狼山地区叠布斯格岩群变形研究及其构造意义

Deformation study of the Diebusige complex in the Langshan area and its tectonic implications

阿拉善东北缘狼山地区的叠布斯格岩群(杂岩)作为阿拉善地块前寒武纪基底之一,主要出露有条痕状黑云斜长片麻岩、斜长角闪片麻岩及透镜状斜长角闪岩,夹透辉石大理岩和磁铁石英岩等。本次研究通过构造解析与填图,系统分析了狼山地区叠布斯格岩群构造变形样式、变形期次与时限。研究显示,古元古代变质杂岩叠布斯格岩群至少记录了四期变形,第一期变形主要表现为片麻岩早期面理的枢纽近E- W向褶皱变形(D1),轴面倾向NNW,应与华北克拉通统一化过程有关;第二期为近N- S向褶皱变形(D2),褶皱枢纽向NNE倾伏,古生代时期阿拉善地块与华北板块增生拼合,在阿拉善地块东缘产生近东西向挤压,在狼山地区形成枢纽近N- S向的褶皱;第三期变形为NE向巴彦乌拉山-狼山断裂带的左行韧性走滑剪切作用(D3),中-晚三叠世扬子板块与华北板块碰撞造成的阿拉善地块相对华北板块沿巴彦乌拉山-狼山断裂发生左行剪切运动,使早期构造发生逆时针旋转,是狼山地区一期重要的变形事件;第四期为NE- SW向紧闭褶皱(D4),褶皱轴面多倾向NW,晚侏罗世来自古太平洋的俯冲和鄂霍茨克洋的闭合产生的NW- SE向挤压,使叠布斯格岩群片麻岩及后期糜棱岩化花岗岩再次发生枢纽NE- SW向褶皱变形。

The Diebusige complex in the Langshan area, as one of the Precambrian basements of the Alxa Block, consists of streaky biotite plagioclase gneiss, plagioclase hornblende gneiss and lenticular amphibolite, with diopside marble and magnetite quartzite intercalations. The basement rocks experienced and recorded the multistage deformation since Proterozoic. Through geological mapping and structural analysis, the study analyzed deformation modes, stages and ages of structural deformation of the Diebusige complex in the Langshan area. Four deformation stages have been identified as follow.(1) The first is characterized by near hinge E-W-striking deformation (D l) of early foliation of gneiss with the axial plane clipping towards NNW in response to the unification process of the North China Craton (NCC) in the Paleoproterozoic.(2) the second is by near N-S-striking folding deformation (D2) with NNE-striking folding hinge in response to eastwards movement of the Alxa Block during the Devonian-Carboniferous.(3) D3 deformation represents NE-SW striking ductile sinistral strike-slip shearing movement caused by the clockwise rotation of the Alxa block due to the collision between the NCC and the Yangtze Craton during the Triassic;the previous deformations were rotated counterclockwise by this crucial event in the Langshan area.(4) D4 deformation is NE-SW-striking folds with axial planes mostly dipping toward SE, which overprinted the previous fabrics in gneiss and mylonite, D4 fabrics were formed by NW-SE striking compression from the subduction of the Paleo-Pacific and the closure of the Mongolia-Okhotsk Ocean during the Late Jurassic.