Zircon U-Pb Chronology and Hf Isotope From the Palawan-Mindoro Block, Philippines: Implication to Provenance and Tectonic Evolution of the South China Sea

摘要

The continental margin of Southeast Asia evolved from a dominantly Andean-type active margin during Mesozoic to a Western Pacific-type since Late Cretaceous. With the spreading of the South China Sea, the Palawan-Mindoro Block drifted from mainland Asia and the Cenozoic strata provide an excellent window to gain insights into the tectonic evolution of the margin of Southeast Asia. Here we present U-Pb age and Hf isotopic data on detrital zircon grains from Cenozoic sedimentary rocks in the Palawan-Mindoro Block, Philippines, to evaluate the provenance and tectonic evolution of the South China Sea. Zircon grains in Eocene-Miocene sedimentary rocks from the Palawan-Mindoro Block show a wide range in age from 60 to 2700 Ma, with four major age groups of 80-120 Ma, 160-180 Ma, 1600-2100 Ma, and 2200-2700 Ma. The cHf(t) of the zircon grains of the samples from Mindoro Island range from -39 to +13.7, and similar Hf isotopic composition is recorded in Paleogene and Neogene strata. Zircon U-Pb ages and Hf isotopic data of the Eocene samples from the Palawan-Mindoro Block show a similar pattern with those from Taiwan, which suggests that the Palawan-Mindoro Block was attached to the margin of South China during Late Cretaceous-Eocene times. The difference of zircon U-Pb age composition in the Miocene samples between the Palawan-Mindoro Block and Taiwan reflects southward drifting of the Palawan-Mindoro Block and seafloor spreading of the South China Sea at that time.