A crustal source for ca. 165 Ma post-collisional granites related to mineralization in the Jianglang dome of the Songpan-Ganzi Orogen, eastern Tiebtan Plateau

The Wenjiaping and Wulaxi granite plutons are located in the Jianglang dome, which is a key domain for providing deep insight into the tectonic evolution of the Songpan-Ganzi Orogen. Two granites are composed chiefly of K-feldspar, quartz, biotite with minor plagioclase and hornblende. This study presents zircon U-Pb chronology, geochemistry and Hf isotope data to explore their petrogenesis and metallogenic implications. Zircon U-Pb dating provides crystallization ages of 164.5 ± 0.9 Ma and 163.4 ± 0.9 Ma for the Wenjiaping granite, and 164.3 ± 1.7 Ma for the Wulaxi granite. This indicates that they were formed synchronously. They also contain inherited zircons related to the Rodinia and Gondwana supercontinents and the Emeishan large igneous province. Their mineral assemblages lack peraluminous (e.g., garnet and cordierite) and high-temperature (e.g., pyroxene and fayalite) minerals. They are characterized by low A/CNK (1.10-0.99), FeOT/MgO (8.55-2.83) and K2O/N2O ratios (1.34-0.51) with low Zr + Nb + Ce + Y concentrations (average 258 ppm) and zircon saturation temperatures (781-651 °C). Their Al2O3, P2O5 and SiO2 contents show negative correlations, and they thus fit the I-type granite definition. Some major and trace elements exhibit strong correlations, implying extensive fractional crystallization (e.g., hornblende and ilmenite) during the magma evolution. Two granites show enrichment in light rare earth elements and large ion lithophile elements, and depletion in high field strength elements. They have low Mg# values (38.7-17.3) and Y/Nb ratios (0.45-0.16), and yield dominantly negative εHf(t) values (1.4-−13.9), indicating a heterogeneous source and their derivation from remelting of ancient continental crust (e.g., Mesoproterozoic Liwu Group in this region) with minor juvenile crust. Combined with prior studies, we conclude that the Wenjiaping and Wulaxi granites were formed in a post-collisional extensional regime, and were responsible for the 163.7-151.1 Ma magmatic hydrothermal Cu-W mineralization in the Jianglang dome. In addition, two granite plutons intrude this dome and they are undeformed, implying that the doming was during the Early to Middle Jurassic.