HR: 12:05h
AN: MR22A-08    [Abstracts]
TI: Aluminum incorporation in post-perovskite from first principles
AU: * Akber-Knutson, S
EM: sofia@gps.caltech.edu
AF: California Institute of Technology, Geological & Planetary Sciences Div. MC 252-21, Pasadena, CA 91125 United States
AU: Steinle-Neumann, G
EM: g.steinle-neumann@uni-bayreuth.de
AF: Bayerisches Geoinstitut, University of Bayreuth, Bayreuth, 95440 Germany
AB: The phase transition of pure MgSiO$_3$ perovskite ({\em Pbnm}) structure to the post-perovskite ({\em Cmcm}) structure has been reported recently at pressures corresponding to the Earth's lowermost mantle. The resulting Clapeyron slopes suggest that the transition pressure may be very sensitive to the presence of impurities (Al, Fe, Ca); it is therefore necessary to determine whether this phase transition survives for realistic mantle compositions. We use ab initio calculations to investigate the effects of aluminum on the transition pressure. We examine three substitution mechanisms of Al in the two structures: Mg + Si $\rightarrow$ 2Al; 2Si + O $\rightarrow$ 2Al + O-vacancy; and Si $\rightarrow$ Al + H. Furthermore, we determine the solubility of aluminum in post-perovskite, and the partitioning of aluminum between the two phases at the phase boundary. Our static phase transition pressure of 106 GPa agrees well with previous studies. Preliminary calculations indicate that charge coupled substitution lowers the transition pressure by approximately 5 GPa.
DE: 3600 MINERALOGY AND PETROLOGY (replaces
DE: 3900 MINERAL PHYSICS
DE: 1025 Composition of the mantle
SC: Mineral and Rock Physics [MR]
MN: 2004 AGU Fall Meeting