Permian Tectonic Evolution Of The Southwestern Ordos Basin, North China: Integrating Constraints From Sandstone Petrology And Detrital Zircon Geochronology

The Late Palaeozoic dynamic setting of the Ordos Basin in the southwestern North China Craton (SW-NCC) is poorly constrained due to limited understanding on the source-to-sink relation. This study presents integrated provenance clues from the Permian strata in the southwestern Ordos Basin to trace the sources and to discuss the tectonic setting of the basin in the SW-NCC. The reconstructed palaeocurrent directions of these Permian sediments generally point to the northeast and suggest the dominant sedimentary influx from the southwest. Modal composition analysis shows the Permian deposits have an overwhelming derivation from mixed sources containing orogeny, continental block, and magmatic arc. Zircons from the lower section yield major age clusters of similar to 300-270 Ma and similar to 2,500-1,700 Ma. While, zircon age spectra for the upper section are marked by the abundance of similar to 1,000-800 Ma and similar to 500-400 Ma ages, and the lack of Permian populations. Sources of the lower section were interpreted to be the arc terrane along the southern border of SW-NCC, in contrast, sources of the upper part were attributed to the Central Qilian Block. Zircons of similar to 300-270 Ma indicate significant magmatic activities in a rapidly uplifting continental arc, yielding an additional clue for the subduction and the existence of the Mianlue Ocean in the northeastern Palaeo-Tethys. The changes in provenance and depositional rate at the Middle Permian indicate the rapid subsidence along with the intensive uplift of the continental basement in the SW-NCC. These signatures likely infer that the back-arc basin may have evolved into a compressional setting at that time.