藏北羌塘中部戈木日榴辉岩的岩石学、矿物学及变质作用pTt轨迹

Petrology, mineralogy and pTt path for the eclogite from central Qiangtang, northern Tibet, China

羌塘中部榴辉岩位于龙木错-双湖缝合带中段,改则县古姆乡片石山地区。榴辉岩的主要矿物成分为石榴子石、绿辉石、多硅白云母、金红石、角闪石等,围岩为石榴白云母片岩和蓝片岩,石榴白云母片岩主要由石榴子石、多硅白云母和石英构成,蓝片岩由石榴子石、角闪石(含蓝闪石)、多硅白云母等构成。岩石学和矿物学研究显示,榴辉岩主要经历了3期变质作用:①峰期榴辉岩相变质作用阶段,以石榴子石、绿辉石和多硅白云母为特征,变质温度和压力分别为500℃和2.3GPa;②绿帘角闪岩相变质作用阶段,以后期形成的冻蓝闪石、镁红闪石、绿帘石、钠长石等交代早期矿物为特征;③绿片岩相变质作用阶段,以毛发状阳起石等为特征。榴辉岩的变质演化过程代表了青藏高原北部古特提斯洋俯冲消减和冈瓦纳与劳亚大陆碰撞造山的过程。

The eclogite from central Qiangtang is located in the central part of Longmucuo–Shuanghu suture zone in Pianshishan area of Gumu Town, Gerze County. Major minerals of eclogite include garnet, omphacite, phengite, rutile and amphibole, and their sorrounding rocks are garnet phengite schist and blueschist. Garnet phengite schist is mainly composed by garnet, phengite and quartz, and blueschist is mainly composed by garnet, amphibolite and phengite. Petrology and mineralogy data suggest that the eclogite has experienced three stages of metamorphism. Stage Ⅰ： Peak eclogite metamorphism featured by Grt ＋ Omp ＋ Phen ＋ Rt, the p-T conditions of the eclogite are 500 °C and 2.3 GPa. Stage Ⅱ： Epidote-amphibolite facies metamorphism is characterized by assemblages of Bar ＋ Ab ＋ Ep of later stage alteration on the early eclogite minerals. Stage Ⅲ： Green schist facies metamorphism is featured by fibrous actinolites. The evolution of eclogite is an evidence of the subduction of Paleo-Tethys and collision between Gondwana and Laurasia in the Northern Tibetan plateau.