HR: 0830h
AN: U51B-0016    [PDF]
TI: Basalt-Iron Reactions at High Pressures and Temperatures
AU: * Lee, V E
EM: vlee@eps.berkeley.edu
AF: University of California, Berkeley, Dept. of Earth \& Planetary Science 307 McCone Hall, Berkeley, CA 94720-4767 United States
AU: Lee, K K
EM: leeka@uclink.berkeley.edu
AF: University of California, Berkeley, Dept. of Earth \& Planetary Science 307 McCone Hall, Berkeley, CA 94720-4767 United States
AU: Jeanloz, R
EM: jeanloz@uclink.berkeley.edu
AF: University of California, Berkeley, Dept. of Earth \& Planetary Science 307 McCone Hall, Berkeley, CA 94720-4767 United States
AB: New experiments designed to simulate the core-mantle boundary, as well as the differentiation of the primordial Earth into silicate- and metal-rich regions, illuminate the reaction of mantle minerals with iron at high pressures and temperatures. Previous investigations have laid the groundwork for documenting reaction products between iron and individual silicate phases (e.g., Knittle \& Jeanloz 1991; Dubrovinsky et al. 2001, 2003), but the Earth's mantle is likely composed of multiphase silicate assemblages that depend on pressure and temperature. In addition, oceanic slabs that have subducted to the core-mantle boundary may provide a source of mineralogically complex rock material that could interact with the outer core. To investigate the reaction products formed between core metal and a natural mineral assemblage at high pressures and temperatures, the laser-heated diamond anvil cell was used to study samples of iron and basalt. These two starting materials were mechanically coupled as single foils and compressed in a quasi-hydrostatic argon pressure medium. High-resolution synchrotron x-ray diffraction was used to determine the mineral assemblages for three distinct regions of the sample: basalt, iron, and the basalt-iron interface. Initial results indicate a lower-mantle mineral assemblage for basalt consisting predominantly of stishovite plus a CaSiO$_{3}$-(Mg,Fe)SiO$_{3}$-Al$_{2}$O$_{3}$ orthorhombic perovskite, in accord with previous results (Funamori et al. 2000). As expected, iron regions consist wholly of $\epsilon$-iron at high pressure. The interface region between metal and silicate shows evidence for the phases found in the distinct basalt and iron regions, and likely FeSi; there are also several as-yet unidentified diffraction peaks. These results could be interpreted as being due to chemical reactions between iron and basalt. Such reaction products may contribute to the long-term geochemical evolution of the core and mantle, as well as to the observed seismic heterogeneity at the core-mantle boundary.
DE: 3924 High-pressure behavior
DE: 3954 X ray, neutron, and electron spectroscopy and diffraction
DE: 8124 Earth's interior--composition and state (old 8105)
SC: U
MN: 2003 Fall Meeting