超高压榴辉岩-脉体体系成因和俯冲带变质流体演化  

Genesis of UHP Eclogite-Vein System and Metamorphic Fluid Evolution in Subduction Zones

作　　者：郭顺[1,2] 唐盼 陈意[1,2] Guo Shun;Tang Pan;Chen Yi(State Key Laboratory of Lithospheric Evolution,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China;CAS Center for Excellence in Tibetan Plateau Earth Sciences,Beijing 100101,China;University of Chinese Academy of Sciences,Beijing 100049,China)

机构地区：[1]中国科学院地质与地球物理研究所岩石圈演化国家重点实验室,北京100029 [2]中国科学院青藏高原地球科学卓越创新中心,北京100101 [3]中国科学院大学,北京100049

出　　处：《地球科学》2019年第12期4072-4080,共9页Earth Science

基　　金：国家重点基础研究发展计划项目(No.2015CB856103);国家自然科学基金项目(No.41672059);中国科学院青年创新促进会项目(No.2017090)

摘　　要：超高压岩石-脉体体系是认识俯冲带流体性质和行为的天然实验室.通过总结大别超高压变质带3个榴辉岩(角闪岩)-脉体体系的研究成果,探讨了大陆俯冲带变质流体的溶解-结晶过程和氧逸度变化规律以及流体对轻元素硼的迁移过程.对榴辉岩-复合高压脉体的研究发现超高压流体通过溶解矿物富集溶质组分,流体随后经历3期结晶过程,分别形成绿辉石-绿帘石脉、绿帘石-石英脉和蓝晶石-绿帘石-石英脉.绿帘石La、Cr和δEu值是判断结晶次序的关键指标.对榴辉岩-角闪岩-低压脉体研究表明大陆俯冲带低压变质流体的氧逸度明显高于高压-超高压变质流体.高氧逸度条件也导致一些反常矿物(如退变金红石)的生长.对含电气石榴辉岩-脉体研究揭示变质碳酸盐岩是大陆俯冲板片中重硼同位素的重要储库,其在汇聚板块边界的脱硼作用显著影响深部硼循环.上述研究成果为理解俯冲带变质流体演化和物质循环提供重要科学依据.The system of ultrahigh-pressure(UHP)metamorphic rocks and veins is a natural laboratory to understand the nature and behavior of metamorphic fluids in subduction zones.This paper presents a review of the studies on three suits of eclogite(amphibolite)-vein system from the Dabie UHP terrane in order to discuss the dissolution and crystallization processes of subduction-zone metamorphic fluids,variation in fluid oxygen fugacity(fO2),and fluid-assisted boron(B)transfer.The study of UHP eclogites and enclosed multiple veins indicates that UHP fluid transferred materials by the dissolution of various components.This solute-rich fluid then experienced a three-stage crystallization process,which produced omphacite-epidote vein,epidote-quartz vein,and kyanite-epidote-quartz vein.La and Cr contents andδEu values of vein epidote are critical geochemical indicators for assessing the precipitating sequence of veins.The investigation on an eclogite-amphibolite-vein system indicates that low-pressure fluids have much higher fO2 conditions than high-pressure(HP)and UHP fluids in continental subduction zones.Such high fO2 conditions also lead to the growth of some unusual minerals(e.g.,low pressure retrograde rutile).The investigation on tourmaline-bearing eclogite-vein system indicates that metacarbonate is an important reservoir of isotopically heavy boron(B)in subducted continental crust,and the release of B of metacarbonate at convergent boundary exerts a significant influence on deep B cycling.The studies above provide important insights into the fluid evolution and material cycling in subduction zones.

关 键 词：超高压榴辉岩 脉体 俯冲带流体 结晶 氧逸度 岩石学 元素迁移 

分 类 号：P595[天文地球—地球化学]