Geochronology, geochemistry, and Sr–Nd–Hf isotopes of the Cretaceous igneous rocks in the Zhilingtou area, SE China, and their geological significance

Abstract

The Zhilingtou deposit is one of the typical porphyry Mo deposits in South China. Disseminated and veinlet Mo ores occur in the roof pendant of the granite porphyry or the contact between the granite porphyry and the Badu Group gneisses, and some orebodies are cut by adamellite dikes. Here we present zircon LA–ICP–MS U–Pb dating yielding crystallization ages of 97 ± 1 Ma for the adamellite and 110 ± 1 Ma for the graniteporphyry. The adamellite and granite porphyry are metaluminous-peraluminous and belong to the high-K calc-alkaline-shoshonite type. They are characterized by high K2O, K2O + Na2O, FeOT, FeOT/(FeOT + MgO) and zircon saturation temperatures (784–817 °C); low MgO, TiO2, P2O5, Sr/Y and La/Yb values; enrichment in trace elements Rb, Th, U, La, Ce and other large ion lithophile elements; and depletion in Ti, Nb and P and other high field strength elements, revealing a highly fractionated A2-type affinity, formed in an extensional tectonic setting. The zircon εHf(t) values of the adamellite and granite porphyry range from −6.3 to −3.2 and from −10.0 to −4.1, respectively, with two-stage Hf model ages (TDM2 (Hf)) of 1559–1367 Ma and 1802–1430 Ma, respectively. The εNd(t) values of the adamellite and granite porphyry range from −19.0 to −11.5 and from −7.5 to −6.2, respectively, with two-stage Nd model ages (TDM2 (Nd)) of 2435–1835 Ma and 1522–1413, respectively, suggesting that they had mixed sources and were mainly formed by partial melting of a late Paleoproterozoic basement in the lower crust. In combination with previous studies, it can be concluded that after the Early Cretaceous, the subduction orientation of the Izanagi plate changed from oblique to parallel with respect to the continental margin, the slab rollback resulted in large-scale lithospheric extension and thinning, asthenospheric upwelling, and the basaltic magma underwent underplating and induced crustal melting, and finally formed the A-type granitic intrusions and related Mo mineralization systems.