Mesozoic intracontinental deformation of the Alxa Block in the middle part of Central Asian Orogenic Belt: A review

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.

陆内变形（intracontinental deformation）是造山带（orogenic belts）演化历史中不可或缺的组成部分。板块边缘造山作用引发的远程效应，可使先期造山带的构造系统复活并遭受强烈改造。作为显生宙（Phanerozoic）中亚造山带（Central Asian Orogenic Belt, CAOB）的重要组成部分，阿拉善地块及其邻区在中生代（Mesozoic）与新生代（Cenozoic）期间经历了多期陆内变形，成为研究板块边缘远程效应的典型区域。中亚造山带的先期构造，以及来自不同方向的对欧亚大陆的持续增生作用，共同控制并影响了阿拉善地块的中生代演化。然而仅用地幔加载作用，无法针对性地解释相关地质现象。晚三叠世时期，受华北克拉通（North China Craton）与扬子克拉通（Yangtze Craton）碰撞以及华北克拉通向北漂移的影响，阿拉善地块沿大致北东-南西向的断裂发生了大规模左旋剪切变形，并伴随逆时针旋转。晚侏罗世，古太平洋板块（Paleo-Pacific Ocean）沿欧亚板块（Eurasian Plate）下方低角度向西俯冲、北部蒙古-鄂霍次克洋（Mongol-Okhotsk Ocean）闭合，以及南部拉萨-羌塘碰撞（Lhasa-Qiangtang collision）等多重作用，从不同方向对阿拉善地块施加变形应力，形成了走向各异的收缩构造，并反转了早期的伸展盆地。晚白垩世，欧亚板块东南缘发生斜向碰撞，同时新特提斯洋（Neo-Tethys）沿其南部边界发生俯冲；阿拉善地块东部发育了板内左旋走滑挤压巨型剪切系统，盆地边缘的山脉随之隆升。阿拉善地块的多期中生代陆内变形现象，佐证了其变形主要受板块边界产生的应力驱动，并受上地壳先期复杂造山构造控制这一学术观点。