Geological and geochemical characteristics and genesis of the Caledonian Wanyangshan granite in the Nanling Mountains, South China

Abstract：Field observations suggest that the Wanyangshan granite batholith is a complex batholith composed of different intrusive units that were sourced from multiple magmatism during the Caledonian. The types of granite in the batholith include biotite granodiorite, biotite monzogranite, and biotite-muscovite monzogranite. There are many very fine-grained mafic xenoliths in biotite granodiorite and biotite monzogranite. U-Pb analyses of zircons show that the Wanyangshan granite batholith formed in the Silurian, at ca 441-462 Ma. Geochemical analyses showed that：the Wanyangshan granite has a SiO2 content of 66.99 to 73.04%, an average K2O content of 3.91% and an average Al2O3 content of 13.74%, with Na2O+K2O=6.26 to 7.39% and K2O/Na2O=1.45 on the average. The Wanyangshan granite has a higher total REE concentration (264.43 g/g). Chondrite-normalized REE patterns show a significant differentiation between LREE and HREE and a remarkable enrichment in LREE. Eu values (Eu=0.53) indicate that the primitive magma was basic and enriched in plagioclase most likely. The Wanyangshan granite is significantly depleted in HFSE (Ta, Nb, Sr, P, and Ti), which indicates that these granite samples are strongly related with subduction. For isotopic compositions, the Wanyangshan granite has a range of initial strontium from 0.71223 to 0.71376, and a range of epsilon strontium (εSr(t)) from 109.8 to 131.5. Epsilon neodymium (εNd(t)) ranges from -7.1 to -8.3, with the depleted mantle model age of 1.74-1.86 Ga. In general, geochemical and isotopic analyses indicate that the Wanyangshan granite is ferruginous, peraluminous, high-K, calc-alkaline S-type granite, with higher concentrations of aluminium and potassium. Its primitive magma could be mainly sourced from melting of the crust, and is most likely to have been contaminated by the mantle in the early stage of magmatism evolution. The Wanyangshan granite formed under the conditions of post-orogenic extension after the collision between the Cathaysian and Yangtze blocks in the Caledonian.