A two-stage mantle plume-sagduction origin of Archean continental crust revealed by water and oxygen isotopes of TTGs

Abstract

Evolution of Archean continental crust involved partial melting of mafic crust to form the tonalite-trondhjemite-granodiorite (TTG) series. However, crustal generation remains enigmatic with both plate tectonic and non-plate tectonic modes proposed. In this study, we show that zircons from the ~2.5–billion years ago TTGs in the Eastern Block (EB) of the North China Craton have low water contents (median of 263 parts per million) and high δ¹⁸O values (median of 6.22‰) and a negative correlation between them, which suggest a thick hybridized and hydrated mafic source. By contrast, zircon water contents of the adjoining coeval TTGs in the Trans-North China Orogen, formed in a supra-subduction zone setting, are notably higher. These results support a two-stage mantle plume-sagduction process for TTG formation. Our study suggests that Archean continental crust, such as that in the EB, most likely originated from plume-related oceanic plateaus, rather than subduction-related island arc magmatism under a plate tectonic regime.