Petrogenesis of Early Cretaceous intrusions and enclaves from the Lushan area, South China Block: Insights into magmatism and their geodynamic processes

Early Cretaceous intermediate-acidic intrusions in the South China Block contain abundant granodioritic enclaves. Integrated zircon U-Pb geochronology, Lu-Hf isotopes, and whole-rock geochemistry reveal that the Lushan granodioritic enclaves and their porphyritic biotite monzogranite hosts share similar crystallization ages and crustal origins. Elevated initial Sr isotope ratios (0.709336∼0.710143, 0.709895∼0.710394), depleted ε Nd(t) (-8.0∼-6.7, -7.8∼-5.7) and negative ε Hf(t) values (-8.8∼-0.9, -9.9∼-2.5), low Th/Nb (0.89∼1.54, 1.15∼1.79) and Nb/U (6.26∼10.39, 4.33∼5.96) ratios, and young two-stage Nd–Hf model ages (1.39–1.58 Ga; 1.21–1.77 Ga) in both the granodioritic enclaves and porphyritic biotite monzogranite mirror the Yangtze Block upper crust, identifying it as the dominant source. The emplacement of the Haihui intrusion is interpreted as resulting from lithospheric extension triggered by Paleo-Pacific slab rollback during the Early Cretaceous. This thermal pulse induced extensive partial melting of the Yangtze upper crust, followed by crystallization, differentiation, and hybridization of cognate magmas in shallow crustal reservoirs. Consequently, the Haihui intrusion exhibits isotopic signatures characteristic of crustal melting. These findings constrain the origin and hybridization history of enclave-host systems in the northern Jiangnan Orogenic Belt, highlighting the role of slab rollback-driven extension in generating Early Cretaceous crustally derived magmatism in the South China Block.