藏南南木林县多角花岗闪长岩锆石U-Pb定年及其地质意义

Zircon U-Pb Dating and Geological implications for the Granodiorites from the Duojiao Region in Nanmulin County,South Tibet

冈底斯带岩浆岩作为地球深部的“探针”,记录了从新特提斯洋俯冲到印度—欧亚板块碰撞整个过程的信息,因此研究这些岩浆岩对帮助我们理解青藏高原的形成与演化具有重要意义。位于冈底斯中段的南木林县多角花岗闪长岩,前人对其年代学研究差距较大,从34.6Ma(K-Ar法)到18Ma(锆石全溶U-Pb定年法),因此本文利用SHRIMP对这一花岗闪长岩的锆石开展原位定年,获得其侵位结晶年龄为49.0Ma,属于同碰撞期岩浆岩。同时,结合前人报道的约50Ma的板片断离事件,本文认为多角花岗闪长岩形成于相同的地球动力学背景。

As the probe of the deep earth,the Gangdese intrusive rocks recorded the information of the subduction of the Neo-Tethyan slab as well as the Indo-Asia collision.Therefore,doing research on these rocks would help us to build a better understanding of the evolution of the Tibet plateau.However,the previous geochronological studies in terms of different methods K-Ar geochronology and zircon solution dating method on the Duojiao granodiorite in Nanmulin county,south Tibet,showed distinct ages,ranging from 34.6 Ma to 18 Ma,which hindered the further research.Consequently,we conducted zircon SHRIMP U-Pb dating on the Duojiao granodiorite in this paper and obtain an age of 49.0 Ma,indicating that these rocks were formed during syn-collisional period.In addition,based on the previous studies that indicated a slab breakoff event at ca.50 Ma,we infer that the genesis of the Duojiao granodiorite are relevant to this geodynamic process.