HR: 0800h
AN: U41B-0423    [Abstracts]
TI: Phase Stability and Equation of State of Fe2SiO4 in the Earths Mantle
AU: * Armentrout, M M
EM: armentrout@ucla.edu
AF: UCLA, 595 Charles Young Drive East 3806 Geology Building Box 951567, Los Angeles, CA 90095,
AU: Kavner, A
EM: akavner@ucla.edu
AF: UCLA, 595 Charles Young Drive East 3806 Geology Building Box 951567, Los Angeles, CA 90095,
AB: It is well known that the bulk mantle is much richer in magnesium than in iron. However a possible reaction at the mantle/core interface would increase the Fe/Mg ratio in surrounding material. The goal of this research is to expand our understanding of the phase relations and equation of state of the Fe2SiO4 system. Experiments were performed at the Advanced Light Source (beamline 12.2.2) in laser heated diamond anvil cells to explore the high end of the stishovite and wustite stability field. Samples were Rockport fayalite, in some cases thermally insulated between layers of NaCl, with a pressure marker of ruby, Au, or Pt. Several sets of experiments were performed generally in pairs either buffered to reducing conditions with an iron gasket, or buffered to oxidizing conditions with hematite. Several heating cycles were performed on each sample at progressively higher temperatures. Pressures of up to 53.9 GPa and temperatures up to 2500 K were achieved. Postmortem analyses of samples were performed with a scanning electron microscope. X-ray diffraction patterns show a transition from alpha-olivine structured Fe2SiO4 to the spinel structure Fe2SiO4. At 14.4 GPa we show a transition to SiO2 stishovite and FeO wustite, in agreement with earlier work. At the highest pressures and temperatures additional as-yet unidentified phase(s) are observed. In addition, X-ray diffraction patterns allow measurements of the density of the phases in the Fe2SiO4 system at mid mantle conditions. We present these results on the thermal equations of state of spinel-structured fayalite and the stishovite + wustite assemblage.
DE: 3612 Reactions and phase equilibria (1012, 8412)
DE: 3620 Mineral and crystal chemistry (1042)
DE: 3919 Equations of state
DE: 3924 High-pressure behavior
SC: Union [U]
MN: 2007 Fall Meeting