Provenance and Palaeogeomorphology study of the southwestern North China Craton during Middle-Late Triassic and its geological implication
The study of tectonic, provenance, and paleogeomorphologic systems is important for defining the basin evolution and it is also the basis for the accurate evaluation of oil and gas potential of a basin. The provenance and paleogeomorphology of the western Ordos Basin and the Hexi Corridor in the southwestern North China Craton(sw-NCC) have long been debated. In this study, detrital zircon geochronology, petrography and geochemistry methods are used to analyse the evolution of provenance and paleogeomorphology in the sw-NCC during the Middle–Late Triassic, and the provenance and paleogeomorphic relationships with tectonic events are discussed. The U–Pb detrital zircon geochronology of the Yaoshan samples in the western Ordos Basin are clear and consistent, and shows that there are three major age populations, 2700–2200 Ma, 2150–1650 Ma and 450–220 Ma. While the age spectrums of the samples from different formations in the Hexi Corridor are complex, showing significant differences. The whole results imply that the Hexi Corridor and the west margin of the Ordos Basin had a unified source during the Middle Triassic, which is the western NCC. However, in the Late Triassic, the sediment of the Hexi Corridor was mainly from the Qilian–Qaidam Terrane while the source of the western Ordos Basin remained unchanged. Besides the provenance analysis, the stratigraphic correlation, petrology and geochemistry analyses also support that the Hexi Corridor was temporarily connected with the Ordos Basin during the Middle Triassic but was separated from the Ordos Basin by a small-scale, underwater paleo-uplift during the Late Triassic. The evolution of the provenance and paleogeomorphology in the southwestern Ordos Basin was related to the closure of the shallow shelf of the Paleo-Tethys Ocean.