西南三江构造体系及演化、成因

西南三江构造体系突出表现为以昌都-兰坪-思茅地块为中轴的不对称走滑对冲构造，次为与走滑断裂相伴的伸展滑脱、走滑拉分盆地构造体系，再次为块体内部的近北东、北西向走滑断裂系。西南三江造山带构造体系演化分为挤压收缩变形、走滑深熔热隆、走滑剪切伸展、走滑剥蚀隆升等4个阶段。自晚白垩世开始，印度板块与欧亚板块碰撞，西南三江造山带对冲体构造体系初始形成。自渐新世开始，印度板块持续向北楔入欧亚大陆，印度板块与扬子克拉通构成力偶，两者相向、相对运动，挤压与剪切特提斯大洋缝合带及两大陆边缘弧盆系等地质体，西南三江造山带对冲体构造体系进一步发展，近南北向剪切走滑构造体系形成，构造方向也由近东西转为近南北向。而与近南北向主走滑断裂带之相伴的伸展滑脱构造、拉分盆地，块体内部近北东、北西“X”型剪切走滑断裂同时相伴形成。这样，就形成了西南三江造山带大规模的对冲、走滑、旋转及其伴生的伸展、拉分盆地构造的构造体系。

Genesis and evolution of the structural systems during the cenozoic in the Sanjiang orogenic belt, Southwest China

The southwest Sanjiang structural systems in the Sanjiang orogenic bett, Southwest China is characterized by asymmetric strike-slip thrust with the Changdu Lanping Simao block as the central axis, the extensional detachment structure and the strike-slip-pull-apart basin system accompanied by strike slip faults, and the near NE-and NW-trending strike slip fault systems within the blocks. The evolution of the tectonic system of the orogenic belt in Southwest China can be divided into compression and contraction deformation stage, strike slipping, deep melting and thermal uplift stage, strike slip shear extension stage and strike slip denudation uplift stage. In the Late Cretaceous, the collision between the Indian plate and the Eurasian plate resulted in the initial formation of the thrust system in the southwest Sanjiang orogenic belt. Since the Oligocene, the Indian plate has been continuing to wedge into the Eurasian continent northward. The Indian plate and the Yangtze craton have formed a couple of forces. They moved in opposite and relative directions. They compressed and sheared the Tethys oceanic suture zone and the arc basin system of the two continental margins. While the southwest Sanjiang orogenic belt developed further, the nearly north-south shear strike slip system was formed, and the tectonic direction also changed from near east-west to near north-south. The extensional detachment structures and pull apart basins, which are accompanied by nearly N-S strike slip fault zone, are formed by shear strike slip faults which of near NE and NW directions. In this way, a large-scale structural system of thrust faults, strike slip faults, rotations and their associated extensional and pull apart basins has formed in the southwest Sanjiang orogenic belt.