大兴安岭北段新巴尔虎右旗韧性剪切带的发现及其地质意义

The discovery of XinBarag Right Banner ductile shear zone in northern Da Hinggan Mountains and its geological implications

大兴安岭北段新发现一条韧性剪切带--新巴尔虎右旗韧性剪切带。根据野外露头观测,该韧性剪切带为左行-逆断层性质。韧性剪切带内变形的最年轻地质体为早三叠世花岗闪长岩,其被侏罗系覆盖,且下侏罗统柴河组未发生韧性变形。通过SHRIMP锆石U-Pb测年,得出早三叠世花岗闪长岩的年龄加权平均值为249.3±4.1 Ma,结合野外地质关系,将新巴尔虎右旗韧性剪切带变形时代归属于中-晚三叠世。根据区域构造演化分析,认为其形成于蒙古-鄂霍茨克洋三叠纪晚期向额尔古纳地块南向俯冲的活动大陆边缘构造背景。通过区域韧性断裂对比,认为新巴尔虎右旗韧性剪切带为额尔古纳河-阿龙山NE向韧性变形域的南部延伸。新巴尔虎右旗韧性剪切带的发现为研究区域韧性变形构造及兴蒙造山带构造演化提供了基础资料。

The XinBarag Right Banner ductile shear zone was firstly found in the western part of northern Da Hinggan Mountains.According to the outcrop, the ductile shear zone should be an overthrust-sinistral strike slip.The latest geological body in the ductile shear zone is Early Triassic granodiorite and its southeast part is covered by Jurassic strata including the undeformed Early Jurassic Chaihe Formation.SHRIMP zircon U-Pb dating shows that the weighted age of the Early Triassic granodiorite is 249.3±4.1 Ma.Integrated with the outcrop geological characteristics of the study area, the authors hold that this large-scale ductile shear zone was formed under an active continental margin setting of the Mongolia-Okhotsk Ocean which subducted southward to the Eergu’Na Block during the Late-Middle Triassic period.A comprehensive analysis of the regional ductile faults shows that the XinBarag Right Banner ductile shear zone is the southward extension of the NE-trending Eergu’Na River-ALongshan ductile shear zone, and this new discovery provides basic data for the study of the regional ductile deformation structure and tectonic evolution in Xing’an-Mongolian Orogenic Belt.