HR: 10:50h
AN: V42A-02    [Abstracts]
TI: Phase assemblage and stability of pyroxenite at Lower-Mantle conditions
AU: * Lee, K K
EM: kanani@gps.caltech.edu
AF: California Institute of Technology, Division of Geological & Planetary Sciences 1200 E. California Blvd MC 170-25, Pasadena, CA 91125 United States
AU: Asimow, P D
EM: asimow@gps.caltech.edu
AF: California Institute of Technology, Division of Geological & Planetary Sciences 1200 E. California Blvd MC 170-25, Pasadena, CA 91125 United States
AU: Tschauner, O
EM: olivert@physics.unlv.edu
AF: University of Nevada, Las Vegas, Department of Physics Box 454002 4505 Maryland Parkway, Las Vegas, NV 89154 United States
AB: We investigated a mixture of natural pyroxenites (MIX1G [Hirschmann et al., Geology, 2003]) in the laser-heated diamond-anvil cell at Lower-Mantle conditions (pressures between 25 and 60 GPa and temperatures above ~2000 K) in order to determine the phase assemblage and stability of this composition and to evaluate its suitability as a candidate deep ocean island basalt (OIB) source or widespread Lower Mantle component. Quenched samples were characterized by in-situ high-pressure synchrotron-based x-ray diffraction. Recovered samples were also analyzed for composition by energy-dispersive x-ray spectroscopy on a scanning electron microscrope in thick-section and thin-film modes. At these Lower-Mantle conditions, pyrolite-like compositions yield a three-phase assemblage (Mg, Fe, Al)SiO₃ orthorhombic perovskite, (Mg, Fe)O magnesiowüstite and CaSiO₃ calcium perovskite. This pyroxenite, on the other hand, shows an excess of silica, evident with the identification of stishovite, as well as a sodium, aluminum-rich phase in addition to (Mg, Fe, Al)SiO₃ orthorhombic perovskite and CaSiO₃ calcium perovskite phases. Whereas pyrolite compositions yield a density ~2% lower than Preliminary Reference Earth Model (PREM), our estimates suggests MIX1G pyroxenite is ~1% denser than PREM. Present mineral physics data therefore suggest a Lower Mantle composition different from the upper mantle but not so enriched as pure pyroxenite.
DE: 1025 Composition of the mantle
DE: 3630 Experimental mineralogy and petrology
DE: 3655 Major element composition
DE: 3924 High-pressure behavior
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2005 Joint Assembly