Geochronology, Petrogenesis and Tectonic Setting of the Late Jurassic I‐type Granites in the North Qinling Orogenic Belt, Central China

Abstract

The North Qinling Orogenic Belt (NQOB) is a composite orogenic belt in central China. It started evolving during the Meso‐Neoproterozoic period and underwent multiple stages of plate subduction and collision before entering intra‐continental orogeny in the Late Triassic. The Meso‐Cenozoic intra‐continental orogeny and tectonic evolution had different responses in various terranes of the belt, with the tectonic evolution of the middle part of the belt being particularly controversial. The granites distributed in the Dayu and Kuyu areas in the middle part of the NQOB can provide an important window for revealing the geodynamic mechanisms of the NQOB. The main lithology of Dayu and Kuyu granites is biotite monzogranite, and the zircon U–Pb dating yielded diagenetic ages of 151.3 ± 3.4 Ma and 147.7 ± 1.5 Ma, respectively. The dates suggest that the biotite monzogranite were formed at the end of the Late Jurassic. The whole‐rock geochemistry analysis shows that the granites in the study areas are characterised by slightly high SiO2 (64.50–68.88 wt%) and high Al2O3 (15.12–16.24 wt%) and Na2O (3.55–3.80 wt%) contents. They are also enriched in light rare earth elements, large ion lithophile elements (e.g. Ba, K, La, Pb, Sr), and depleted in high field strength elements (HFSEs) (e.g. Ta, Nb, P, Ti). Additionally, the granites demonstrated weakly negative‐slightly positive Eu anomalies (δEu = 0.91–1.19). Zircon Lu–Hf isotopic analysis showed ɛHf(t) = −6.1–−3.8, and the two‐stage model age is T2DM(crust) = 1.5–1.6 Ga. The granites in the study areas are analyzed as weak peraluminous high‐K calc‐alkaline I‐type granites. They formed by partial melting of the thickened ancient lower crust, accompanied by the addition of minor mantle‐derived materials. During magma ascent, they experienced fractional crystallisation, with residual garnet and amphibole for a certain proportion in the magma source region. Comprehensive the geotectonic data suggest that the end of the Late Jurassic granite magmatism in the Dayu and Kuyu areas represents a compression‐extension transition regime. It may have been a response to multiple tectonic mechanisms, such as the late Mesozoic intra‐continental southward subduction of the North China Craton and the remote effect of the Paleo‐Pacific Plate subduction.