The Experts below are selected from a list of 1473 Experts worldwide ranked by ideXlab platform
Joseph R. Smyth - One of the best experts on this subject based on the ideXlab platform.
-
fe 2 substitution in coexisting Wadsleyite and clinopyroxene under hydrous conditions implications for the 520 km discontinuity
Physics and Chemistry of Minerals, 2020Co-Authors: Li Zhang, Joseph R. SmythAbstract:Chemical compositions and crystal structures of coexisting Wadsleyite, clinopyroxene, and phase E (synthesized at 1400 °C and 18 GPa under hydrous conditions) have been analyzed by electron microprobe, single-crystal X-ray diffraction, and Raman spectroscopy. Single-crystal X-ray diffraction analyses indicate that Fe2+ substitution in the crystal structure significantly decreases the configurational entropies of Wadsleyite and clinopyroxene in the middle transition zone under water-saturated conditions, providing a new thermodynamic constraint on the stability of ferromagnesian silicates near the Wadsleyite–ringwoodite phase boundary (about 520 km). The variation in the depth of the 520-km discontinuity under hydrous conditions can be partly due to Fe2+ incorporation into Wadsleyite.
-
transition metals in the transition zone partitioning of ni co and zn between olivine Wadsleyite ringwoodite and clinoenstatite
Contributions to Mineralogy and Petrology, 2018Co-Authors: Joseph R. Smyth, Takaaki Kawazoe, Li Zhang, Steven D JacobsenAbstract:Ni, Co, and Zn are widely distributed in the Earth’s mantle as significant minor elements that may offer insights into the chemistry of melting in the mantle. To better understand the distribution of Ni2+, Co2+, and Zn2+ in the most abundant silicate phases in the transition zone and the upper mantle, we have analyzed the crystal chemistry of Wadsleyite (Mg2SiO4), ringwoodite (Mg2SiO4), forsterite (Mg2SiO4), and clinoenstatite (Mg2Si2O6) synthesized at 12–20 GPa and 1200–1400 °C with 1.5–3 wt% of either NiO, CoO, or ZnO in starting materials. Single-crystal X-ray diffraction analyses demonstrate that significant amounts of Ni, Co, and Zn are incorporated in octahedral sites in Wadsleyite (up to 7.1 at%), ringwoodite (up to 11.3 at%), olivine (up to 2.0 at%), and clinoenstatite (up to 3.2 at%). Crystal structure refinements indicate that crystal field stabilization energy (CFSE) controls both cation ordering and transition metal partitioning in coexisting minerals. According to electron microprobe analyses, Ni and Co partition preferentially into forsterite and Wadsleyite relative to coexisting clinoenstatite. Ni strongly prefers ringwoodite over coexisting Wadsleyite with \({D}_{\text{Ni}}^{\text{Rw}/\text{Wd}}\) = 4.13. Due to decreasing metal–oxygen distances with rising pressure, crystal field effect on distribution of divalent metal ions in magnesium silicates is more critical in the transition zone relative to the upper mantle. Analyses of Ni partitioning between the major upper-mantle phases implies that Ni-rich olivine in ultramafic rocks can be indicative of near-primary magmas.
-
transition metals in the transition zone crystal chemistry of minor element substitution in Wadsleyite
American Mineralogist, 2016Co-Authors: Joseph R. Smyth, Takaaki Kawazoe, Li Zhang, Julien Allaz, Steven D JacobsenAbstract:As the most abundant solid phase at depths of 410–525 km, Wadsleyite constitutes a large geochemical reservoir in the Earth. To better understand the implications of minor element substitution and cation ordering in Wadsleyite, we have synthesized Wadsleyites coexisting with pyroxenes with 2–3 wt% of either TiO 2 , Cr 2 O 3 , V 2 O 3 , CoO, NiO, or ZnO under hydrous conditions in separate experiments at 1300 °C and 15 GPa. We have refined the crystal structures of these Wadsleyites by single-crystal X-ray diffraction, analyzed the compositions by electron microprobe, and estimated M3 vacancy concentration from b / a cell-parameter ratios. According to the crystal structure refinements, Cr and V show strong preferences for M3 over M1 and M2 sites and significant substitution up to 2.9 at% at the tetrahedral site (T site). Ni, Co, and Zn show site preferences similar to those of Fe with M1≈ M3 > M2 > T. The avoidance of Ni, Co, and Fe for the M2 site in both Wadsleyite and olivine appears to be partially controlled by crystal field stabilization energy (CFSE). The estimated CFSE values of Ni 2+ , Co 2+ , and Zn 2+ at three distinct octahedral sites show a positive correlation with octahedral occupancy ratios [M2/(M1+M3)]. Ti substitutes primarily into the M3 octahedron, rather than M1, M2, or T sites. Ti, Cr, and V each have greater solubility in Wadsleyite than in olivine. Therefore these transition metal cations may be enriched in a melt or an accessory phase if hydrous melting occurs on upward convection across the Wadsleyite-olivine boundary and may be useful as indicators of high-pressure origin.
