西藏尼木变质岩特征及变质温压条件  

Characteristics and pressure-temperature conditions of Nimu metamorphic rocks, Tibet.

作　　者：孙凯[1,2] 周肃[1] 赵志丹[1] 张琳琳[1] 刘栋[1] 

机构地区：[1]中国地质大学地质过程与矿产资源国家重点实验室,北京100083 [2]核资源与环境教育部重点实验室,东华理工大学,南昌330013

出　　处：《岩石学报》2011年第12期3718-3726,共9页Acta Petrologica Sinica

基　　金：国家973项目(2011CB403100、2009CB421000);国家自然科学基金项目(40572048、40830317、40873023)联合资助

摘　　要：出露于雅鲁藏布江缝合带北侧尼木县的变质岩主要由石榴黑云片麻岩和黑云斜长角闪角岩组成。研究表明岩石变质程度达到角闪角岩相-辉石角岩相;石榴子石变斑晶具有生长环带,角闪石均为钙质角闪石,黑云母大多为铁质黑云母和铁叶云母,长石多为更长石和中长石,少量为正长石。利用石榴子石-黑云母温度计、石榴子石-黑云母-斜长石-石英压力计和角闪石-斜长石温度及压力计计算获得石榴黑云片麻岩和黑云斜长角闪角岩的变质温度分别为619～661℃,695～702℃,压力范围分别为1.86～1.94kbar和3.69～4.56kbar。野外和室内研究认为岩石原岩为冈底斯带南缘叶巴组火山岩及其上部沉积岩,岩石经历了高温低压的接触变质作用。结合已有冈底斯带陆缘岩浆活动特征,对变质岩的形成环境和过程进行了反演。The Nimu metamorphic rocks are mainly composed of garnet biotite gneiss and biotite-plagioclase hornblende hornfels, which are exposed on the north side of Yarlung suture zone, southern Tibet. Our studies show that the rocks have metamorphosed to hornblende hornfels facies-pyroxene hornfels facies; garnet porphyroblasts with growth zonation, amphiboles are calcic amphiboles, most of the biotites are ferrobiotites and siderophyllites, most of the feldspars are oligoclases and andesine, with a small amount of orthoclases. Calculations based on garnet-biotite thermometer, garnet-biotite-plagioclase-quartz geobarometry and plagioclase-hornblende thermobarometry suggest metamorphic temperature of 619~661℃ and 695~702℃, and pressure of 1.86~1.94kbar and 3.69~4.56kbar for biotite gneiss and biotite-plagioclase hornblende hornfels. Results of both field and laboratory studies indicate that the protolith were the Yeba volcanic rocks and the upper sedimentary rocks in the southern margin of the Gangdese, which underwent high-temperature and low-pressure contact metamorphism. Furthermore, we retrieved the formation of metamorphic rocks by combining with the characteristics of Gangdese continental margin magmatic activities.

关 键 词：变质岩 温压条件 尼木 西藏 

分 类 号：P588.345[天文地球—岩石学]