蓝岭地区蓝片岩和含硬柱石多硅白云母片岩变质P-T轨迹  

Metamorphic P-T Paths of Blueschist and Lawsonite-Bearing Phengite Schist in Lanling Area,Central Qiangtang

作　　者：王仕林 杜瑾雪[1] 王根厚[1] 梁晓[1] Wang Shilin, Du Jinxue, Wang Genhou, Liang Xiao(School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, Chin)

机构地区：[1]中国地质大学地球科学与资源学院,北京100083

出　　处：《地球科学》2018年第4期1237-1252,共16页Earth Science

基　　金：国家自然科学基金项目(No.41502059);中央高校基本业务费专项资金项目(No.2652015041);中国地质调查局二级项目(No.DD20160026);大学生创新创业训练计划项目(No.201611415006)

摘　　要：羌塘中部蓝岭地区的蓝片岩呈透镜状包裹于多硅白云母片岩中.首次在多硅白云母片岩中发现的硬柱石被包裹于石榴石边部的石英颗粒中,正确厘定蓝片岩和含硬柱石多硅白云母片岩的变质P-T轨迹对进一步探讨龙木错-双湖低温高压变质带的形成与演化具有重要意义.详细的岩相学和相平衡模拟显示,蓝片岩经历了较为明显的热驰豫过程(压力峰期条件为490℃/2.4GPa、温度峰期条件为540℃/2.1GPa),而含硬柱石多硅白云母片岩却经历了相对较弱的热驰豫过程(峰期温压条件为530℃/2.2GPa).另外,蓝片岩和含硬柱石多硅白云母片岩经历了相似的近等温降压的退变质轨迹,这可能暗示着密度较大的基性蓝片岩在折返过程中是借助于大面积、低密度的含硬柱石多硅白云母片岩的浮力才得以折返至地壳层次.The blueschist is lenticularly wrapped in the lawsonite-bearing phengite schist in Lanling area,central Qiangtang.The lawsonite included in quartz,which,on its part,is enclosed in porphyroblastic garnet in the phengite schist,is discovered for the first time.Studying on the metamorphic P-T paths of the blueschist and lawsonite-bearing phengite schist is important for the further research of the formation and evolution of the Longmu Co-Shuanghu low-temperature and high-pressure metamorphic belts.The detailed petrography and phase equilibria modeling reveal that the blueschist experienced a more obvious thermal relaxation process（the peak pressure conditions are 490℃and 2.4 GPa,and the peak temperature conditions are 540℃,2.1 GPa）while the lawsonite-bearing phengite schist has barely experienced a thermal relaxation process（the peak temperature and pressure conditions are 530℃and 2.2 GPa）.The similarity of the retrograde P-Tpaths of the blueschist and lawsonite-bearing phengite schist reveals that the exhumation of the blueschist from Lanling area,central Qiangtang,may have resulted from the exhumation of the low-density lawsonite-bearing phengite schist,which carried the denser blueschist to the earth＇s crust levels.

关 键 词：青藏高原 羌塘中部 蓝岭 蓝片岩 含硬柱石多硅白云母片岩 变质P-T轨迹 岩石学 

分 类 号：P581[天文地球—岩石学]