Geochronology and Geochemistry of the Yajiangqiao Plutonic Rocks in the Central South China Block: Implication for Petrogenesis and Tectonic Setting

Clarify the petrogenesis and dynamics mechanism of Triassic magmatic rock in the South China Block (SCB) is crucial for understanding the geological evolution and mineralization of South China. A series of metal deposits (including lead, zinc, tungsten, tin, uranium, etc.) have been discovered inside and near the Yajiangqiao plutonic rock, which is important ore-forming granite in the eastern Hunan region. However, its petrogenesis and tectonic setting are still controversial. Here, we present new zircon U–Pb ages and trace elements, and whole-rock major- and trace- element compositions, and in-situ Hf isotope data obtained from the Yajiangqiao granites in central SCB. LA-ICP-MS zircon U–Pb dating reveals that the granites were emplaced in the late Triassic (227 ± 2 and 226 ± 2 Ma). The geochemical characteristics of zircon and whole-rock trace elements indicate that the Yajiangqiao granites are S-type granite, which originated from the partial melting of crustal material mainly composed of metapelitic sources, with a small amount of mantle-derived material added and undergoing strong fractional crystallization. In combination with regional geological data, we suggest that the late Triassic granites in the central SCB likely were the response to the underplating of mantle-derived magmas in a post-collision setting.