Fractionated sulfur isotopes in sulfides of the Kaidun meteorite

Abstract

Abstract-The Kaidun meteorite contains carbonaceous chondrite (CM 1) clasts that have been highly altered by reactions with hydrothermal fluids. Pyrrhotite in these clasts occurs as unusual needles wrapped by sheaths of phyllosilicate, and pentlandite forms veins that crosscut aggregates of phyllosilicate and garnet but not pyrrhotite. The isotopic compositions of S (d34SCDT) in individual sulfide grains, measured by ion microprobe, are fractionated compared to troilite in ordinary chondrites. The S in Kaidun sulfides is isotopically light (as much as 4 . 2 % 0 for pyrrhotite and -5.7%0 for pentlandite), unlike sulfides in other carbonaceous chondrites, which are enriched in 34S. The unusual S-isotopic composition of these texturally unique sulfides supports the hypothesis that Kaidun CM1 clasts were pervasively altered under extreme thermal conditions, possibly by fluids that had lost isotopically heavy S 0 2 .

Sulfur isotopic composition of Fe‐Ni sulfide grains in CI and CM carbonaceous chondrites

“…(1965) showed that the isotopic composition of these components is consistent with the formation of sulfates by oxidation of sulfide grains, and δ 34 S CDT in sulfate grains indicates that the oxidation of sulfide grains preferentially removes 32 S, enriching the residual sulfide in the heavier isotopes of sulfur. This disagrees with the suggestion of McSween et al. (1997) who states that “sulfate scavenges isotopically heavy sulfur.”Monster et al.…”

“…Several previous studies have reported sulfur isotopic values within CI1 chondrites (e.g., Monster et al. 1965; Kaplan and Hulston 1966; Gao and Thiemens 1993) and CM chondrites (e.g., Kaplan and Hulston 1966; Gao and Thiemens 1993; McSween et al. 1997).…”

Biogeochemistry of Sulfur Isotopes

“…For example, δ 34 S values for sulfides from mantle-derived peridotites and pyroxenites have yielded δ 34 S values from -5 ‰ to 4.5 ‰, with up to 6 ‰ differences observed on individual grains (Chaussidon and Lorand 1990). Up to 5 ‰ differences in δ 34 S have also been measured for pyrrhotites within the Kaidun meteorite, where isotope fractionation is presumed to have occurred when the original troilite was re-crystalized to pyrrhotite (McSween et al 1997). Furthermore, a relatively large zonation of 20 ‰ has been observed in the δ 34 S of hydrothermal pyrite crystals in silicified rhyolite tuffs where a biogenic source of sulfide is not obvious (McKibben and Riciputi 1998).…”

Sulfur isotope composition of putative primary troilite in chondrules from Bishunpur and Semarkona

“…Chondrites have received much less attention, although Paterson et al (1997) reported a couple of techniques for analysis of troilite in ordinary chondrites and McSween et al (1997) measured sulfides in the Kaidun meteorite.…”