俯冲带流体——来自(超)高压变质岩石的证据  

The subduction-zone fluid:Evidence from (ultra-) high-pressure metamorphic rocks

作　　者：高俊[1,2,3] 李继磊 马智佩[1,2,3] Reiner KLEMD GAO Jun;LI Jilei;MA Zhipei;Reiner KLEMD(Key Laboratory of Mineral Resources,Institute of Geology and Geophysics.Chinese Academy of Sciences,Beijing 100029,China;Innovation Academy for Earth Science,Chinese Academy of Sciences,Beijing 100029,China;College of Earth and Planetary Sciences,University of Chinese Academy of Sciences,Beijing 100049,China;GeoZentrum Nordba yern,Universitat Erlangen,Schlossgarten 5a,91054 Erlangen,Germany)

机构地区：[1]中国科学院地质与地球物理研究所,北京100029 [2]中国科学院地球科学研究院,北京100029 [3]中国科学院大学,北京100049 [4]Geo Zentrum Nordbayern,Universität Erlangen,Schlossgarten 5a91054 Erlangen,Germany

出　　处：《地质学报》2024年第3期758-782,共25页Acta Geologica Sinica

基　　金：国家重点研发计划项目(编号2018YFA0702700);国家自然科学基金项目(编号42122011、42172234);中国科学院地质与地球物理研究所重点部署项目(编号IGGCAS-202204)资助的成果。

摘　　要：俯冲带是地球上岩浆活动、高压—超高压变质作用、中深源地震、壳幔物质交换、元素循环和铜金大规模成矿的集中发生场所。富水流体不仅调控了这些地质作用,而且也深刻影响了全球C、S等挥发分的循环。当蚀变大洋岩石圈及上覆沉积物进入俯冲带中深部(15~300 km),伴随由葡萄石-绿纤石相至超高压榴辉岩相的递进变质作用,含水矿物在不同深度的分解造成流体释放为一连续过程。除极端高地温梯度环境之外,大多数俯冲带洋壳释放的流体为富水流体。但,俯冲带不同深度所产生的流体特征有明显差异。出露于全球造山带的高压—超高压变质地体保存了分凝体、脉体、水压致裂角砾岩等流体作用的有力证据,绿辉石、石榴子石、绿帘石等矿物中原生流体包裹体为流体的直接记录。在俯冲带中等深度(<65 km),流体是溶质含量很低的含卤化物水溶液,可含CO_(3)^(2-)、SO_(4)^(2-)、HS^(-)等组分,其所含Si、Al、Ca、Mg、Fe、Na主量元素溶质相当于海水中固化物量的2~3倍,并具大离子亲石元素(LILE)、轻元素(B、Li)富集和高场强元素(HFSE)亏损的特点。当深度≥65 km时,流体转化为类似于超临界性质的溶液,含CH_(4)、C_(2)H_(6)、H_(2)S等挥发分,其所含主量元素溶质显著增加,微量元素除LILE等外,还负载相当量的HFSE和过渡族成矿元素。俯冲带65~100 km深度,为富水流体向超临界流体转变的区间。这种流体具有“亚超临界”性质,发生了氧化还原性质和元素溶解能力的渐变,并伴随硬柱石和角闪石的最终耗尽。高压变质岩石及相关脉体的O、Sr、Nd和金属同位素示踪研究表明俯冲带流体的源区多样,有蚀变基性洋壳、地幔橄榄岩和沉积物,并保存了海底热液蚀变作用的印迹。流体以脉冲方式沿网络状裂隙呈隧道式运移和传输,规模可达千米级,时间尺度在数月至数百年。目前通过高压—�The oceanic subduction zone is the locality where the magmatic activity,the high-to ultra-high-pressure metamorphism,the intermediate-depth earthquake,mass transfer between crust and mantle,the element recycling and the large-scale mineralization of copper and gold occur concentratedly on the earth.The H_2O-rich fluid not only controls these geological processes but also deeply influences the global recycling of volatiles such as carbon,sulfur and etc.After the altered oceanic lithosphere and the overlying sediments are subducted into the intermediate to the deep depth to a subduction zone(15~300 km),the fluid is continuously released by the breakdown of hydrous minerals at different depths,accompanied by the prograde metamorphism from the prehnite-pumpellyite facies to ultra-high-pressure eclogite facies.The fluid released by the subducted oceanic crust is mainly aqueous in most subduction zones,except in an ultra-high geothermal environment.However,the characteristics of fluids obviously vary with the depth at which the fluid is generated.The high-pressure to ultra-high-pressure terranes exposed in global orogens have preserved robust evidence of the fluid activity,such as segregations,veins,hydro-breccias and etc.The primary fluid inclusion entrapped in omphacite,garnet,epidote and other minerals is a direct record of fluids.This fluid is a type of chloride-bearing dilute aqueous solution containing the components,such as CO_3~(2-),SO_4~(2-),HS~- and etc.at the intermediate depth(<65 km) in a subduction zone.Furthermore,the major element solute(Si,Al,Ca,Mg,Fe,Na) content of fluids has two to three times the total dissolved solids of seawater and the trace element concentration displays the enrichment of large ion lithophileelements(LILEs) and light elements(B and Li),and the depletion of high field strength elements(HFSEs).Moreover,the fluid will change to the volatile(CH_4,C_2H_6,H_(2S) and etc.)-bearing solution with a character resembling the supercritical fluid when the subduction depth is over 65 km.The c

关 键 词：俯冲带流体 地质证据 流体相性质 化学成分 C-S循环 

分 类 号：P588.3[天文地球—岩石学] P618.2[天文地球—地质学]