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Elasticity of single-crystal low water content hydrous pyrope at high-pressure and high-temperature conditions

Fan Dawei, Xu Jingui, Chang Lu, Sergey N. Tkachev, Li Bo, Ye Zhiling, Huang Shijie, Vitali B. Prakapenka and Zhou Wenge
Elasticity of single-crystal low water content hydrous pyrope at high-pressure and high-temperature conditions
American Mineralogist (July 2019) 104 (7): 1022-1031


The elasticity of single-crystal hydrous pyrope with approximately 900 ppmw H (sub 2) O has been derived from sound velocity and density measurements using in situ Brillouin light spectroscopy (BLS) and synchrotron X-ray diffraction (XRD) in the diamond-anvil cell (DAC) up to 18.6 GPa at room temperature and up to 700 K at ambient pressure. These experimental results are used to evaluate the effect of hydration on the single-crystal elasticity of pyrope at high pressure and high temperature (P-T) conditions to better understand its velocity profiles and anisotropies in the upper mantle. Analysis of the results shows that all of the elastic moduli increase almost linearly with increasing pressure at room temperature, and decrease linearly with increasing temperature at ambient pressure. At ambient conditions, the aggregate adiabatic bulk and shear moduli (KS0, G0) are 168.6(4) and 92.0(3) GPa, respectively. Compared to anhydrous pyrope, the presence of approximately 900 ppmw H (sub 2) O in pyrope does not significantly affect its KS0 and G0 within their uncertainties. Using the third-order Eulerian finite-strain equation to model the elasticity data, the pressure derivatives of the bulk [(delta K (sub S) /delta P) (sub T) ] and shear moduli [(delta G/delta P) (sub T) ] at 300 K are derived as 4.6(1) and 1.3(1), respectively. Compared to previous BLS results of anhydrous pyrope, an addition of approximately 900 ppmw H (sub 2) O in pyrope slightly increases the (delta K (sub S) /delta P) (sub T) , but has a negligible effect on the (delta G/delta P) (sub T) within their uncertainties. The temperature derivatives of the bulk and shear moduli at ambient pressure are (delta K (sub S) /delta T) (sub P) = -0.015(1) GPa/K and (delta G/delta T) (sub P) = -0.008(1) GPa/K, which are similar to those of anhydrous pyrope in previous BLS studies within their uncertainties. Meanwhile, our results also indicate that hydrous pyrope remains almost elastically isotropic at relevant high P-T conditions, and may have no significant contribution to seismic anisotropy in the upper mantle. In addition, we evaluated the seismic velocities (delta P and delta S) and the delta P/delta S ratio of hydrous pyrope along the upper mantle geotherm and a cold subducted slabs geotherm. It displays that hydrogen also has no significant effect on the seismic velocities and the delta P/delta S ratio of pyrope at the upper mantle conditions.

ISSN: 0003-004X
EISSN: 1945-3027
Serial Title: American Mineralogist
Serial Volume: 104
Serial Issue: 7
Title: Elasticity of single-crystal low water content hydrous pyrope at high-pressure and high-temperature conditions
Affiliation: Chinese Academy of Sciences, Institute of Geochemistry, Guiyang, China
Pages: 1022-1031
Published: 20190701
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 110
Accession Number: 2019-063834
Categories: Geophysics of minerals and rocks
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 4 tables
Secondary Affiliation: University of Texas at Austin, USA, United StatesUniversity of Chicago, USA, United StatesUniversity of Chinese Academy of Sciences, CHN, China
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Abstract, copyright, Mineralogical Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 2019
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