冲绳海槽中部Jade热液活动区中块状硫化物的稀土元素地球化学特征

Rare Earth Element Geochemistry of Massive Sulphides from the Jade Hydrothermal Field in the Central Okinawa Trough

用ICP-MS对冲绳海槽Jade热液活动区中6个块状硫化物样品进行了稀土元素分析。除一个样品表现出极微弱的正Eu异常外(δEu=1.09),其他样品均表现出负Eu异常(δEu=0.58～0.71)和LREE相对富集((La/Yb)_N=1.29～47.87)的球粒陨石标准化配分模式。块状硫化物样品之间稀土元素组成的变化是由于热液流体-岩石的相互作用以及海水和热液流体不同程度混合的结果。与深海沉积物,火山岩和海水稀土元素配分模式对比,表明块状硫化物的REE部分来自沉积物和火山岩,海水的混合作用对块状硫化物的REE配分模式具有一定的影响。海底热液硫化物稀土元素组成的变化可以一定程度的反映出热液流体的演化特征。

Rare earth elements of 6 massive sulphide samples from the Jade hydrothermal field in the central Okinawa Trough have been analyzed with the ICP-MS. Except one sample (δEu=1. 09) , the chondrite-normalized REE patterns of the massive sulphide samples are characterized by negative Eu anomalies (δEu = 0. 58-0. 71) and varying levels of LREE enrichment ((La/Yb)N = 1. 29 - 47. 87). The variation of REE compositions of different massive sulphides is a result of hydrothermal fluid-rock interaction and the mixing of hydrothermal fluid and seawater in different proportions in the seafloor hydrothermal circulation system. By comparing with the REE distributive patterns of pelagic sediments, volcanics and seawater from the Okinawa Trough, it is suggested that the REE in massive sulphides is partially from pelagic sediments and volcanics, and the REE distributive patterns of seafloor hydrothermal sulphides are influenced by the mixing of seawater. The variation of REE concentrations in the massive sulphide samples appears to be an indicator of the evolutionary characteristics of the hydrothermal fluid.