Two Late Cretaceous A-type granites related to the Yingwuling W–Sn polymetallic mineralization in Guangdong province, South China: Implications for petrogenesis, geodynamic setting, and mineralization

Abstract

Major and trace elements, whole rock Sr–Nd–Pb isotopes, LA–ICP–MS U–Pb zircon dating, zircon trace elements and Hf isotope data are reported for a suite of A-type granites from Yingwuling pluton in western Guangdong province, South China. Zircon U–Pb ages obtained by laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) show that biotite granite and alkali feldspar granite were emplaced in 81.3±0.6Ma and 80.6±0.5Ma, respectively. Both of the two suites have the petrographic and geochemical characteristics of A-type granite. These granitic rocks are metaluminous to weakly peraluminous and have pronounced contents of total alkalis (Na2O+K2O=7.80–8.84%), Fe2O3T/MgO and Ga/Al ratios. They exhibit low MgO, CaO and TiO2 contents, enrichment in some LILEs and HFSEs (except for Zr, Eu and Y), depletion in Ba, Sr, P and Ti. They show A2 subtype affinity and were probably formed a temperature of ~800°C. The Yingwuling biotite granite has relatively high (87Sr/86Sr)i ratios of 0.70655 to 0.70928, low εNd(t) values of −5.8 to −4.2 and zircon εHf(t) values (−5.70–1.37). Whole-rock Nd isotopic and zircon Hf isotopic two-stages model ages mostly vary from 1057 to 1506Ma. The alkali feldspar granite display bulk rock εNd(t) values and (87Sr/86Sr)i ratios in the range of −6.6 to −6.1 and 0.70640 to 0.71077, respectively, and zircon εHf(t) values from −5.44 to 0.54, with Mesoproterozoic T2DM for both Nd and Hf isotopes. Geochemical and isotopic data indicate the Yingwuling A-type granitic magmas were drived from mantle–crust interaction. Zircon grains of Yingwuling granites have relatively low Eu/Eu* and Ce4+/Ce3+ ratios, indicating low oxygen fugacity. The visible tetrad effect in the Yingwuling granites indicates that it experienced strong fractionation and is close relationship to the W–Sn mineralization. Our new data together with previous published data indicate that Late Mesozoic A-type granitiods or alkaline intrusive rocks in South China can be grouped into four pulses: 195–180Ma, 180–149Ma, 136–116Ma and 110–79Ma. After 135Ma, with a change in the polarity of the subduction of paleo-Pacific plate, the crust and lithospheric mantle in eastern China became progressively thinned causing the upwelling of asthenosphere, which would have triggered crustal rocks to partially melt and generate Yingwuling A-type granitic magmas.