西藏南部聂拉木地区前寒武纪结晶基底的组成及其特征

在对肉切村岩群的岩石组合、变质特点以及区域综合对比研究基础上,根据其中锆石U-Pb法年龄值686Ma、黑云母斜长变粒岩全岩Rb-Sr法年龄值796±103Ma,认为其原岩形成于新元古代,时代属震旦纪;前人划分的震旦—寒武系肉切村群,实际上是前寒武纪变质岩地层,聂拉木地区并未出露寒武纪地层。将前寒武纪地层划分为聂拉木岩群和肉切村岩群,并将聂拉木岩群划分为友谊桥岩组、曲乡岩组、康山桥混合岩和江东岩组4个构造岩石地层单元,将肉切村岩群划分为扎西宗混合岩和塔吉岭岩组两个构造岩石地层单元。

Precambrian crystalline basement in the Nyalam region,southern Xizang

The Precambrian crystalline basement arranged in the Nyalam-Qomolangma zone,southern Xizang is believed to be the most important metamorphic belt in the Himalayan orogen.In terms of lithologic association,metamorphism and regional correlation,in combination with a SHRIMP zircon U-Pb age of 686 Ma for the Rouqiecun Group Complex and a whole-rock Rb-Sr age of 796±103 Ma for the biotite-plagioclase granulite,the authors contend that their protoliths are all traced back to the Neoproterozoic,i.e.to the Sinian in age.The formerly Sinian-Cambrian Rouqiecun Group should be redefined as the Precambrian metamorphic strata.Actually,no Cambrian strata crop out in the Nyalam region.In this respect,the Precambrian strata are divided into the Nyalam and Rouqiecun Group Complexes.The former is subdivided into four tectonic-lithostratigraphic units including the Youyiqiao Formation Complex,Quxiang Formation Complex,Kangshanqiao Migmatites and Jiangdong Formation Complex,and the latter into two tectonic-stratigraphic units including Zhaxizong Migmatites and Tajiling Formation Complex.