Abstract:

The Lujiazhai granitic pluton located in the southern Dabie Orogen was studied by zircon LAICPMS UPb dating, zircon Hf isotope and bulk geochemistry analyses. LAICPMS zircon UPb dating gave the age of 816±17 Ma for the Lujiazhai granites, revealing that the pluton was emplaced in the Neoproterozoic. All bulk samples are high in SiO2 (6913%—7547%), with moderate A/CNK values (098—101, averaged at 10), inferring an Itype granite affinity. The concentration of total rare earth elements (REEs) varies in the range of 2743×10-6 to 16066×10-6. The Lujiazhai granites are characterized by an enriched LREE pattern with slightly negative to positive Eu anomalies. They are enriched in large ion lithophile elements (e.g. K, Ba, Sr), but depleted in high field strength elements (e.g. P, Nb, Ti). Zircon Hf isotopic data indicate that the Lujiazhai Neoproterozoic granitic pluton in the southern Dabie Orogen was likely formed by magmas derived from partial melting of Early Precambrian metamorphic complex, accompanied by the heating and possible assimilation of mantlederived magmas. By combining studies of the paleogeographic reconstruction of the Rodinia supercontinent, we propose that since the early Neoproterozoic, the northeastern margin of the Yangtze block might have been under an active continental margin setting induced by subduction of an oceanic plate. In this tectonic regime, the Lujiazhai granites were derived by partial melting of ancient crustal materials induced by the underplating or intracrustal heating of hot mantlederived magmas. After the cease of subduction and consequent continentarc collision, this area was then likely dominated by postcollisional extension or rifting tectonically, related to the breakup of the Rodinia supercontinent.

Key words: Lujiazhai pluton, zircon UPb age, zircon Hf isotopes, Dabie Orogen, Neoproterozoic magmatism