昌都地块宁多岩群形成时代研究：北羌塘基底存在的证据  

Research on the formation age of Ningduo Rock Group in Changdu Block:Evidence for the existence of basement in the North Qiangtang

作　　者：何世平[1] 李荣社[1] 王超[1] 辜平阳[1] 于浦生[1] 时超[1] 查显锋[1] 

机构地区：[1]中国地质调查局西安地质调查中心西安地质矿产研究所,陕西西安710054

出　　处：《地学前缘》2013年第5期15-24,共10页Earth Science Frontiers

基　　金：中国地质调查局项目“青藏高原前寒武纪地质、古生代构造-古地理综合研究”(1212010610102)

摘　　要：位于青藏高原腹地的羌塘地区是否存在前寒武纪基底备受关注,宁多岩群作为北羌塘昌都地块的变质岩系之一,其形成时代的有效限定便显得至关重要。通过高精度的LA-ICP-MS锆石微区原位U-Pb同位素测年,获得青海玉树县小苏莽一带宁多岩群黑云斜长片麻岩(副变质岩)的最新蚀源区年龄为(1 044±30)Ma,代表宁多岩群形成时代的下限;侵入宁多岩群的片麻状黑云母花岗岩(古侵入体)的形成年龄为(991±4)Ma,可代表宁多岩群形成时代的上限。将小苏莽一带宁多岩群的形成时代限定为(1 044±30)^(991±4)Ma,相当于中元古代末—新元古代初。宁多岩群黑云斜长片麻岩还出现了530Ma的次峰值年龄,可能代表泛非运动在羌塘地区的年龄信息。It is closely concerned that whether pre-Cambrian basement exist in Qiangtang area, Qinghai-Tibet Plateau. The formation age of Ningduo Rock Group that belongs to one of the metamorphic rocks of the Changdu Block shows great significance in resolving this question. The age 1044-30 Ma of the youngest erosion provenance is obtained by LA-ICP-MS zircon dating in biotite plagioclase gneiss （para metamorphic rock） from the Ningduo Rock Group in Xiaosumang area, Yushu County, Qinghai Province. This age repre- sents the lower limit formation age of the Ningduo Rock Group. Meanwhile, the crystallization age 990. 5 - 3.7 Ma of the gneissie biotite granite that intruded into the Ningduo Rock may represents the upper limit formation age of the Ningduo Rock Group. The formation age of the Ningduo Rock Group can be constrained between 1044 - 30 and 990.5 -3.7 Ma （Late Mesoproterozoic to Early Neoproterozoic）. In addition, there is a second peak age of 530 Ma of the biotite plagioclase gneiss of the Ningduo Rock Group, which may represent the age information of Pan-African Movement in Qiangtang area.

关 键 词：昌都地块 小苏莽 宁多岩群 锆石U-PB年代学 中-新元古代 

分 类 号：P588.3[天文地球—岩石学]