HR: 0800h
AN: U11A-0021    [Abstracts]
TI: Constraints on Core Formation From Systematic Study of Temperature Effect on Metal- Silicate Partitioning
AU: * Siebert, J
EM: siebert2@llnl.gov
AF: LLNL, 7000 east avenue, livermore, CA 94550, United States
AU: Ryerson, F
EM: ryerson1@llnl.gov
AF: LLNL, 7000 east avenue, livermore, CA 94550, United States
AU: watson, h
EM: watson40@llnl.gov
AF: LLNL, 7000 east avenue, livermore, CA 94550, United States
AB: Models of core formation are currently established through metal-silicate partitioning results at high pressure and high temperature. Although a large effect of temperature on metal-silicate equilibrium is expected on thermodynamic grounds, very little experimental work has been dedicated to separate this effect from pressure and provide a systematic study of partitioning coefficients across a wide range of temperatures. Utilizing free energy of pure oxides formation data at atmospheric pressure to predict the temperature effect on metal-silicate partitioning might be a source of large uncertainties for some recent core formation models [1, 2]. The present study is aimed at constraining the temperature dependence of partition coefficients for a large number of elements and extending the existing database to extreme temperatures. Using a new piston-cylinder design assembly [3] allows us to determine a suite of isobaric partitioning experiments at 3 GPa within a temperature range from 1600 to 2700°C. Systematic partitioning behaviors between molten metal and peridotite or basaltic melts of elements normally regarded as moderately siderophile, slightly siderophile and refractory lithophile are presented. These include Ni, Co, W, Mo, Cr, Mn, V, P, Ga as well as elements that are usually poorly integrated with any accretion or core formation models (Ge, Nb, Ta, Te, Zn). Absolute measurements of partitioning coefficients combining EMP and LA-ICPMS analytical methods are provided. The individual effects of oxygen fugacity and pressure have also been studied through piston cylinder experiments (2200°C, 3 GPa) between IW- 1.5 to IW-4 and multi-anvil experiments to 15 GPa. These partitioning results are then combined with literature data to refine our understanding of core formation and place constraints on the highly debated Earth's accretion mechanism issue. [1] Wade and Wood, EPSL, 2005. [2] Corgne et al., GCA, in press. [3] Cottrell and Walker, GCA, 2006.
DE: 1015 Composition of the core
DE: 3612 Reactions and phase equilibria (1012, 8412)
DE: 3630 Experimental mineralogy and petrology
DE: 3656 Ultra-high temperature metamorphism
SC: Union [U]
MN: 2007 Fall Meeting