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
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
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对南非巴伯顿绿岩带 3.2 Ga 黄铁矿的高分辨率四重硫同位素分析揭示了对硫化物同位素阵列的独特环境控制
DOI：
10.1016/j.gca.2013.04.027
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发表时间：
2013
影响因子：
5
通讯作者：
T. Reimer
中科院分区：
文献类型：
--
作者：
D. Roerdink;P. Mason;M. Whitehouse;T. Reimer
古太古代黄铁矿中的多种硫同位素记录了早期硫循环中大气过程和新兴微生物活动的宝贵信息。本文报道了南非巴伯顿绿岩带一个3.26-3.23 Ga沉积重晶石存款中黄铁矿的二次离子质谱分析的四重硫同位素数据（32 S，33 S，34 S，36 S）。我们的研究结果表明，在无重晶石和富含重晶石的样品中存在不同的黄铁矿种群和可重复的同位素阵列。在重晶石中的浸染状黄铁矿中发现了大多数具有弱正Δ 33 S/δ 34 S的34 S亏损特征，而仅在硅质岩、白云岩、砾岩和角砾岩中观察到负Δ 33 S/δ 34 S和Δ 36 S/Δ 33 S = −0.9 ± 0.2的正Δ 33 S值。我们解释这些变化与当地的氧化还原反应和硫化物相混合，而不是单独代表主要的大气变化。岩性和同位素组成之间的强相关性表明不同的硫化物形成环境与当地硫酸盐浓度和不同硫代谢的波动输入有关。在富含重晶石的沉积物中，当[SO 42 −] > 200 μM时，微生物硫酸盐还原形成了34 S严重亏损的硫化物，而在陆源碎屑岩沉积过程中，当硫酸盐水平降低时，同位素效应受到抑制。正Δ 33 S值表明，当硫酸盐浓度低于200 μM时，来自元素硫代谢的硫化物输入增加。我们的研究结果支持了一个重要的作用，当地的硫酸盐浓度的生物硫同位素签名在地球上最古老的岩石的表达。
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 most34S-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. Strongly34S-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.