Mechenism Of Basin And Evaluation Of Oil Gas In Mesozoic Downfaulted Basins In Northeast China

This text takes aim east, middle part and west in northeast ,studying the Mesozoic geotectonic activities, interactivities between crust-mantle and influences of the palaogeographic configuration on basin evolution. Try to analysis and generalize formation mechanism and evolutionary process of the Mesozoic downfaulted basins from multi-angles.This text is based on basin analyse, rift basin module and mantle plume theory, according to analyse the geology in northeast, geophysics, oil gas data and consult coherent passages, after doing a great deal of research work, this text considers the Mesozoic downfaulted basins in northeast rift basin of the internal continent on the function of mantle uplift - crust creep. High elevation uplifts in front of rift in Songliao basin; high mountain with belts of vegetation is existence in Songliao basin during the period of depression; the relief in Songliao basin has reverse relationship to do with its surrounding regions.Seen from regional geology and basin evolution, the early Mesozoic downfaulted basins in northeast china have similar establishment, they are downfaulted basins on the function of continent spreading. However , basins evolve apparently after the taphrogenic period, take Sanjiang basin for example, the east basins lift and denude heavily due to being located on the continental east edge forming some split minitype basins. It is extensive sedimentation in Songliao basin after the taphrogenic period forming large-scale umbilicate type basin, it is weak tectonic pressure in later period. It is depression process after the taphrogenic period in Hailaer basin , lifting and denudation are little in later period.The research of Modern continental spreading basin indicates that the formation of large-scale basin has relationship with low-density materials of deep-seated mantle haunching up and crustal spreading,The interacting of crust-mantle is main dynamic mechanism of the sedimentation of extensional basin, the formation of basin is the result of isostasy on the function of thermo and convection of thermal materials.The giant system on east Asia continent is the result of active distortion of middle-late lithospheric in the region of east Asia continental margin and west Pacific marginal sea. Lithosphere in the east Asian is pulled and then has been disintegrated from Mesozoic era(150Ma),asthenosphere materials of the upper mantle upwells and volcanic activities are strong, the large-scale thermal event generated huge tectonism and magmatic activity, the thickness of lithosphere is reduced from 200km to 50-70km.Under the background of the continental activities, the continental rift system began to format by splitting of continent, soft flow layer's extravasations and thinning of lithosphere, since the Mesozoic, on the eastern area of Asian Continent. Correspondingly, in eastern area of China, a broad mantle's and lithosphere's uplift area which had been thinned had formatted, form the gravity gradient zone of Daxinganling - Taihang eastward to the Japan Sea.The eastern area of Daxinganling was uplift area of crustal and mantle in northeast region of china. Because of the strong crust-mantle interaction, a mass of volcanic rocks had developed on the boundary of uplift area.The existence of Volcanic prove that basalt of the northeastern region wan formatted in the environment of the continental rift which gradually extended since the Early Cretaceous(130Ma). Since the late Mesozoic, mantle magmatic activity, symmetrical pattern of distribution of Mesozoic and Cenozoic volcanic rocks and the deep rift that we discovered through geophysical research was consistent. the development of the Central Basin and the western basin which formed at in Early Cretaceous was correspondence.At the beginning of the Early Cretaceous, there was a lot of volcanic construction in Songliao Basin and Hailar Basin than lacked of lacustrine sediments. The coal-bearing construction and lacustrine sediments developed at the beginning of faulting. When the Songliao Basin had changed into depression the Hailar Basin had been denudated as tectonic compression and high terrain. The QingShankou formation in Songliao basin and the QingYuangang formation were counterparts. Since this era, the two basins changed into depression.Based on the evidence of the paleomagnetic and pollen fossils, we thought that Songliao Basin and Hailar Basin was in high altitude low-latitude areas form Late Jurassic to Early Cretaceous. stratigraphic correlation and analysis of sedimentary facies showed that the low-lying eastern basin was filled by mixed deposition of sea and land in the period of the Rift Valley (faulted phase) in Songliao basin.The sedimentary that was deposited in glacial period,cedar pollen fossils and the palaeogeographic environment indicate the existence of the mountains in the east of Songliao Basin in Quantou formation.Through the comprehensive study, we thought that the northeast region of china was composed of mainland rift basin that formed by mantle uplift and squirm, Late Jurassic to Cretaceous in Mesozoic. Based on the individual differences and other factors of formation of basins, the basins can be divided into broad patterns and narrow rift basins. Through overall development process of Songliao basin that was uplift before the beginning of rift, its topography changes were inconsistent with area around it.