Age, nature, and origin of early cretaceous plutons in the Dabie Mo Mineralization belt: the Xinxian example

The Mesozoic granitoids in the Dabie Orogen are of particular geological interest as indicators for Mesozoic lithospheric evolution and because of their close association with porphyry Mo mineralization. Here, we present a study using zircon laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U–Pb dating, petrogeochemistry, and Hf isotopic data to constrain the timing of the magmatism and petrogenesis of the Xinxian granites in the Dabie Mo mineralization belt (DMB), Henan Province, China. Field investigations combined with previously published data show that the Xinxian pluton mainly consists of four phases. Zircon LA-ICP-MS U–Pb dating yielded ages from 153.4 ± 1.1 Ma for Phase 1 to 146.4 ± 1.6 Ma for Phase 2, 131.6 ± 1.8 Ma for Phase 3, and 125.5 ± 1.5 Ma for Phase 4. The Xinxian granites have high SiO2 contents of 74.94–78.70 wt.% (average: 76.63 wt.%), Al2O3 contents of 11.59–13.68 wt.% (average: 13.01 wt.%), and K2O contents of 3.85–4.86 wt.% (average: 4.36 wt.%) with Na2O/K2O ratios of 0.78–1.03 (average: 0.92) and low MgO (0.04–0.15 wt.%), TiO2 (0.03–0.13 wt.%), and P2O5 (0.006–0.07 wt.%) contents. They are enriched in Rb, U, K, and Hf, but depleted in Ba, Nb, Ta, Sr, P, and Ti. The zircon εHf(t) values for Phases 1, 2, 3, and 4 vary as follows: from – 22.8 to – 20.3 with TDM2 values from 2682 to 2869 Ma, from – 24.2 to – 21.2 with TDM2 values from 2738 to 2925 Ma, from −24.5 to −21.5 with TDM2 values from 2722 to 2915 Ma, and from −22.9 to −19.4 with TDM2 values from 2421 to 2643 Ma, respectively. By integrating previous geological, geochronological, and geochemical data for the DMB, we propose that the Xinxian pluton was dominantly sourced from the crust. The granites were most likely derived from the partial melting of the Northern Dabie Complex (NDC) with some Yangtze lower crust and Southern Dabie Complex (SDC). The Xinxian pluton may have formed in a post-collision extensional setting.