Pressure-induced velocity softening in natural orthopyroxene at mantle temperature
- Department of Geosciences, Stony Brook University, Stony Brook, New York 11794, U.S.A.
- Mineral Physics Institute, Stony Brook University, Stony Brook, New York 11794, U.S.A.
- Department of Earth and Planetary Sciences, American Museum of Natural History, New York, New York 10024, U.S.A.
- Department of Geosciences, Stony Brook University, Stony Brook, New York 11794, U.S.A.; Mineral Physics Institute, Stony Brook University, Stony Brook, New York 11794, U.S.A.
Abstract In this study, we have measured the compressional and shear wave velocities of (Mg1.77Fe0.22Ca0.01)Si2O6 natural orthopyroxene up to 13.5 GPa and 873 K using ultrasonic interferometry in conjunction with in situ synchrotron X-ray diffraction and imaging techniques. Previous acoustic experiments on orthoenstatite (OEn) MgSiO3 indicated that both compressional and shear velocities (VP and VS) of OEn undergo continuous velocity softening above 9 GPa at room temperature, which has been attributed to the phase transition from OEn to the metastable, high-pressure clinoenstatite HPCEn2. For the first time, our results suggest that pressure-induced velocity softening can occur in natural orthopyroxene at high-temperature conditions relevant to the Earth's cold subduction zones. Estimates of the impedance and velocity contrasts between orthopyroxene (Opx) and high-pressure clinopyroxene (HPCpx) have been calculated, and the possibility of this phase transformation being a plausible candidate for seismic X-discontinuities at depth around 250–350 km is re-evaluated.
- Research Organization:
- Univ. of Chicago, IL (United States); State Univ. of New York (SUNY), Albany, NY (United States); Argonne National Lab. (ANL), Argonne, IL (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC)
- DOE Contract Number:
- FG02-94ER14466; NA0002907; AC02-06CH11357
- OSTI ID:
- 1610259
- Journal Information:
- American Mineralogist, Vol. 104, Issue 8; ISSN 0003-004X
- Publisher:
- Mineralogical Society of America
- Country of Publication:
- United States
- Language:
- English
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