Water content drives distinct evolution trajectory of Early Cretaceous granitoids in inland and coastal southeast China

Abstract

Water plays a crucial role in determining the crystallization sequence of magma, which subsequently influences the chemical compositions of magmatic rocks across different tectonic settings. In this study, we compared the evolutionary features of granitic rocks along the coast and inland areas of southeast China, aiming to identify the key factors influencing their evolution. Our work indicates that multiple granitic intrusions formed between 126 and 142 Ma in the coastal region of southeastern China, which is consistent with the formation ages of large-scale granitoids in the inland Gan-Hang Belt. Isotopic characteristics suggest that the granitic rocks in southern Fujian originated from the melting of juvenile crust, while those in northern Fujian and eastern Zhejiang were formed from the partial melting of ancient crustal rocks, incorporating mafic magma evolved from the mantle. Most of the granitoids from the coastal region of southeastern China exhibit low zircon saturation temperatures (680–800 °C) and Zr/Sr ratios (<1), suggesting their origin from a cold, wet magma reservoir. The porphyritic quartz diorite and porphyritic monzogranite represent the residual cumulate rocks of this hydrous magma reservoir, whereas the granitic porphyry and high-silica equigranular alkali feldspar granite evolved from the felsic melts extracted from the same reservoir. In contrast, most of the Early Cretaceous granitoids in the Gan-Hang Belt, located in the inland areas of southeast China, display high zircon saturation temperatures (800–900 °C) and Zr/Sr ratios (>1), indicating their origin from hot, water-poor magma reservoirs. The porphyritic granites in this region represent residual cumulate rocks formed in water-poor magma reservoirs, whereas the high-silica equigranular granites evolved from hot felsic melts extracted from similar magma reservoirs. In the Early Cretaceous, the coastal region of southeastern China was closer to the Late Mesozoic paleo-Pacific subduction zone, where crystal-melt segregation within cold, wet magma reservoirs predominantly influenced magma evolution. Conversely, the granitoids in the Gan-Hang Belt in the inland region, located farther from the Late Mesozoic paleo-Pacific subduction zone, were associated with a rift tectonic setting and formed through crystal-melt segregation within hot, water-poor magma reservoirs. Our study underscores the critical role of water content in magma reservoirs in shaping the chemical composition of granitic rocks through crystal-melt segregation, thereby deepening our understanding of crustal formation processes across diverse tectonic environments.