Rheology of omphacite at high temperature and pressure and significance of its lattice preferred orientations

Details Rheology of omphacite at high temperature and pressure and significance of its lattice preferred orientations Rheology of omphacite at high temperature and pressure and significance of its lattice preferred orientations

Jun 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006e%26psl.246..432z&link_type=abstract

Earth and Planetary Science Letters, Volume 246, Issue 3-4, p. 432-443.

Mathematics

Logic

3

Scientific paper

We have investigated the rheology of hot-pressed polycrystalline omphacite (Di58Jd42, space group C2/c) at strain rates of 10- 4 10- 5/s, temperatures of 1300 1500 K and a pressure of 3 GPa, using a 5 GPa Griggs-type deformation apparatus. The rheological constitutive equation of omphacite is determined with a stress exponent of 3.5 ± 0.2 and an activation energy of 310 ± 50 kJ/mol. Our study shows that: (1) the creep strength of omphacite falls between those of diopside and jadeite; (2) experimental omphacite microfabrics are indistinguishable from natural ones: S-type fabric and its mesoscopic foliation develop under conditions of axially symmetric shortening, whereas L-type fabric and its mesoscopic lineation develop under conditions of general strain, with L parallel to the greatest elongation; (3) as in naturally deformed omphacite, the deformation substructure is characterized by the dominant slip systems {110}1/2<110>, {110}[001] and (100)[001]. We conclude that both S- and L-type omphacite fabrics are produced by these slip systems; fabric differences arise solely from variation of the geometry and orientation of the finite strain ellipsoid. We also confirm the previous suggestion that Na-bearing pyroxenes are significantly weaker than Na-free pyroxenes.

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