In-situ iron isotope analyses of pyrites from 3.5 to 3.2Ga sedimentary rocks of the Barberton Greenstone Belt, Kaapvaal Craton
In-situ iron isotope analyses of pyrites from 3.5 to 3.2Ga sedimentary rocks of the Barberton Greenstone Belt, Kaapvaal Craton
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DOI：
10.1016/j.chemgeo.2015.03.007
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发表时间：
2015-05
期刊：
影响因子：
3.9
通讯作者：
Kazumi Yoshiya;Y. Sawaki;T. Shibuya;S. Yamamoto;T. Komiya;T. Hirata;S. Maruyama
中科院分区：
文献类型：
--
作者：
Kazumi Yoshiya;Y. Sawaki;T. Shibuya;S. Yamamoto;T. Komiya;T. Hirata;S. Maruyama
南非巴伯顿绿岩带（BGB）由3.5 ~ 3.2 Ga沉积的火山-沉积和沉积岩系组成，可分为三组：翁韦尔瓦赫特、无花果树和穆迪。沉积后，巴伯顿绿岩带经历了相对较低的构造事件，使估计中太古代的地表环境事件和生物演化。同位素研究表明，产甲烷菌，硫酸盐还原菌，光合细菌在3.4 Ga的活动。微生物异化铁还原（英语：Microbial dissimilatory iron reduction）也被认为是地球上最早的代谢表现之一，但在太古代微生物异化铁还原的同位素信号仍不确定。我们performedin-situiron同位素分析的沉积岩中的个别黄铁矿从BGB，使用飞秒激光烧蚀多接收器ICP-MS技术（fs-LA-MC-ICP-MS）找到同位素证据的微生物活动。我们得到的δ 56 Fe值变化很大，范围从-1.84 ‰到+3.79 ‰。Hooggenoeg杂岩中黄铁矿的δ 56 Fe值大部分为正值，而Noisy杂岩及后续沉积序列中黄铁矿的δ 56 Fe值变化较大，从负值到正值。这些复合体之间的主要区别之一是它们的沉积深度。Hooggenoeg复合体可能沉积在深海环境中，而Noisy复合体则沉积在浅水中。翁韦尔瓦赫特群Noisy杂岩中黄铁矿颗粒的δ 56 Fe值为负，表明中太古代浅海中存在微生物DIR引起的部分还原。
The Barberton Greenstone Belt (BGB), South Africa, consists of volcano-sedimentary and sedimentary successions deposited between 3.5 and 3.2 Ga, which are subdivided into three groups: the Onverwacht, Fig Tree, and Moodies. After deposition, the Barberton Greenstone Belt underwent relatively low-grade tectonothermal events, enabling estimation of surface environmental events and biological evolution in the Middle Archean. Isotopic studies suggest the activity of methanogen, sulfate-reducing bacteria, and photosynthetic bacteria at 3.4 Ga. Microbial dissimilatory iron reduction (DIR) is also considered one of the earliest expressions of metabolism on Earth, but the isotopic signal of microbial DIR is still uncertain in the Archean. We performedin-situiron isotope analyses of individual pyrites in sedimentary rocks from the BGB, using a femtosecond laser ablation multi-collector ICP-MS technique (fs-LA-MC-ICP-MS) to find isotopic evidence for the microbial activity. We obtained a large variation in δ56Fe values, ranging from − 1.84 to + 3.79‰. Most of the δ56Fe values of pyrites from the Hooggenoeg Complex show positive values, whereas those from the Noisy Complex and subsequent sedimentary sequences show a wide variation from negative to positive δ56Fe values. One of the main differences between these complexes is their depositional depth. The Hooggenoeg Complex was probably deposited in a deep-ocean environment, whereas the Noisy Complex was in shallow water. The negative δ56Fe values of pyrite grains in the Noisy Complex, Onverwacht Group indicate the occurrence of partial reduction caused by microbial DIR in a Middle Archean shallow sea.