Diachronous slab-driven Early Cretaceous crustal extension and pulsed magmatic response in southeastern China: Insight from A-type granite and related rocks

Abstract

The Late Mesozoic magmatic belt in southeastern (SE) China, stretching over 1300 km, resulted from southwestward subduction of the paleo-Pacific plate. Our study focuses on the origin of Early Cretaceous syenite and A-type granite in SE China, utilizing zircon U-Pb and Hf isotopic analyses, bulk-rock compositions, and Nd-Hf isotopic compositions. Findings indicate that ∼ 142 Ma silica-unsaturated syenites in the southwest form through small degrees of partial melting of the metasomatized lithospheric mantle, while ∼ 142 Ma A-type granites originate from partial melting of juvenile felsic rocks. The ∼ 130 Ma A-type granites in the northeast result from mixing of ancient crustal-derived magma and mantle-derived magma. The southwest and northeast regions display distinct magmatic histories, with flare-ups and lulls occurring at different times. These variations suggest diverse extensional and compressional histories. A spatially migrating extensional regime is observed from the southwest (∼147 Ma) to the northeast (∼120 Ma) of SE China. Magmatic flare-ups in the southwest involve reworking juvenile crust, while in the northeast, they modify ancient crust, likely related to paleo-Pacific plate subduction and northeastward slab rollback. Slab subduction rate correlates strongly with observed geological events, indicating diachronous crustal extension, magmatic flare-ups, and lulls during ca. 147–110 Ma due to northeastward slab rollback and changing subduction rate.