Zircon U-Pb age and geochemical characteristics of Qinlingliang rapakiwi granite from Western Qinling orogenic belt in Shaanxi

Based on geological, petrological and geochemical studies, the authors investigated Qinlingliang rapakiwi granite intrusion, porphyritic biotite rapakivi granite, porphyritic hornblende biotite rapakivi granite and medium-grained biotite monzonitic granite. LA-ICP-MS zircon U-Pb analysis suggests that Qinlingliang rapakiwi granite intrusion was formed in late Triassic(215.1±2.5Ma). Qinlingliang rapakiwi granite belongs to high-K calc-alkaline series with aluminous-peraluminous nature, and is characterized by enrichment of Rb, Th, K, Pb and Nd, depletion of Ba, Nb, Ta, La, P and Eu, and significant loss of Nb, Ta and P. In addition, this intrusion has moderate-low REE concentration and right-inclined distribution curve. The magma probably mainly originated from partial melting of the crust, and also had the characteristics of crust-mantle mixing. In combination with regional geological background, the authors hold that Qinlingliang rapakiwi granite intrusion probably originated from a post orogenic extension environment.