Geochronology and petrogenesis of the Early Cretaceous A-type granite from the Feie'shan W-Sn deposit in the eastern Guangdong Province, SE China: Implications for W-Sn mineralization and geodynamic setting

Abstract

The Feie'shan greisen–type W–Sn deposit in the eastern Guangdong Province forms part of the Southeastern Coastal Metallogenic Belt (SCMB) in South China. Here we present zircon LA–ICP–MS U–Pb geochronology of the biotite granite which shows a weighted mean 206Pb/238U age of 134.7±2.0Ma, consistent with the zircon U–Pb, biotite 40Ar–39Ar and molybdenite Re–Os ages in the previous study. The biotite granite is peraluminous and belongs to high–K calc–alkaline type. It is characterized by high SiO2, K2O, F, K2O+Na2O and FeOt/(FeOt+MgO), and low CaO, MgO, TiO2 and P2O5 contents, enrichment in Rb, Cs, Th and U, and depletion in Ba, Sr, Zr, Ti and P, with flat REE patterns and distinctly negative Eu anomalies, showing an A2–type affinity. The rocks also display extremely low Ba, Sr and Ti concentrations and high Rb/Sr, Rb/Ba and low CaO/(Na2O+K2O) ratios, indicating high degree of fractionation. Zircon grains from the granite have low Eu/Eu⁎ and Ce4+/Ce3+ ratios, suggesting low oxygen fugacity. The highly fractionated and reduced features imply that the Feie'shan mineralization is genetically related to the biotite granite. The εNd(t) values and zircon εHf(t) values of the biotite granite range from −2.96 to −1.95 and −5.69 to 0.62, with two–stage Nd and Hf model ages (TDM2) of 1083 to 1164Ma and 1150 to 1552Ma, indicating that they were derived from magma hybridization between anatectic granitic and mantle–derived mafic magmas. In combination with previous studies, we propose a geodynamic model for the 145―135Ma W–Sn mineral system and related magmatism in the southwestern domain of the SCMB. After ca. 145Ma, the subduction orientation of the Izanagi plate changed from oblique to parallel with respect to the continental margin resulting in large–scale lithosphere extension and thinning, which led to the upwelling of asthenosphere. The ascending mantle–derived mafic magmas provided not only supplied the heat for crustal remelting but also added juvenile mantle–derived melts resulting in the formation of mafic dikes, and I– or A–type granitic intrusions related to the W–Sn ore mineral systems.