内蒙古苏尼特左旗纬向推覆构造的发现及地质意义

THE LATITUDINAL NAPPE STRUCTURE IN THE SUNITEZUOQI OF INNER MONGOLIA

内蒙古苏尼特左旗中部吐哈默—哈拉干—交其尔—线发现有一条呈纬向延伸达６０余公里的推覆构造带。中晚元古代浅变质的绿片岩系自南向北以低角度辗掩于晚古生代花岗岩基之上。推覆构造上盘变质岩中同斜倒转褶皱发育，轴面向北倾倒，伴有一组向南倾斜的叠瓦式冲断面；下盘见有较宽的韧性剪切带；还发现有一系列飞来峰与构造窗沿推覆构造带分布，推测推覆距离在２０ｋｍ以上。这一构造的发现为纬向挤压构造带的存在提供了有力佐证，并显示了本区古生代末期以来岩壳沿经线方向的巨大缩减。

long the line connecting Tuhamohalagan and Jiaoqier, in the central left Sunite Banner of the Inner Mongolia Autonomous Region, the authors have found a latitudinal nappe zone extending for some 60km. Within the belt,the mid-late Proterozoic(epimetamorphic) green-schists were ovethrust from south to north onto the late Paleozoic granitic batholith at a low angle. On the hanging wall of the nappe (thrust),isoclinal folds are developed with the axial planes inclined to the north in association with imbricated thrusts dipping to the south. In the foot wall,there exist rather wide ductile shear zones. Also,a set of structural windows and klippen are distributed along the zone. The distance of the dislpacement is estimated at about more than 20km. This discovery provides strong evidence for the existence of a latitudinal compressed belt, and shows a considerable shortening of the crust in the meridional direction since the end of Paleozoic.