西藏冈底斯西部地区花岗岩锆石U-Pb年龄及其地质意义

Age of Zircon U-Pb and its Geological Significance of Granite from Western Gangdese in Tibet

对西藏冈底斯西部措勤县打加错地区粗粒二长花岗岩、中粒二长花岗岩、花岗岩进行LA-ICP-MS锆石U-Pb法定年、锆石同位素组成、主量元素测定,获得年龄值分别为(43.5±1.5)Ma、(44.2±2.6)Ma及(44.2±1.7)Ma,结合区域岩浆侵位规律,根据侵入岩地质特征、岩石学、同位素年代学、岩石化学等特征,将研究区出露的花岗岩划分为喜山早期侵入岩,属冈底斯-念青唐古拉中酸性杂岩带南亚带重要组成部分之一。其物质来源与上地壳变质泥岩的部分熔融有关,所形成的构造环境与区域构造背景息息相关,是始新世末喜马拉雅陆块同冈底斯陆块碰撞,陆-陆碰撞造山结束后相对松弛阶段的产物,构造环境同碰撞花岗岩。

The age of zircon U-Pb by LA-ICP-MS,the isotopic composition of zircon and the main elements of the coarse grained,monzonitic granite,medium grained monzonitic granite and granite are measured,which are collected from Dajiacuo region in Cuoqin county,western region of Gangdese,Tibet. The age obtained of each type are（43 ± 1. 5） Ma,（44. 2 ± 2. 6） Ma and（44. 2 ± 1. 7） Ma respectively,combining with the regularity of regional magmatic emplacement,granite exposed in this area were divided into early Himalayan volcanic intrusive rock according to the characteristics of geology,the characteristics of petrology,isotope chronology and petrochemistry. It belongs to the acid complex belt from Gangdese-nianqing tangula,one of the important parts in south of Asia. The material source has a relevant with the partial melting of the metamorphic mudstone from the crustal.The tectonic environment is closely related to regional tectonic background. It is the product of the relatively loose phase after the continent-continent collision of late Eocene Himalayan block with the Gangdese continent,tectonic environment is the same as collision granite.