马里亚纳弧前蛇纹岩泥火山无机成因甲烷–氢气水合物形成条件与稳定带发育特征  

The abiotic methane-hydrogen hydrate stability zone in Mariana forearc serpentinite mud volcanoes

作　　者：汤加丽 曹运诚[1] 陈多福[1] TANG Jiali;CAO Yuncheng;CHEN Duofu(Shanghai Engineering Research Center of Hadal Science and Technology,College of Marine Sciences,Shanghai Ocean University,Shanghai 201306,China)

机构地区：[1]上海海洋大学海洋科学学院上海深渊科学工程技术研究中心,上海201306

出　　处：《地球化学》2022年第2期194-201,共8页Geochimica

基　　金：国家自然科学基金项目(41776050,42176069,41776080)资助。

摘　　要：海洋水合物的成藏不仅需要合适的温度、压力条件,而且需要充足的气源。一般认为大洋区海底沉积物缺乏丰富的有机质,不具备天然气水合物发育的气源条件。然而最近研究表明洋壳广泛的蛇纹岩化作用可以产生大量的无机成因甲烷,并找到了与蛇纹岩化有关的水合物发育证据。蛇纹岩化过程中不仅有甲烷生成,还生成大量的氢气,很可能形成甲烷–氢气水合物。本文根据IODP 366航次钻探资料,应用甲烷–氢气水合物的热力学模型,计算了马里亚纳弧前三个蛇纹岩泥火山钻探实测获得的不同氢气含量条件下的甲烷–氢气水合物稳定带分布特征。结果显示氢气比例越高,计算获得的甲烷–氢气水合物稳定带底界深度越浅。研究的6个马里亚纳弧前蛇纹岩泥火山站位中, IODP 1491、1492、1496、1498四个站位可能具备甲烷–氢气水合物发育温压和气体成分组成条件;IODP 1493、1497站位几乎不具备甲烷–氢气水合物的温压和气体组成条件。Although thermodynamic conditions for hydrate stability are satisfied throughout most of the world’s oceans, most marine hydrates have been discovered along continental margins where methane is supplied by the conversion of organic carbon within sediments. Abiotic methane has recently been recognized as an additional sub-seafloor gas source generated during the serpentinization of ultramafic rocks. A large amount of hydrogen is also produced during serpentinization, which forms hydrogen gas hydrate, implying that thermodynamic conditions and gas resources are quite different from that of previously recovered methane hydrate. In this study, we estimated the methane-hydrogen hydrate formation conditions and the base depth of methane-hydrogen hydrate at six sites drilled at the Mariana forearc serpentinite mud volcano for gas mixtures with concentrations of hydrogen from 1%to 90%. Our calculations show that the base of the methane-hydrogen hydrate stability zone would be shallow and the partial pressure of methane needed for methane-hydrogen hydrate formation is constant at a given temperature and pressure when the ratio of hydrogen is high. Additionally, the methane-hydrogen hydrate formation conditions can be satisfied at four sites: IODP 1491, 1492, 1496, and 1498. Hydrogen was the dominant gas at IODP sites 1493 and 1497, where methane-hydrogen hydrates could not be formed.

关 键 词：甲烷–氢气水合物 蛇纹岩泥火山 无机成因甲烷 水合物稳定带 马里亚纳弧前 

分 类 号：P67[天文地球—海洋地质]