Late Mesozoic Wangxiang Composite Granitic Pluton, South China Block: Implications to Magma Emplacement and Evolution from Geochemical Proxies

Composite granitic pluton with distinct units is a potential target for identifying its detailed magma evolution. Here, we present zircon U-Pb ages and Hf isotope, whole-rock major and trace element compositions and Nd-Pb isotopes of the Wangxiang composite pluton, South China. New ages obtained show that these rocks were generated in Late Jurassic (ca. 156–158 Ma). The rocks are divided into low silica (SiO2 < 67 wt.%, biotite granodiorites and their dioritic enclaves) and high silica ones (SiO2 > 71 wt.%, two-mica granites, garnet-bearing muscovite granites and muscovite granites). The high silica rocks are enriched in light rare earth elements (LREEs) relative to heavy REEs (HREEs) ((La/Yb)N = 15.6–41.9, while the low silica rocks are not (0.7–76.6). All rocks show various negative Ti, Sr, Eu and strong positive Pb anomalies. The low silica rocks have less negative values of εNd(t) (−8.79 to −6.99), similar values of (206Pb/204Pb)i (18.155–18.346) and εHf(t) (−9.51 to −3.47, except one −12.84), compared to the high silica rocks (εNd(t) = −11.14 to −10.26; (206Pb/204Pb)i = 17.935–19.093; εH(t) = −12.03 to −7.15, except one −2.41). Data suggest that the parental magma of the studied rocks (represented by enclaves) was produced by partial melting of a garnet-free crustal source. Subsequently those crustal magmas formed the more evolved units through assimilation and fractional crystallization processes, and fluid enrichment during the final magmatic activity. Combining our results with previous multidisciplinary studies, we propose that the key factor to control the evolution of Wangxiang composite pluton is discrete emplacement of crustal magmas by dyking.