冲绳海槽唐印热液区中硬石膏的化学及其硫同位素组成  

Chemical and sulfur isotopic compositions of anhydrite from the Tangyin hydrothermal field in the Okinawa Trough

作　　者：曾志刚[1,2,3,4] 陈祖兴 齐海燕 陈帅[1,2,3,5] ZENG Zhigang;CHEN Zuxing;QI Haiyan;CHEN Shuai(Institute of Oceanology,Chinese Academy of Sciences,Qingdao 266071,China;Key Laboratory of Marine Geology and Environment,Institute of Oceanology,Chinese Academy of Sciences,Qingdao 266071,China;Laboratory for Marine Mineral Resources,Laoshan Laboratory,Qingdao 266237,China;University of Chinese Academy of Sciences,Beijing 100049,China;Center for Ocean Mega-Science,Chinese Academy of Sciences,Qingdao 266071,China)

机构地区：[1]中国科学院海洋研究所,青岛266071 [2]中国科学院海洋地质与环境重点实验室,青岛266071 [3]崂山实验室海洋矿产资源评价与探测技术功能实验室,青岛266237 [4]中国科学院大学,北京100049 [5]中国科学院海洋大科学研究中心,青岛266071

出　　处：《海洋地质与第四纪地质》2023年第5期1-16,共16页Marine Geology & Quaternary Geology

基　　金：国家自然科学基金项目“深海界面过程和化能生态系统”(42221005),“西太平洋俯冲体系中岩浆活动及其对热液物质供给的制约”(91958213);中国科学院战略性先导科技专项子课题“热液/冷泉区岩浆物质贡献与流体化学过程”(XDB42020402);国家重点基础研究发展计划(973计划)项目“典型弧后盆地热液活动及其成矿机理”(2013CB429700);泰山学者工程资助项目。

摘　　要：硬石膏是最早构成热液烟囱体壁的矿物之一,其对于了解流体-海水混合以及海底热液系统中元素的迁移与循环具有重要的意义。为此,对西太平洋冲绳海槽唐印热液区中的硬石膏,进行了微区原位元素以及硫同位素组成分析。根据硬石膏的结晶形态,可以将硬石膏分为两种类型:较早形成的I型硬石膏,其呈半自形或他形晶,似针状、放射状及不规则晶的集合体产出;较晚形成的II型硬石膏,其呈自形晶,以板状及粒状晶的集合体产出。当热液流体初次遇到海水时,将快速沉淀形成I型硬石膏,并构成了热液烟囱体的壁。随后,II型硬石膏经历了一个相对充分的生长阶段。同时,硬石膏中的Ba、Al、Sr、Ni、Fe、Mn和Cr含量明显高于海水,表明产生硬石膏沉淀的热液流体来自于海底面以下,是经历了流体-岩石和/或沉积物相互作用的流体。硬石膏的Mg含量明显分别低于海水和高于喷口流体,表明其是流体-海水混合的结果。I型硬石膏,其Sr含量明显低于II型硬石膏,表明在形成自形、板片状或粒状硬石膏的期间,来自热液流体的Sr,主要进入II型硬石膏中。硬石膏的Fe、As、Sr、Ba和Pb含量,明显高于冲绳海槽喷口流体的,则表明这些来自流体中的元素更容易随着硬石膏的沉淀而进入硬石膏中,并导致硬石膏富集该类元素。硬石膏的稀土元素组成及其配分模式,具正Ce和负Eu异常的特征,其是流体在海底面以下从火山岩和/或沉积物中淋滤出来,并经历了流体-海水混合作用的结果。此外,在流体-海水混合期间,硬石膏中的硫主要来自海水。Anhydrite is one of the earliest minerals in forming the hydrothermal chimney walls,which is important for understanding the fluid-seawater mixing,and elemental migration and cycling in the seafloor hydrothermal system.Anhydrite minerals samples from the Tangyin hydrothermal field in the southwestern Okinawa Trough,western Pacific were investigated on the in-situ element concentrations and sulfur(S)isotopic compositions.The crystal morphology of anhydrite could be divided into two types.Type I anhydrite formed earlier is subhedral or anhedral and occurred in radial or irregular crystal aggregation,and Type II anhydrite formed later is euhedral and occurred in plate or granular crystal aggregation.When the hydrothermal fluid first met with seawater,Type I anhydrite precipitated rapidly and formed the wall of the hydrothermal chimney.Subsequently,Type II anhydrite experienced relatively longer growth stage.However,the Ba,Al,Sr,Ni,Fe,Mn,and Cr contents of anhydrite are significantly higher than that of seawater,suggesting that those elements are derived mainly from hydrothermal fluid duo to the subseafloor fluid-rock and/or sediment interactions.The Mg content of anhydrite is significantly lower/higher than that of seawater/vent fluids,which was resulted from the fluid-seawater mixing.Most of the Sr contents of Type I anhydrite are significantly lower than that of Type II anhydrite,suggesting that more Sr from fluids were involved into Type II anhydrite and formed euhedral,plate,or granular minerals.The Fe,As,Sr,Ba,and Pb contents of anhydrite are significantly higher than that of vent fluids in the Okinawa Trough,which indicates that these elements enter preferentially anhydrite from the fluids,and resulted in the enrichment of these elements in the anhydrite.REEs of anhydrite and their REE patterns show positive Ce and negative Eu anomalies,which could be resulted from fluids leaching out from local sub-seafloor volcanic rocks and/or sediments and having undergone fluid-seawater mixing.Furthermore,S in the anhydri

关 键 词：硬石膏 化学及其硫同位素组成 热液烟囱体 喷口流体 唐印热液区 

分 类 号：P736.4[天文地球—海洋地质]