下扬子区伸展拆离构造

在郯庐断裂带以东,包括苏北-南黄海地区在内的下扬子区,晚白垩世-古近纪时期,在太平洋板块由南向北俯冲消减的运动过程中,东亚大陆被牵引,发生了由南向北的大型左行平移走滑运动和岩石圈上地壳递进减薄拉张的伸展拆离构造运动。从苏、皖南的南陵-广德、句容-常州断陷盆地开始,经苏北东台、盐阜坳陷-南黄海南部的青岛坳陷,再向北至南黄海北部的烟台坳陷,形成了3条呈NE-近EW走向的断陷盆地构造带。盆地为具有南断北超的箕状半地堑结构,呈多米诺骨牌式自南向北排列;并与其间近E-W走向的南京-南通-勿南沙和滨海-南黄海中部的崂山古生界地层的核部杂岩褶隆带,共同构成较大区域范围的盆-岭构造。这一期构造运动一方面再次改造了下扬子区海相古生代盆地,为海相古生界烃源岩系在经历了抬升剥蚀后的再次深埋,以及晚期二次生烃提供了可能性;另一方面也控制了中新生代油气的生成与聚集分布。

Extensional detachment structures in the Lower Yangtze region

From the Late Cretaceous to Paleogene, the Pacific Plate subducted from south to north. As a result, the East Asia Continent was sheared. Large-scale left-lateral strike-slip movements from south to north and extensional detachment movements which caused the thinning of the crust took place in the Lower Yangtze region (the area to the east of Tanlu Fault, including the northern Jiangsu and South Yellow Sea regions). Three NE-EW oriented rift basin zones developed, including:(1) the Nanling-Guangde and Jurong-Changzhou rift basins in Jiangsu and the southern Anhui; (2) the Dongtai and Funing depressions in the northern Jiangsu and the Qingdao Depression in the southern South Yellow Sea Basin; (3) the Yantai Depression in the northern South Yellow Sea Basin. These basin zones had half-graben structures which were faulted in the south and onlapping in the north. They arranged like dominos from south to north, and formed basin and range structures together with the EW oriented Nanjing-Nantong-Wunansha and Binhai-South Yellow Sea uplifts. These tectonic activities reformed the marine Paleogene basins in the Lower Yangtze region. Marine source rocks in the Paleogene might be deeply buried after uplifting and erosion, which made secondary hydrocarbon generation possible and controlled hydrocarbon generation and distribution in the Miocene.