扬子地块北缘晚古生代-早中生代裂谷系统的分布及成因分析

Distribution and origin of the Late Paleozoic-Mesozoic rift systems in the northern margin of the Yangtze block

晚二叠世长兴期-早三叠世印度期,在扬子地块的西北缘发育了一系列北西向展布的深水盆地区。根据成因分析证实,它们为伸展背景下形成的裂谷系统或者裂谷盆地群。平面上各裂谷盆地彼此近于平行,与北侧的南秦岭造山带在走向上呈正交和大角度斜交的排列,自西向东依次为开江-梁平裂谷、城口-鄂西裂谷和荆门-当阳裂谷。其中的开江-梁平裂谷东西两侧发现了巨大的天然气田而引起石油勘探家和地质学家的关注。本文对于这些控制油气资源储备的裂谷体系的分布和形成机制进行研究后,认为它们形成于南秦岭洋闭合时的碰撞作用,是南秦岭造山带和扬子地块拼合时同生的巨型"碰撞裂谷系统"。

During the Late Permian Changhsingian Stage-Early Triassic Induan Stage, a series of NW-trending deep-water rift basins formed along the northwestern margin of Yangtze block,which are named as the Kaijiang-Liangping rift, the Chengkou-Exi rift and the Jinmen-Dangyang rift respectively from west to east. They are approximately parallel to each other, but perpendicular or sub-perpendicular to the strike of the South Qinling orogen to the north. Giant gas field has been discovered along the edges of the Kaijiang-Liangping rift, which draws broad attention to these rift basins from geologists and oil gas explorers. In this paper, we study the distribution and formation mechanism of these rift systems which have good prospect in oil gas exploration, and indicate that they were collision rifts forming during the closure of the south Qinling Ocean by the initial contact between the Yangtze block and the South Qinling orogen.