鲜水河断裂带中南段同位素年代学及其地质意义

Isotope Chronology for Syntectonic Granite and Ductile Shear Zone in the Xianshuihe Fracture Zone and Its Geological Implication

鲜水河断裂带是青藏高原东部一条现今仍在活动的大型平移型剪切带,其形成可追溯至印支期扬子西缘在拉伸环境下形成的一系列陆缘裂谷。渐新世以来,伴随鲜水河断裂带大型左行平移剪切活动,导致地壳局部熔融和同构造花岗岩侵位。笔者对鲜水河断裂带中南段塔公-康定一线的折多山同构造花岗岩及其内部的韧性剪切带进行同位素年代学研究,分析认为鲜水河断裂带中南段在渐新世以来至少经历了三期构造-热事件,记录了三次强烈剪切作用,依次为32~27Ma、18~15Ma和5.5~3Ma。

The Xianshuihe fracture zone is an active major displacement shear one.It is composed of a series of epicontinental rifts formed on the western margin of the Yangtze plate in the Indo-Sinian epoch.In the Oligocene,the Zheduoshan syntectonic granite intrusive was emplaced due to partial melting of the Earth's crust resulting from left-lateral translation shear activity of the Xianshuihe fracture zone.Isotope chronology study of the syntectonic granite and ductile shear zone in the Lhakang-Kangding-Zheduoshan belt indicates that the Xianshuihe fracture zone has undergone at least three tectonic-thermal events and three strong shearing during 32~27 Ma,18~15 Ma and 5.5~3 Ma since the Oligocene.