Provenance analysis of the Middle Triassic Ordos Basin: Constraints from zircon U-Pb geochronology

Abstract

The Ordos Basin is a large interior continental sedimentary basin in western China； its Mesozoic evolution was controlled by surrounding orogenic belts. To constrain the evolution of the southern Ordos Basin, four samples from the southern Ordos Basin were analyzed for U-Pb ages. Similar detrital zircon U-Pb age patterns of the samples suggest no provenance change occurred during the Middle Triassic. Detrital zircons from the samples are divided into three major groups based on their U-Pb ages: 360-250 Ma, 2000-1600 Ma and 2800-2200 Ma. The first group of zircons is consistent with Paleozoic igneous zircons from the northern margin of the North China Craton (NCC). Detrital zircons of the second and third groups are likely derived from the basement of the NCC northern margin. In the Middle Triassic, detritus from the Qinling Orogenic belt may only have reached the piedmont deep depression. The absence of the Qilian Mountain source suggests that the Ordos Basin may not have been connected with the Hexi Corridor Basin in the Middle Triassic. Combining our results with those of previous studies, we suggest that the southern borderline of the Ordos Basin may not have reached the Qinling Orogenic Belt. The northern margin of the NCC, the Qinling Orogenic Belt and the pre-Middle Triassic sedimentary rocks of the eastern NCC provided sources for the Southern Ordos Basin in the Late Triassic. The rapid uplift of the Qinling Orogenic belt occurred in the Late Triassic. This event was response to collision between the NCC and the South China Block. The deposition and evolution of the Ordos Basin were controlled by the Indosinian movement. The change in source areas for the Southern Ordos Basin was closely related to the development and evolution of the Qinling Orogenic Belt. The Qinling Orogenic Belt shows good coupling with the sedimentation and structures of the Southern Ordos Basin.