| Wide rifting is one of an important continental extension modes,which represents one of the most important geodynamical processes affecting the lithosphere-asthenosphere system,but the study degree is very limited at present.According to the geological structure and geodynamic evolution of the southern Songliao Basin,we can understand the structural style and genetic mechanism of wide rifting.Based on the region of interest,s newly seismic profiles,drilling and geological mapping,the paper builds up the district stratigraphic system.According to the development characteristics of regional unconformity surface,subdivide tectono-stratigraphic sequence,and combine the distribution characteristics of the basin controlling fault system to subdivide the southern Songliao Basin,and then research basin structural characteristics of each zone.Combining analysis of growth strata and burial history,restore evolution history of key sag.According regional geological cross-section,to identify regional detachment surface,then through the regional tectonic evolution cross-section to reveal the tectonic evolution of the Songliao Basin.By using geophysical field,chronology and geochemistry of the volcanic rocks,promulgate geodynamic background of the region of interest,finally establish geodynamic model of the south Songliao wide rift.Studies suggest that the southern Songliao Basin develop three regional unconformity surfaces,including the bottom of Lower Crataceous Yixian Formation,the bottom of Lower Crataceous Quantou Formation and the bottom of Upper Crataceous Sifangtai Formation,and four sets of tectono-stratigraphic sequence as well as basement structural layer,rift structural layer,depression structural layer,structural layer of basin inversion.The southern Songliao Basin can subdivide four sag zones,including Lujiapu,Dongshen-Manghan,Zhangwu-Qianjiadian and Tiefa-Changtu.Dongshen-Manghan sag zone is maily controlled by NE-trending faults,which exhibits right-order echelon style under controlled by sinistral strike-slip torsional stress.Zhangwu-Qianjiadian sag zone is maily controlled by NW-trending faults,which exhibits left-order echelon style under controlled by dextral strike-slip torsional stress.Tiefa-Changtu sag zone maily exhibits NNW-trending tandem style under controlled by EW-trending extensional stress.The extension strength of the study area in Early Cretaceous was small,and the depth of the regional detachment surface is 8000m,which is controlled by simple shear or decoupled extension.The basement settlement is 3000 m,including two tectonic inversion event,which are the final deposition of the Formation of Fuxin and Nenjiang.The study aera experienced inntraplate extensional tectonic environment of subduction during Late Jurassic-Early Cretaceous,and led to extensional tectonic setting of the pack plate because of the retreat of the paleo-Pacific plate subduction zone.Controlled by basal shear slip,the stretch of the study area performanced "wide rift" shape above the detachment surface,which showed diffuse deformation,as well as localised deformation in four sag zone,who developed sags of different strength.The southern Songliao Basin has particularity in structural styles and genetic mechanism compared with the typical wide rifling,and it developed Early Cretaceous petroleum systems.Reservoir evolution experienced both deeply buried into hydrocarbon accumulation and adjustment process of later uplift,furthermore,reservoirs have characteristics of "small scale,encircling distributed by oil source sub-sag. |
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