HR: 09:00h
AN: U41A-04    [Abstracts]
TI: Chemical dynamics in the core: Contributions from high-pressure phase equilibria of Fe-X systems
AU: * Campbell, A J
EM: ajc@umd.edu
AF: University of Maryland, Dept. of Geology, College Park, MD 20742, United States
AU: Seagle, C T
EM: seagle@uchicago.edu
AF: University of Chicago, Dept. of the Geophysical Sciences, Chicago, IL 60637, United States
AU: Heinz, D L
EM: heinz@uchicago.edu
AF: University of Chicago, Dept. of the Geophysical Sciences, Chicago, IL 60637, United States
AB: We discuss advances in mineral physics of Fe-X binary systems, and their implications for dynamics of the core and core-mantle interactions. Recent progress, using both experimental and theoretical methods, has improved our understanding of phase diagrams and equations of state of Fe-rich binary systems. Synchrotron x-ray diffraction methods, in particular, have allowed a more detailed picture of several Fe-X phase diagrams at high pressures and temperatures, and also improved the high-P,T equations of state of relevant metallic phases. The liquidus slope, dT/dC, is an important parameter driving the rate of chemical buoyancy release during crystallization of the core. Experimental constraints on this parameter are improving: dT/dC for the Fe-O system is estimated to be about 4 times lower than dT/dC in the Fe-S system at 60 GPa. An oxygen rich core would consequently generate more compositional buoyancy, per degree of cooling, during inner core crystallization than a sulfur rich core would. The composition of a eutectic, relative to the outer core composition, is an important constraint on allowable phase diagrams to describe the core. The Fe-S eutectic decreases rapidly with increasing pressure from 31.6 wt% at 1 bar to 15 wt% at 20 GPa, but changes very little at higher pressures to at least 60 GPa. The Fe-O eutectic is only 2 wt% O at 16 GPa, which is not consistent with the requirements of crystallization of metal from the outer core; however, recent work demonstrates that the eutectic increases in O content with pressure, reaching 10 wt% O at 90 GPa. Ternary systems are less well investigated, but are becoming increasingly important as more detailed geochemical estimates of core composition are proposed.
DE: 1015 Composition of the core
DE: 1213 Earth's interior: dynamics (1507, 7207, 7208, 8115, 8120)
DE: 3924 High-pressure behavior
SC: Union [U]
MN: 2007 Joint Assembly