Late Mesozoic magmatism in Southeast China extensively reworked the Cathaysia Block’s crust, linked to the Paleo-Pacific Plate subduction beneath East Asia. The northeastern Cathaysia Block, largely covered by Cretaceous volcanic-sedimentary basins, has limited Jurassic exposure to Early Cretaceous intrusions, which provides critical insights into deep crust-mantle processes. In this study, we present zircon U-Pb geochronology and Hf isotope, whole-rock geochemistry, and Sr-Nd isotopes of the Middle Jurassic syenite-granite suites and Early Cretaceous granites with enclaves in the Qingyuan area (SW Zhejiang Province) to constrain their petrogenesis and tectonic significance. Middle Jurassic syenites and alkali-feldspar granites (169–167 Ma) exhibit calc-alkaline to shoshonitic affinities and weakly peraluminous compositions. Early Cretaceous granites (134 Ma) and their enclaves (136 Ma) are high-K calc-alkaline and weakly peraluminous to metaluminous. All samples show LILE and LREE enrichment, HFSE depletion, and negative Eu and Sr anomalies, with only syenites displaying negative Ce anomalies. We suggest that the Middle Jurassic syenites originated from the partial melting of an enriched lithospheric mantle influenced by subduction-related metasomatism. Alkali-feldspar granites derived from partial melting of the basement of the Cathaysia Block. Early Cretaceous granites formed by partial melting of lower crustal mafic rocks, with enclaves representing earlier crystallization products, which were then mechanically mixed with granites. We propose the NE Cathaysia Block underwent significant reworking from the Middle Jurassic to the Early Cretaceous. Middle Jurassic syenites formed in a compressional setting linked to Paleo-Pacific Plate subduction, while Early Cretaceous magmatism reflects lithospheric extension and crust-mantle interaction triggered by slab rollback.

During the Mesozoic, NE Asia experienced intense tectonic and magmatic activity, including the closure of the Mongol–Okhotsk Ocean (MOO), the subduction and demise of the Mudanjiang Oceanic Plate (MOP), and the continuous westward subduction of the Paleo-Pacific Plate (PPP). The evolution of the MOP remains highly contentious, particularly regarding its final closure timing and subduction polarity, and warrants further investigation. The Heilongjiang Complex (HLC), primarily distributed within the Mudanjiang Suture Zone (MSZ), which separates the Jiamusi and Songnen blocks, preserves key geological records of the Mudanjiang Oceanic subduction and closure. By employing detailed structural analysis, zircon U-Pb dating, and tomographic imaging, we reconstruct the tectonic history of the HLC and propose its five stages of deformation since the Mesozoic. The first stage, which occurs from the Late Triassic to the Early Jurassic, is characterized by SE-dipping schistosity within the HLC. Integrating the identification of the east-dipping remnants of the oceanic lithosphere west of the MSZ by tomographic imaging suggests an eastward subduction of the MOP underneath the Jiamusi Block during the Early Mesozoic. The second stage, spanning the Early Jurassic to the Late Jurassic, is characterized by E–W-striking tight folds associated with the MOO’s SSE-ward subduction and PPP’s NNW-ward subduction. The third stage of deformation, occurring from the Late Jurassic to Early Cretaceous, features S–N-striking box folds, indicative of the final amalgamation of the Jiamusi, Songnen, and Nadanhada terranes. The fourth stage, taking place in the late Early Cretaceous, is marked by near E–W-striking thrust faults that are associated with the closure of the eastern segment of the MOO. Finally, the fifth stage, which follows the Early Cretaceous, involves nearly NE-striking thrust faults related to NW-ward subduction of the PPP.