阿尔泰山脉南部线性花岗岩锆石SHRIMP U-Pb定年及其地质意义

Zircon SHRIMP U-Pb dating of two linear granite plutons in southern Altay Mountains and its tectonic implications

在阿尔泰山脉南部发育长轴呈NW-SE走向的小型线性花岗岩,它们的围岩分别为遭受强烈左行韧性剪切变形的泥盆纪和石炭纪火山沉积岩系。构造变形特征显示,这些线性花岗岩是与该区左行韧性剪切变形同时侵位的。本文报道了对采自其中的阿勒泰南黑云母花岗岩和沙尔布拉克南二云母花岗岩样品的锆石进行SHRIMPU-Pb定年的研究结果,根据地质、岩石学和构造变形等方面的特征和锆石阴极发光图像特征,笔者把沙尔布拉克南二云母花岗岩的(275.1±1.7)Ma年龄解释为该岩体的侵位时代,据此推测该区左行韧性剪切作用可能开始于275Ma前后。结合已有资料,还对阿尔泰山脉南部二叠纪的构造演化进行了初步讨论。

In southern Altay Mountains, some NW-SE striking small linear granite plutons are exposed, which were intruded into Devonian and Early Carboniferous volcano-sedimentary sequences that had undergone intense sinistral ductile shearing. Structural deformation of these granites implies that their intrusion occurred simultaneously with shearing deformation. This paper describes SHRIMP dating data of zircons from two of these granites, namely the southern Altay biotite granite body and the southern Shaerbulake two-mica granite body. Zircons form the southern Shaerbulake intrusive body yield an apparent ^206Pb/^238U age of （275.1±1.7） Ma, which is interpreted as the intrusive age of the granite pluton, as evidenced by geological, petrological and deformational characteristics of the granite plutons and related zircon CL images. Based on the new dating data, the authors infer that the sinistral ductile shear deformation of Erqis faulted zone and southern Altay Mountains probably occurred posterior to 275 Ma. In combination with available data, this paper deals briefly with the Permian tectonic evolution in southern Altay Mountains.