Geochronology of Cretaceous A-type granitoids or alkaline intrusive rocks in the hinterland, South China: constraints for late-Mesozoic tectonic evolution.

In the hinterland of South China, there are some Cretaceous A-type granitiods or alkaline intrusive rocks, e. g. , Huashan aegiriteaugite riebeckite granite in Anhui, Dayuancun aegiriteaugite arfvedsonite granite in Fujian, Ejinao nepheline sodalite syenite in Guangdong and Daheshan pyroxene quartz syenite porphyry and Sucun geode-like Kf-granite in Zhejiang. The geochronology of zircon SHRIMP and some minerals (amphibole and K-feldspar) 40Ar -39Ar dating indicates that they were mainly formed in 137 - 86 Ma. Combining with previous published isotopic ages of Late Mesozoic A-type granitiods or alkaline intrusive rocks in South China, our study also suggests that these A-type granitoids alkaline intrusive rocks may be classified as three periods. (1) Jurassic (184 - 152Ma) rocks: they distribute along the southern segment of the ' Shi-Hang rift zone' and in the south of Jiangxi, and their petrogenesis was possibly related to the strike-slip and extension due to low-speed and oblique subducting or transcurrent moving of paleo-Pacific plate or lithospheric extension which was independent of the movement of paleo-Pacific plate. (2) Early Cretaceous (139 - 123Ma) rocks: they distribute to the west of Zhenghe-Dapu fault zone and the lithospheric thinning or back-arc extension in relation to fast-speed and oblique subducting of paleo-Pacific plate is a likely responsible mechanism for their formation. (3) Late Cretaceous (101 - 86Ma) rocks: they mainly occur along the coastal of Fujian-Zhejiang area but distribute sporadically in the hinterland of South China, and they possibly resulted from the lithospheric extension owing to the collapse of the continental marginal arc or the roll-back of subducting oceanic crust.