-
Coupled substitution of Fe3+and H+for Si in Wadsleyite: A study by polarized infrared and Mössbauer spectroscopies and single-crystal X-ray diffraction
American Mineralogist, 2016Co-Authors: Takaaki Kawazoe, Joseph R. Smyth, Alok Chaudhari, Catherine MccammonAbstract:Coupled substitution of Fe 3+ and H + for Si in Wadsleyite was studied by polarized infrared and Mossbauer spectroscopies and single-crystal X-ray diffraction. Single crystals of Fe-bearing hydrous Wadsleyite were synthesized at 16 GPa and 1870 K using a Kawai-type multi-anvil apparatus. Water and Fe contents of the sample were 0.19–0.26 wt% H 2 O and Fe/(Mg+Fe) of 0.099(2), respectively. Mossbauer spectra showed 13(4)% Fe 3+ /∑Fe and Fe 3+ at the tetrahedral site with 5(3)% IV Fe 3+ /∑Fe. Crystal structure refinement by single-crystal X-ray diffraction indicated that Fe (presumably Fe 3+ ) occupied 4.9(5)% of the tetrahedral site. Infrared light polarized with the electric vector E // a and c was absorbed at 3477(2) cm −1 while no absorption was observed at the region in spectra with E // b . The pleochroic behavior of the 3477 cm −1 band can be interpreted as protonation of silicate oxygen O3 in Fe-bearing hydrous Wadsleyite. The protonation of O3 together with the presence of Fe 3+ at the tetrahedral site confirms the coupled substitution of Fe 3+ and H + for Si in Fe-bearing hydrous Wadsleyite.
-
coupled substitution of fe3 and h for si in Wadsleyite a study by polarized infrared and mossbauer spectroscopies and single crystal x ray diffraction
American Mineralogist, 2016Co-Authors: Takaaki Kawazoe, Joseph R. Smyth, Alok Chaudhari, Catherine MccammonAbstract:Coupled substitution of Fe 3+ and H + for Si in Wadsleyite was studied by polarized infrared and Mossbauer spectroscopies and single-crystal X-ray diffraction. Single crystals of Fe-bearing hydrous Wadsleyite were synthesized at 16 GPa and 1870 K using a Kawai-type multi-anvil apparatus. Water and Fe contents of the sample were 0.19–0.26 wt% H 2 O and Fe/(Mg+Fe) of 0.099(2), respectively. Mossbauer spectra showed 13(4)% Fe 3+ /∑Fe and Fe 3+ at the tetrahedral site with 5(3)% IV Fe 3+ /∑Fe. Crystal structure refinement by single-crystal X-ray diffraction indicated that Fe (presumably Fe 3+ ) occupied 4.9(5)% of the tetrahedral site. Infrared light polarized with the electric vector E // a and c was absorbed at 3477(2) cm −1 while no absorption was observed at the region in spectra with E // b . The pleochroic behavior of the 3477 cm −1 band can be interpreted as protonation of silicate oxygen O3 in Fe-bearing hydrous Wadsleyite. The protonation of O3 together with the presence of Fe 3+ at the tetrahedral site confirms the coupled substitution of Fe 3+ and H + for Si in Fe-bearing hydrous Wadsleyite.
Daniel J. Frost - One of the best experts on this subject based on the ideXlab platform.
-
comparative compressibility of hydrous Wadsleyite and ringwoodite effect of h2o and implications for detecting water in the transition zone
Journal of Geophysical Research, 2015Co-Authors: Sylviamonique Thomas, Steven D Jacobsen, Craig R Bina, Catherine Mccammon, Yun Yuan Chang, Joseph R. Smyth, Daniel J. Frost, Tiziana Boffa Ballaran, Erik H HauriAbstract:Review of recent mineral physics literature shows consistent trends for the influence of Fe and H2O on the bulk modulus (K0) of Wadsleyite and ringwoodite, the major phases of Earth's mantle transition zone (410–660 km). However, there is little consensus on the first pressure derivative, K0′ = (dK/dP)P=0, which ranges from about 4 to >5 across experimental studies and compositions. Here we demonstrate the importance of K0′ in evaluating the bulk sound velocity of the transition zone in terms of water content and provide new constraints on the effect of H2O on K0′ for Wadsleyite and ringwoodite by conducting a comparative compressibility study. In the experiment, multiple crystals of hydrous Fo90 Wadsleyite containing 2.0 and 0.25 wt % H2O were loaded into the same diamond anvil cell, along with hydrous ringwoodite containing 1.4 wt % H2O. By measuring their pressure-volume evolution simultaneously up to 32 GPa, we constrain the difference in K0′ independent of the pressure scale, finding that H2O has no effect on K0′, whereas the effect of H2O on K0 is significant. The fitted K0′ values of hydrous Wadsleyite (0.25 and 2.0 wt % H2O) and hydrous ringwoodite (1.4 wt % H2O) examined in this study were found to be identical within uncertainty, with K0′ ~3.7(2). New secondary-ion mass spectrometry measurements of the H2O content of these and previously investigated Wadsleyite samples shows the bulk modulus of Wadsleyite is reduced by 7.0(5) GPa/wt % H2O, independent of Fe content for upper mantle compositions. Because K0′ is unaffected by H2O, the reduction of bulk sound velocity in very hydrous regions of transition zone is expected to be on the order of 1.6%, which is potentially detectible in high-resolution, regional seismology studies.
