Crustal structure between the eastern margin of the Songliao Basin and its geological implication:deep seismic reflection

Abstract

In tectonics,the east margin of the Songliao basin lies in the east of the Songnen-Zhangguangcai mountain microplate,which has experienced the influences of the regional tectonic stress field,such as the northward extrusion generated by closing of the suture zone in Xilamulun River,and the extruding at the east and north-east side of the domain generated by scissor-type closing from west to Wast of the Mongolia-Okhotsk ocean,as well as the extruding generated by westward subduction of the western Pacific plate,thus resulting in complicated crustal variation.A series of new understandings have been obtained by deep seismic reflection in the Songliao-Drep research.While whether these knowledge are also correct for the eastern margin of the basin remains unclear.In addition,what kind of changes took place in the macro and micro characteristics of the Moho-discontinuity from the Songliao basin to its east margin and what is the formation mechanism are also needed to be further studied.In order to answer these questions,a west-east deep seismic reflection profile was set up,which extends from the west of Harbin to the nearby Shangzhi city with a length about 150 km.The research shows that there is an obvious crustal difference between the east margin domain and Songliao basin,i.e.from the tri-partition of Songliao basin crust changing into the bi-partition of the east margin.The depth of the Moho-discontinuity is about 26 km at the east edge of the profile,and the formation mechanism of its morphology can be explained by the equilibrium theory.A group of large two-way thrusting structures are present in the upper crust,and the main body overridden is speculated to be the palaeo-Asian ocean sedimentary layer,that is the C-P system marine facies layer.These understandings provide a theoretical basis for further investigating Neopaleozoic marine facies strata in Northeast China as well as crustal structure of Northeast Asia.