa34-41) adjacent to or entrained in the shock melt vein and melt pockets of Martian meteorite olivine-phyric shergottite Dar al Gani 735 dissociated into (Mg,Fe)SiO3 perovskite (Pv)+Magnesiowustite (Mw), whereby perovskite partially vitrified during decompression. Transmission electron microscopy observations reveal that microtexture of olivine dissociation products evolves from lamellar to equigranular with increasing temperature at the same pressure condition. This is in accord with the observations of synthetic samples recovered from high-pressure and high-temperature experiments. Equigranular (Mg,Fe)SiO3 Pv and Mw have 50–100 nm in diameter, and lamellar (Mg,Fe)SiO3 Pv and Mw have approximately 20 and approximately 10 nm in thickness, respectively. Partitioning coefficient, KPv/Mw = [FeO/MgO]/[FeO/MgO]Mw, between (Mg,Fe)SiO3 Pv and Mw in equigranular and lamellar textures are approximately 0.15 and approximately 0.78, respectively. The dissociation of olivine implies that the pressure and temperature conditions recorded in the shock melt vein and melt pockets during the dynamic event were approximately 25 GPa but 700 °C at least.
Russell J. Hemley - One of the best experts on this subject based on the ideXlab platform.
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single crystal synchrotron x ray diffraction study of wustite and Magnesiowustite at lower mantle pressures
Journal of Synchrotron Radiation, 2005Co-Authors: Steven D Jacobsen, Guoyin Shen, Vitali B Prakapenka, Jung-fu Lin, Ho-kwang Mao, Ross J Angel, Przemyslaw Dera, Russell J. HemleyAbstract:This study demonstrates the use of monochromatic synchrotron X-ray radiation of 40 keV for high-precision equation-of-state studies on sets of single crystals analysed individually in the same diamond-anvil pressure cell. Angle-dispersive zone-axis diffraction patterns were obtained from crystals of wustite-Fe0.93O and Magnesiowustite-(Mg0.73Fe0.27)O to 51 GPa in a hydrostatic helium pressure medium. The rhombohedral phase of Fe0.93O was observed above 23 GPa, and its isothermal bulk modulus (K0) was determined to be 134 (±4) GPa, assuming K′ = 4. The rhombohedral phase of Fe0.93O is more compressible than B1-structured Fe0.93O, with K0 = 146 (±2) GPa. Magnesiowustite-(Mg0.73Fe0.27)O remains cubic over the experimental pressure range, and has a bulk modulus of 154 (±3) GPa with K′ = 4.0 (±0.1).
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spin transition of iron in Magnesiowustite in the earth s lower mantle
Nature, 2005Co-Authors: Jung-fu Lin, Ho-kwang Mao, Viktor V Struzhkin, Steven D Jacobsen, Paul Chow, Jennifer Kung, Haozhe Liu, Russell J. HemleyAbstract:Iron is the most abundant transition-metal element in the mantle and therefore plays an important role in the geochemistry and geodynamics of the Earth's interior. Pressure-induced electronic spin transitions of iron occur in Magnesiowustite, silicate perovskite and post-perovskite. Here we have studied the spin states of iron in Magnesiowustite and the isolated effects of the electronic transitions on the elasticity of Magnesiowustite with in situ X-ray emission spectroscopy and X-ray diffraction to pressures of the lowermost mantle. An observed high-spin to low-spin transition of iron in Magnesiowustite results in an abnormal compressional behaviour between the high-spin and the low-spin states. The high-pressure, low-spin state exhibits a much higher bulk modulus and bulk sound velocity than the low-pressure, high-spin state; the bulk modulus jumps by approximately 35 percent and bulk sound velocity increases by approximately 15 percent across the transition in (Mg0.83,Fe0.17)O. Although no significant density change is observed across the electronic transition, the jump in the sound velocities and the bulk modulus across the transition provides an additional explanation for the seismic wave heterogeneity in the lowermost mantle. The transition also affects current interpretations of the geophysical and geochemical models using extrapolated or calculated thermal equation-of-state data without considering the effects of the electronic transition.
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Stability of magnesiowüstite in Earth's lower mantle
Proceedings of the National Academy of Sciences of the United States of America, 2003Co-Authors: Jung-fu Lin, James M Devine, Dion L. Heinz, Ho-kwang Mao, Russell J. Hemley, Guoyin ShenAbstract:Magnesiowustite [(Mg,Fe)O] is the second most abundant mineral of Earth's lower mantle. Understanding its stability under lower mantle conditions is crucial for interpreting the physical and chemical properties of the whole Earth. Previous studies in an externally heated diamond anvil cell suggested that Magnesiowustites decompose into two components, Fe-rich and Mg-rich Magnesiowustites at 86 GPa and 1,000 K. Here we report an in situ study of two Magnesiowustites [(Mg0.39,Fe0.61)O and (Mg0.25,Fe0.75)O] at pressures and temperatures that overlap with mantle conditions, using a laser-heated diamond anvil cell combined with synchrotron x-ray diffraction. Our results show that addition of Mg in wustite (FeO) can stabilize the rock-salt structure to much higher pressures and temperatures. In contrast to the previous studies, our results indicate that Mg-rich Magnesiowustite is stable in the rock-salt structure in the lower mantle. The physical and chemical properties of Magnesiowustite should change gradually and continuously in the lower mantle, suggesting that it does not make a significant contribution to seismic-wave heterogeneity of the lower mantle. Stable Mg-rich Magnesiowustite in lowermost mantle can destabilize FeO in the core–mantle boundary region and remove FeO from the outer core.
