HR: 08:45h
AN: MR21A-04    [Abstracts]
TI: High Temperature Effects on Pt Partitioning Between Metal and Mafic Silicate Liquids: Implications for Core Formation
AU: * Cottrell, E
EM: ecottrell@gl.ciw.edu
AF: Lamont-Doherty Earth Observatory, Columbia University, RT 9W, Palisades, NY 10964 United States
AU: Walker, D
EM: dwalker@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, Columbia University, RT 9W, Palisades, NY 10964 United States
AB: A new high temperature piston cylinder design has enabled the measurement of platinum solubility in mafic melts at temperatures up to to 2500°C, 2.2GPa pressure, and under reducing conditions for 1 - 10 hours. These high temperatures and low f_O2 conditions may mimic a magma ocean during planetary core formation. Under these conditions, we measured tens to hundreds of ppm Pt in the quenched silicate glass corresponding to D_Pt^{metal/silicate} ~ 10^3-4, 4 to 12 orders of magnitude lower than extrapolations from high f_O2 experiments at 1 bar and at temperatures no higher than 1550°C. Moreover, the new experiments provide strong evidence that noble metal micronuggets, ubiquitous in experimental studies of the HSE, can be produced on quench. We measure equally high Pt concentrations in nugget-bearing and nugget-free regions of the quenched silicate, consistent with the quench interpretation. We find that both temperature and melt composition exercise strong control on D_Pt^{metal/silicate} and that Pt⁰ and Pt⁺¹ may contribute significantly to the total dissolved Pt such that low f_O2 does not imply low Pt solubility. Equilibration of metal alloy with liquid silicate in a hot primitive magma might not have depleted platinum to the extent previously believed.
UR: http://www.gl.ciw.edu/cottrell
DE: 1015 Composition of the core
DE: 1065 Major and trace element geochemistry
DE: 3621 Mantle processes (1038)
DE: 3630 Experimental mineralogy and petrology
DE: 3672 Planetary mineralogy and petrology (5410)
SC: Mineral and Rock Physics [MR]
MN: Fall Meeting 2005