Cenozoic source-to-sink driven by tectono-geomorphic evolution: A systematic detrital zircon U-Pb analysis in the central northern South China Sea

To decipher the geomorphic and drainage evolution between Tibet and the South China Sea (SCS), the Cenozoic source-to-sink evolution of the central northern SCS has always been a research hotspot. However, previous provenance studies mainly focus on Cenozoic deposits in the central Pearl River Mouth Basin (PRMB) and their implications on the evolution of the Pearl River and the source areas in South China, leaving the provenance characteristics of other places, especially the western and eastern PRMB, and their relationship with surrounding tectono-geomorphic evolution unknown. We obtained some new data from the western and eastern PRMB, which allows for a complete story about the Cenozoic source-to-sink evolution of the central northern SCS. Based on comparative analyses of zircon U-Pb and geochemical data of Cenozoic sediments and pre-Cenozoic bedrocks in the PRMB as well as modern river sand in surrounding potential drainage systems, considering tectonic and geomorphic evolution in/around the SCS, we find that the Cenozoic provenance of the central northern SCS varies both in time and space. Generally, most of the Eocene sediments show almost the same age spectra as their adjacent pre-Cenozoic bedrock highs/uplifts, implying that intrabasinal source-to-sink processes dominated before the latest Eocene; the Oligocene and upward deposits display similar age spectra to modern river sand in adjacent drainage systems, suggesting that extrabasinal have taken over since Oligocene; while sediments between them show more complex age spectra that vary vertically, indicating that provenance shifts from intrabasin to extrabasin occurred during Late Eocene. Geomorphic changes resulting from regional tectonic activities between Tibet and the SCS control the source-to-sink and drainage system evolution in/around the central northern SCS. The ENE-tilting axial topography and its differential evolution of the northern SCS have controlled the supply and changes of detritus from Central Vietnam eastwards to the Zhu II Depression since the Eocene. By contrast, the gradual topographic inversion of South China from W-tilting to E-tilting has resulted in the headward erosion and growth of drainage systems in South China since the latest Eocene and subsequent provenance shift and evolution in the central northern SCS. With the geomorphic and drainage evolution, the Pearl River provided detritus mainly to the central PRMB, while other smaller drainage systems fed to their adjacent area, and the South China detritus supply has become dominant in the central northern SCS since the Oligocene, in which the components from Cathaysia Block remained as the main contributor, though detritus from Yangtze Block did increase gradually.