Evolutionary characteristics and key controlling factors of the volcanic rocks in the Lower Cretaceous Changling fault depression, Songliao Basin, China

The Songliao Basin is a large petroliferous basin located in Northeast Asia; the complex structure and volcanic filling are obstructions to the petroleum geological exploration of the Lower Cretaceous strata in the basin. Based on seismic, logging and lithologic data, this paper reveals the tectonic-stratigraphic characteristics of the Changling fault depression in the Songliao Basin, identifies the depression's volcanic rocks and summarizes their distribution patterns and changes, and finally analyzes the main factors controlling volcanic rock development combined with the regional tectonic background. The research shows the fault extension and subsidence caused the Changling fault depression to gradually evolve from an independent fault depression group to a connected large lake basin. The volcanic rocks in the fault depression are mainly "sill-like" volcanic lava and mounded volcaniclastic rocks, and their development can be divided into several stages. In the early Valanginian to Barremian, volcanic rocks show a large range of contiguous bedded and buninoid-structured rocks, which separate several small sedimentary sags; during the early Barremian to the late Aptian, volcanic rocks stopped developing; from the late Aptian to the late Albian, the volcanic rocks in the basin underwent multiple evolu-tionary periods, and their morphology gradually changed from mats and gentle mounds to high-angle cones and domes. Mantle upwelling caused by plate activity in Northeast Asia is the main driving force of extension and volcanic eruptions in the Songliao Basin, and the deep basement faults that formed by extensional activity control the magma upwelling channel, thus affecting the active periods, scale, morphology and distribution characteristics of volcanic rocks.