-
water in the earth s mantle a solid state nmr study of hydrous Wadsleyite
Chemical Science, 2013Co-Authors: John M Griffin, Stephen Wimperis, Daniel J. Frost, Andrew J Berry, Sharon E AshbrookAbstract:Wadsleyite, β-(Mg,Fe)2SiO4, is the main component of the transition zone in the Earth's mantle, at depths of 410–530 km below the surface. This mineral has received considerable interest as a potential reservoir for the vast amount of hydrogen, as hydroxyl, referred to as water, that is thought to be contained within the mantle. However, the exact way in which water is incorporated into the structure of Wadsleyite is not fully understood and has been the subject of considerable debate. In this work, 17O, 25Mg, 29Si, 1H and 2H solid-state NMR spectra were obtained from isotopically enriched samples of anhydrous and hydrous β-Mg2SiO4. First-principles DFT calculations were also carried out for a range of model structures to aid interpretation of the experimental data. The results are consistent with a model for hydrous Wadsleyite whereby hydrogen bonds to the O1 site to form hydroxyl groups that are charge balanced by cation vacancies on the Mg3 site. Structural models containing cation vacancies on the Mg2 site are found to be energetically less favourable and calculated NMR parameters show poor agreement with the experimental data. Disorder was also observed in the hydrous Wadsleyite samples, and 1H and 2H NMR are consistent with not only Mg–O1–H but also more strongly hydrogen-bonded Si–O–H environments. These silanol protons can be incorporated into the structure with only a small increase in energy. Two-dimensional 1H–29Si and 1H–17O NMR correlation experiments confirm that the additional resonances do not correspond to Mg–OH protons and enable the identification of 29Si and 17O species within the Si–OH groups. This assignment is also confirmed by first-principles DFT calculations of NMR parameters. Silanol protons within Mg3 vacancies could account for up to 20% of the protons in the structure.
-
high temperature structural behaviors of anhydrous Wadsleyite and forsterite
American Mineralogist, 2012Co-Authors: Dmytro M Trots, Alexander Kurnosov, Tiziana Boffa Ballaran, Daniel J. FrostAbstract:The thermal expansion of anhydrous Mg 2 SiO 4 Wadsleyite and forsterite was comprehensively studied over the temperature ranges 297–1163 and 297–1313 K, respectively, employing X-ray powder diffraction. Experiments were carried out with two separately synthesized samples of Wadsleyite (numbered z626 and z627), for which room temperature unit-cell volumes differed by 0.05%, although the determined thermal expansions were identical within error. The high-temperature thermal expansions of Wadsleyite and forsterite were parameterized on the basis of the first-order Gruneisen approximation using a Debye function for the internal energy. Values for hypothetical volume at T = 0 K, Debye temperature and Gruneisen parameter are 536.86(14) A 3 , 980(55) K, 1.28(2) and 537.00(13) A 3 , 887(50) K, 1.26(1) for z626 and z627, respectively, with the bulk modulus fixed to a literature determination of 161 GPa. For forsterite, the respective values are 288.80(2) A 3 , 771(9) K, and 1.269(2) with a constrained bulk modulus of 125 GPa. These quantities are in good agreement with literature values obtained independently from sound velocity and heat capacity measurements, giving strong support to the applicability of Gruneisen theory in describing the thermal expansion of Wadsleyite and forsterite. In addition, high-temperature structural variations were determined for Wadsleyite from Rietveld analysis of the X-ray diffraction data. The pronounced anisotropy in thermal expansion of Wadsleyite with a more expandable c -axis, similar to the compressional anisotropy, arises from specific features of the crystal structure consisting of the pseudolayers of MgO 6 octahedra parallel to the a - b plane with cross-linking Si 2 O 7 dimers along the c -axis. Although anisotropic compression and expansion originate from the same structural features, the details of structural changes with pressure differ from those caused by temperature. The longest Mg-O bonds, which are roughly parallel to the c -axis in all three octahedral sites of Wadsleyite, dominate the compression, but these bonds do not exhibit the largest expansivities.
-
Olivine–Wadsleyite–pyroxene topotaxy: Evidence for coherent nucleation and diffusion-controlled growth at the 410-km discontinuity
Physics of the Earth and Planetary Interiors, 2012Co-Authors: Joseph R. Smyth, David C Rubie, Nobuyoshi Miyajima, G R Huss, E Hellebrand, Daniel J. FrostAbstract:We have synthesized a hydrous peridotite-composition sample at 13 GPa and 1400 C with co-existing coarse grains (100 lm) of olivine, Wadsleyite, clinoenstatite, plus melt in a multi-anvil press. Some of the olivine grains contain fine-scale (0.5–2 lm-wide) lamellae of Wadsleyite and clinoenstatite that likely resulted from transformation caused by small temperature fluctuations during the four-hour experiment. Phase compositions were determined by electron probe microanalysis (EPMA) and secondary ion mass spectroscopy (SIMS). The olivine ranges from Fo94 to Fo90 in composition and contains about 4000 ppm wt. H2O. The Wadsleyite is Fo87±1 in composition and contains about 10,000 ppm wt. H2O. The clinoenstatite is En93±1 in composition and about 1400 ppm wt. H2O. Transmission electron microscopy of the Wadsleyite lamellae and host olivine shows that the two phases share their close-packed oxygen planes so that the Wadsleyite lamellae are nearly planar and perpendicular to the [1 0 0] of olivine. The Wadsleyite lamellae thus have their {1 0 1} and {0 2 1} planes parallel to the (1 0 0) plane of olivine. Additionally, larger incoherent grains of Wadsleyite in olivine are found. Dislocation microtexures in the olivine and iron concentration profiles across the lamella interface suggest heterogeneous nucleation and diffusion-controlled growth of coherent Wadsleyite lamellae on defects in the olivine followed by the nucleation of faster-growing incoherent grains on the lamellae. The results show that, under hydrous conditions, the olivine–Wadsleyite transformation occurs close to equilibrium at conditions of the 410km discontinuity. Furthermore, inheritance of crystallographic preferred orientations (and therefore seismic anisotropy) across the 410-km discontinuity is unlikely to be significant. In addition, hydrogen distributions among the various phases indicate that dehydration by melt extraction at 410 km will be inefficient and that H contents greater than about 4000 ppm wt. H2O are needed to initiate melting at 410 km. 2012 Published by Elsevier B.V.
