扬子西缘泛非造山与绵阳－长宁克拉通裂陷的沉积充填过程研究

Study on the deposition and filling process of the Mianyang-Changning cratonic rift: Implications for the Pan-African orogeny on the western margin of Yangtze Block

关键词:  扬子西缘  泛非运动  克拉通边缘裂陷  四川盆地  盆地动力学过程  深层油气

Key words:  West margin of Yangtze Block  Pan-African Orogeny  craton margin rift  Sichuan Basin  basin dynamics process  deep oil and gas

摘要:

四川盆地安岳震旦—寒武系特大型气田的发现，掀起了探索四川盆地深层油气勘探新领域的热潮。然而对于川西北深层原型盆地沉积充填过程及其动力学机制的认识尚处于探索阶段。本文通过对扬子西北缘及盆内典型钻井震旦—寒武纪地层序列的综合调查与区域对比研究，基于关键事件序列的系统厘定，重建了扬子西北缘及邻区新元古代—寒武纪原型盆地沉积充填格架；对比全球冈瓦纳大陆汇聚与泛非造山过程，系统厘定了泛非运动在扬子西缘的沉积－构造－岩浆作用记录，进一步明确了华南扬子克拉通为新元古代末期冈瓦纳大陆的一部分。同时，结合盆内最新深层钻井和二维地震资料解析，研究认为绵阳－长宁克拉通边缘裂陷的成生、发展、充填与折返隆升过程主要受控于扬子西缘的泛非期弧后伸展、弧陆碰撞及陆陆碰撞造山过程，研究提出绵阳－长宁克拉通边缘裂陷经历了如下6个演化阶段：①陡山沱早期克拉通边缘裂陷开启，表现为克拉通边缘的裂陷与快速沉降；②陡山沱晚期—灯影早期为克拉通裂陷的持续沉降与克拉通碳酸盐台地的补偿性生长，区域沉积分异明显；③灯影晚期为克拉通裂陷扩展、定型与碳酸盐台地的活化与重建；④麦地坪期为克拉通边缘的差异隆升与碳酸盐台地的风化剥蚀；⑤筇竹寺期为克拉通增生陆块边缘的构造活化与克拉通边缘的挤压挠曲沉降；⑥沧浪铺期为陆陆碰撞造山与克拉通边缘裂陷的快速充填。至沧浪铺末期，绵阳－长宁克拉通裂陷沉积充填结束，并快速折返隆升为天井山－川中古隆起。因此，本文对扬子西缘克拉通边缘裂陷的盆地动力学过程重塑，不仅为华南板块在冈瓦纳古大陆重建中的构造定位提供了新资料，亦将对探索川西北乃至四川盆地深层油气勘探新领域、新方向具有重要的启示意义。

Abstract:

The discovery of Moxi Sinian-Cambrian mega gas field has set off a new exploration boom of deep oil and gas in Sichuan Basin. However, the understanding of the filling process and the dynamic mechanism of the deep prototype marine basin in northwestern Sichuan is still in the probing stage. Through a comprehensive investigation and regional comparison, the deposition and filling frame of the new Proterozoic-Cambrian prototype basin in the northwest margin and its adjacent area have been reconstructed based on the systematic determination of key events. Compared with the global Gondwana assembly and the pan-African orogeny process, the deposition-structure-magmatic records of the Pan-African orogeny have been systematically determined, which indicates that the Yangtze block was a part of the Gondwana supercontinent at the end of the Neoproterozoic. The latest deep drilling data and two-dimensional seismic data analysis suggest that the whole process of the onset, development, filling and return to uplift of the Mianyang-Changning cratonic margin rift was mainly controlled by Pan-African arc extension and arc-land collision on the west margin of Yangtze block,revealing that Mianyang-Changning cratonic rift went through six stages:①The Early Doushantuo period in which the cratonic margin rift was opening and followed by the subsidence and rapid filling;②The Late Doushantuo to Early Dengying period in which cratonic margin rift continuously subsided with the compensatory growth of carbonate platform and the obvious regional deposition differences; ③The Late Dengying period through which the craton margin rift went expansion and shaping and the carbonate platform experienced activating and reconstruction; ④ The Maidiping period in which differential uplift of the craton margin was accompanied with the weathering and erosion of the carbonate platform; ⑤The Qiongzhusi period through which Yangtze craton went structure activation and compressing subsidence; ⑥The Canglangpu period in which the craton margin rift was rapidly filled due to the arc-continent and continent-continent collision. By the end of the Canglangpu period, the Mianyang-Changning cratonic rift finished filling and quickly turned into the Tianjing Mountain-Middle Sichuan uplift. The remodeling of the basin's dynamic process on the west margin of Yangtze craton not only provides new information of the positioning of the South China plate for the reconstruction of Gondwana, but also has important implications for the exploration of new fields of deep oil and gas in northwestern Sichuan Basin.