俯冲带变质脱水作用与流体性质

Metamorphic dehydrations and fluid nature in subduction zones

俯冲带不仅是全球最大的物质循环的枢纽,还是地球内部流体活动最为强烈的场所之一。在板片俯冲过程中,经洋底蚀变的洋壳、上覆沉积物和下伏蛇纹石化岩石圈地幔随着温压的升高发生变质脱水反应形成俯冲带流体。脱水过程主要受俯冲板片中含水矿物的稳定性控制,而其流体效应主要受控于俯冲带热结构等因素。俯冲带流体按其含水和溶质比例可分为富水流体、超临界流体和含水熔体等不同类型,流体不仅可以携带传统的LILE,还可以携带HREE、HFSE、金属元素和重要挥发分(如C、N和S等)进行迁移,在制约俯冲板片-岛弧物质循环方面起着重要作用。本研究在回顾俯冲板片的脱水机制、流体作用及其地球化学行为的基础上,对俯冲带流体的研究前景进行了展望。

Subduction zones are not only the pivot of the largest cycling system on Earth but also one of the prominent loci of fluid activity within the Earth interior.In the process of slab subduction,the seawater-altered oceanic crust,overlying sediments and underlying serpentinized lithospheric mantle are heated up and form fluids through the metamorphic dehydration.The dehydration process is mainly dictated by the stability of hydrous minerals and the hydrodynamic effect is largely determined by the thermal structure of subduction zones.Based on the proportion of water and solute,subduction zone fluids can be divided into aqueous fluid,hydrous silicate melt,and supercritical fluid.The fluids can transport not only the traditional mobile large ion lithophile elements(LILEs)but also the immobile heavy rare earth elements(HREEs)and high field strength elements(HFSEs),the metals,and the critical volatiles(such as C,N and S),playing a central role in slab-arc element and material cycling.This paper reviews the dehydration mechanism,hydrodynamic effect and geochemical behavior of subduction zone fluids and suggests some research directions in future studies on subduction zone fluids.