南京大学地球科学系成矿作用国家重点实验室

There is a suite of shoshonitic volcanic rocks in the Huichang area, southern Jiangxi Province, which is located at the eastern part of EW-trending Early Yanshanian volcanic belt. The dominant rock types include trachybasalts, basaltic trachyandesites, trachyandesites and trachytes. In this work, we present LA-ICPMS U-Pb zircon dating, LA-MC-ICPMS zircon Hf isotopic and geochemical results for the representative samples from the Huichang volcanics. Zircon U-Pb dating results yield an crystallization age of ∼ 181 Ma, indicating that the Huichang volcanics may have been formed at the late stage of Early Jurassic. The magmatic zircons from the Huichang volcanics show a large variation of ε_Hf(t) values ranging from 2. 1 to 11. 6. A few zircons, with ages from 213Ma to 225Ma and ε_Hf(t) values of around -8. 5, may be inherited from the Fucheng granite body. The Huichang volcanics are enriched in LREE and LILE, and have obvious Nb-Ta depletions in the primitive mantle-normalized trace element patterns. It is suggested that the Huichang volcanic magma may be produced by the mixing of asthenosphere-derived melts with magma from enriched lithospheric mantle, and the magma might experienced a small amount of crustal contamination during its ascending. Since the Huichang volcanics were generated during the period of intra-continental magmatism event which's related to the paleo-Pacific plate subduction, they may record the asthenosphere-lithosphere-crust interactions under intraplate extensional regime, similar to the other Early-Middle Jurassic mantle-derived igneous rocks in southern Jiangxi Province.