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Single‐crystal elasticity of natural Fe‐bearing orthoenstatite across a high‐pressure phase transition
Author(s) -
Zhang Jin S.,
Bass Jay D.
Publication year - 2016
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 - 10.1002/2016gl069963
Subject(s) - brillouin spectroscopy , phase transition , materials science , bulk modulus , anisotropy , shear modulus , elasticity (physics) , elastic modulus , mineralogy , thermodynamics , analytical chemistry (journal) , geology , brillouin scattering , composite material , chemistry , optics , physics , chromatography , optical fiber
Sound velocities and elastic moduli have been measured on Fe‐bearing orthoenstatite (OEN) single crystals up to 12 GPa by Brillouin spectroscopy. The ambient adiabatic bulk modulus ( K s 0 ) and shear modulus ( G 0 ) are determined to be 113(1) GPa and 75.9(7) GPa, respectively. A fourth‐order finite strain fit to the data yields pressure derivatives of K s 0 ′ = 8.8(1), K s0 ″ = −0.68(6), G 0 ′ = 2.9(1), and G 0 ″ = −0.40(2). These values are significantly higher than those for other major mantle minerals up to 10.5 GPa but lower than some previous measurements on OEN. A pronounced increase of shear anisotropy was observed at a pressure of 12.06(9) GPa, coinciding with a phase transition from orthoenstatite to a recently discovered high‐pressure phase with space group P2 1 /c. A high‐pressure phase transition in OEN is unlikely to be the cause of the X discontinuity in the 250–325 km depth range. Rather, a change in seismic anisotropy would be expected to accompany the orthoenstatite‐to‐P2 1 /c phase transition in the upper mantle at greater depths.