Abiogenesis not required to explain the origin of volcanic-hydrothermal hydrocarbons
Abiogenesis not required to explain the origin of volcanic-hydrothermal hydrocarbons
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DOI：
10.7185/geochemlet.1920
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发表时间：
2019-07-29
影响因子：
4.9
通讯作者：
Mountain, B. W.
中科院分区：
文献类型：
--
作者：
Fiebig, J.;Stefansson, A.;Mountain, B. W.
正烷烃的非生物形成被假定发生在地壳内。明显的证据主要是基于不寻常的碳和氢同位素分布模式，将甲烷及其高链同源物与微生物生产和有机物封闭系统热降解相关的生物同位素组成区分开来。本文首次在全球范围内研究了玄武岩、安山岩、粗面岩和流纹岩等火山岩-热液中正构烷烃的碳、氢同位素组成。我们发现这些气体的体积同位素组成遵循有机物高温、开放系统降解的特征。在无沉积物系统中，有机质由通过储层岩石循环的地表水（海水、大气水）提供。我们的数据集有力地表明，有机质的热降解能够满足以前分类为指示生物发生的同位素标准。进一步考虑到地壳中无处不在的地表水，非生物碳氢化合物的出现可能被大大高估了。
Abiotic formation of n-alkane hydrocarbons has been postulated to occur within Earth's crust. Apparent evidence was primarily based on uncommon carbon and hydrogen isotope distribution patterns that set methane and its higher chain homologues apart from biotic isotopic compositions associated with microbial production and closed system thermal degradation of organic matter. Here, we present the first global investigation of the carbon and hydrogen isotopic compositions of n-alkanes in volcanic-hydrothermal fluids hosted by basaltic, andesitic, trachytic and rhyolitic rocks. We show that the bulk isotopic compositions of these gases follow trends that are characteristic of high temperature, open system degradation of organic matter. In sediment-free systems, organic matter is supplied by surface waters (seawater, meteoric water) circulating through the reservoir rocks. Our data set strongly implies that thermal degradation of organic matter is able to satisfy isotopic criteria previously classified as being indicative of abiogenesis. Further considering the ubiquitous presence of surface waters in Earth's crust, abiotic hydrocarbon occurrences might have been significantly overestimated.