首页|Simultaneous fractionation of sulfur dioxide explains mass independent fractionation of sulfur isotopes in Archean sedimentary pyrites
Simultaneous fractionation of sulfur dioxide explains mass independent fractionation of sulfur isotopes in Archean sedimentary pyrites
扫码查看
点击上方二维码区域，可以放大扫码查看
原文链接
NSTL
Elsevier
The relationship between Δ~(36)S and Δ~(33)S in Archean sedimentary pyrites has been used to evaluate early geologic processes, including photochemical reactions in the anoxic atmosphere, biological activity and thermochemical alteration during sediment deposition. We have applied statistical methods to quadruple S isotope analyses of Archean sedimentary pyrites, using data compiled from the literature. Most of the best-fit lines, on plots of Δ~(36)S against Δ~(33)S, have Archean reference array-like Δ~(36)S/Δ~(33)S slopes that vary between - 1.5 and - 0.9. Rigorous statistical tests were conducted to calculate the probability of the best-fit lines passing through the origin. Seventeen of 23 Δ~(36)S-Δ~(33)S regression lines, which pass our reliability filter of R~2 ≥ 75% and Δ~(33)S range ≥ 2‰, have positive intercepts on the Δ~(36)S axis, and 13 of these have a probability of < 5% of a zero intercept on the Δ~(36)S axis. The observed Δ~(36)S/Δ~(33)S slopes and the non-negative intercepts, which requires at least two massindependent fractionation source reactions to operate simultaneously, can be produced by UV radiation in the atmosphere at low SO_2 partial pressures by combining collision-induced intersystem crossing in the SO_2 photoexcitation band (240-340 nm), with the self-shielding effect in the SO_2 photolysis band (190-220 nm). The two SO_2 photochemical processes must occur simultaneously in a single atmospheric reservoir in order that the fraction contributed by the end-member process remains constant across the full range of Δ~(33)S values. We call this process simultaneous fractionation. We applied a two-end-member model to calculate the fraction of S contributed by the SO_2 photoexcitation end-member (f) needed to produce the observed Δ~(36)S/Δ~(33)S gradients and variable intercepts on the Δ~(36)S axis in the Archean sedimentary pyrites, when the other end-member is SO_2 photolysis with the self-shielding. The simplest explanation
NSTL
Elsevier