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displacive transition in Magnesiowustite
Journal of Physics: Condensed Matter, 2002Co-Authors: Wendy L Mao, Jinfu Shu, Russell J. Hemley, Ho-kwang MaoAbstract:Magnesiowustite (Mg0.1Fe0.9)O was studied at ambient temperature under both hydrostatic and quasihydrostatic pressures to 35 GPa. The elastic behaviour, equation of state, transition pressure, and the structure before and after the B1–rhombohedral transition were determined. K0-and K0 '-values for the B1 phase were calculated to be 155 ± 10 and 3.6 ± 0.8 GPa respectively under hydrostatic conditions. The second-order B1–rhombohedral transition occurred at 20 GPa. Quasihydrostatic conditions were used to determine the stress/strain in different crystallographic directions to elucidate the transition mechanism which is triggered by the softening of the c44 in the B1 phase.
Eiji Ohtani - One of the best experts on this subject based on the ideXlab platform.
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phase transition processes of olivine in the shocked martian meteorite tissint clues to origin of ringwoodite bridgmanite and Magnesiowustite bearing assemblages
Physics of the Earth and Planetary Interiors, 2016Co-Authors: Ahmed El Goresy, Shin Ozawa, Eiji Ohtani, Masaaki Miyahara, Philippe GilletAbstract:Abstract Tissint is a heavily shocked olivine-phyric shergottite. We investigated and documented several phase transformations and dissociation phenomena of olivine adjacent to and in many shock-induced melt-pockets of Tissint. Olivine grains entrained in the melt-pockets dissociated to equigranular Magnesiowustite + bridgmanite (latter now vitrified). With approaching to the boundaries between the melt-pockets and host-rocks of Tissint, some olivine grains entrained in the melt-pockets are incompletely dissociated. Spherulitic Magnesiowustite + bridgmanite assemblages occur in the incompletely dissociated olivine. Several residual olivine domains are retained at the center of spherulitic texture. With further approaching to the boundaries between the melt-pockets and host-rocks, some olivine grains entrained in the melt-pockets are segmented with a cellular-like texture, presumably induced by defect arrangement. Many fine-grained Magnesiowustite occurs around the individual “cells” of the segmented olivine grains. Considering the temperature gradient in the melt-pockets and the arrangement of dissociation and segmentation textures, olivine dissociation reaction was presumably initiated by the segmentation of olivine, subsequently followed by Magnesiowustite crystallization around the individual “cells” of the segmented olivine, and, by bridgmanite formation. Subsequently, spherulitic Magnesiowustite + bridgmanite assemblages occur around residual olivine domain, and finally, olivine completely dissociates to equigranular Magnesiowustite + bridgmanite assemblage. Olivine grains adjacent to the melt-pockets transform to randomly oriented polycrystalline ringwoodite assemblages. In rare case, ahrensite occurs in the more iron-rich portions of the olivine grains. With increasing distance from the melt-pockets, sets of ringwoodite lamellae occur in increasing abundance into the interior of the olivine grains. The lamellae consist of almost crystallographically oriented polycrystalline ringwoodite assemblages. The phase transitions from olivine to ringwoodite were presumably promoted by interface-controlled incoherent mechanism. The ringwoodite would be metastable phase which formed in the stability field where olivine dissociates into Magnesiowustite + bridgmanite.
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evidence for multiple dynamic events and subsequent decompression stage recorded in a shock vein
Earth and Planetary Science Letters, 2011Co-Authors: Masaaki Miyahara, Shin Ozawa, Eiji Ohtani, M Kimura, Toshiro Nagase, Masahiko Nishijima, Kenji HiragaAbstract:We investigated a shock vein of the Yamato 791384 L6 chondrite to clarify the nature and sequence of the dynamic processes that resulted from the shock events. The chondritic host-rock of Y-791384 mainly consists of olivine (Fa24–25), low-Ca pyroxene (Fs18–22), albitic feldspar (An9–10Ab84–86Or5–7), troilite and metallic Fe–Ni. The shock vein contains majorite (or majorite-pyropess) and Magnesiowustite (+ minor jadeite) as high-pressure polymorphs. Two different dynamic events were recorded in the shock vein. The majorite grain contained vitrified (Mg,Fe)SiO3-perovskite inclusions. The (Mg,Fe)SiO3-perovskite was crystallized from a chondritic melt, and is a remnant of a first dynamic event. The majorite and Magnesiowustite were also crystallized directly from a chondritic melt but induced by a second dynamic event. The pressure condition for the first and second dynamic events would be >~24 GPa and <~22 GPa, respectively. Pervasive feather-shaped olivine (Fa16) nucleated on the Magnesiowustite and majorite. This feather-shaped olivine is evidence for rapidly grown olivine from the melt related to the shock event. Phase relations deduced from high-pressure melting experiments of the Allende meteorite and peridotite indicate that the Magnesiowustite and majorite + olivine pair cannot coexist at equilibrium condition. The disequilibrium assemblage reflects a decompression stage. These features demonstrate the complexity of events during a natural dynamic process.
