Fractionation of Sulfur Isotopes in the Formation of Mars

Based on geochemical models, high-pressure experiments, moment of inertia measurements, and siderophile element abundances in martian meteorites, it has been argued that a significant amount of sulfur was incorporated into the martian core. In this study, high pressure and temperature piston cylinder experiments were performed to determine if the sulfur incorporated into the martian core left an isotopic signature on the planet. Since it is thought that Mars differentiated at ~2200 ° C and 1 GPa (Kong et al., 1999), experiments were conducted at 1 GPa and at various temperatures (1600° C, 1700° C, 1850°C) in order to determine the temperature dependent curve. Samples consisted of an oxide mix of Al2O3, SiO2, MgO, CaO, Na2O, and Fe2O3 with Fe and FeS to represent the Martian interior. Experimental run products were characterized on the SEM and electron microprobe and the isotopic fractionation factor was determined in situ on the Carnegie Institution of Washington’s Cameca ims 6f SIMS. Preliminary results show a resolvable fractionation at high temperature. The fractionation factor found will establish a new baseline for the Martian mantle and require a reassessment of the sulfur isotopic data of the martian meteorites. References: Kong, P., Ebihara, M., Palme, H., 1999, Siderophile elements in Martian meteorites and implications for core formation in Mars: Geochimica et Cosmochimica Acta, v. 63, no. 11/12, p. 1865-1875.