俯冲带水岩相互作用:来自西南天山(超)高压变质岩的矿物学证据  

Fluid⁃Rock Interaction in Subduction Zones:Mineralogical Evidence of Metamorphic Rock from Southwestern Tianshan

作　　者：窦萍 肖媛媛[2,3,4] 林晋炎 姚永祥[2,3,5] Dou Ping;Xiao Yuanyuan;Lin Jinyan;Yao Yongxiang(Department of Geology,Northwest University,Xi’an 710069,China;CAS Key Laboratory of Marine Geology and Environment,Institute of Oceanology,Chinese Academy of Sciences,Qingdao 266071,China;Laoshan Laboratory,Qingdao 266061,China;Center for Ocean Mega-Science,Chinese Academy of Sciences,Qingdao 266071,China;University of the Chinese Academy of Sciences,Beijing 100049,China)

机构地区：[1]西北大学地质学系,陕西西安710069 [2]中国科学院海洋研究所海洋地质与环境重点实验室,山东青岛266071 [3]崂山实验室,山东青岛266061 [4]中国科学院海洋大科学研究中心,山东青岛266071 [5]中国科学院大学,北京100049

出　　处：《地球科学》2024年第8期2751-2765,共15页Earth Science

基　　金：崂山实验室科技创新项目(No.LSKJ202204104);泰山学者工程。

摘　　要：西南天山(超)高压变质带内发育有大规模被流体交代的变质岩,其脉体和围岩记录了重要的俯冲带流体信息.在以往对有脉体发育的俯冲带变质岩全岩地球化学研究的基础上,进一步对该样品脉体和围岩中的石榴石、帘石、绿辉石、多硅白云母等矿物成分进行原位分析,对比同一矿物在脉体和围岩中的成分区别,以深入理解脉体和围岩的全岩成分差异、俯冲带水岩相互作用中相关元素的地球化学行为及流体性质.根据岩石学特征,该样品分为富蓝闪石脉体、富帘石和碳酸盐的过渡部分及富绿辉石内部.元素储库计算揭示全岩的元素组成和元素赋存矿物及其丰度具有一致性,脉体中更高的中重稀土元素(MHREE)含量显示该部分更多的石榴石对M-HREE的赋存,过渡部分更高的REE-Th-U-Pb-Sr等元素含量反映了大量存在的帘石族矿物、碳酸盐对这些元素的控制,富绿辉石内部更高的K-Rb-Ba-Cs等元素含量则反映了这部分更多的白云母对这些元素的控制.另外,同一矿物在样品不同部分的成分差异可直接反映元素在不同变质阶段和不同水化程度下的地球化学变化,相较于受流体改造较少的富绿辉石内部,富蓝闪石脉体和过渡部分的多硅白云母和绿辉石丰度降低但更富集K-Rb-Ba-Cs等元素;石榴石丰度升高但其所含的HREE含量更低;帘石丰度升高但其所含的Th-U-轻稀土元素(LREE)含量更低.结合过渡部分出现的大量碳酸盐矿物,推测外来流体为含碳酸盐的蛇纹岩衍生流体.水岩相互作用后,流体的LILE含量显著升高,碳酸盐组分明显降低,其余元素含量变化不大.Southwestern Tianshan HP-UHP metamorphic belt developed subduction-zone metamorphic rocks affected by large-scale fluid flows,its veins and host rocks provide important informations about the infiltrating fluid in subduction zone.Based on the previous bulk-rock geochemical studies on metamorphic rocks developed veins in the subduction zone,We have conducted an in situ element study of glaucophane,garnet,omphacite,phengite and other minerals in the veins and host rocks of the metamorphic rock samples to compare the compositional differences of the same mineral in veins and host rocks.This study aims to deeply understand the differences of bulk rock compositions between veins and host rocks,and the geochemical behaviors of related elements in the fluid-rock interaction and fluid properties in subduction zones.According to the petrological characteristics,the samples can be divided into glaucophane-rich veins,epidote and carbonate-rich transitional part and the omphacite-rich interiors.The calculation of element budgets reveal that the relationship between the difference of bulk-rock compositions and host minerals and their abundances.The higher contents of medium-heavy rare earth element(M-HREE)in veins reflects the occurrence of M-HREE by more garnets in veins;and the higher contents of rare earth elements-Th-U-Pb-Sr in the transitional part reflects a large number of epidote group minerals and carbonates controlthese elements;the higher contents of K-Rb-Ba-Cs in omphacite-rich interiors reflects the control of these elements by phengite.On the other hand,the compositional differences of the same mineral in different parts of the rock samples can reflect the geochemical changes of elements in different metamorphic stages and different rehydration degrees directly.Compared with the omphacite-rich interior representing the least fluidinfiltration,the rehydration of external fluid decreased the abundances of phengite and omphacite in the veins and transitional part,and enriched K-Rb-Ba-Cs-Pb-Sr;increased abundance of

关 键 词：西南天山 俯冲变质作用 流体活动 赋存矿物 元素地球化学行为 地球化学 

分 类 号：P595[天文地球—地球化学] P67[天文地球—地质学]