Abstract The sulfur mass independent fractionation (S-MIF) of Mesoarchean is distinct from the other Archean periods by the dampened magnitudes of Δ33S and a steeper slope of Δ36S/Δ33S compared with the Archean Reference Array (ARA) according to previous studies. However, samples available of this interval are limited owing to poor or no preservation. Additionally, the majority of the data were obtained by analysis of bulk rocks, thus are essentially the sulfur isotopic compositions of mixed sulfur components due to multiple stages of post-diagenesis overprints and modifications. This study systematically measured the multiple sulfur isotopic compositions of pyrites (nodular, disseminated) in ca. 3.2–2.72 Ga metasedimentary rocks from the Pilbara Craton, Western Australia, where one of the best-preserved Archean records occur, using the upgraded SHRIMP-SI, after detailed pyrite generation and genesis investigation by BSE imaging and NaOCl etching. The results show that Δ33S values of the diagenetic pyrites in these metasedimentary rocks range from −2.4 to 0.8‰. Such a range is inconsistent with the other Archean intervals and any experiment producing S-MIF so far, where the magnitude of the maximum positive Δ33S value is considerably larger than the corresponding minimum negative Δ33S value. The dampened positive Δ33S is explained in several ways from the perspective of production and preservation, including original photochemical products with larger magnitudes of negative Δ33S than positive Δ33S in a different atmospheric composition, non-zero Δ33S of initial SO2, different mechanism producing S-MIF (chain formation), and destruction of positive Δ33S by subduction. The downward Δ36S/Δ33S deviations from ARA in the diagenetic pyrites of 2.72 Ga Tumbiana Formation can be attributed to modifications induced by microbial activities. This is based on the negative (0.9Δ33S + Δ36S) values similar to biological products and the large range of negative δ34S values. The downward Δ36S/Δ33S offsets in the hydrothermally altered diagenetic pyrites of 2.78 Ga Mt. Roe Basalt are most likely mixing of primary sulfur on ARA with later sulfur disobeying ARA. The upward Δ36S/Δ33S deviations in the diagenetic pyrites of 2.93 Ga Mosquito Creek Formation likely reflect different atmospheric composition.

中文翻译：

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黄铁矿的原位四重硫同位素组成。来自西澳大利亚皮尔巴拉克拉通的 3.2-2.72 Ga 变质沉积岩

摘要 根据先前的研究，与太古代参考阵列（ARA）相比，中太古代的硫质量独立分馏（S-MIF）与其他太古代时期的区别在于Δ33S的衰减幅度和Δ36S / Δ33S的更陡峭的斜率。然而，由于保存不佳或没有保存，此区间的可用样本有限。此外，大部分数据是通过分析大块岩石获得的，因此，由于成岩后叠印和修改的多个阶段，混合硫组分的硫同位素组成基本上是。该研究系统地测量了约 10 年中黄铁矿（结节状、播散状）的多种硫同位素组成。来自西澳大利亚皮尔巴拉克拉通的 3.2-2.72 Ga 变质沉积岩，这里是保存最完好的太古代记录之一，在通过 BSE 成像和 NaOCl 蚀刻进行详细的黄铁矿生成和成因调查后，使用升级的 SHRIMP-SI。结果表明，这些变沉积岩中成岩黄铁矿的Δ33S值为-2.4～0.8‰。这样的范围与其他太古代间隔和迄今为止产生 S-MIF 的任何实验不一致，其中最大正 Δ33S 值的幅度远大于相应的最小负 Δ33S 值。从生产和保存的角度对衰减的正Δ33S进行了解释，包括不同大气成分中负Δ33S的量级大于正Δ33S的原始光化学产物，初始SO2的非零Δ33S，产生S-MIF的不同机制（链形成），以及通过俯冲破坏正 Δ33S。2.72 Ga Tumbiana 组成岩黄铁矿与 ARA 的向下 Δ36S/Δ33S 偏差可归因于微生物活动诱导的修饰。这是基于类似于生物制品的负值 (0.9Δ33S + Δ36S) 和大范围的负 δ34S 值。2.78 Ga Mt 的热液蚀变成岩黄铁矿中向下的 Δ36S/Δ33S 偏移。鱼子玄武岩很可能是 ARA 上的初级硫与后来不符合 ARA 的硫混合。2.93 Ga 蚊溪组成岩黄铁矿的Δ36S/Δ33S 向上偏差可能反映了不同的大气成分。9Δ33S + Δ36S) 值类似于生物制品和大范围的负 δ34S 值。2.78 Ga Mt 的热液蚀变成岩黄铁矿中向下的 Δ36S/Δ33S 偏移。鱼子玄武岩很可能是 ARA 上的初级硫与后来不符合 ARA 的硫混合。2.93 Ga 蚊溪组成岩黄铁矿的Δ36S/Δ33S 向上偏差可能反映了不同的大气成分。9Δ33S + Δ36S) 值类似于生物制品和大范围的负 δ34S 值。2.78 Ga Mt 的热液蚀变成岩黄铁矿中向下的 Δ36S/Δ33S 偏移。鱼子玄武岩很可能是 ARA 上的初级硫与后来不符合 ARA 的硫混合。2.93 Ga 蚊溪组成岩黄铁矿中Δ36S/Δ33S 向上偏差可能反映了不同的大气成分。