内蒙额济纳旗霍布哈尔地区构造片岩带的发现及其构造意义

DISCOVERY OF STRUCTURAL SCHIST BELT IN HUOBUHAER AREA OF EJINAQI, INNER MONGOLIA: IMPLICATION FOR ITS TECTONIC SIGNIFICANCE

野外调查发现在靠近中蒙边界的额济纳旗霍布哈尔地区存在带状构造片岩,片理倾向南东,拉伸线理沿北东向,片岩内存在指示左行剪切的旋转碎斑系、不对称压力影等显微剪切组构。显微构造尺度上,片理结构由片理域与微片石组成,形成极易开裂的潜在破裂面。区内构造片岩是北东向韧性剪切带的组成部分,成因与韧性的剪切运动有关,经样品UY-1的LA-ICP-MS锆石U-Pb测年法测定,得到糜棱岩化的流纹斑岩年龄为286.3Ma±2.0Ma,后期侵入的闪长岩年龄为284.2Ma±2.4Ma,约束了构造片岩的形成时代为286.3Ma^284.2Ma(早二叠世)。结合区域地质资料,认为构造片岩带的形成与早二叠世阿尔金-东蒙古断裂的左行走滑剪切活动有关。

Field investigation shows that a structural schist zone occurs in Ejina Huobuhaer near the border of China and Mongolia.The schistosity in the zone dips toward the southeast with a northeast stretching lineation. Rotated porphyroclasts,pudding structures,mica fish as well as asymmetric pressure shadow indicate a sinistral shear deformation.The structural schist in the zone is composed of cleavage domain and microlithon domain and possesses easily splitted fractures.This deformation zone is actually part of the northeast trending ductile shear zone resulted from the ductile shear deformation in the area.LA-ICP-MS zircon U-Pb dating for sample UY-1 of mylonitized rhyolite porphyry yields an age of 286.3 Ma±2.0 Ma and the undeformed later intrusive diorite has an age of 284.2 Ma±2.4 Ma,indicating that the formation age of the structural schist is 286.3 Ma^284.2 Ma.It is considered that the structural schist zone is resulted from sinistral shear movement of Alty Tagh-East Mongolia fault in early Permian period.