Structural Features And Evolution Of Urxun And Beier Depressions Of Hailar Basin

Urxun and Beier depressions in Hailar basin formed duringMesozoic and Cenozoic, they are located in the Paleozoicorogenic belt in Inner Mongolia-Daxing'anling area. The fourdirections of structural belts are found in research area. Thefaults of NE, NEE and NS directions form earlier, active for along time, and control the basin evolution;the faults of NWdirection form later, remake the older structures.Urxun depression is a faulted basin, it is controlled by Wuxifaulted zone (fault Wux 1 and fault Wuxi 2). Wuxi faulted zoneand a series of listric normal faults which are NS direction(Wuzhong faulted zone and its flower structure), NE faulted zone(Surennuoer faulted zone) and NEE faulted zone (Huangqimiaofaulted zone) constitute the main structures of Urxun depression.The extension amount of Urxun depression is bigger in themiddle part than other part, the average is 10.5, the extensionrate is 0.81%, and extension factor is 1.81.Beier depression is consists of a series of semi-grabenswhich are controlled by listric normal faults with NE direction(such as Sunainuoer faulted zone) and NNE direction(Huoduomoer, Suderte and Aonaohai faulted zones). Otherwise,a few faults with NS and NW directions are found in Beierdepression.Urxun-Beier depression experienced four deformation stagein the lower Cretaceous: the extension stage of NW-NE directionduring Xing'anling period to Nantun period;the compressivestage of NW-NE direction during Damoguaihe period to earlyYimin period;the extension stage of near EW direction duringlate Yimin period;the compressive stage of near EW directionduring last Yimin period to early Qingyuangang period.Urxun-Beier depression experienced extension stage andcompressive stage of NW-SE direction respectively during lateQingyuangang period of upper Cretaceous to Cenozoic.