-
olivine Wadsleyite pyroxene topotaxy evidence for coherent nucleation and diffusion controlled growth at the 410 km discontinuity
Physics of the Earth and Planetary Interiors, 2012Co-Authors: Joseph R. Smyth, David C Rubie, Nobuyoshi Miyajima, G R Huss, E Hellebrand, Daniel J. FrostAbstract:We have synthesized a hydrous peridotite-composition sample at 13 GPa and 1400 C with co-existing coarse grains (100 lm) of olivine, Wadsleyite, clinoenstatite, plus melt in a multi-anvil press. Some of the olivine grains contain fine-scale (0.5–2 lm-wide) lamellae of Wadsleyite and clinoenstatite that likely resulted from transformation caused by small temperature fluctuations during the four-hour experiment. Phase compositions were determined by electron probe microanalysis (EPMA) and secondary ion mass spectroscopy (SIMS). The olivine ranges from Fo94 to Fo90 in composition and contains about 4000 ppm wt. H2O. The Wadsleyite is Fo87±1 in composition and contains about 10,000 ppm wt. H2O. The clinoenstatite is En93±1 in composition and about 1400 ppm wt. H2O. Transmission electron microscopy of the Wadsleyite lamellae and host olivine shows that the two phases share their close-packed oxygen planes so that the Wadsleyite lamellae are nearly planar and perpendicular to the [1 0 0] of olivine. The Wadsleyite lamellae thus have their {1 0 1} and {0 2 1} planes parallel to the (1 0 0) plane of olivine. Additionally, larger incoherent grains of Wadsleyite in olivine are found. Dislocation microtexures in the olivine and iron concentration profiles across the lamella interface suggest heterogeneous nucleation and diffusion-controlled growth of coherent Wadsleyite lamellae on defects in the olivine followed by the nucleation of faster-growing incoherent grains on the lamellae. The results show that, under hydrous conditions, the olivine–Wadsleyite transformation occurs close to equilibrium at conditions of the 410km discontinuity. Furthermore, inheritance of crystallographic preferred orientations (and therefore seismic anisotropy) across the 410-km discontinuity is unlikely to be significant. In addition, hydrogen distributions among the various phases indicate that dehydration by melt extraction at 410 km will be inefficient and that H contents greater than about 4000 ppm wt. H2O are needed to initiate melting at 410 km. 2012 Published by Elsevier B.V.
Takaaki Kawazoe - One of the best experts on this subject based on the ideXlab platform.
-
high pressure single crystal elasticity of Wadsleyite and the seismic signature of water in the shallow transition zone
Earth and Planetary Science Letters, 2018Co-Authors: Johannes Buchen, Takaaki Kawazoe, Tiziana Boffa Ballaran, Hauke Marquardt, Sergio Speziale, Alexander KurnosovAbstract:Abstract Earth's transition zone at depths between 410 km and 660 km plays a key role in Earth's deep water cycle since large amounts of hydrogen can be stored in the nominally anhydrous minerals Wadsleyite and ringwoodite, ( Mg,Fe ) 2 SiO 4 . Previous mineral physics experiments on iron-free Wadsleyite proposed low seismic velocities as an indicative feature for hydration in the transition zone. Here we report simultaneous sound wave velocity and density measurements on iron-bearing Wadsleyite single crystals with 0.24 wt-% H 2 O . By comparison with earlier studies, we show that pressure suppresses the velocity reduction caused by higher degrees of hydration in iron-bearing Wadsleyite, ultimately leading to a velocity cross-over for both P-waves and S-waves. Modeling based on our experimental results shows that wave speed variations within the transition zone as well as velocity jumps at the 410-km seismic discontinuity, both of which have been used in previous work to detect mantle hydration, are poor water sensors. Instead, the impedance contrast across the 410-km seismic discontinuity that is reduced in the presence of water can serve as a more robust indicator for hydrated parts of the transition zone.
-
transition metals in the transition zone partitioning of ni co and zn between olivine Wadsleyite ringwoodite and clinoenstatite
Contributions to Mineralogy and Petrology, 2018Co-Authors: Joseph R. Smyth, Takaaki Kawazoe, Li Zhang, Steven D JacobsenAbstract:Ni, Co, and Zn are widely distributed in the Earth’s mantle as significant minor elements that may offer insights into the chemistry of melting in the mantle. To better understand the distribution of Ni2+, Co2+, and Zn2+ in the most abundant silicate phases in the transition zone and the upper mantle, we have analyzed the crystal chemistry of Wadsleyite (Mg2SiO4), ringwoodite (Mg2SiO4), forsterite (Mg2SiO4), and clinoenstatite (Mg2Si2O6) synthesized at 12–20 GPa and 1200–1400 °C with 1.5–3 wt% of either NiO, CoO, or ZnO in starting materials. Single-crystal X-ray diffraction analyses demonstrate that significant amounts of Ni, Co, and Zn are incorporated in octahedral sites in Wadsleyite (up to 7.1 at%), ringwoodite (up to 11.3 at%), olivine (up to 2.0 at%), and clinoenstatite (up to 3.2 at%). Crystal structure refinements indicate that crystal field stabilization energy (CFSE) controls both cation ordering and transition metal partitioning in coexisting minerals. According to electron microprobe analyses, Ni and Co partition preferentially into forsterite and Wadsleyite relative to coexisting clinoenstatite. Ni strongly prefers ringwoodite over coexisting Wadsleyite with \({D}_{\text{Ni}}^{\text{Rw}/\text{Wd}}\) = 4.13. Due to decreasing metal–oxygen distances with rising pressure, crystal field effect on distribution of divalent metal ions in magnesium silicates is more critical in the transition zone relative to the upper mantle. Analyses of Ni partitioning between the major upper-mantle phases implies that Ni-rich olivine in ultramafic rocks can be indicative of near-primary magmas.
