Provenance of Late Sinian-Cambrian Sandstones in Northeastern Guangxi: Constraints on Early Paleozoic Tectonic Evolution of South China Block

Late Sinian-Cambrian sandstones are well preserved in the northeastern area of the Guangxi Zhuang Autonomous Region, which is the western part of the Nanling Metallogenic Belt and the southern extension of the Jiangshan-Shaoxing fault zone, and can thus provide crucial information to constrain the Early Paleozoic tectonic evolution of the South China Block. This study presents petrological, geochemical and geochronological data of the Late Sinian-Cambrian sandstones in order to reveal their provenance and to constrain the Early Paleozoic tectonic evolution of the South China Block. Results show that the quartzofeldspathic sandstone and quartzose greywacke in the Yongfu and Hezhou areas are generally characterized by the enrichment of light Rare Earth Elements (REE), depletion of heavy REE, with negative Eu and Ce anomalies. The detritus could have been dominated by the recycled felsic igneous rocks and sedimentary components. Geochemical results suggest that the Late Sinian-Cambrian sandstones in the Yongfu and Hezhou areas may have been deposited in a tectonic setting that resembles passive continental margin. U-Pb ages of detrital zircon grains in the Yongfu Late Sinian sandstones peak at 900 to 780 Ma, with subordinated peak at 2.0 Ga, showing an affinity with the Yangtze Block. The Cambrian sandstones in the Yongfu area and the Late Sinian-Cambrian sandstones in the Hezhou area are characterized by large amounts of ca.1.0 Ga detrital zircon grains, showing an affinity with the Cathaysia Block. Combined with paleogeography, the shift of provenance of the Cambrian sandstones in the Yongfu area suggests that the Nanhua rift basin became shallower and smaller during the Early Cambrian. The Yangtze Block and the Cathaysia Block began to assemblage again during the early-Middle Cambrian (>520 Ma), with a southwestern boundary between the Yongfu and the Hezhou areas. Based on detrital zircon provenance analyses, we propose that the South China Block was located at the periphery of the northwestern margin of India in East Gondwana during the Late Sinian to Cambrian. © 2021, Science Press. All right reserved.