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Elasticity of a majorite‐pyrope solid solution
Author(s) -
Bass Jay D.,
Kanzaki Masami
Publication year - 1990
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 - 10.1029/gl017i011p01989
Subject(s) - enstatite , pyrope , shear modulus , diopside , bulk modulus , mineralogy , brillouin spectroscopy , elasticity (physics) , solid solution , materials science , thermodynamics , pyroxene , elastic modulus , geology , analytical chemistry (journal) , olivine , brillouin scattering , chemistry , composite material , optics , physics , metallurgy , meteorite , chromatography , astronomy , optical fiber , chondrite
The elastic properties of a solid solution consisting of 59 mole percent pyropic garnet and 41 percent Mg 4 Si 4 O 12 ‐majorite (a high‐pressure form of pyroxene), have been measured by Brillouin spectroscopy under ambient conditions. Values of the adiabatic bulk modulus, K s =164±15 GPa, and shear modulus, G = 89.4±3.7 GPa, are similar to those for low‐pressure aluminosilicate garnets. The enstatite‐majorite reaction is characterized by a large (49%) increase in K s and a much smaller (13%) increase in G . The properties of low‐pressure garnets suggest that the contrast in shear moduli for this reaction is probably larger in Ca‐rich systems. Taken at face value, the STP properties of these phases imply that large quantities of Ca‐rich clinopyroxene are needed in order to satisfy seismiologically determined shear modulus gradients in the transition zone. This suggestion is, however, subject to considerable uncertainties in the pressure and temperature derivatives of elastic properties for mantle minerals, and the velocity structure of the transition zone.