Geochronology and geochemistry of the Yidi'nan quartz diorite in the West Qinling, China: Implications for evolution of the Palaeo‐Tethys Ocean

Abstract

The Xiahe‐Hezuo polymetallic district, located the northwest portion of the West Qinling orogen, has a wide distribution of granitoid rock. Thus, information on the widespread Triassic granitoids in this area is important to constrain the tectono‐magmatic processes. However, the tectonic setting and genetic mechanism for the granitoids in this area are still controversial. In this study, we present a detailed description of zircon U–Pb ages, whole‐rock geochemistry, and Hf isotopes for the Yidi'nan quartz diorite and elucidate their petrogenesis and geodynamic implications. The quartz diorite was crystallized at 240.6 ± 1.8 Ma, based on its zircon U–Pb age. The quartz diorite belongs to the high‐K calc‐alkaline, metaluminous, I‐type granites and its fractionated REE patterns show enrichment of Rb, U, and Th, depletion of Ba, Sr, Nb, and Ta, and negative Eu. The zircons have negative εHf(t) values in a range of −7.66 to −2.72, corresponding to two‐stage model ages ranging from 1.66 to 1.48 Ga. The integrated data from petrology, geochronology, and bulk geochemistry suggest that the quartz diorite is formed along an active continental margin, and from the partial melting of the Lower Proterozoic crust. It is associated with the Palaeo‐Tethys oceanic crust that suffered northward subduction beneath the South Qinling Block from Permian to Early Triassic.