-
application of scanning precession electron diffraction in the transmission electron microscope to the characterization of deformation in Wadsleyite and ringwoodite
Minerals, 2018Co-Authors: Billy Clitton Nzogang, Takaaki Kawazoe, Simon Thilliez, Alexandre Mussi, Jeremie Bouquerel, Nobuyoshi Miyajima, Patrick CordierAbstract:The mantle transition zone represents an important layer in the interior of the Earth that is characterized by phase transformations of olivine polymorphs. Constraining the rheology difference between Wadsleyite and ringwoodite is important in determining the viscosity contrast at a depth of 520 km. In this study, we perform a post-mortem by transmission electron microscopy of a Wadsleyite + ringwoodite aggregate, deformed at high-pressure and high-temperature, in a deformation-DIA apparatus. From orientation maps acquired by scanning precession electron diffraction, we calculate local misorientations and misorientation-gradients, which are used as a proxy of plastic strain. We show that at 17.3 GPa, 1700 K, the plastic responses of Wadsleyite and ringwoodite are comparable, although recovery by subgrain boundary migration is more easily activated in Wadsleyite.
-
transition metals in the transition zone crystal chemistry of minor element substitution in Wadsleyite
American Mineralogist, 2016Co-Authors: Joseph R. Smyth, Takaaki Kawazoe, Li Zhang, Julien Allaz, Steven D JacobsenAbstract:As the most abundant solid phase at depths of 410–525 km, Wadsleyite constitutes a large geochemical reservoir in the Earth. To better understand the implications of minor element substitution and cation ordering in Wadsleyite, we have synthesized Wadsleyites coexisting with pyroxenes with 2–3 wt% of either TiO 2 , Cr 2 O 3 , V 2 O 3 , CoO, NiO, or ZnO under hydrous conditions in separate experiments at 1300 °C and 15 GPa. We have refined the crystal structures of these Wadsleyites by single-crystal X-ray diffraction, analyzed the compositions by electron microprobe, and estimated M3 vacancy concentration from b / a cell-parameter ratios. According to the crystal structure refinements, Cr and V show strong preferences for M3 over M1 and M2 sites and significant substitution up to 2.9 at% at the tetrahedral site (T site). Ni, Co, and Zn show site preferences similar to those of Fe with M1≈ M3 > M2 > T. The avoidance of Ni, Co, and Fe for the M2 site in both Wadsleyite and olivine appears to be partially controlled by crystal field stabilization energy (CFSE). The estimated CFSE values of Ni 2+ , Co 2+ , and Zn 2+ at three distinct octahedral sites show a positive correlation with octahedral occupancy ratios [M2/(M1+M3)]. Ti substitutes primarily into the M3 octahedron, rather than M1, M2, or T sites. Ti, Cr, and V each have greater solubility in Wadsleyite than in olivine. Therefore these transition metal cations may be enriched in a melt or an accessory phase if hydrous melting occurs on upward convection across the Wadsleyite-olivine boundary and may be useful as indicators of high-pressure origin.
-
Coupled substitution of Fe3+and H+for Si in Wadsleyite: A study by polarized infrared and Mössbauer spectroscopies and single-crystal X-ray diffraction
American Mineralogist, 2016Co-Authors: Takaaki Kawazoe, Joseph R. Smyth, Alok Chaudhari, Catherine MccammonAbstract:Coupled substitution of Fe 3+ and H + for Si in Wadsleyite was studied by polarized infrared and Mossbauer spectroscopies and single-crystal X-ray diffraction. Single crystals of Fe-bearing hydrous Wadsleyite were synthesized at 16 GPa and 1870 K using a Kawai-type multi-anvil apparatus. Water and Fe contents of the sample were 0.19–0.26 wt% H 2 O and Fe/(Mg+Fe) of 0.099(2), respectively. Mossbauer spectra showed 13(4)% Fe 3+ /∑Fe and Fe 3+ at the tetrahedral site with 5(3)% IV Fe 3+ /∑Fe. Crystal structure refinement by single-crystal X-ray diffraction indicated that Fe (presumably Fe 3+ ) occupied 4.9(5)% of the tetrahedral site. Infrared light polarized with the electric vector E // a and c was absorbed at 3477(2) cm −1 while no absorption was observed at the region in spectra with E // b . The pleochroic behavior of the 3477 cm −1 band can be interpreted as protonation of silicate oxygen O3 in Fe-bearing hydrous Wadsleyite. The protonation of O3 together with the presence of Fe 3+ at the tetrahedral site confirms the coupled substitution of Fe 3+ and H + for Si in Fe-bearing hydrous Wadsleyite.
Shunichiro Karato - One of the best experts on this subject based on the ideXlab platform.
