HR: 0800h
AN: MR31A-0144    [Abstracts]
TI: Results From in Situ High P-T Melting and Phase Equilibria Experiments on the Allende Meteorite
AU: * Danielson, L
EM: lisa.r.danielson@nasa.gov
AF: NASA Johnson Space Center, Mail Code KT 2101 NASA Parkway, Houston, TX 77058, United States
AU: Righter, K
EM: kevin.righter-1@nasa.gov
AF: NASA Johnson Space Center, Mail Code KT 2101 NASA Parkway, Houston, TX 77058, United States
AU: Leinenweber, K
EM: kurtl@asu.edu
AF: Arizona State University, Dept. of Chemistry and Biochemistry Arizona State University, Tempe, AZ 85287-1604, United States
AU: Wang, Y
EM: wang@cars.uchicago.edu
AF: University of Chicago, GSECARS APS ANL 9700 South Cass Ave., Bldg. 434A, Argonne, IL 60439, United States
AB: Because chondritic materials are thought to be the building blocks of terrestrial planets and planetesimals, crystallization of chondritic and peridotitic material can be used to simulate accretion and differentiation of a bulk planet. The objective of this study is to measure the liquidus phases and temperatures for a number of planetary mantle analog materials at P>20 GPa. Experiments were conducted in the Large Volume Press at the Advanced Photon Source, Argonne National Laboratory. Phases were identified using energy-dispersive X-ray diffraction (EDXRD) with a fixed diffraction angle (2θ) of ~6° and data collection times of 60 sec. Heating runs up to 2200°C were performed at 400, 600, and 700 tons, sampling a pressure range from 18-32 GPa. A 3mm TEL beamline modified Fei-type assembly was used in experiments: a Re furnace with lanthanum chromite insulating sleeve, alumina or MgO end caps, graphite capsule packed with powdered starting materials, and X-ray windows of a slit in the Re furnace and alumina or graphite plugs in the lanthanum chromite. A pressed pellet of MgO powder doped with diamond powder was used as a pressure standard and packed between the capsule and thermocouple. The majorite liquidus temperature occurs near 2050°C, comparable to previous results (Agee et al. 1995; Asahara et al., 2004). The majorite-Mg-perovskite cotectic occurs at 22 GPa, as opposed to around 25 GPa. However, given the limited number of experiments and uncertainties introduced from previously not applying (1) a P-T relationship from relaxation of the assembly during heating, and (2) a thermal gradient from temperatures measured at the thermocouple across the capsule, significant differences in P and T are not surprising. It is possible to apply a P-T correction based on (1) and (2) above, and identify a majorite-ferropericlase cotectic for previous studies at around 22 GPa. This is particularly true for Agee et al. (1995), where calibrations were performed at 1200°C. Pressure at 2000°C can be 3 GPa lower than that at 1200°C (Leinenweber et al., 2006). Although Mg-perovskite was identified as the liquidus phase above 22 GPa, the ferropericlase-out line is very steep, and may become the liquidus phase above 25 GPa. This shallow liquidus is more consistent with a deeper, hotter magma ocean model.
DE: 1025 Composition of the mantle
DE: 1027 Composition of the planets
DE: 3612 Reactions and phase equilibria (1012, 8412)
DE: 3630 Experimental mineralogy and petrology
DE: 5455 Origin and evolution
SC: Mineral and Rock Physics [MR]
MN: 2007 Fall Meeting