SIDEROPHILE ELEMENT ABUNDANCES IN Fe-S-Ni-O MELTS SEGREGATED FROM PARTIALLY MOLTEN ORDINARY CHONDRITE UNDER DYNAMIC CONDITIONS. T . Rushmer,

Introduction: Early differentiation in evolving planetesimals likely involved a variety of different physical mechanisms. Fe-rich metallic liquid segregation can occur in a solid, partially molten, or purely molten silicate body, with or without the presence of deformation. Deformation may assist the segregation of low degree metallic melts. Segregation of Fe-S-Ni liquids formed by variable degrees of partial melting of chondrites imparts distinct geochemical signatures on the composition of the resulting metal. These chemical signatures vary according to initial parent body composition, segregation mechanisms and the degree to which early S-rich, and possibly O-rich, core-forming liquids were extracted. In addition, the presence of deformation may enhance both kinetics and efficiency of the physical segregation process. To explore the relationship between core formation scenarios and geochemistry, the siderophile element compositions of metals formed during deformation experiments on the Kernouvé H6 ordinary chondrite were determined by laser ablation ICP-MS [1]. We present results on siderophile concentrations in Fe-S-Ni-O quench and associated Fe-Ni metal dynamically segregated at different degrees of partial melting, and determine partition coefficients for different solid metal/liquid metal compositions as a function of temperature, strain rate and amount of silicate melt present. Further, the IIE irons are related to H chondrites by their oxygen isotope composition [2], and were argued to have formed by solidification of melts on the H chondrite parent body [3]. We apply our data to evaluate this hypothesis. Experimental study and Analytical approach: Experiments were conducted on solid cores of Kernouvé H6 chondrite, 0.6" long and 0.25" in diameter, using a Griggs rock deformation apparatus. The Kernouve cores (KM) were heated and pressurized to run conditions, then deformed while partially molten. Temperatures (T) are given for the center of the charge, but T is higher in the lower part of the charge due to a temperature gradient; details are given in [4]. Laser ablation ICP-MS analyses of individual large metal grains from Kernouvé starting material were given in [5]. Quench Fe-S-Ni of different compositions and associated residual Fe-Ni metal from four KM experiments were analyzed using a spot size varying between 25-50 μm. Peaks monitored included 3 P, 3 S, 5 Fe, 5 Co, 6 Ni, 6 Cu, 6 Ga, 7 Ge, 7 As, W, Re, Os, Ir, and Au. Hoba IVB, Filomena IIA and NIST SRM1263a were used as standards [1-4]. Results: KM-10 (P=1.0 GPa, T=925C, strain rate=10/s, 40% strain) contained no silicate melt, and areas of quench Fe-S-Ni-O in high stress cataclastic domains were present in the lower portion of the charge. Earlier analyses in a sheared Fe-Ni vein and from unmodified zones [3] located in the center and upper portions of the charge showed that the highly strained metal did not differ significantly from starting Kernouvé metal concentrations. New analyses in the cataclastic zone provided data on both solid metal and quench Fe-S-Ni-O compositions (23.8 wt% S, green lines in Fig 1). The data are shown in Fig. 1 ordered according to their compatibility in the solid metal-liquid metal system [6], with the most compatible (Ir) on the left.