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Elasticity of Orthoenstatite at High Pressure and Temperature: Implications for the Origin of Low V P / V S Zones in the Mantle Wedge
Author(s) -
Qian Wangsheng,
Wang Wenzhong,
Zou Fan,
Wu Zhongqing
Publication year - 2018
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/2017gl075647
Subject(s) - mantle (geology) , geology , geodynamics , mantle wedge , shear modulus , bulk modulus , shear (geology) , elasticity (physics) , thermodynamics , geophysics , mineralogy , petrology , physics , subduction , seismology , tectonics
Orthopyroxene (opx) is an important mineral in petrologic models for the upper mantle. Its elastic properties are fundamental for understanding the chemical composition and geodynamics of the upper mantle. Here we calculate the elastic properties of orthoenstatite (MgSiO 3 ), the Mg end‐member orthopyroxene under upper mantle pressure and temperature conditions using first principle calculations with local density approximation. Bulk and shear moduli increase nonlinearly with pressure at mantle temperatures, but the shear modulus and V S show very weak pressure dependence in comparison with V P . Compared to other major minerals in the upper mantle, orthoenstatite has the lowest compressional velocities ( V P ), shear velocities ( V S ), and V P / V S ratio down to the depth of approximately 300 km. The enrichment of opx in the upper mantle can cause the unusually low V P / V S observed in the mantle wedge.