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A possible new Al-bearing hydrous Mg-silicate (23 A phase) in the deep upper mantle (2015)

Cai, N., Inoue, T., Fujino, K., Ohfuji, H., Yurimoto, H.

Mineralogical Society of America

In: American Mineralogist

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Publication Date: 2015-10-02

Description: A new Al-bearing hydrous Mg-silicate that we named as 23 Å phase was synthesized at 10 GPa and 1000 °C, while also coexisting with diaspore and pyrope in the following system: phase A [Mg 7 Si 2 O 8 (OH) 6 ] + Al 2 O 3 + H 2 O. The chemical composition of this new 23 Å phase is Mg 11 Al 2 Si 4 O 16 (OH) 12 , and it contains about 12.1 wt% water. Powder X-ray diffraction and electron diffraction patterns show that this new 23 Å phase has a hexagonal structure, with a = 5.1972(2), c = 22.991(4) Å, and V = 537.8(2) Å 3 , and the possible space group is P c 2, P 6 3 cm , or P 6 3 / mcm . The calculated density is 2.761 g/cm 3 accordingly, which was determined by assuming that the formula unit per cell ( Z ) is 1. This crystal structure is quite unique among mantle minerals in having an extraordinarily long c axis. Several experiments revealed that its stability region is very similar to that of phase A. We further confirmed that this new 23 Å phase was stable in the chlorite composition at 10 GPa and 1000 °C. The present results indicate that this new 23 Å hydrous phase will form in an Al-bearing subducting slab, and transport water together with Al into the deep upper mantle or even into the upper part of the transition zone.

Print ISSN: 0003-004X

Electronic ISSN: 1945-3027

Topics: Geosciences

Published by Mineralogical Society of America

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Co2+ and Ni2+ diffusion in olivine determined by secondary ion mass spectrometry (1999)

Ito, M. ; Yurimoto, H. ; Morioka, M. ; [et al.]

Springer

Physics and chemistry of minerals 26 (1999), S. 425-431

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ISSN: 1432-2021

Keywords: Key words SIMS ; Depth profiling ; Forsterite Diffusion ; Arrhenius plot ; Activation energy

Source: Springer Online Journal Archives 1860-2000

Topics: Chemistry and Pharmacology , Geosciences , Physics

Notes: Abstract Diffusion coefficients of Co2+ and Ni2+ in synthetic single crystal forsterite along the c-axis were determined in the temperature ranges, 700–1200 °C and 800–1300 °C, respectively. The synthesized forsterite specimens were coated with thin evaporated films of CoO and NiO on the c-surface and annealed for diffusion experiments. The short penetration distance of diffusing ions in forsterite was measured by secondary ion mass spectrometry using the depth profile method. The diffusion coefficients of Co (700–1200 °C) and Ni (800–1300 °C) are given by: and The observed diffusion coefficient values show good linear relationships in Arrhenius plots and the activation energy values obtained agree well with the previous values, although the diffusion coefficient values observed at the high temperature end of the experimental range deviate from the previous values. These results indicate that Co and Ni diffuse in olivine with a single mechanism within the temperature range observed, possibly with an extrinsic in nature as in the case of Mg tracer diffusion observed by Chakraborty et al. 1994 and of Fe-Mg interdiffusion by Chakraborty.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s002690050204

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Stability of dense hydrous magnesium silicate phases in the systems Mg2SiO4-H2O and MgSiO3-H2O at pressures up to 27 GPa (2000)

Ohtani, E. ; Mizobata, H. ; Yurimoto, H.

Springer

Physics and chemistry of minerals 27 (2000), S. 533-544

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ISSN: 1432-2021

Keywords: Key words High pressure ; High temperature ; DHMS ; phases A ; G

Source: Springer Online Journal Archives 1860-2000

Topics: Chemistry and Pharmacology , Geosciences , Physics

Notes: Abstract We conducted high-pressure phase equilibrium experiments in the systems MgSiO3 with 15 wt% H2O and Mg2SiO4 with 5 wt% and 11 wt% H2O at 20 ∼ 27 GPa. Based on the phase relations in these systems, together with the previous works on the related systems, we have clarified the stability relations of dense hydrous magnesium silicates in the system MgO-SiO2-H2O in the pressure range from 10 to 27 GPa. The results show that the stability field of phase G, which is identical to phase D and phase F, expands with increasing water contents. Water stored in serpentine in the descending cold slabs is transported into depths greater than 200 km, where serpentine decomposes to a mixture of phase A, enstatite, and fluid. Reaction sequences of the hydrous phases which appear at higher pressures vary with water content. In the slabs with a water content less than about 2 wt%, phase A carries water to a depth of 450 km. Hydrous wadsleyite, hydrous ringwoodite, and ilmenite are the main water reservoirs in the transition zone from 450 to 660 km. Superhydrous phase B is the water reservoir in the uppermost part of the lower mantle from 670 to 800 km, whereas phase G appears in the lower mantle only at depths greater than 800 km. In cold slabs with local water enrichment greater than 2 wt%, the following hydrous phases appear with increasing depths; phase A to 450 km, phase A and phase G from 450 km to 550 km, brucite, superhydrous phase B, and phase G from 550 km to 800 km, and phase G at depths greater than 800 km.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s002690000097

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Patterns in the hydrogen and trace element compositions of mantle olivines (1997)

Kurosawa, M. ; Yurimoto, H. ; Sueno, S.

