Mantle induced hydration and oxidation of intracontinental granite sources in the North China Craton

Abstract

Arc magmatism is typically highly oxidized, due to the influx of oxidizing aqueous fluids released from the subducting plate. The observation that some intracontinental A- and I-type granites also exhibit high oxidation presents a significant challenge in igneous petrology and geodynamics. This is particularly true for regions such as the North China Craton (NCC), situated over 1000 km from the trench. In this study, we measured water content, oxygen fugacity ($f{O}_2$), and O-Hf isotopes in zircons from the late Mesozoic granites from the NCC. The results reveal positive correlations between water content and $f{O}_2$, and between water content and ${\epsilon }_{\text{Hf}}\left(t\right)$, indicating the predominant control of primary magma composition, rather than magmatic differentiation, on water content and $f{O}_2$ of zircon. The Early Cretaceous A-type and I-type granites, which involved greater amount of mantle-derived melts, exhibit more elevated water, Nb, Ta, and $f{O}_2$ than the Jurassic granites. This suggests that the hydration and oxidization of intracontinental granitoids of the NCC are strongly influenced by the ingress of mantle-derived oxidized hydrous melts/aqueous fluids to the granitoid source, which were likely released from the Paleo-Pacific plate at a greater depth than the sub-arc mantle. The proposed model involves significant water in intracontinental crustal melting, thereby challenging the paradigm of intraplate A- and I-type granite genesis and shedding light on the crustal and mantle processes during cratonic destruction.