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孙贺,肖益林,顾海欧,王洋洋,王晓霞. 2018. 北大别铙钹寨榴辉岩的多期变质与熔流体交代作用. 岩石学报, 34(12): 3497-3508
北大别铙钹寨榴辉岩的多期变质与熔流体交代作用
作者单位
孙贺 合肥工业大学资源与环境工程学院, 合肥 230009 
肖益林 中国科学院壳幔物质与环境重点实验室, 中国科学技术大学地球和空间科学学院, 合肥 230026 
顾海欧 合肥工业大学资源与环境工程学院, 合肥 230009 
王洋洋 中国科学院壳幔物质与环境重点实验室, 中国科学技术大学地球和空间科学学院, 合肥 230026 
王晓霞 中国科学院壳幔物质与环境重点实验室, 中国科学技术大学地球和空间科学学院, 合肥 230026 
基金项目:本文受国家自然科学基金项目(41473033、41673031、41603005、41504042)资助.
摘要:
      铙钹寨镁铁-超镁铁质岩体被认为是北大别地体下方岩石圈地幔的碎块,并随着三叠纪的华北和华南的大陆碰撞而一同经历了深俯冲和折返过程,对其进行详细的研究可以为我们更好地理解陆-陆碰撞过程中的壳幔相互作用、物质迁移、多期变质和熔流体交代等地球动力学过程提供信息。本文应用电子探针和LA-ICP-MS对铙钹寨榴辉岩进行了系统的元素环带、出溶结构和熔体包裹体研究,揭示出该岩体至少经历了三期变质事件,两期矿物出溶和两期熔体交代过程。峰期变质矿物组合为含金红石出溶体的石榴石核部+其内包裹的绿辉石,石榴石中金红石±磷灰石矿物出溶体和绿辉石包裹体中的金红石±石英±磷灰石出溶片晶指示该岩体确定经历过超高压变质作用,流体活动以高盐度的卤水±氮气的流体为主,峰期变质作用过程中无熔体活动痕迹。高压麻粒岩相变质矿物组合为Ⅱ期石榴石+紫苏辉石+基质具有出溶石英片晶结构的富Na单斜辉石,流体活动以CO2流体为主,熔体包裹体记录了在折返初期,高压麻粒岩相变质之前存在一期小规模的硫化物熔体活动。晚期角闪岩相退变质矿物组合为透辉石+角闪石+长石,流体活动以低盐度水溶液为主,并伴随着一期壳源的硅酸盐熔体交代事件。根据矿物环带、出溶结构和熔体包裹体化学组合及分布特征,并结合前人的研究成果,我们得出了该岩体较为完整的变质演化和熔-流体交代的P-T-t-E/F/M轨迹。
英文摘要:
      The Raobazhai ultramafic massif, which exposed in the North Dabie, is thought to be a segment of subcontinental lithospheric mantle that was subducted and exhumed during the Triassic collision. Study on these ultramafic rocks can provides intriguing information on geodynamic processes and material fluxes between mantle and crust during continent-continent collision. In this study, using the EMPA and LA-ICP-MS technique, we investigate in detail the Raobazhai eclogite. On the basis of mineral zonations, exsolution texture and melt inclusion studies, at least three metamorphic events, two-stages of exsolution processes and two pulses of melt infiltrations can be identified. Peak metamorphic mineral assemblages are the cores of porphyroblastic garnets and omphacite inclusions therein, the needle like rutile±apatite exsolutions in the cores of porphyroblastic garnets and the rutile±quartz±apatite exsolution lamella in omphacite inclusions indicate the Raobazhai eclogite has experienced ultra-high-pressure metamorphism. Fluid inclusions indicate high-salinity brine+N2 rich fluid activity during peak metamorphism. Granulite facies metamorphic mineral assemblages are Grt Ⅱ+hypersthene+matrix Na-rich diopside with quartz exsolution lamella. Fluid and melt inclusions indicate CO2 rich fluid and sulfide melt metasomatism. Late amphibolite facies metamorphic mineral assemblages are matrix diopside+amphibole+plagioclase, fluid and melt activity was dominated by low salinity water and crustal derived silicate melt. Combined the present finding and the previous fluid inclusion and geochronology studies, we can outline the entire subduction and exhumation history of the studied eclogite body with detailed metamorphic evolution and fluid/melt metasomatism information integrated in the P-T-t-E/F/M (Pressure-Temperature-time-Exsolution/Fluid/Melt) diagram.
关键词:榴辉岩  出溶体  熔体包裹体  矿物环带  熔/流体交代
投稿时间:2018-02-14  修订日期:2018-07-13
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主办单位:中国矿物岩石地球化学学会
印刷版(Print): ISSN 1000-0569 网络版(Online): ISSN 2095-8927
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