The Petrogenesis and Tectonic Implication of Wengong Intrusion in the Nanling Range

Gan Chengshi; Wang Yuejun; Cai Yongfeng; Liu Huichuan; Zhang Yuzhi; Song Jingjing; Guo Xiaofei

doi:10.3799/dqkx.2016.002

Abstract：The early Yanshanian geology of southeastern China is characterized by widespread igneous rocks,especially granites. However,the petrogenesis and tectonic implication of these granites in South China remain highly controversial.The A-type granites are the important carrier for better understanding the tectonic evolution of the South China block since the formation is commonly related to extensional tectonic setting.In this study,a set of new zircon U-Pb geochronological,elemental and Sr-Nd-Hf isotopic data is presented for the Wengong A-type granite in eastern Nanling range in northern Guangdong Province.La-ser zircon U-Pb dating for the Wengong granitic sample give a weighted mean age of 1 96.9 ±4.4 Ma and in-situ zirconεHf (t ) values ranging from +2.1 to +7.7.Their whole rockεNd (t )values range from -2.7 to -0.5.The Wengong granites are en-riched in SiO 2 (69.22%-76.33%)and total alkalis (7.77%-8.35%).They are metaluminous-peraluminous with A/CNK val-ues ranging from 0.95 to 1.10.These samples have high rare earth element contents,FeOt/MgO (4.40 -9.75)and 10 000× Ga/Al ratios (2.9-3.3),as well as significant Sr,Ti and Eu negative anomalies.Based on these geochemical data,it is pro-posed that the Wengong granites originated from mafic lower crust in response to the earliest Jurassic extensional setting.In combination with available data,it is inferred that the A-type granites in the Nanling range predominantly formed at 1 96 -1 56 Ma,suggesting an early Yanshanian extensional event in SE China.These A-type granites probably formed in intra-plated extensional environment,indicating the transformation from Paleotethyan to Paleopacific domain after earliest Jurassic.