-
an experimental study of grain scale microstructure evolution during the olivine Wadsleyite phase transition under nominally dry conditions
Earth and Planetary Science Letters, 2018Co-Authors: Anwar Mohiuddin, Shunichiro KaratoAbstract:Abstract The grain-scale microstructure evolution during the phase transformation of olivine to Wadsleyite was investigated using a multi-anvil high-pressure apparatus. We identified three stages in the microstructure evolution during olivine to Wadsleyite phase transformation: (1) nucleation of Wadsleyite along potential nucleation sites (e.g., grain boundaries (and grain corners), inside of grains (dislocations, stacking faults)), (2) development of an interconnected network of fine-grained Wadsleyite along grain boundaries (3) growth of Wadsleyite into olivine. Our observations suggest that at low over pressures ( 3 GPa), intra-crystalline nucleation makes a significant contribution to the volume fraction transformed. The rheological properties of a sample undergoing the phase transformation are controlled by the grain-size and the connectivity of newly formed grains. Based on the model of grain-size evolution involving both nucleation and growth, we show that the initial grain-size of Wadsleyite is controlled by the competition between nucleation rate and growth rate when phase transformation takes place near the equilibrium boundary (at relatively higher temperatures, >1200 K) but mostly by critical size for nucleation when phase transformation takes place away from the equilibrium boundary (at relatively low temperatures,
-
High-pressure and high-temperature deformation experiments on polycrystalline Wadsleyite using the rotational Drickamer apparatus
Physics and Chemistry of Minerals, 2015Co-Authors: Robert Farla, Nobuyoshi Miyajima, George Amulele, Jennifer Girard, Shunichiro KaratoAbstract:High-pressure, torsional deformation experiments on polycrystalline Wadsleyite were carried out using the rotational Drickamer apparatus (RDA). The experimental conditions ranged between temperatures of ~2000–2200 K at pressures of ~20 ± 1 GPa. Prior to deformation, the fine-grained (1–5 µm) Wadsleyite specimens were synthesized from San Carlos olivine in a Kawai-type multi-anvil apparatus. The samples were loaded in the RDA, pressurized and heated, and deformed at stepped strain rates of 5–60 × 10^−6 s^−1. The stress was determined through the analysis of the orientation dependence on changes in lattice spacing for the (141), (240) and (040) planes. The strain was determined from the orientation of a molybdenum strain marker. Most stepped strain-rate tests reveal the stress exponent n to be 4.7 ± 0.5, suggesting power-law dislocation creep operated. Various samples exhibit grain-size reduction (to 0.1–0.6 µm), possibly associated with dynamic recrystallization or with partial phase transformation to ringwoodite. Transmission electron microscopy and electron backscatter diffraction analyses provide information on the dominant slip system in Wadsleyite as 1/2〈111〉 slip on {101} planes, as well as slip in the [100] direction. Dislocation density, even in recrystallized grains, is very high (likely >10^14 m^−2), reflecting the final high stresses in the samples during deformation. The results provide greater constraints on the regimes of various deformation mechanisms in Wadsleyite at various experimental conditions.
-
plastic deformation experiments to high strain on mantle transition zone minerals Wadsleyite and ringwoodite in the rotational drickamer apparatus
Earth and Planetary Science Letters, 2013Co-Authors: J W Hustoft, George Amulele, Junichi Ando, Kazuhiko Otsuka, Zhixue Du, Zhicheng Jing, Shunichiro KaratoAbstract:We report the results of plastic deformation experiments on polycrystalline Wadsleyite and ringwoodite performed at 15–23 GPa and 1300–2100 K conducted using the rotational Drickamer apparatus (RDA). Wadsleyite was synthesized from fine-grained ( � 2 mm) San Carlos olivine in a Kawai-type multianvil apparatus; the average grain size of the resulting Wadsleyite was 1.2 mm. The initial water content of the undeformed Wadsleyite was 24,000–26,000 H/10 6 Si but the final water content is variable and less than the initial water content. Ringwoodite was synthesized from Wadsleyite in situ in the RDA. Both strain and stress were measured in situ using a synchrotron x-ray facility. Determinations of strains and strain rates were made from x-ray radiographs of the sample, using a Mo foil strain marker in the sample assembly. The state of stress was determined from the observed d-spacing of multiple lattice planes as a function of azimuth angle. Samples were deformed at various strain rates at around 10 � 4 –10 � 5 s � 1 . Deformation mechanisms were inferred from the stress exponent and the microstructures. We determined the stress exponent n for Wadsleyite to be 673, suggesting dislocation creep was the dominant deformation mechanism in Wadsleyite. At grain sizes of � 1 mm, our samples were still deforming primarily by dislocation creep. However, small dislocation-free grains are also observed suggesting that diffusion creep may operate in some parts of our samples. & 2012 Published by Elsevier B.V.
-
shear deformation of polycrystalline Wadsleyite up to 2100 k at 14 17 gpa using a rotational drickamer apparatus rda
Journal of Geophysical Research, 2010Co-Authors: Takaaki Kawazoe, Shunichiro Karato, Junichi Ando, Kazuhiko Otsuka, Zhicheng Jing, J W HustoftAbstract:Shear deformation experiments on polycrystalline Wadsleyite (water content, -200-2200 H/10{sup 6} Si) have been conducted at 14.4-17.0 GPa, 1690-2100 K, and strain rates of 2.6-16 x 10{sup -5} s{sup -1} using a rotational Drickamer apparatus (RDA) at a synchrotron facility. The stress was measured from the orientation dependence of lattice spacing for the (013), (211), (141), (240) and (244) planes. On the basis of the mechanical and microstructural observations, we infer that deformation occurs by exponential creep through the Peierls mechanism at relatively low temperatures of 1690-2030 K. However, a sample deformed at the temperature of 2100 K showed significant grain-size reduction, and most of small grains are dislocation-free, although sub-boundaries were observed in some grains in the sample. We interpret these observations as evidence for dynamic recrystallization and that diffusion creep (and grain boundary sliding) plays an important role after dynamic recrystallization caused by power law creep. Consequently, the strength observed in the high-temperature conditions determined by the present study provides an important constraint on strength of diffusion creep and a lower limit for that of the power law dislocation creep. We conclude that the strength of Wadsleyite in the power law dislocation creep is higher than or comparablemore » to that of olivine and the strength of Wadsleyite in the Peierls regime is similar to that of olivine.« less
