大洋橄榄岩的蛇纹石化过程:从海底水化到俯冲脱水SCIEI北大核心CSCD

蛇纹石化是海底最重要的水岩相互作用之一,指基性岩和超基性岩中的橄榄石和辉石等镁铁质矿物在相对低温条件下发生水热蚀变产生蛇纹石等矿物的热液变质作用。蛇纹石族矿物主要有三种,分别是利蛇纹石、纤蛇纹石和叶蛇纹石。低温状态蛇纹石族矿物主要以利蛇纹石和纤蛇纹石的形式存在,高温状态下主要以叶蛇纹石的形式存在。影响大洋蛇纹石化过程的因素不容忽视,温度、氧化还原程度、pH值、水岩比(W/R)等都在其中扮演着重要的角色。总的来说,地幔物质易出露在地壳减薄区域和断裂构造处,这有利于与流体充分接触反应,从而决定了大洋蛇纹石化作用发生的可能位置。对蛇纹石化程度的描述,当前人们大多通过岩石微观结构、地球化学指标来定性指示,磁学指标有望实现对蛇纹石化程度的定量解释。蛇纹石化作用对海底磁异常、地球生命演化进程、成矿作用等都有一定的贡献。此外,俯冲带脱水及弧岩浆的形成都与之有联系。总之,基性与超基性岩石蛇纹石化与俯冲带蛇纹岩脱水过程是地球水循环过程的重要机制,但未来揭示蛇纹岩的磁学性质和俯冲变质过程,仍需进一步探索。

The process of oceanic peridotite serpentinization:From seafloor hydration to subduction dehydration

As one of the most important water-rock interactions on earth, serpentinization refers to the hydrothermal alteration of mafic and ultramafic rocks under medium-low temperature conditions. Serpentinization is mainly the water-rock metasomatism of olivine, orthopyroxene and amphibole and other magnesia end-members. There are three kinds of serpentine group minerals, including 1izardite, chrysotile and antigorite. They reside at different temperatures, e.g., 1izardite and chrysotile at low temperature, while antigorite at high temperature. Serpentinization process is controlled by temperature, the degree of redox, pH value, water-rock ratio (W/R), etc. In general, serpentinization is prone to occur at the areas with the thinning of the crust or the existence of faulted structures where mantle materials are easy to expose to contact and react with fluids. The serpentinization degree is generally quantified by the rock microstructure and geochemical methods, however, magnetic parameter is a prospective proxy for this index. Serpentinization makes a certain contribution to the marine magnetic anomalies, the biological evolution process on the earth, and the mineralization, in particular to the dehydration at the subduction zone and the formation of arc magma. However, much more investigations on the detailed mechanism are needed in the future work.