Early Cretaceous Xiuyan adakitic granitoids in the Liaodong Peninsula, eastern China: petrogenesis and implications for lithospheric thinning of the North China Craton

Abstract

Mesozoic magmatic rocks are widely distributed in the North China Craton (NCC) and are crucial to understanding the timing, location, and geodynamic mechanisms of lithospheric thinning of the NCC. In this study, we report geochronological, petrogeochemical, and Lu–Hf isotopic data for adakitic granitoids from different parts of Xiuyan pluton in the Liaodong Peninsula, aiming to constrain their magma sources, petrogenesis, and tectonic implications. The adakites are metaluminous to weakly peraluminous and are classified as high-K calc-alkaline I-type granite with Early Cretaceous zircon U–Pb ages of 129–126 Ma. They exhibit adakite-like geochemical characteristics, such as high Sr content and low Yb and Y contents, coupled with high Sr/Y and no pronounced Eu anomalies. They are enriched in Rb, U, and light rare-earth elements and are depleted in Ta, Nb, P, and Ti. The adakites from the eastern part of the pluton have low εHf(t) values (–8.5 to –4.0) with old TDM2 ages (1.57–1.31 Ga), indicating they were derived from the lower crust containing juvenile mantle-derived materials. In contrast, adakites from the northern part of the pluton have lower εHf(t) values (–19.7 to –16.6) with older TDM2 ages (2.21–2.03 Ga), indicating that they were derived mainly from an ancient crust. Our results show that both adakitic magmas were derived from partial melting of delaminated lower crust. Their relatively high MgO and Ni contents and Mg# values indicate that the melts interacted with mantle peridotites. The lower crust delamination beneath the Liaodong Peninsula resulted from paleo-Pacific plate subduction during the Early Cretaceous, which resulted in thinning of Mesozoic crust in the Xiuyan area.