华南晚古生代末超高温变质作用:以十万大山花岗岩中麻粒岩包体为例  

Late Paleozoic ultrahigh-temperature metamorphism in South China: A case study of granulite enclaves in the Shiwandashan granites

作　　者：赵亮[1,2] 郭锋[2] 范蔚茗[2] 李超文[2] 覃小锋[3] 李红霞[2] 

机构地区：[1]中国科学院南海海洋研究所边缘海重点实验室,广州510301 [2]中国科学院广州地球化学研究所同位素地球化学国家重点实验室,广州510640 [3]中国地质科学院矿产资源研究所,北京100037

出　　处：《岩石学报》2011年第6期1707-1720,共14页Acta Petrologica Sinica

基　　金：中国科学院知识创新工程方向性项目(KZCX2-YW-Q08-3-7;KZCX1-YW-15-2)资助

摘　　要：广西东南部大容山-十万大山地区过铝质(S型)花岗岩中包含丰富的副变质麻粒岩包体。部分麻粒岩包体保留了尖晶石+石英、斜方辉石+夕线石±石英等超高温变质矿物组合,指示这些麻粒岩包体曾经历了超高温变质作用。矿物温压估算结果显示:峰期温压条件为7.5～8.0kbar,950～1000℃,峰后退变质温压条件为3.2～3.7kbar,790～820℃。矿物共生组合、变质反应结构以及温压条件估算表明,大容山-十万大山花岗岩中的麻粒岩包体经历了从单相夕线石的稳定域,到尖晶石+石英和紫苏辉石+夕线石±石英的矿物共生组合的稳定域,最后发生了近等温降压退变质作用,形成了紫苏辉石+斜长石和紫苏辉石+堇青石冠状体后成合晶,构成了典型的顺时针P-T演化轨迹,反映区域当时经历了造山过程中地壳增厚,而后折返快速抬升到地表的动力学过程。The Darongshan-Shiwandashan Indo-Sinian S-type granites from SE Guangxi Province contain abundant metasedimentary granulite enclaves.The mineral assemblages of spinel＋quartz and orthopyroxene＋sillimanite±quartz in some granulites indicated ultrahigh-temperature metamorphism in the region.Using garnet-orthopyroxene geothermobarometry,the estimated P-T conditions for peak metamorphism are： P=7.5~8.0kbar and T=950~1000℃,and P=3.2~3.7kbar and T=790~820℃ for retrograde stage.Combined mineral assemblages and metamorphic reaction textures with P-T calculation,the granulite enclaves in the Shiwandashan area experienced a three-stage metamorphic history.The early prograde metamorphism extended into the stable field of sillimanite;The peak stage of the ultrahigh-temperature metamorphism was characterized by the mineral assemblages of spinel＋quartz and orthopyroxene＋sillimanite±quartz,and the retrograde metamorphism was marked by formation of orthopyroxene＋cordierite and/or orthopyroxene＋plagioclase symplectites and coronas around garnet,suggesting a near-isothermal decompression path.This clockwise P-T path in granulites was consistent with the Late Paleozoic to Early Mesozoic crustal evolution,including initial crustal thickening,subsequent rapid exhumation and cooling and remelting.

关 键 词：超高温变质作用 麻粒岩包体 十万大山 华南 

分 类 号：P588.34[天文地球—岩石学]