The Upper Paleozoic detrital zircon U-Pb geochronology and its tectonic significance in southwestern Ordos Basin

Aimed at exploration of provenance and basin-mountain coupling relationship in southwestern Ordos Basin, the authors selected detrital zircons from the first member of Shanxi Formation and the eighth member of Shihezi Formation of the late Paleozoic in southwestern Ordos Basin and conducted LA-ICP-MS detrital zircon U-Pb isotope analysis. The result reveals that the 105 analytical points of the magma-genetic detrital zircons yielded four age groups:(1) The first group which ranges from 260 to 340Ma accounting for 21.9% of the total analytical points, indicating that the provenance might have come from the North Qinling orogenic belt and the West Qinling orogenic belt; (2) The second group which ranges from 370 to 470 Ma accounting for 24.8% of the total analytical points, suggesting that the provenance was mainly derived from the North Qinling orogenic belt, the West Qinling orogenic belt and the North Qilian orogenic belt; (3) The third group which ranges from 1600 to 2000 Ma accounting for 32.4% of the total analytical points, implying that the provenance might have come from the North Qinling orogenic belt and the North Qilian orogenic belt; (4) The last group which ranges from 2300 to 2600 Ma accounting for 15.2% of the total analytical points, indicating that the provenance was derived from the North Qinling orogenic belt, the West Qinling orogenic belt, the North Qilian orogenic belt and the crystalline basement of the North China plate. This study indicates that the provenance of southwestern Ordos Basin had multiple origins:the North Qinling orogenic belt, the West Qinling orogenic belt, the North Qilian orogenic belt and the crystalline basement of the North China plate, mainly from the North Qinling orogenic belt and the North Qilian orogenic belt. The Paleozoic detrital zircons have also proved that the southwestern Ordos Basin passive continental margin was developed during the Ordovician, then it evolved into continent-continent collisional orogenic belt during the Silurian-Devonian, and finally gradually evolved into a sedimentary basin during the Carboniferous-Permian period.