DETRIAL ZIRCON PROVENANCE OF SOUTH CHINA SEA BASINS SIGNAL DRAINAGE REORGANIZATIONS ACROSS EAST ASIA TIED TO TECTONICS AND CLIMATE

This study presents a compilation of detrital zircon U-Pb ages from modern sands of major rivers across East Asia, that aid in defining the likely provenance of major sediment source regions and and their contributions to Cenozoic sediments in basins of the northern South China Sea (SCS). These include the Yinggehai, Qiongdongnan, and Beibuwan basins in the western SCS and Pearl River Mouth, Southwest Taiwan, and Taiwan Strait basins in the eastern SCS. The compilation demonstrates that the ages of igneous rocks that make up the basement of the offshore basins are relatively narrow, defined by ~80-190 Ma ages. In contrast, the age distributions of the onshore sediment source regions are more complex. For example, the provenance of east Cathysia is defined 80-150 Ma, 200-290 Ma, 400-450 Ma, and 1700-2100 Ma age groups. While west Cathaysia’s provenance is similar, it lack 1700-2100 Ma ages, also missing from Red River region and Northeast Vietnam. The Tibetan Plateau contains the youngest zircons, with a recognizable peak at ~80 Ma. The compilation also documents changes in provenance within the SCS basins that may be tied drainage reorganizations linked to tectonic and climatic processes onshore. Prior to the Eocene, age distributions of sediments from northern SCS basins were relatively simple, dominated by <500 Ma. However, since the Oligocene, ages distributions have become more complex and include 700-1000 Ma, 1700-2100 Ma, and 2400-2600 Ma age groups. Our analysis reveals four main stages, tied to reorganizations of onshore rivers. (1) From the Late Jurassic to Middle Eocene, the western basins received sediments that were largely derived from western Cathaysia rivers, while intra-basin basement was the primary source of sediments to eastern basins. (2) In the Late Eocene to Early Oligocene, Northern Vietnam becomes the primary source region for the western basins, while eastern basins receive a mix of sediments derived from intra-basin sources and sediments eroded from the Cathaysia Plate. (3) In the Late Oligocene, catchments expand and Northeast Vietnam and its surrounding region become the main sediment sources area for western basins, while the Cathaysia Plate plays a dominant role in the provenance to the eastern basins. (4) From the Miocene to Quaternary, the Red River catchment becomes a major contributor of sediments, together with contributions from Northern Vietnam and the western Cathsysian rivers.