Pressure-induced velocity softening in natural orthopyroxene at mantle temperature

Wang, Siheng; Chen, Ting; Cai, Nao; Qi, Xintong; Fiege, Adrian; Liebermann, Robert C.; Li, Baosheng

doi:10.2138/am-2019-6935

Title: Pressure-induced velocity softening in natural orthopyroxene at mantle temperature

Abstract

In this study, we have measured the compressional and shear wave velocities of (Mg_1.77Fe_0.22Ca_0.01)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 (V_P and V_S) 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. As a result, 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.

Authors:

Wang, Siheng ^[1]; Chen, Ting ^[1]; Cai, Nao ^[1]; Qi, Xintong ^[1]; Fiege, Adrian ^[2]; Liebermann, Robert C. ^[1]; Li, Baosheng ^[1]

Stony Brook Univ., NY (United States)
American Museum of Natural History, New York, NY (United States)

Publication Date:: Thu Aug 01 00:00:00 EDT 2019

Research Org.:: Stony Brook Univ., NY (United States)

Sponsoring Org.:: USDOE National Nuclear Security Administration (NNSA); National Science Foundation (NSF)

OSTI Identifier:: 1638237

Grant/Contract Number:: NA0003886; EAR-1524078; EAR-1634415; FG02-94ER14466; AC02-06CH11357

Resource Type:: Accepted Manuscript

Journal Name:: American Mineralogist

Additional Journal Information:: Journal Volume: 104; Journal Issue: 8; Journal ID: ISSN 0003-004X

Publisher:: Mineralogical Society of America

Country of Publication:: United States

Language:: English

Subject:: 36 MATERIALS SCIENCE; 58 GEOSCIENCES; 75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; high pressure and high temperature; elasticity; velocity softening; orthopyroxene; ultrasonic interferometry

Citation Formats


                    Wang, Siheng, Chen, Ting, Cai, Nao, Qi, Xintong, Fiege, Adrian, Liebermann, Robert C., and Li, Baosheng. Pressure-induced velocity softening in natural orthopyroxene at mantle temperature.  United States: N. p., 2019. 
Web.  doi:10.2138/am-2019-6935.

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                    Wang, Siheng, Chen, Ting, Cai, Nao, Qi, Xintong, Fiege, Adrian, Liebermann, Robert C., & Li, Baosheng. Pressure-induced velocity softening in natural orthopyroxene at mantle temperature.  United States.  https://doi.org/10.2138/am-2019-6935

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                    Wang, Siheng, Chen, Ting, Cai, Nao, Qi, Xintong, Fiege, Adrian, Liebermann, Robert C., and Li, Baosheng. Thu .  
"Pressure-induced velocity softening in natural orthopyroxene at mantle temperature".  United States.  https://doi.org/10.2138/am-2019-6935.  https://www.osti.gov/servlets/purl/1638237.

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@article{osti_1638237,

  title        = {Pressure-induced velocity softening in natural orthopyroxene at mantle temperature},

  author       = {Wang, Siheng and Chen, Ting and Cai, Nao and Qi, Xintong and Fiege, Adrian and Liebermann, Robert C. and Li, Baosheng},

  abstractNote = {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. As a result, 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.},

  doi          = {10.2138/am-2019-6935},

  journal      = {American Mineralogist},

  number       = 8,

  volume       = 104,

  place        = {United States},

  year         = {Thu Aug 01 00:00:00 EDT 2019},

  month        = {Thu Aug 01 00:00:00 EDT 2019}

}

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Figures / Tables:

Table 1: Elasticity properties of Fe-bearing natural orthopyroxene at high temperature and pressure

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