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Elasticity and lattice dynamics of enstatite at high pressure

Zhang, Dongzhou and Jackson, Jennifer M. and Chen, Bin and Sturhahn, Wolfgang and Zhao, Jiyong and Yan, Jinyuan and Caracas, Razvan (2013) Elasticity and lattice dynamics of enstatite at high pressure. Journal of Geophysical Research. Solid Earth, 118 (8). pp. 4071-4082. ISSN 2169-9313. http://resolver.caltech.edu/CaltechAUTHORS:20131106-092800614

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Abstract

The behavior of synthetic-powdered ^(57)Fe-enriched enstatite (Mg_(0.980)Fe_(0.020(5)))(Mg_(0.760)Fe_(0.240))Si_2O_6 has been explored by X-ray diffraction (XRD) and nuclear resonant inelastic X-ray scattering (NRIXS). The Pbca-structured enstatite sample was compressed in fine pressure increments for our independent XRD measurements. One structural transition between 10.1 and 12.2 GPa has been identified from the XRD data. The XRD reflections observed for the high-pressure phase are best matched with space group P2_1/c. We combine density functional theory with Mössbauer spectroscopy and NRIXS to understand the local site symmetry of the Fe atoms in our sample. A third-order Birch-Murnaghan (BM3) equation of state fitting gives K_(T0)=103±5 GPa and K'_(T0)=13±2 for the Pbca phase. At 12 GPa, a BM3 fitting gives K_(T12)=220±10 GPa with K'_(T12)=8±4 for the P2_1/c phase. NRIXS measurements were performed with in situ XRD up to 17 GPa. The partial phonon density of states (DOS) was derived from the raw NRIXS data, and from the low-energy region of the DOS, the Debye sound velocity was determined. We use the equation of state determined from XRD and Debye sound velocity to compute the isotropic compressional (V_P) and shear (V_S) wave velocities of enstatite at different pressures. Our results help constrain the high-pressure properties of Pbca-structured enstatite in the Earth's upper mantle. We find that candidate upper mantle phase assemblages containing Pbca-structured enstatite are associated with shear velocity gradients that are higher than the average Earth model PREM but lower than regional studies down to about 250 km depth.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1002/jgrb.50303DOIArticle
http://onlinelibrary.wiley.com/doi/10.1002/jgrb.50303/abstractPublisherArticle
Additional Information:© 2013 American Geophysical Union. Received 18 February 2013; revised 16 July 2013; accepted 22 July 2013; published 27 August 2013. We thank C. A. Murphy, J. K.Wicks, and A. S. Wolf for help in conducting experiments and Y. Fei for synthesizing the sample. We thank the NSF (CAREER EAR-0956166) and the Tectonics Observatory at Caltech (funded through the Gordon and Betty Moore Foundation) for support of this research. Use of the Advanced Photon Source was supported by the U.S. D.O.E., O.S., and O.B.E.S. (DE-AC02-06CH11357). Use of the Advanced Light Source was supported by the U.S. D.O.E., O.S., and O.B.E.S. (DE-AC02-05CH11231). Sector 3 operations, the gasloading system at GSECARS, and beamline 12.2.2 are supported in part by COMPRES under NSF Cooperative Agreement EAR 06-49658.
Group:Caltech Tectonics Observatory, Seismological Laboratory
Funders:
Funding AgencyGrant Number
NSFEAR-0956166
Caltech Tectonics ObservatoryUNSPECIFIED
Gordon and Betty Moore FoundationUNSPECIFIED
Department of Energy (DOE)DE-AC02-06CH11357
Department of Energy (DOE)DE-AC02-05CH11231
NSFEAR 06-49658
Subject Keywords:enstatite; elasticity; lattice dynamics; upper mantle; sound velocities; equation of state
Record Number:CaltechAUTHORS:20131106-092800614
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20131106-092800614
Official Citation:Zhang, D., J. M. Jackson, B. Chen,W. Sturhahn, J. Zhao, J. Yan, and R. Caracas (2013), Elasticity and lattice dynamics of enstatite at high pressure, J. Geophys. Res. Solid Earth, 118, 4071–4082, doi:10.1002/jgrb.50303.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:42265
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:06 Nov 2013 18:18
Last Modified:01 Feb 2017 19:19

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