The Early Cretaceous tectonic deformation stages and detrital zircon U-Pb ages of Pingshanhu Basin in Hexi Corridor

Pingshanhu basin, located in the north of Hexi Corridor, is bounded by the Longshou Mountain in the south, the Beida Mountain in the north, and Heli Mountain in the west. The deposition and evolution of Pingshanhu basin were controlled by overthrust fault in the Early Cretaceous. In this paper, the authors deepened the study of the Early Cretaceous Miaogou Group, mainly about the geometry of the basin, the tectonic stress field and detrital zircon. The authors made a detail discussion on the tectonic evolution of Pingshanhu Basin. In Pingshanhu Basin, Miaogou Group exhibits an upward-fining sedimentary sequence. The tectonic deformation is dominated by NE-SW trending compression and E-W trending extension. The latest zircon age is (129.3±1.8) Ma, which may represent the earlieset time of the upper rock formation and the formation age of graben. On the basis of the sedimentary facies of Early Cretaceous Miaogou Group, the tectonic style, tectonic stress field and zircon ages of clastic rocks, the authors hold that Pingshanhu Basin was a compressional basin in the early Early Cretaceous. The growth strata restricted the compressional structure ages. It was an extensional rifted basin in late Early Cretaceous. The conversion time was posterior to 129.3 Ma.