Tectonic Evolution And Regional Dynamics Background Of Lishu Subbasin, Songliao Basin

Lishu subbasin is a superposed subbasin composed of fault-subsidence and depression. It is located in the Southeast uplift area of Songliao basin, a part of Solon-Xarmoron-Changchun-Yanji suture zone between medium-small plots of Jihei and North China plate. The basement rock are composed of early Yanshanian granite, late Variscan metamorphic rock, Precambrian basement, Variscan and Caledonian granite. According to the fault depression period deposition pattern of Lishu subbasin, it is divided into four Secondary structural unit:Shiwu sags the eastern slopes Shuanglong sag and Sujiatun sag, on which based,four second-order tectonic belt can be recognised:Sangshutai fault belt, Xiaokuan fault belt, Qinjiatun fault belt and Pijia fault belt.The faulting evolution of Lishu subbasin can be divided into Huoshiling stage, Shahezi stage, Yingcheng stage and Denglouku-early Quantou stage in early Cretaceous.Late Cretaceous was depression period, and late-reformation of basin occured in the end of Cretaceous-Cenozoic. Late-reformation of each major phase were weak in the faulting period; Both subsidence and deposition peaked during depression period; Then the Lishu subbasin was strong reformed in the end of Cretaceous-Cenozoic.In Huoshiling stage, the prototype of Lishu subbasin emerged in the background of mantle converge, crust lacunae, Sangshutai faut and Qinjiatun fault strong stretching. In Shahezi stage, Sangshutai fault zone (include Sangshutai fault, Jinshan fault, Sujiatun fault and Side joint belt) stretched, Xiaokuan fault belt emerged, Qinjiatun fault belt activity was weak; In Yingcheng stage, all the fault were strong stretched; Denglouku stage-Early Quantou stage, Xiaokuan fault trough (D) and Shuanglong sag (A) strike-slip extensional, Xiaokuan uplift (C) strike-slip extrusion, Xiaokuan fault belt B section parallel strike-slip, Qinjiatun fault belt compressed uplift, Pijia fault belt further teared.In the Late Quantou stage-Nenjiang stage, Lishu subbasin was covered by very thick upper Quantou stage-Nenjiang stage; In the end of Nenjiang stage-Mingshui stage, under the SE-NW compression, strong fold uplift and erosion appeared near the Xiaokuan fault belt, Qinjiatun fault belt uplift too; In Paleogene, the east of Lishu subbasin rifted, roughly along the Yilan-Yitong grabens was in the process of sedimentation and deposition, with basic volcanic rock activitis. Tectonic activity and reform in Cenozoci was relative weak in Lishu subbasin and Northern part of Songliao basin.As a part of early Cretaceous basin in Northeastern Asia fault basin system, the evolution of Lishu subbasin was controlled by NW-SE tension stress, resulting from a convergence between North China plate and Siberian plate. Tectonic dynamics environment of East-Asian continent enhanced after the subduction of Pacific plate at the end of the early cretaceous. In late cretaceous, the west aera of Great Khingan deposition reduced, even stopped to suffer erosion, then the east aera of Great Khingan (include Lishu subbasin and Songliao basin) went into depression period and was thickly deposited. From the end of late cretaceous, large-scale Songliao basin began to be lifted and extinct, the sequence of Cenozoic sedimentary was incomplete and the deposition was unequal in basin.The half-graben structure dominated the distribution of the gas and oil in the Lishu subbasin generally. Hydrocarbons is toroidal-fanned located around the deep sag:gas is mostly distributed circularity inner the Sangshutai fault such as Gujiazi, Houwujiahu gas field, while the oil field is distributed outside the ramp region and the mixing area is between the two. The main productive series are Q1, Q2, Yingcheng and the upper Shahezi Formation. Second-order tectonic belt controlled hydrocarbon obviously, most oil and gas traps are found near the second-order tectonic belt. Because the hydrocarbon began to generated in Quantou stage, the second-order tectonic belt, which located in the Oil and gas migration direction turned active relative late, it took a long time to capture oil and gas, and adjust the earlier gathered hydrocarbon.