| Sunwu- Jiayin Basin, located to the north of Songliao Basin, is one of the late Mesozoic extension basins in Northeast China. Studies of the basin help us to understand the structural characteristics of extensional basin, the dynamics of basin formation and the origin of volcanics in late Mesozoic, and especially the processes of Mesozoic-Cenozoic lithosphere extension and thinning in east China.Based on field geological survey, analysis of geophysical and geochemical data, this paper discussed the relationship between tectonic activities, magmatic processes and basin evolution, that may provide constraints on regional geodynamic evolution. Detailed discussion is focused on the structural characteristics, evolution, mechanism of formation, dynamic regimes and and controlling factors of formation of the Sunwu- Jiayin basin.Sunwu- Jiayin Basin has a typical binary structure, including pre-Mesozoic basement and Mesozoic- Cenozoic cover. The basement is composed of Proterozoic and Paleozoic, mainly granitic plutons and metamorphic rocks. The cover is composed of Mesozoic- Cenozoic sedimentary rocks including early Cretaceous Ningyuancun group volcanic rocks. From bottom to top, the sedimentary sequence includes Ningyuancun, Taoqihe, Yongancun, Taipinglinchang, Yuliangzi, Wuyun and Sunwu formations.Twenty two faults were recogniaed in Sunwu- Jiayin Basin, based on gravity and geomagnetic interpretations, NE trending faults are numerous large scale faults. Early Cretaceous volcanic activities and structural framework of the basin is controlled by such faults. NW trending faults cut across the NE trending faults and they controll the faulting and distribution of fault basins in northern part of Sunwu-Jiayin Basin. The NE faults are formed by regional extension in NE direction, but the NW faults are formed by dextral strike sliping, in a transtensional stress field. Based on characteristics of basement, buried depth, thicknesses and types of sediments, and geophysical characteristics, the basin can be subdivided into 6 tectonic units (grade I), including 2 rises and 4 rifts; and subdivided into 19 structural units (grade II), including 10 sags and 9 domes. The depths of basement in the basin gradually become greater from south to north, and the basins are alternated with each other from east to west. Both the depths and alternation are controlled by the NE trending basement faults.The Sunwu-Jiayin Basin is a Mesozoic-Cenozoic volcanic sedimentary basin. It experienced stages of extension, rifting, uplifting, depression and uplifting. In early Cretaceous, the basin is dominated by regional extension and rifting. Faulting and massive volcanic eruption contributed to very thick volcano-sedimentary rocks of Ningyuancun Group in the early stage. Afterwards, the basin basement is entirely uplifted, rifting gradually becomes small and weak。Affected by Yanshan movement in late Early Cretaceous, the rift basin began to uplift and to be eroded in a stage of stable depressioin. A sequence of detrital sediments are deposited in Taoqihe group, with coarse-grained sediments in the lower part and fine-grained in the upper. In late Cretaceous, the basin experienced a stage of regional depression. Yongancun formation and Taipinglinchang formation represent the most flourished depression development. In latest Cretaceous, there is a tectonic inversion due to effects of Pacific tectonic activities, faulting and folding accompanying sedimentation in Yuliangzi Formation.The Early Cretaceous tectonic and volcanic activities in Sun Wu-Jiayin Basin are part of a regional event throughout East Asian. They are characteristics of regional tectonic extension of Late Mesozoic and important shallow responses to regional lithospheric thinning. As a part of detachment faulting and thinning of the crust in East Asia, they are controlled by a uniform regional extensional stress field.
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