冲绳海槽CLAM热液区低硫逸度热液成矿  

Low sulfur fugacity mineralization in CLAM hydrothermal field

作　　者：张侠 孙治雷 ZHANG Xia;SUN Zhilei(Deep-Sea Multidisciplinary Research Center,Laoshan Laboratory,Qingdao 266237,China;Ministry of Natural Resources,Qingdao Institute of Marine Geology,Qingdao 266237,China)

机构地区：[1]崂山实验室深海多学科交叉研究中心,青岛266237 [2]中国地质调查局青岛海洋地质研究所,青岛266237

出　　处：《海洋地质与第四纪地质》2023年第5期17-25,共9页Marine Geology & Quaternary Geology

基　　金：国家自然科学基金面上项目“海洋甲烷拦截带对冷泉流体的消耗研究:来自南海东沙海域的观测与研究”(42176057)。

摘　　要：冲绳海槽是琉球俯冲系统的重要组成部分,该区热液硫化物研究对揭示非成熟弧后盆地内部热液成矿作用特征具有重要意义。CLAM热液区位于冲绳海槽中部(27°33′N、126°58′E),大量研究表明,该区成矿作用特征与海槽其他热液区存在显著差异,但其成因尚不明确。对CLAM热液区硫化物矿物组成、共生组合关系及闪锌矿微区元素组成进行了系统分析测试,在此基础上提出,该区特殊的矿物学特征及矿物化学组成可能受热液流体硫逸度控制。本文研究样品为富Fe型块状硫化物,主要由磁黄铁矿及低温闪锌矿组成,磁黄铁矿的大量结晶暗示着该区热液流体具有低硫逸度特征。热液成矿过程中,流体温度及硫逸度经历了由低到高的演化。闪锌矿中极高的Fe含量同样受控于该区流体低硫逸度条件,计算结果表明,热液流体的硫逸度值为–15,与其他受沉积物影响的热液活动区一致。流体-沉积物反应过程中,沉积物中有机质的分解可能是导致CLAM热液区热液流体硫逸度系统性降低的主要原因。The Okinawa Trough is an important part of Ryukyu subduction system and the sulfide research in this region is important for uncovering the hydrothermal mineralization characteristics in incipient back-arc basin.Many researches have demonstrated that the mineralization characteristics of CLAM hydrothermal system are different from those of others in Okinawa Trough.However,the cause of these differences are still unclear.The mineralogical characteristics and sphalerite in situ trace element contents of CLAM Fe-rich type sulfides are determined systematically.On these basis,we propose the unique mineralogical compositions and geochemical characteristics in CLAM are controlled by sulfur fugacity of hydrothermal fluid.The studied samples are mainly composed of pyrrhotite and low-temperature sphalerite.The occurrence of large amounts of pyrrhotite implies that the hydrothermal fluid possesses low sulfur fugacity.During the mineralization process,both temperature and sulfur fugacity conditions for the mineralization evolved from low to high.The high Fe contents also support the low sulfur fugacity condition during the CLAM sulfide mineralization.The calculation indicates that the sulfur fugacity value of hydrothermal fluid is–15,which is equal to those of other sediment-hosted hydrothermal systems.The decomposition of organism in sediments during hydrothermal circulation is the major cause of low sulfur fugacity in CLAM fluid.

关 键 词：硫逸度 热液成矿 CLAM热液区 冲绳海槽 

分 类 号：P736[天文地球—海洋地质]