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A seawater-sulfate origin for early Earth’s volcanic sulfur
Nature Geoscience ( IF 18.3 ) Pub Date : 2020-07-20 , DOI: 10.1038/s41561-020-0601-6
Hiroshi Ohmoto

Mass-independent fractionation of sulfur isotopes (MIF-S)—as recorded primarily in pre-2.5 billion years ago (Ga) sedimentary rocks—has been interpreted as evidence of photolysis of volcanic SO2 in an anoxic troposphere. Here, I present thermodynamic and kinetic calculations, combined with data on the geology, mineralogy and chemical and isotopic compositions of modern and Archaean (3.8–2.5 Ga) aged volcanic samples from different tectonic settings, to examine early Earth’s sulfur cycle. Based partly on the similarities between submarine hydrothermal deposits and arc volcanic rocks in pyrite (FeS2) abundances and sulfur isotopic compositions (for example, the presence of both positive and negative δ34S values), I conclude that degassing of sulfur (mostly as SO2) into the atmosphere has been carried out primarily by subaerial eruptions of oxidized, arc-like magmas since at least 3.5 Ga. The generation of volcanic SO2 requires plate tectonics and the involvement of sulfate-rich seawater, which requires large exposed lands and an oxygenated atmosphere. I propose that the MIF-S signatures in sedimentary rocks were created by ultraviolet photochemical reactions between SO2 from explosive volcanic eruptions and O2 in the stratosphere, above an oxygen-rich troposphere, or by high-temperature reactions between organic compounds and sulfate in the oceans.



中文翻译:

地球早期火山硫的海水硫酸盐来源

主要在25亿年前(Ga)沉积岩中记录的硫同位素(MIF-S)的质量无关分馏已被解释为缺氧对流层中火山SO 2光解的证据。在这里,我介绍了热力学和动力学计算,并结合了来自不同构造背景的现代和古生代(3.8–2.5 Ga)年龄火山岩的地质,矿物学,化学和同位素组成的数据,以检验地球早期的硫循环。部分基于海底热液沉积物之间和电弧在黄铁矿火山岩(FES的相似2)的丰度和硫同位素组成(例如,正的和负δ的存在34价值观),我的结论硫的该脱气(主要是作为SO 2)到大气中已经主要通过陆上喷发进行氧化,圆弧状的岩浆因为至少3.5佐治亚火山SO的生成2需要板块构造和富含硫酸盐的海水的参与,这需要大面积的裸露土地和含氧气氛。我认为沉积岩中的MIF-S信号是由爆发性火山喷发的SO 2与平流层中富氧对流层上方的O 2之间的紫外线光化学反应,或有机化合物与硫酸盐之间的高温反应产生的。海洋。

更新日期:2020-07-20
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