-
comments on electrical conductivity of Wadsleyite as a function of temperature and water content by manthilake et al
Physics of the Earth and Planetary Interiors, 2009Co-Authors: Shunichiro KaratoAbstract:Abstract In a recent paper, Manthilake et al. [Manthilake, M.A.G.M., et al. Electrical conductivity of Wadsleyite as a function of temperature and water content. Physics of the Earth and Planetary Interiors, in press] presented the results of experimental study on the electrical conductivity of Wadsleyite and concluded that the influence of water is small at transition zone temperatures and that a high concentration of water (hydrogen) cannot explain the observed conductivity in the transition zone as oppose to the conclusion originally obtained by Huang et al. [Huang, X., Xu, Y., Karato, S., 2005. Water content of the mantle transition zone from the electrical conductivity of Wadsleyite and ringwoodite. Nature 434, 746–749) from a similar experimental study. In this note, we discuss the causes of discrepancies between the results by two groups and show that almost all the differences are due to the experimental artifacts in the studies by Manthilake et al. and Yoshino et al. [Manthilake, M.A.G.M., et al. Electrical conductivity of Wadsleyite as a function of temperature and water content. Physics of the Earth and Planetary Interiors, in press; Yoshino, T., Manthilake, G., Matsuzaki, T., Katsura, T., 2008a. Dry mantle transition zone inferred from the conductivity of Wadsleyite and ringwoodite. Nature 451, 326–329] namely (i) the use of inappropriate method of determining electrical conductivity and (ii) the use of the data from a sample of Wadsleyite with a substantial amount of water as a “dry” conductivity. A comparison of electrical conductivity of truly “dry” Wadsleyite and olivine shows that the conductivity is similar at the same pressure and temperature. We also show that the use of one frequency method results in systematic errors in the conductivity measurements that explains the discrepancies in the results by two sets of studies. When an appropriate method for determining electrical conductivity (i.e., the impedance spectroscopy) is used and when the results of truly dry sample are used for the background dry conductivity, we find that the influence of water (hydrogen) is large enough to explain a majority of variation of electrical conductivity by the regional variation in water content.
Patrick Cordier - One of the best experts on this subject based on the ideXlab platform.
-
Forsterite to Wadsleyite phase transformation under shear stress and consequences for the Earth's mantle transition zone
Physics of the Earth and Planetary Interiors, 2020Co-Authors: S. Demouchy, David Mainprice, Andrea Tommasi, Helene Couvy, Fabrice Barou, D.j. Frost, Patrick CordierAbstract:We have studied the phase transformation of forsterite to Wadsleyite under shear stress at the Earth's transition zone pressure and temperature conditions. Two-step experiments were performed using a multi-anvil press. First, we hot pressed iron-free forsterite at 6 or 11 GPa and 1100 degrees C. Then we deformed a slab of this starting material using a direct simple shear assembly at 16 GPa and 1400 degrees C for 1, 15, 35, 40, or 60 min. Both the starting material and the deformed samples were characterized using optical and scanning electron microscopy including measurements of crystal preferred orientations (CPO) by electron back scattered diffraction (EBSD), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FTIR). The phase transformation occurs very rapidly, in less than 1 min, and metastable forsterite relics are not observed after deformation. The grain size of Wadsleyite is slightly smaller than the forsterite starting material. The water contents obtained from FTIR analyses in forsterite and Wadsleyite are 65-124 wt ppm H2O and 114-736 wt ppm H2O, respectively, which are well below water solubility at similar conditions in the presence of free water. Wadsleyite aggregates display weak CPO patterns with [1 0 0] axes concentrated at low angle to the shear direction, [0 1 0] axes perpendicular to the shear plane and nearly random [0 0 1] axes. Only a few dislocations were observed in Wadsleyite with TEM. This observation is consistent with the assumption that most dislocations formed during the initial high-stress stages of these stress-relaxation experiments, were consumed in the phase transformation, probably enhancing the transformation rate. CPO patterns vary as a function of the water content: with increasing water content the density of [1 0 0] axes parallel to the shear direction decreases, and the density of [0 0 1] axes increases. Viscoplastic self-consistent modeling of CPO evolution using previously reported glide systems for Wadsleyite, i.e., [1 0 0]{0 k 1} and 1/2 (1 1 1){1 0 1}, cannot reproduce the measured CPO, unless the [0 0 1](0 1 0) system, for which dislocations have not been observed by TEM, is also activated. In addition, Wadsleyite grain growth suggests the participation of diffusion-assisted processes in deformation. Calculated anisotropies for P and S-waves using measured CPO are always below 1%. This very low anisotropy is due to both the low finite strain achieved in the experiments, which leads to weak Wadsleyite CPO, and to the diluting effect of added majorite. The present experiments emphasize the importance of stress, grain size evolution and water content in the forsterite to Wadsleyite phase transformation and subsequent deformation in the transition zone
-
application of scanning precession electron diffraction in the transmission electron microscope to the characterization of deformation in Wadsleyite and ringwoodite
Minerals, 2018Co-Authors: Billy Clitton Nzogang, Takaaki Kawazoe, Simon Thilliez, Alexandre Mussi, Jeremie Bouquerel, Nobuyoshi Miyajima, Patrick CordierAbstract:The mantle transition zone represents an important layer in the interior of the Earth that is characterized by phase transformations of olivine polymorphs. Constraining the rheology difference between Wadsleyite and ringwoodite is important in determining the viscosity contrast at a depth of 520 km. In this study, we perform a post-mortem by transmission electron microscopy of a Wadsleyite + ringwoodite aggregate, deformed at high-pressure and high-temperature, in a deformation-DIA apparatus. From orientation maps acquired by scanning precession electron diffraction, we calculate local misorientations and misorientation-gradients, which are used as a proxy of plastic strain. We show that at 17.3 GPa, 1700 K, the plastic responses of Wadsleyite and ringwoodite are comparable, although recovery by subgrain boundary migration is more easily activated in Wadsleyite.
