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In situ measurements of sound velocities and densities across the orthopyroxene → high-pressure clinopyroxene transition in MgSiO3 at high pressure |
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| Authors: | Jennifer Kung Baosheng Li Yanbin Wang Robert C Liebermann |
| Institution: | a Mineral Physics Institute and Department of Geosciences, Stony Brook University, Stony Brook, NY 11794, USA b GSECARS, Argonne National Laboratory, Center for Advanced Radiation Sources, The University of Chicago, Chicago, IL 60439, USA c Laboratoire de Physique des Geomateriaux, Institut de Physique du Globe, Paris 75252, France |
| Abstract: | Using acoustic measurement interfaced with a large volume multi-anvil apparatus in conjunction with in situ X-radiation techniques, we are able to measure the density and elastic wave velocities (VP and VS) for both ortho- and high-pressure clino-MgSiO3 polymorphs in the same experimental run. The elastic bulk and shear moduli of the unquenchable high-pressure clinoenstatite phase were measured within its stability field for the first time. The measured density contrast associated with the phase transition OEN → HP-CEN is 2.6-2.9% in the pressure of 7-9 GPa, and the corresponding velocity jumps are 3-4% for P waves and 5-6% for S waves. The elastic moduli of the HP-CEN phase are KS=156.7(8) GPa, G = 98.5(4) GPa and their pressure derivatives are KS′=5.5(3) and G′ = 1.5(1) at a pressure of 6.5 GPa, room temperature. In addition, we observed anomalous elastic behavior in orthoenstatite at pressure above 9 GPa at room temperature. Both elastic wave velocities exhibited softening between 9 and 13-14 GPa, which we suggest is associated with a transition to a metastable phase intermediate between OEN and HP-CEN. |
| Keywords: | Pyroxene Elasticity High pressure Elastic softening Unquenchable Phase transformation |
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