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natural dissociation of olivine to mg fe sio3 perovskite and Magnesiowustite in a shocked martian meteorite
Proceedings of the National Academy of Sciences of the United States of America, 2011Co-Authors: Masaaki Miyahara, Ahmed El Goresy, Shin Ozawa, Eiji Ohtani, Toshiro Nagase, Kenji Hiraga, Naohisa Hirao, Makoto Kimura, Takeshi Sakai, Yasuo OhishiAbstract:We report evidence for the natural dissociation of olivine in a shergottite at high-pressure and high-temperature conditions induced by a dynamic event on Mars. Olivine (Fa34-41) adjacent to or entrained in the shock melt vein and melt pockets of Martian meteorite olivine-phyric shergottite Dar al Gani 735 dissociated into (Mg,Fe)SiO3 perovskite (Pv)+Magnesiowustite (Mw), whereby perovskite partially vitrified during decompression. Transmission electron microscopy observations reveal that microtexture of olivine dissociation products evolves from lamellar to equigranular with increasing temperature at the same pressure condition. This is in accord with the observations of synthetic samples recovered from high-pressure and high-temperature experiments. Equigranular (Mg,Fe)SiO3 Pv and Mw have 50–100 nm in diameter, and lamellar (Mg,Fe)SiO3 Pv and Mw have approximately 20 and approximately 10 nm in thickness, respectively. Partitioning coefficient, KPv/Mw = [FeO/MgO]/[FeO/MgO]Mw, between (Mg,Fe)SiO3 Pv and Mw in equigranular and lamellar textures are approximately 0.15 and approximately 0.78, respectively. The dissociation of olivine implies that the pressure and temperature conditions recorded in the shock melt vein and melt pockets during the dynamic event were approximately 25 GPa but 700 °C at least.
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fe mg partitioning between mg fe sio3 post perovskite perovskite and Magnesiowustite in the earth s lower mantle
Geophysical Research Letters, 2005Co-Authors: Yusuke Kobayashi, Eiji Ohtani, Tadashi Kondo, Takehiko Yagi, Toshiro Nagase, Naohisa Hirao, Nobuyoshi Miyajima, Takumi KikegawaAbstract:[1] We report here new data on pressure dependence of Fe-Mg partitioning between (Mg, Fe)SiO3 perovskite (Pv) and Magnesiowustite (Mw), KPv/Mw, and (Mg, Fe)SiO3 post-perovskite (PPv) and Mw, KPPv/Mw, up to 123.6 GPa at 1600 K measured by synchrotron X-ray diffraction method and analytical transmission electron microscopy (ATEM). We observed a high FeO content in PPv coexisting with Mw [KPPv/Mw = (FeO/MgO)PPv/(FeO/MgO)Mw = 0.30] compared to that in Pv [KPv/Mw = (FeO/MgO)Pv/(FeO/MgO)Mw = 0.12] observed from 23.0 to 95.4 GPa. KPv/Mw keeps a constant value of 0.12 up to the PPv phase boundary. Our results also support the possibility that a metallic phase may form in the lower mantle. The assemblage of PPv and Mw is 1.5–1.7% denser than the Pv bearing assemblage, which results in a gravitational stabilization of the lowermost mantle.
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element partitioning between metallic liquid Magnesiowustite and silicate liquid at 20 gpa and 2500 c a secondary ion mass spectrometric study
Geophysical Research Letters, 1996Co-Authors: Eiji Ohtani, Hisayoshi YurimotoAbstract:We determined the partition coefficients of 20 elements between metallic liquid, Magnesiowustite, and silicate liquid at 20 GPa and 2500°C. The partition coefficients of V, Cr, Mn, Co, Ni, and Cu between metallic liquid and Magnesiowustite are similar to those between metallic liquid and silicate liquid. The partitioning behavior of Si, P, W and Pb between metallic liquid and Magnesiowustite show remarkable differences to that between metallic liquid and silicate liquid, reflecting incompatibility of these elements in Magnesiowustite. Comparison of the present data with the previous ones implies that the metallic liquid-siicate liquid partition coefficients of Co, Ni, W, and Mo decrease whereas those of Cr, and Mn increase due to the combined effect of pressure and temperature, although some other factors such as the liquid composition might play some roles on a large difference in D for Mo and W. The core and mantle concentrations for Co and Ni estimated by Allegre et al. [1995] are consistent with the metal-silicate equilibrium at lower mantle conditions, although other models such as inhomogeneous accretion are also able to explain the core-mantle concentrations.
