Meso-Cenozoic Tectonic Uplift Process Of The Eastern Sichuan Basin

The eastern Sichuan basin is a key demonstration area for shale gas exploration in China.The Meso-Cenozoic tectonic uplift in eastern Sichuan basin has undergone many stages which result in complex multi-layer detachment folding and significant changes and adjustments in the occurrence of shale gas in the Lower Paleozoic strata.The continuous Cenozoic sedimentary strata are generally absent in eastern Sichuan basin,which makes it difficult to systematically study and restore the periods,duration and denudation of the Meso-Cenozoic tectonic uplift.Simultaneously,Jura-type folds are well-developed in the eastern Sichuan basin.The formation process and dynamic mechanism of this complex fold deformation are still controversial.In this paper,the Meso-Cenozoic uplift periods,duration and denudation and the formation process and dynamic mechanism of the eastern Sichuan fold belt were constrained by thermo-kinematic method composed of physical simulation,discrete element numerical simulation and low-temperature thermochronology method.The results show that the formation mechanism of the eastern Sichuan fold belt is fault-related folding of the sedimentary cover above the ladder-type system composed of basement decollement horizon,Qiyueshan fault,Silurian detachment layer and Huayingshan fault caused by northwestward extrusion between Pacific plate and Eurasian plate.The dip angle of pre-existing fault,the spacing between pre-existing faults,the compression rate and the friction coefficient of rigid layer are the main controlling factors for the development of Jura-type folds.The essential reason is that the connection mode of deep and shallow detachment layers is controlled in the process of the transformation from fault-propagation folding to fault-bend folding,which ultimately determines the varied conversion efficiency of lateral and longitudinal displacement.The eastern Sichuan basin has experienced a "fast-slow-fast" cooling process in Meso-Cenozoic,which is probably caused by the varied rate and direction of subduction between the Pacific plate and the Eurasian plate.At 170-70 Ma,the rapid cooling occurred in eastern Sichuan basin,which is the main finalization period of the eastern Sichuan tectonic belt.At 70-30 Ma,the eastern Sichuan basin slowly cooled,and the cooling rate of each tectonic part was close,stable at 0.5-0.8?/Ma.At about 30 Ma,the eastern Sichuan basin re-cooled rapidly.The Meso-Cenozoic tectonic uplift process in eastern Sichuan basin includes five main stages: trough-like folding stage(170-125 Ma),transition stage(125-100 Ma),ejective folding and finalizing trough-like folds(100-70 Ma),finalizing ejective folds(70-30 Ma)and overall uplifting stage(30 Ma to date).The total denudation of the ejective fold belt is approximately 4 km and the denudation of the anticline core can reach 5 km.The denudation of the transition zone is similar to that of the eastern Sichuan fold belt.Due to the complex fold deformation,the denudation of the western Hunan and eastern Hubei fold belt varies within 5-7 km.The denudation thickness of the Xuefeng uplift can exceed 8 km.