High Water Contents in Zircons Suggest Water-Fluxed Crustal Melting During Cratonic Destruction

Water is essential for the formation of granites, but its origin and role in granite generation (i.e., dehydration vs. water-fluxed melting) remain uncertain. These issues are addressed by combining water abundances and other geochemical indices in zircons from Late Mesozoic granites generated during the destruction of the North China Craton (NCC). The water contents in zircons from the NCC Early Cretaceous granites (763 ppm, median) are much higher than those of the NCC Jurassic granites (424-513 ppm), upper mantle and continental arc magmas (92-477 ppm). More importantly, the higher water contents in the voluminous Early Cretaceous granites also have higher zircon saturation temperatures, epsilon(Hf)(t), and lower delta O-18 values. These observations suggest a predominantly mantle origin for the water, and water-fluxed crustal melting, in which larger water ingression produced more voluminous melts. The high-water flux was likely related to the subduction of the Paleo-Pacific Plate, which ultimately destabilized the NCC.