Petrogenesis Of Jurassic Volcanic Rocks In Eastern Guangdong And Its Geological Significance

Southeastern(SE)China has long been widely accepted to be controlled by paleo-Pacific tectonic regime during Late Mesozoic.It is widely accepted that the widespread Cretaceous volcanic rocks in SE China were formed at the late stage of the paleo-Pacific subduction.On the contrary,the geological response of the early stage of the subduction remains unclear.It will make a big difference by determining the exact migration pattern of the magmatic zones and the role played by crust-mantle interaction.Late Mesozoic volcanic rocks in SE China are widely distributed and continuously formed with plenty standard stratigraphic sections,thus they are more representative both spatially and temporally but less concerned than their intrusive counterparts.This study presents the systematic zircon U-Pb ages and Lu-Hf isotopic features of the Jurassic volcanic sections in eastern Guangdong,to determine their spatial-temporal framework and influences and changes of crust-mantle interaction in their petrogenesis.The results offer new perspectives and contribute to better understanding the paleo-Pacific subudction mechanism and Late Mesozoic tectono-magmatic evolution in SE China.Zircon U-Pb dating results reveal that the Jurassic volcanic rocks were formed intermittently at 192–183 Ma(Songling Fm.),177–163 Ma(Jilingwan Fm.)and 162–156 Ma(Gaojiping Gp.).Thus,a younging trend along eastern Guangdong to eastern Fujian to southeastern Zhejiang could be identified for the entire Late Mesozoic volcanic rocks in SE China.Zircon Lu-Hf isotopic analyses show that the Jurassic volcanic rocks were mainly derived by remelting of the Paleoproterozoic crustal basement,with decreasing involvement of juvenile components in their origin over time from Early to Late Jurassic.The petrogenesis of the Jurassic volcanic rocks in eastern Guangdong suggests decreasing crustal extension,corresponding to the forward subduction of the paleo-Pacific slab.Thus,the Jurassic volcanic rocks in eastern Guangdong record the early stage of the paleo-Pacific subduction,and further suggest that the subduction started at around Early Jurassic.