کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
4702369 1638040 2013 13 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
High-resolution quadruple sulfur isotope analyses of 3.2 Ga pyrite from the Barberton Greenstone Belt in South Africa reveal distinct environmental controls on sulfide isotopic arrays
موضوعات مرتبط
مهندسی و علوم پایه علوم زمین و سیارات ژئوشیمی و پترولوژی
پیش نمایش صفحه اول مقاله
High-resolution quadruple sulfur isotope analyses of 3.2 Ga pyrite from the Barberton Greenstone Belt in South Africa reveal distinct environmental controls on sulfide isotopic arrays
چکیده انگلیسی

Multiple sulfur isotopes in Paleoarchean pyrite record valuable information on atmospheric processes and emerging microbial activity in the early sulfur cycle. Here, we report quadruple sulfur isotope data (32S, 33S, 34S, 36S) analyzed by secondary ion mass spectrometry from pyrite in a 3.26–3.23 Ga sedimentary barite deposit in the Barberton Greenstone Belt, South Africa. Our results demonstrate the presence of distinct pyrite populations and reproducible isotopic arrays in barite-free and barite-rich samples. The most 34S-depleted signatures with weakly positive Δ33S/δ34S were found in disseminated pyrite in barite, whereas positive Δ33S-values with negative Δ33S/δ34S and Δ36S/Δ33S = −0.9 ± 0.2 were exclusively observed in pyrite hosted by chert, dolomite, conglomerate and breccia. We interpret these variations to be related to local redox reactions and mixing in the sulfide phase, rather than representing primary atmospheric variability alone. The strong correlation between lithology and isotopic composition indicates distinct environments of sulfide formation linked to local sulfate concentrations and fluctuating inputs from different sulfur metabolisms. Strongly 34S-depleted sulfide was formed by microbial sulfate reduction at [SO42−] > 200 μM during deposition of barite-rich sediments, whereas isotope effects were suppressed when sulfate levels decreased during deposition of terrigeneous clastic rocks. Positive Δ33S-values indicate an increased input of sulfide derived from elemental sulfur metabolisms when sulfate concentrations fell below 200 μM. Our results support an important role for local sulfate concentrations on the expression of biogenic sulfur isotope signatures in some of the oldest rocks on Earth.

ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Geochimica et Cosmochimica Acta - Volume 117, 15 September 2013, Pages 203–215
نویسندگان
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