自然界岩石样品中的超临界流体记录

Supercritical Fluid Records in Natural Rocks

超临界流体是有别于富水流体和含水熔体的一种低粘度、高迁移性和高元素携带能力的一类流体,在变质岩体系中,其形成的温压条件一般高于对应的H2O-岩体系的第二临界端点。俯冲带岩石是自然界最有可能保存超临界流体活动记录的地方,而超临界流体的活动对于地球内部物质循环、俯冲带岩浆作用和俯冲带成矿等方面可以发挥巨大作用。目前对于天然岩石和矿床样品中超临界流体的识别仍处于经验推测阶段,缺乏定量的岩相学和地球化学指标。本文主要基于目前已有研究结果,介绍自然体系中超临界流体的地质特征,包括俯冲带超高压变质岩、高压-超高压脉体以及地幔楔岩石中的超临界流体记录,主要是一些多相包裹体及元素迁移变化的记录,最后讨论超临界流体的相分离与岛弧岩浆作用之间的关系。

Supercritical fluid is characterized with low viscosity,high mobility,and high element-carrying capability.It is strikingly different from aqueous fluid and hydrous melt.In metamorphic rock system supercritical fluid is generally formed at p-t conditions which are higher than those of the second critical point of corresponding water-rock system.Supercritical fluid activity could be most possibly recorded in rocks of the subduction zone in nature.It could have played vital roles for the material cycling in the Earth’s interior,and the subduction zone-related magmatism and mineralization.So far quantitative petrological and geochemical indices for the recognition of supercritical fluid in samples of natural rocks and ore depositsare scarce.By contrast,the majority of recognition depends on empirical deduction.In this contribution,based on currently existed research achievements,we have introduced the geological features of supercritical fluids recorded in natural rocks,including high pressure and ultra-high pressure metamorphic rocks and veins,and rocks of the mantle wedges in subduction zones,via multiphase inclusions and by variation of elemental transport between different rocks or minerals,and finally have discussed the phase separation of supercritical fluid and relationship between the supercritical fluid and arc magmatism.