江苏下扬子区中、古生界构造特征及其演化

Tectonic characteristics and evolution of Mesozoic and Paleozoic in Lower Yangtze region,Jiangsu

佘晓宇 徐宏节 何治亮

She Xiaoyu Xu Hongjie He Zhiliang

江苏下扬子区中、古生界在印支晚期-燕山中期由稳定的洋-陆板块构造体制变格为板内形变体制,形成苏北由NW向SE和苏南由SE向NW的对冲推覆构造格局。苏北地区震旦系及古生界沿陡山沱组及次级滑脱层逆冲推覆;苏南地区,上古生界沿高家边组滑脱层系逆冲推覆,下古生界受控于两套区域滑脱层系并形成双冲构造。燕山中期,NNE向左旋压扭和NW向右旋压扭走滑对早期推覆构造有改造作用。燕山晚期,区域应力背景转变为NW-SE向拉张环境,使逆冲推覆体受重力作用沿断坡回滑,形成后缘凹陷(或箕状断陷)。苏南地区由于下古生界双冲构造和上古生界逆冲推覆在志留系之上而纵向位移势能受限回滑较难,后经历喜山晚期隆升,最终形成苏南中、古生界高台阶,苏北低台阶的构造格局。

During late Indo-Sinian epoch and middle Yanshan epoch, the Mesozoic and Paleozoic in Lower Yangtze region in Jiangsu changed from a stable oceanic-continental plate tectonic system into an intraplate deformation system,resulting in a ramp thrust tectonic framework with NW to SE thrusting in northern Jiangsu and SE to NW thrusting in southern Jiangsu.In northern Jiangsu, the Sinian and Lower Paleozoic overthrusted along the Doushantuo Formation and a subsidiary detachment;while in southern Jiangsu,the Upper Paleozoic overthrusted along the Gaojiabian Formation detachment,and the Lower Paleozoic became duplex thrust structure under the control of the two detachments.In middle Yanshan epoch,NNE left lateral compresso shear and NW right-lateral compresso-shear strike-slip movements modified the former thrust structures.In late Yanshan epoch,the regional stress setting turned into NE-SE extensional environment,in which the overthrust nappe slipped back along fault ramps under gravitational force,resulting in a half graben like fault depression.While in southern Jiangsu,the Lower Paleozoic duplex thrust structure and the Upper Paleozoic thrusting over Silurian made it difficult to slip back, due to limited potential energy of vertical displacement.The uplifting in late Himalayan epoch finally led to the tectonic framework of Mesozoic Paleozoic being high in southern Jiangsu and low in northern Jiangsu.

10.11743/ogg20040219