The equation of state of Al,H-bearing SiO2 stishovite to 58 GPa |
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Authors: | Dmitry L Lakshtanov Carine B Vanpeteghem Jennifer M Jackson Jay D Bass Guoyin Shen Vitali B Prakapenka Konstantin Litasov Eiji Ohtani |
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Institution: | (1) Department of Geology, University of Illinois at Urbana-Champaign, 1301 W Green St, Urbana, IL 61801, USA;(2) Consortium for Advanced Radiation Sources, The University of Chicago, Chicago, IL 60637, USA;(3) Institute of Mineralogy, Petrology and Economic Geology, Tohoku University, Aza Aoba Aramaki, Sendai 980-8578, Japan |
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Abstract: | We have determined the P-V equation of state of Al-rich H-bearing SiO2 stishovite by X-ray powder diffraction at pressures up to 58 GPa using synchrotron radiation. The sample contained 1.8 wt%
Al2O3 and up to 500 ppm H2O, and had a composition that would coexist with Mg-silicate perovskite in a subducted slab. By fitting a third-order Birch-Murnaghan
equation of state to our compression data, we obtained a bulk modulus K
T0=298(7) GPa with K′=4.3(5). With K′ fixed to a value of 4, the bulk modulus K
T0=304(3) GPa. Our results indicate that Al3+ and H+ have a small effect on the elastic properties of stishovite. Compared with data obtained up to 43.8 GPa, peak intensities
changed and we observed a decreased quality of fit to a tetragonal unit cell at pressures of 49 GPa and higher. These changes
may be an indication that the rutile↔CaCl2 transition occurs between these pressures. After laser annealing of the sample at 58.3(10) GPa and subsequent decompression
to room conditions, the cell volume is the same as before compression, giving strong evidence that the composition of the
recovered sample is also unchanged. This suggests that Al and H are retained in the sample under extreme P-T conditions and
that stishovite can be an agent for transporting water to the deepest lower mantle. |
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Keywords: | Water in the mantle High pressure Synchrotron X-ray diffraction Equation of state Water-bearing stishovite |
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