The Mechanic And Tectonic Evolution Of Mesozoic Basins In Northwestern Junggar Orogenic Belt

This dissertation had analyzed Mesozoic basins the mechanic and tectonic evolution of Mesozoic basins in Northwestern Junggar orogenic belt. The main conclusions and progresssions in research are as following.The evolution of Mesozoic basins in Northwestern Junggar orogenic belt was divided into three stages. The early was contractive stage during Triassic; strike-slip extension played an important role during early-middle Jurassic; and extrusive depression dominanted during late Jurassic to early Cretaceous.The Heshituoluogai basin was a strike-slip extensional basin in early-middle Jurassic. There existed various depositional system and showed obvious spatial distribution. Alluvial fan and fan-delta sedimentary systems dominated the north areas of the basin; while the southwestern of the basin was composed of braided and meandering river facies; and the lacustine sediments distributed mostly in the east or northeastern of the basin. Imbricated- pebbles in conglomerate and cross-bedding in sandstone indicated that the paleocurrents in north area and southwest area were southward and eastward, respectively. The phenomenon implied the main provenance of the basin was the north and southwest late-Paleozoic folded mountains.Whereas, palaeocurrent in Kelamayi basin was different from Heshituoluogai basin's in early Mesozoic. They were distinct basins actually.The data of granitic fission-track in northwestern Junggar indicated that the Zircon Fission-track age was 136 Ma, apatite Fission-track age were 67-135 Ma. Thermal history modeling showed that the Junggar northwestern orogeny had mostly undergone twice uplifts. The first one occurred in later Jurassic to Cretaceous (160-80 Ma); the second one occurred in later Neozoic (29-9 Ma). Uplifting velocity was about 58-22 m/Ma by thermal history modeling, and 74.7 m/Ma by Apatite-Zircon mineral pair. The uplift process in northwest Junggar denoted that structural setting had transited from extension to contraction in later Mesozoic. Zhayier Mountain offered sediments for Heshentuoluogai and kelamayi basins.Because of the closure of Tethys Ocean, Qiangtang(230-200 Ma) and Lhasa(145-120 Ma) terrances had ensuingly collided with Eurasia plate. Distant effects of these collisions induced inner-plate orogenesis and controlled forming of Mesozoic basin in Central Asia.The evolution of Mesozoic basins was closely related with the multi-stages conversion of structural setting in Northwest Junggar area. Northwest Junggar basins formed in contractive environment in Triassic firstly. At the second time, Heshentuoluogai basin was extension-faulted basin controlled by strike-slip in early-middle Jurassic. Ultimately, the uplift of northwest Junggar resulted in the reversion of these basins'structural property and formed contractive basin during late Jurassic to early Cretaceous.