Sandwich lithospheric structure of Xinjiang and its relation to petroleum resources

Abstract：Gravity survey is a method commonly used in petroleum basin reconnaissance. Satellite gravity is favorable for studying lithospheric structure because from it we can not only get more deep information of inhomogeneity in the lithosphere but also resolve the gravity field into different layers to show the inhomogeneity at different depths. According to the satellite gravitational data, the lithosphere of the Xinjiang region may be divided into three megalayers. The top is a megalayer consisting of Meso-Cenozoic continental downfaulted basins, including the Yining basin, Junggar basin, Tarim basin, Tuha basin and Tarim basin, surrounded by the Altay, Tianshan and Altyn Tagh mountains. The middle megalayer consists of a series of Paleozoic marine parallel ranges and basins formed by strong compressional folding during the Indosinian-Yanshanian. The lowest megalayer is the low-density block basement. The sandwich lithospheric structure formed by reworking of the Xinjiang lithosphere beneath the continent assembled at the end of the Paleozoic due to Cenozoic northeastward subduction of the Indian plate. The Borohoro, Qapqal, Alagou, Erbeng and Horo mountains of the West Tianshan mountain system were uplifted transversely and they together with the South Tianshan mountain system divided the Xinjiang block into a series of new mountains and basins. This study leads to a conclusion that petroleum exploration in western China should not be restricted in Cenozoic basins but that we should consider the controls of deep structure on the basin-and-range structure exposed at the surface.