Springer

Physics and chemistry of minerals 24 (1997), S. 385-395

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ISSN: 1432-2021

Source: Springer Online Journal Archives 1860-2000

Topics: Chemistry and Pharmacology , Geosciences , Physics

Notes: Abstract The concentrations of hydrogen and the other trace elements in olivines from mantle xenoliths have been determined by secondary ion mass spectrometry (SIMS) for clarifying the incorporation mechanism and the behavior of the hydrogen. The hydrogen contents in olivines from mantle xenoliths range from 10 to 60 ppm wt. H2O and the concentration range is consistent with the previous infrared (IR) spectroscopic data. IR spectra of the olivine crystals show no effects of the weathering or secondary alteration. The hydrogen is distributed homogeneously among olivine grains in each mantle xenolith. However, the hydrogen contents of the olivine crystals are less than those for the olivine phenocrysts crystallized from the host magma. Olivine inclusions in diamonds also show similar hydrogen contents to the xenolithic olivines. Thus the hydrogen content of xenolithic olivines does not attain equilibrium with water in the host magma during the transportation from the Earth's mantle to the surface, and is taken as a reflection of the hydrogen condition in the mantle. Correlations of hydrogen with trivalent cation contents in garnet peridotitic olivines indicate the incorporation of hydrogen into mantle olivines by a coupled substitution mechanism, with the hydrogen present in the form of hydroxyl in oxygen positions adjacent to the M site vacancies. The hydrogen content of xenolithic olivines increases with pressure but decreases with increasing temperature, suggesting importance of olivine as a water reservoir at low temperature regions such as in subducting slabs.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s002690050052

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Synthesis of large and homogeneous single crystals of water-bearing minerals by slow cooling at deep-mantle pressures (2015)

Okuchi, T., Purevjav, N., Tomioka, N., Lin, J.-F., Kuribayashi, T., Schoneveld, L., Hwang, H., Sakamoto, N., Kawasaki, N., Yurimoto, H.

Mineralogical Society of America

In: American Mineralogist

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Publication Date: 2015-07-02

Description: The presence of water in the Earth’s deep mantle is an issue of increasing interest in the field of high-pressure mineralogy. An important task for further advancing research in the field is to create homogeneous single crystals of candidate deep-mantle water-bearing minerals of 1 mm or larger in size, which is required for applying them for the time-of-flight (TOF) single-crystal Laue diffraction method with a third-generation neutron instrument. In this study, we perform several experiments to demonstrate an improved methodology for growing hydrous crystals of such large sizes at relevant transition zone and lower-mantle conditions via very slow cooling over a maximum period of 1 day. Successfully synthesized crystals using this methodology include dense hydrous magnesium silicate (DHMS) phase E, hydrous wadsleyite, hydrous ringwoodite, and bridgmanite (silicate perovskite). It is also demonstrated that these hydrous crystals can be grown from deuterium enriched starting materials in addition to those having a natural hydrogen isotope ratio. Magnitudes of chemical and crystallographic heterogeneities of the product crystals were characterized by comprehensive analysis of X-ray precession photography, single-crystal X-ray diffraction (SCXRD), field-emission scanning electron microscope (FE-SEM), electron probe microanalyzer (EPMA), secondary ion mass spectroscopy (SIMS), powder X-ray diffraction (PXRD), and TOF neutron powder diffraction (TOF-NPD). The product crystals were confirmed to be inclusion free and crystallographically homogeneous. Compositional and isotopic differences of major elements and hydrogen isotope abundances were lower than 1 and 3%, respectively, among intracrystals and intercrystals within each recovered sample capsule. Phase E crystals up to 600 μm in the largest dimension were grown at a constant temperature of 1100 °C kept for 3 h. Using a lattice parameter-to-temperature relation of phase E, the thermal gradient in the sample capsules for the phase E synthesis has been evaluated to be 20 °C/mm. Hydrous wadsleyite crystals up to 1100 μm in the largest dimension were grown at 1390 °C with a temperature reduction of 70 °C during heating for 10 h. Hydrous ringwoodite crystals up to 1000 μm in the largest dimension were grown at around 1400 °C with a temperature reduction of 110 °C during heating for 12 h. Bridgmanite crystals up to 600 μm in the largest dimension were grown at 1700 °C with a temperature reduction of 30 °C during heating for 12 h. A TOF single-crystal diffraction instrument has been successfully used for analyzing one of the hydrous wadsleyite crystals, which demonstrated that single crystals appropriate for their expected usage are created using the method proposed in the present study.

Print ISSN: 0003-004X

Electronic ISSN: 1945-3027

Topics: Geosciences