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

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.