Pyrite in a sulfate-poor Paleoarchean basin was derived predominantly from elemental sulfur: Evidence from 3.2 Ga sediments in the Barberton Greenstone Belt, Kaapvaal Craton
Pyrite in a sulfate-poor Paleoarchean basin was derived predominantly from elemental sulfur: Evidence from 3.2 Ga sediments in the Barberton Greenstone Belt, Kaapvaal Craton
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富含硫酸盐的古太古代盆地中的黄铁矿主要来自元素硫：来自卡普瓦尔克拉通巴伯顿绿岩带 3.2 Ga 沉积物的证据
DOI：
10.1016/j.chemgeo.2016.12.006
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发表时间：
2017
期刊：
影响因子：
3.9
通讯作者：
Galic A
中科院分区：
文献类型：
--
作者：
Galic A
太古代沉积岩中多种硫同位素的变异性对地球最早期大气的组成提供了限制。质量独立异常的幅度和符号不仅反映了大气过程，但也转换由于太古代海洋硫循环之前保存成沉积黄铁矿。影响太古代海洋硫循环的过程以及黄铁矿形成过程中微生物或非生物氧化还原反应的作用仍不清楚。本文结合联合收割机的单个黄铁矿颗粒的铁（Fe）和硫（S）同位素数据，结合岩相学信息和一维反应迁移模型，探讨了古太古代沉积盆地中黄铁矿中Fe和S的来源。黄铁矿是从泥岩，砂岩和燧石中选出的，这些燧石是从一个钻孔岩芯中获得的。3.2南非卡普瓦尔省巴伯顿绿岩带无花果树群和翁韦尔瓦赫特群的Ga Mapepe组和Mendon组。黄铁矿结构和δ 56 Fe区分了早期成岩黄铁矿和晚期成岩黄铁矿，前者由孔隙水亚铁形成（浸染状颗粒，δ 56 Fe平均= 0‰），后者由氧化铁矿物硫化形成（层状和集合体，δ 56 Fe平均= + 1‰）。黄铁矿中硫同位素随质量的变化很小（δ 34黄铁矿变化范围为-1.1至+3.3 ‰），而Δ 33黄铁矿（变化范围为+0.3至+2.1 ‰）和Δ 36黄铁矿（变化范围为-3.08至+0.27 ‰）的变化也很小，这表明缺乏与其他不同硫源的沉积后再作用。我们结合铁和硫同位素数据是最容易解释的黄铁矿硫化物来自微生物改造的固体元素S。氧化铁矿物是缓冲硫化物浓度和提供有利条件的微生物硫净化进行所必需的。缺乏负Δ 33 S信号表明，相对较深的海洋成岩环境中的黄铁矿只记录了部分大气光解产物，与古太古代海洋中的低硫酸盐浓度一致。
Multiple sulfur isotope variability in Archean sedimentary rocks provides constraints on the composition of the Earth’s earliest atmosphere. The magnitude and sign of mass-independent anomalies reflect not only atmospheric processes, but also transformations due to the Archean marine sulfur cycle prior to preservation into sedimentary pyrite. The processes affecting the Archean marine sulfur cycle and the role of microbial or abiotic redox reactions during pyrite formation remain unclear. Here we combine iron (Fe) and multiple sulfur (S) isotope data in individual pyrite grains with petrographic information and a one-dimensional reactive transport model, to investigate the sources of Fe and S in pyrite formed in a Paleoarchean sedimentary basin. Pyrites were selected from mudstones, sandstones and chert obtained from a drill core in the ca. 3.2 Ga Mapepe and Mendon Formations of the Fig Tree and Onverwacht Groups, respectively, in the Barberton Greenstone Belt, Kaapvaal Craton, South Africa. Pyrite textures and δ56Fe distinguish early-diagenetic pyrite formed with pore-water ferrous iron (disseminated grains with average δ56Fepyrite= 0‰) from late-diagenetic pyrite formed through sulfidation of iron oxide minerals (layered and aggregate forms with average δ56Fepyrite= + 1‰). Mass dependent S isotope variability in pyrite was small (δ34Spyriteranged from − 1.1 to + 3.3‰) with a correspondingly minor spread in Δ33Spyrite(ranging from + 0.3 to + 2.1‰) and Δ36Spyrite(ranging from − 3.08 to + 0.27‰) that indicates a lack of post-depositional re-working with other distinct sulfur sources. Our combined Fe and S isotope data are most readily explained with pyrite sulfide derived from microbial-reworking of solid elemental S. Iron oxide minerals were necessary to buffer sulfide concentrations and provide favorable conditions for microbial sulfur disproportionation to proceed. The lack of a negative Δ33S signal indicates that pyrite from relatively deep marine diagenetic environments only partially records the products of atmospheric photolysis, consistent with low sulfate concentrations in the Paleoarchean ocean.