Late Jurassic to Early Cretaceous mafic to felsic magmatism reveals the coupled processes of crustal growth and thinning in Southeast China

Abstract

The study investigates the petrogenesis, deep magmatic processes, and tectono-magmatic evolution of Late Jurassic to Early Cretaceous mafic-felsic igneous rocks from the Guangdong-Fujian border area in Southeast China, using detailed field, petrographic observation, zircon U-Pb geochronology, Hf isotopes geochemistry, bulk-rock major-trace elements and Sr-Nd isotope geochemistry. Zircon U-Pb dating reveals three distinct magmatic activities. The Late Jurassic (ca. 152 Ma) granitoids, identified as fractionated both I-type and A-type granites, exhibit low ε_Hf (t) (−8.3 to −1.9) values and enriched Sr-Nd isotopes that are consistent with melting of psammitic sources. The Late Cretaceous complex (ca. 105 Ma) with initial ⁸⁷Sr/⁸⁶Sr ratios (0.7059 to 0.7067) and ε_Nd (t) values (−4.0 to −2.9), together with relatively high ε_Hf (t) values (−5.6 to 1.4), suggesting binary mixing of melts from psammitic and basaltic sources. The Cenozoic mafic rocks display varied ⁸⁷Sr/⁸⁶Sr ratios (0.7048 and 0.7096) and positive ε_Nd (t) values (4.0 and 1.0), indicating an asthenospheric mantle source. Fractional crystallization played a key role in the magmatic evolution of the rocks. The Late Jurassic magmatism may indicate that Southeast China was primarily under a setting of lithospheric extension since 152 Ma, driven by slab rollback. The Late Cretaceous magmatism reflects large-scale lithospheric extension and thinning, triggered by a change in the subduction direction of the Palaeo-Pacific slab from oblique to parallel with the continental margin. Our data suggest that the rollback of the subducted Palaeo-Pacific slab in the Guangdong-Fujian border region created a back-arc extensional setting, leading to substantial crustal thinning. The extension-induced melting of the middle to lower crust, combined with mantle-derived basaltic magma underplating, were primary drivers of granitoid magmatism in Southeast China during the Late Jurassic to Early Cretaceous. In the extensional environment, crustal growth and thinning were interconnected, forming a unified geological process.