A Geochemical and Osmium Isotopic Study of Group IVB Irons and Ungrouped Irons Chinga, Tishomingo and Willow Grove

Abstract

Re-Os isotopic and highly siderophile element (HSE) systematics of IVB irons and ungrouped iron meteorites Chinga, Tishomingo and Willow Grove are presented. IVB iron composition has been constrained by HSE (Re, Os, Ru, Ir, Pt, and Pd) abundances, showing a limited range of Pt concentration (31.15 to 32.75 ppb) despite a wide range in nickel (Ni) content (15.64 to 18.02 wt %). Using the Re-Os system, a crystallization age of 4575 ± 56 Ma was determined for the group. Fractional crystallization modeling suggests these samples crystallized from a non-chondritic parent-body. Chinga is shown to be unrelated to the IVBs through HSE abundances, and fractional crystallization modeling. Willow Grove and Tishomingo have HSE patterns comparable to the IVBs. Tishomingo has a platinum concentration within the range of the IVBs. The high Ni content of these two irons (>27 wt %) poses a problem for their formation by simple fractional crystallization.