Siderophile elements in Martian meteorites and implications for core formation in Mars

Noble metals, Mo, W, and 24 other elements were determined in six SNC meteo rites of presumably Martian origin. Based on element correlations, represen tative siderophile element concentrations for the silicate mantle of Mars w ere inferred. From a comparison with experimentally determined metal/silica te partition coefficients of the moderately siderophile elements: Fe, Ni, C o, W, Mo, and Ga, it is concluded that equilibrium between core forming met al and silicates in Mars has occurred at high temperatures (around 2200 deg rees C) and low pressures (<1 GPa). This suggests that metal segregation oc curred concurrently with rapid accretion of Mars, which is consistent with the inference from excess W-182 in Martian meteorites (Lee and Halliday, 19 97). Concentrations of Ir, Os, Ru, Pt, and An in the analyzed Martian meteo rites, except ALH84001, are at a level of approximately 10(-2)-10(-3) x CI. The comparatively high abundances of noble metals in Martian meteorites re quire the addition of chondritic material after core formation. The similar ity in Au/La and Pt/Ca ratios between ALH84001 and the other Martian meteor ites suggests crystallization of ALH84001 after complete accretion of Mars. Copyright (C) 1999 Elsevier Science Ltd.