Sound velocities of skiagite–iron–majorite solid solution to 56 GPa probed by nuclear inelastic scattering
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High-pressure experimental data on sound velocities of garnets are used for interpretation of seismological data related to the Earth’s upper mantle and the mantle transition zone. We have carried out a Nuclear Inelastic Scattering study of iron-silicate garnet with skiagite (77 mol%)–iron–majorite composition in a diamond anvil cell up to 56 GPa at room temperature. The determined sound velocities are considerably lower than sound velocities of a number of silicate garnet end-members, such as grossular, pyrope, Mg–majorite, andradite, and almandine. The obtained sound velocities have the following pressure dependencies: V p [km/s] = 7.43(9) + 0.039(4) × P [GPa] and V s [km/s] = 3.56(12) + 0.012(6) × P [GPa]. We estimated sound velocities of pure skiagite and khoharite, and conclude that the presence of the iron–majorite component in skiagite strongly decreases V s . We analysed the influence of Fe3+ on sound velocities of garnet solid solution relevant to the mantle transition zone and consider that it may reduce sound velocities up to 1% relative to compositions with only Fe2+ in the cubic site.
KeywordsNuclear inelastic scattering Sound velocities Skiagite Khoharite Garnet Mantle transition zone
The authors are grateful to Dr. R. Mittal for the provided data. We thank the European Synchrotron Radiation Facility for the provision of synchrotron radiation (ID18). N.D. thanks the German Research Foundation (Deutsche Forschungsgemeinschaft, DFG, projects no. DU 954-8/1 and DU 95411/1) and the Federal Ministry of Education and Research, Germany (BMBF, grants no. 5K13WC3 and 5K16WC1) for financial support. C.M. and L.D. acknowledge DFG funding through projects MC 3–18/1 and MC 3–20/1 and the CarboPaT Research Unit FOR2125. Partial support was also provided by the German Academic Exchange Service (DAAD).
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