The Structure Characteristics Of Chagandelesu Fault Depression And Its Petroleum Accumulation Condition

Chagan fault depression is a secondary tectonic unit in Chagandelesu subbasin, northeastern Yingen-Ejinaqi basin, and the basement of the basin is a Paleozoic fold belt of continental margin or island arc with the character of erogenic belt at the connection region of North China plate, Tarim plate and Kazakstan plate.The structure units are redivided. The main structure style of Chagan fault depression is summarized, in which the extensional structure are the principle part. Its kinematics characteristics are analysed. It is suggested that "Maodun intrusion" may be an pre-Cretaceous intrusion, that the early Cretaceous "Hantamiao secondary depression" divided by the predecessor may not exist. Maonan fault might activited strongly during pre-Cretaceous.Yinggete-Bagemaode metamorphic core complex belt with three-layer construction is put forward, which evolved from late Jurassic to Cretaceous. The extensional simple shear model of the Chagan fault depression is established.The tectonic evolution and the dynamics character of Chagan fault depression and its adjacent Mesozoic-Cenozoic basins are discussed:At the end of Triassic continental orogeny increased crust thickness crust uplift and denudation were happened; Jurassic was a period of local partly extensional collapse of erogenic belt and Cretaceous was a period of widely extensional collapse of postorogenic erogenic belt; Cenozoic was a period of the development of stable intracontinental depression with the character of long distant collision response and weaked compression flexure.It could be divided into six paleogeotemperature evolution stages from Early Cretaceous to recent based on the result of apatite fission-tracks analysis; subsidence-buried history analysis shows that Chagan experienced fault depression stage during early Cretaceous Bayingebi-Suhongtu period, transional stage from fault depression to sag in Yingen period, and sag stage since Wulansuhai stage.Chagan fault depression has favorable petroleum geology conditions, the evolution of its source rocks could be divided into three stages. Lower Cretaceous Bayingebi group had higher organic abundance, generating hydrocarbon intensity and hydrocarbon expulsion efficiency. There were petroleum migration and accumulation in three phases through the analysis of fluid inclusion. The northeast Ehen secondary fault depression, maoxi fault-nose and maonan slope should be favorable places for prospecting in the near future.