Phanerozoic tectonothermal events of the Xuefengshan Belt, central South China: Implications from U-Pb age and Lu-Hf determinations of granites

The Xuefengshan Belt, characterized by large-scale fold and thrust structures and widespread granites, is a key area to decipher the tectonic evolution of the South China block. In this belt, two magmatic episodes are recorded by Early Paleozoic and Early Mesozoic granites. In this paper, we carried out precise SIMS zircon U-Pb dating and in situ Lu-Hf isotopes measurements on these granitic plutons. Our study indicates that the Early Paleozoic and the Early Mesozoic granites are late-orogenic products of the Early Paleozoic orogen and the Middle Triassic Xuefengshan orogen, respectively. In the Xuefengshan Belt, the Early Paleozoic event is poorly registered, since this area corresponds to the outer zone of the early Paleozoic orogen. The Silurian-Early Devonian granites are late-orogenic plutons emplaced after the main tectonic and metamorphic stage in the Wuyi-Baiyun-Yunkai belt, coeval with a widespread, subsequent extensional event in eastern and southern South China. On the other hand, Triassic granites are formed in an intracontinental environment with weakly to strongly peraluminous signatures. Zircon U-Pb ages presented here, associated with a summary of newly acquired data in the same region, suggest that the emplacement of anatectic granites occurred around 225-215 Ma, not in a rather wide range of ca. 245-200 Ma. In situ zircon epsilon(Hf)(t) values indicate a crust-derived source without a mantle-derived input for the two generations of granites. Combining our data with recent studies, we infer that the central area of the South China block has experienced two tectonothermal events: the Early Paleozoic magmatism developed as a result of the collapse of the Early Paleozoic orogen, while these Early Mesozoic granites can be the late-orogenic products of the intracontinental Xuefengshan orogen, most likely manifesting the far field effect by the subduction of the Paleo-Pacific ocean plate at the southeastern margin of the South China block. (C) 2012 Elsevier B.V. All rights reserved.