Sulfur Isotopic Compositions in Pyrrhotite Grains From the Los Angeles Meteorite

Details Sulfur Isotopic Compositions in Pyrrhotite Grains From the Los Angeles Meteorite Sulfur Isotopic Compositions in Pyrrhotite Grains From the Los Angeles Meteorite

Dec 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufm.p12b1065m&link_type=abstract

American Geophysical Union, Fall Meeting 2003, abstract #P12B-1065

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3662 Meteorites, 3672 Planetary Mineralogy And Petrology (5410), 6225 Mars

Scientific paper

Compared to other basaltic shergottites, the Los Angeles martian meteorite is more differentiated and contains higher concentrations of incompatible elements and late-stage phases such as phosphates. Los Angeles is composed mainly of plagioclase and pyroxene, with minor amounts of titanomagnetite, ilmenite, fayalite, pyrrhotite, phosphates and alkali- and phosphate-rich glass. We first performed chemical analyses of sulfides in LA sample ME3277,1 with the electron microprobe. Then sulfur ratios were measured by ion microprobe using a Cs+ primary beam and monitoring S- secondary ions with extreme energy filtering of 300eV. Instrumental mass bias was corrected using the Norilsk pyrrhotite as a standard. Pyrrhotite has nearly constant composition in LA, with minor, varying amounts of cobalt, nickel and titanium present. Our results compare well with previously published compositions of shergottite sulfides, confirming compositional homogeneity throughout the meteorite. Average δ 34S for the pyrrhotite in Los Angeles was 0.5+/- 0.3‰ with a range of -0.2 to +1.3‰ . Our S isotopic measurements also compared well with those of other basaltic shergottites, where δ 34S values cluster around 0\permil, the same value associated with terrestrial ocean floor basalts. The δ 34S values for LA are those expected for a magmatic (primary) origin. The range measured is well within the reported range of all shergottites of -2.9 to +3.8‰ . The similarity of Martian basalt S isotopic ratios to those in terrestrial MORBs suggests that the recent Martian mantle sulfur reservoir is similar to that of the Earth's. However, some Martian samples, which are significantly older, e.g. ALH48001, have values that are far removed from zero. This suggests that these samples were affected by a different fractionation processes or that the S reservoir has been heterogeneous in time and/or space.

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