论文部分内容阅读
念青唐古拉花岗岩体位于西藏当雄县境内,是拉萨地块中部出露的巨型侵入岩岩基,其面积超过1500km2,以大面积出露的黑云母二长花岗岩为主体。本文分别应用单矿物K-Ar法、全岩-单矿物Rb-Sr等时线法和高灵敏度高分辨率离子探针法(SHRIMP-)对念青唐古拉岩体不同位置上的代表性岩石样品进行同位素测年,得到中细粒黑云母二长花岗岩的K-Ar年龄为8.49±0.14Ma,Rb-Sr等时线年龄为8.07±0.35Ma和8.70±1.40Ma,SHRIMPU-Pb年龄为18.3±0.4Ma;中粗粒黑云母二长花岗岩的K-Ar年龄为9.80±0.35Ma,Rb-Sr等时线年龄为9.33±0.41Ma,SHRIMPU-Pb年龄为11.01±0.24Ma。不同方法测年结果均表明念青唐古拉花岗岩形成于中新世,属拉萨地块内部最年轻的巨型花岗岩岩基,其侵位结晶时代处于青藏高原地壳由南北向挤压增厚向东西向伸展的转变时期,岩浆来源于地壳局部熔融,属后碰撞构造-岩浆活动的产物。
The Nyainqentanglha granite body is located in the territory of Damxung County, Tibet. It is a massive intrusive rock basement exposed in the central part of Lhasa massif. Its area exceeds 1500 km 2 and is dominated by biotite monzogranite that is exposed in a large area. In this paper, the representative rock samples from different positions of the Nyainqentanglt rock mass, such as single mineral K-Ar method, all rock-single mineral Rb-Sr isochron method and high sensitivity and high resolution ion probe method (SHRIMP- The K-Ar ages of medium-fine biotite monzogranites were 8.49 ± 0.14Ma, the Rb-Sr isochrones were 8.07 ± 0.35Ma and 8.70 ± 1.40Ma, and the SHRIMPU-Pb age was 18.3 ± 0.4Ma. The K-Ar age of medium-grained biotite monzogranite is 9.80 ± 0.35Ma, the age of Rb-Sr is 9.33 ± 0.41Ma, and the SHRIMPU-Pb age is 11.01 ± 0.24Ma. The dating results of different methods indicate that the Nyainqentanglha granite was formed in the Miocene stage and belongs to the youngest giant granite basement within the Lhasa block. During the emplacement and crystallization age, the crust in the Qinghai-Tibet Plateau stretches from north to south to eastern and western extensometers During the transitional period, the magma originated from local melting of the crust and is a product of post-collision tectono-magmatic activity.