Ages and geochemistry of Cretaceous igneous rocks record the transition from compression to extension in Fujian Province, South China

Late Mesozoic magmatism in South China provides critical insights into East Asia continental margin evolution. Cretaceous magmatic rocks in coastal Fujian Province, South China, record the coupled magmatic-tectonic evolution of this area, yet key questions remain regarding magma source transformation, timing of the compressional-extensional transition, and its driving mechanisms. This study focused on Cretaceous magmatic rocks in eastern Fujian, South China, employing zircon U-Pb dating, zircon Hf isotope analyses, and whole-rock analyses. These samples are categorized as undifferentiated I-type granites, highly differentiated I-type granites, and A-type granites. The I-type granites were derived from ancient crustal melting with crust-mantle interaction, while the A-type granites were generated by high-temperature and anhydrous remelting of enriched crustal components, with plagioclase fractionation in an extensional environment. In combination with available geochemical data in this area, magma sources shifted from 130 Ma to 80 Ma due to changing crustal contributions and enhanced fractional crystallization accompanied by melt extraction from the magma chamber. The following dynamic model is proposed: During 130−110 Ma, Paleo-Pacific plate subduction caused compression and thickened the crust, generating I-type granites via crust-mantle hybridization and crystallization differentiation. From 110 Ma to 100 Ma, slab rollback increased the subduction angle, triggering asthenospheric upwelling and lithospheric delamination, shifting stress from compression to extension. Lithospheric thinning dominated the 100−80 Ma interval, during which extensional tectonics facilitated the formation of A-type granites.