Provenance variation of the Cambrian-Ordovician sedimentary rocks across South China and implication for its paleogeography in East Gondwana

Abstract

The tectonic nature of the Early Paleozoic Kwangsian event in the South China Block (SCB) and the paleogeographic position of the SCB in East Gondwana remain enigmatic. Clastic rocks contain significant clues for their detritus provenances, paleogeographic reconstruction and tectonic setting. This study presents detailed detrital zircon UPb geochronology and Hf isotope analyses for the Cambrian sandstones in the SCB, as well as summarizing previously-published data of other Cambrian-Ordovician sedimentary rocks. All the Cambrian-Ordovician sedimentary samples can be subdivided into three groups: the ZD-CL (between Zhenghe-Dapu and Chenzhou-Linwu faults), CL-AL (between Chenzhou-Linwu and Anhua-Luocheng faults) and AL-West (west of Anhua-Luocheng Fault) zones. These three subgroup samples have similar detrital zircon age spectra, cumulative proportion curves and εHf(t) values. Their detrital zircon age spectra are characterized by one prominent age-peak at ∼953 Ma and three subordinate age-peaks at ∼2500 Ma, ∼788 Ma and ∼ 529 Ma. Such signatures argue against provenance variation throughout the SCB during the Early Paleozoic, suggesting an intra-continental affinity for the Kwangsian event in the SCB. The Cambrian-Ordovician sedimentary samples in the SCB have similar detrital zircon age spectra and cumulative proportion curves to those in Australia, Qiangtang and Himalaya. The detrital zircons of ∼953 Ma and ∼ 529 Ma age-clusters in the SCB have similar εHf(t) values to those in Australia and Qiangtang. These features imply that the SCB was located at the nexus between Australia and India during the Cambrian-Ordovician, receiving sediment detritus both from India and Australia.