大洋俯冲带的水岩作用——蛇纹石化

Water-Rock Interaction in Oceanic Subduction Zone:Serpentinization

蛇纹石化是地球上最重要的水岩作用之一。它的发生对于岛弧的形成、地震的产生、海底流体活动乃至生命起源、演化等具有重要的意义。本文介绍了大洋俯冲带中洋中脊玄武岩和橄榄岩在俯冲过程中的相变和水岩相互作用,尤其是含水矿物的稳定情况,揭示由于不同的地温梯度,冷、热俯冲带存在的含水矿物组合会有所不同,导致弧前、弧下或弧后深度的流体活动及蛇纹石化规模有所不同。在此基础上,归纳总结了蛇纹石化作用的代表性化学反应和相应产物,指出蛇纹石化作用主要是橄榄石、斜方辉石和角闪石等镁质端元的水岩交代,除了生成特征矿物蛇纹石以外,还可以产生磁铁矿、水镁石、滑石、透闪石、菱镁矿等矿物以及氢气、甲烷、已烷、二氧化碳等气体组分,同时可伴生铬铁矿、铁镍矿、自然铜等金属矿产。

Serpentinization is one of the most important water-rock interactions on earth, which plays a sig-nificant role on formation of island arc, generation of earthquake, activity of seafloor fluid, and origin and evolu-tion of life. This paper introduces the phase transitions, water-rock interactions, and in particular water-rich min-eral’s stabilities during subduction occurring in mid-ocean ridge basalt and peridotite in oceanic subduction zone, and reveals discrepant water-rich mineral assemblages between cold and hot subduction zones due to distrinct geothermal gradient, resulting in different fluid activities and serpentinization scales beneath the fore-arc, sub-arc and back-arc in subduction zone. This paper further summarizes the representative chemical reactions of serpenti-nization and their products.