-
Modeling dislocation glide and lattice friction in Mg2SiO4 Wadsleyite in conditions of the Earth’s transition zone
American Mineralogist, 2016Co-Authors: Sebastian Ritterbex, Philippe Carrez, Patrick CordierAbstract:Thermally activated dislocation glide in Mg 2 SiO 4 Wadsleyite at 15 GPa has been modeled to investigate its potential contribution to plastic deformation of Wadsleyite in the Earth’s transition zone. Modeling is based on a multiphysics approach that allows calculating the constitutive equations associated with single slip for a wide range of temperatures and strain rates typical for the laboratory and the Earth’s mantle. The model is based on the core structures of the rate limiting ½ {101} and [100](010) dissociated screw dislocations. After quantifying their lattice friction, glide is modeled through an elastic interaction model that allows calculating the critical configurations that trigger elementary displacements of dissociated dislocations. The constitutive relations corresponding to glide are then deduced with Orowan’s equation to describe the average intracrystalline plasticity. The high stresses predicted by the model are found to be in good agreement with experimental data on plastic deformation of Wadsleyite at high-pressure conditions. Moreover, it is found that even at appropriate mantle strain rates, glide of dislocations remain difficult with critical resolved shear stress ( CRSS ) values typically larger than 100 MPa. This implies the inefficiency of dislocation glide to the overall plastic deformation of Mg 2 SiO 4 Wadsleyite under transition zone conditions.
-
modeling dislocation glide and lattice friction in mg2sio4 Wadsleyite in conditions of the earth s transition zone
American Mineralogist, 2016Co-Authors: Sebastian Ritterbex, Philippe Carrez, Patrick CordierAbstract:Thermally activated dislocation glide in Mg 2 SiO 4 Wadsleyite at 15 GPa has been modeled to investigate its potential contribution to plastic deformation of Wadsleyite in the Earth’s transition zone. Modeling is based on a multiphysics approach that allows calculating the constitutive equations associated with single slip for a wide range of temperatures and strain rates typical for the laboratory and the Earth’s mantle. The model is based on the core structures of the rate limiting ½ {101} and [100](010) dissociated screw dislocations. After quantifying their lattice friction, glide is modeled through an elastic interaction model that allows calculating the critical configurations that trigger elementary displacements of dissociated dislocations. The constitutive relations corresponding to glide are then deduced with Orowan’s equation to describe the average intracrystalline plasticity. The high stresses predicted by the model are found to be in good agreement with experimental data on plastic deformation of Wadsleyite at high-pressure conditions. Moreover, it is found that even at appropriate mantle strain rates, glide of dislocations remain difficult with critical resolved shear stress ( CRSS ) values typically larger than 100 MPa. This implies the inefficiency of dislocation glide to the overall plastic deformation of Mg 2 SiO 4 Wadsleyite under transition zone conditions.
-
forsterite to Wadsleyite phase transformation under shear stress and consequences for the earth s mantle transition zone
Physics of the Earth and Planetary Interiors, 2011Co-Authors: Sylvie Demouchy, Daniel J. Frost, David Mainprice, Andrea Tommasi, Helene Couvy, Fabrice Barou, Patrick CordierAbstract:We have studied the phase transformation of forsterite to Wadsleyite under shear stress at the Earth’s transition zone pressure and temperature conditions. Two-step experiments were performed using a multi-anvil press. First, we hot pressed iron-free forsterite at 6 or 11 GPa and 1100 ◦ C. Then we deformed a slab of this starting material using a direct simple shear assembly at 16 GPa and 1400 ◦C for 1, 15, 35, 40, or 60 min. Both the starting material and the deformed samples were characterized using optical and scanning electron microscopy including measurements of crystal preferred orientations (CPO) by electron back scattered diffraction (EBSD), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FTIR). The phase transformation occurs very rapidly, in less than 1 min, and metastable forsterite relics are not observed after deformation. The grain size of Wadsleyite is slightly smaller than the forsterite starting material. The water contents obtained from FTIR analyses in forsterite and Wadsleyite are 65–124 wt ppm H2O and 114–736 wt ppm H2O, respectively, which are well below water solubility at similar conditions in the presence of free water. Wadsleyite aggregates display weak CPO patterns with [1 0 0] axes concentrated at low angle to the shear direction, [0 1 0] axes perpendicular to the shear plane and nearly random [0 0 1] axes. Only a few dislocations were observed in Wadsleyite with TEM. This observation is consistent with the assumption that most dislocations formed during the initial high-stress stages of these stress-relaxation experiments, were consumed in the phase transformation, probably enhancing the transformation rate. CPO patterns vary as a function of the water content: with increasing water content the density of [1 0 0] axes parallel to the shear direction decreases, and the density of [0 0 1] axes increases. Viscoplastic self-consistent modeling of CPO evolution using previously reported glide systems for Wadsleyite, i.e., [1 0 0]{0 k l} and 1/2 � 111 � { 101 }, cannot reproduce the measured CPO, unless the [0 0 1](0 1 0) system, for which dislocations have not been observed by TEM, is also activated. In addition, Wadsleyite grain growth suggests the participation of diffusion-assisted processes in deformation. Calculated anisotropies for P and S-waves using measured CPO are always below 1%. This very low anisotropy is due to both the low finite strain achieved in the experiments, which leads to weak Wadsleyite CPO, and to the diluting effect of added majorite. The present experiments emphasize the importance of stress, grain size evolution and water content in the forsterite to Wadsleyite phase transformation and subsequent deformation in the transition zone.