海南岛白垩纪快速剥露的40Ar/39Ar年代学证据及其古地理意义OA

The pre-Cenozoic paleogeographic pattern of the southern margin of the South China Block is essential for understanding the formation and evolution of the South China Sea.Hainan Island,located at the northern margin of the South China Sea and adjacent to the southern edge of the South China Block,serves as a key region for investigating the paleogeographic features of the passive continental margin of the South China Sea.In this study,we conducted biotite 40Ar/39Ar geochronological analyses on Triassic to Cretaceous granites from Hainan Island to explore their Mesozoic exhumation characteristics and topographic evolution.The results show that the cooling ages obtained from biotite 40Ar/39Ar range from 107 to 92 Ma.Consistent cooling ages from granitic plutons along the periphery of Hainan Island suggest rapid cooling during this period.Synthesizing available biotite 40Ar/39Ar age data reveals a"younger on the periphery,older in the center"cooling age distribution,indicating that peripheral regions experienced more significant exhumation than the central areas during this time.This implies that during the Late Mesozoic,Hainan Island exhibited a"high periphery,low center"topographic pattern.Based on these findings,we selected suitable samples for paleoelevation reconstruction using detrital zircon Eu/Eu* anomalies and whole-rock(La/Yb)N and Sr/Y ratios.The results indicate that the Cretaceous paleoelevation of Hainan Island's periphery exceeded 3000 meters.Rapid exhumation of the peripheral granitic plutons provided a substantial detrital material to the low-lying Baisha Basin in the central region,further supporting the"higher periphery,lower center"topography.A comprehensive analysis of geochronological,geochemical,and provenance data from the South China Sea's peripheral blocks reveals a widespread exhumation/cooling event during the Early to Late Cretaceous.This suggests that,at least during the Late Mesozoic,the southern and northern margins of the South China Sea still existed as a unified landmass,implying that the initiation of the South China Sea rifting occurred after this period.