下扬子地区古生代盆地的改造变形

包括苏北-南黄海地区在内的下扬子区海相古生界盆地,在中三叠世末以来的构造演化过程中,经历了3期不同性质构造作用的改造变形。(1)在中三叠世末-早、中侏罗世的印支运动期,发生了江南-雪峰基底拆离体由南东向北西方向(同时派生由南向北,由东向西方向)的逆冲推覆,以及后缘弹性松弛断陷构造作用的改造,使海相古生界盆地发生了第Ⅰ期的由强及弱、递进衰减的逆冲 褶皱变形。(2)在晚侏罗-早白垩世的燕山运动期,叠加了第Ⅱ期以郯庐断裂带为代表的NNE向大陆平移走滑构造的左行简单剪切,以及拉分断陷构造作用的改造变形。(3)在晚白垩世-古近纪的喜马拉雅运动期,下扬子区在由南向北的伸展拆离与多米诺式拉张断陷构造作用下,受到了第Ⅲ期的变形改造。这3期构造变形作用促使扬子板块海相油气的早期聚集、晚期热演化和再分配。文中将重点讨论下扬子区板内海相古生界盆地自中三叠世末以来所经历的3期不同性质构造作用的改造变形。

Transformation and deformation of the Paleozoic basins in lower Yangtze areas.

Paleozoic sea facies basins including North Jiangsu South Yellow Sea area have undergone three episodes of tectonic transformation and deformation since the end of the Middle Triassic. The first episode occurred in the Indo Chinese epoch from the end of the Middle Triassic to the Early Middle Jurassic, in which the Meso Paleozoic marine basins underwent thrusting folding deformation with progressively decreasing intensity, which is caused by the SE NW over thrust of the decoupling body of Jiangnan Xuefeng basement（with the induced S N and E W overthrusting) and the transformation of faulted depression with resilient relaxation at the trailing edge. The second episode occurred in the Yanshan epoch from the Late Jurassic to the Early Cretaceous, in which the basins were superposed by the simple shear caused by the NNE trending horizontal strike slip structures (represented by the Tan Lu fracture zone) and the deformation induced by pull apart and faulting tectonic mechanism. The last episode occurred in the Himalayan epoch from the Late Cretaceous to the Paleogene, in which the lower Yangtze area underwent the transformation and deformation caused by the S N extension and detachment as well as domino type of pulling apart and faulting structures. These three episodes of transformation and deformation facilitated the early accumulation, later thermal evolution and redistribution of marine oil and gas in the Yangtze Plate. This paper discusses the three episodes of tectonic transformation and deformation of the Paleozoic sea facies basins in lower Yangtze area since the end of the Middle Triassic.