ABSTRACT

Intracontinental deformation is an inseparable element of the evolutionary history of orogenic belts. It can reactivate and intensely modify the structures of previous orogenic belts due to remote effects of plate margin orogenesis. As an important part of the Phanerozoic Central Asian Orogenic Belt (CAOB), the Alxa Block and its vicinity experienced multistage intracontinental deformation during the Mesozoic and Cenozoic and became a representative region to study remote effects from plate margins. Both the previous structures of the CAOB and continuous accretion to the Eurasian continent from different directions controlled and affected the Mesozoic evolution of the Alxa Block. However, mantle loading can’t pertinently explain the geological phenomena alone. In the Late Triassic, the Alxa Block was deformed by large-scale left-lateral shearing along largely northeast-southwest-trending faults and rotated anticlockwise caused by the collision between the North China Craton and Yangtze Craton and the northward movement of the North China Craton. In the Late Jurassic, the low-angle westward subduction of the Paleo-Pacific Ocean beneath the Eurasian Plate, the closure of the Mongol-Okhotsk Ocean to the north and/or the Lhasa-Qiangtang collision to the south combined to deform the Alxa Block from different directions, forming contraction structures with various strikes and invert previous extensional basins. In the Late Cretaceous, the Eurasian Plate experienced oblique collision along its southeastern margin and the subduction of the Neo-Tethys along its southern boundary, an intraplate sinistral transpressional megashear system developed along the eastern Alxa Block, and the uplift of mountain ranges along the basin margins. The multistage Mesozoic intracontinental deformation of the Alxa Block supports the view that they are driven by stresses generated at plate boundaries largely, and controlled by previous complicated orogenic structures in the upper crust.

摘要

陆内变形是造山带演化历史不可分割的组成部分。由于板块边缘造山作用的远程影响，它可以重新激活并强烈改变先前造山带的结构。作为显生宙中亚造山带（CAOB）的重要组成部分，阿拉善地块及其附近在中、新生代经历了多期陆内变形，成为研究板块边缘远程影响的代表性区域。CAOB的前期构造和欧亚大陆不同方向的不断增生控制和影响了阿拉善地块的中生代演化。然而，单靠地幔载荷并不能中肯地解释地质现象。在三叠纪晚期，阿拉善地块在华北克拉通与扬子克拉通的碰撞和华北克拉通北移的作用下，沿主要为东北-西南走向的断裂发生大规模左旋剪切变形，逆时针旋转。晚侏罗世，欧亚板块下古太平洋低角度向西俯冲、北面蒙古-鄂霍次克洋的闭合和/或南面的拉萨-羌塘碰撞共同使阿拉善地块变形从不同的方向，形成不同走向的收缩构造，并反转先前的伸展盆地。晚白垩世，欧亚板块东南缘发生斜向碰撞，南缘发生新特提斯洋俯冲，阿拉善地块东部发育板内左旋横切巨剪系统，盆地边缘山脉隆升。阿拉善地块多期中生代陆内变形支持了其主要受板块边界应力驱动，并受上地壳先前复杂造山构造控制的观点。