Provenance evolution of the Fushan Sag (Hainan Island, Southern China): Constraints from U-Pb geochronology on detrital zircons

The Fushan Sag, situated on the southeast of the Beibuwan Basin in the northern Hainan Island, represents a semi-graben fault sag, characterized by a near NEE trend. In this study, we conducted LA-ICP-MS U-Pb age dating on detrital zircon from both the Liushagang and Weizhou formations in the Fushan Sag. By integrating our findings with previous research and considering the geological characteristics and bedrock conditions of the surrounding areas, we aimed to ascertain the provenance of the Fushan Sag. The obtained detrital zircon ages (1059 with 80% concordance) can be primarily categorized into three distinct age groups: Mesozoic (90-250 Ma), Paleozoic (250-450 Ma), and Proterozoic (450-2500 Ma). Specifically, detrital zircon grains from the Weizhou Formation reveal three prominent age peaks, approximately falling within the ranges of 100-150 Ma, 250-300 Ma, and 400-450 Ma. Conversely, the detrital zircon grains extracted from the Liushagang Formation predominantly exhibit two age peaks, approximately spanning 100-150 Ma and 200-300 Ma, with a weaker peak observed at 350-450 Ma in the second member, implying a potential change in provenance during this period. A comparative analysis of detrital zircon age characteristics strongly suggests that the primary provenance of the study area is Hainan Island, with the possibility of contributions from the YunKai Massif. Base on the preliminary geochronological data gathered, and in conjunction with extant scholarly research, an inference can be formulated regarding the paleogeographic evolution of the Beibuwan Basin spanning from the Eocene to the Oligocene. This analysis offers insights into the basin's geological history and dynamic changes over this extensive time frame.