Pre‐Breakup Continental Crust Evolution in the South China Sea Region

The formation of the Cenozoic South China Sea (SCS) via rifting/spreading was based on a Late Mesozoic collisional setting, yet pre‐breakup continental differentiation remains debated. This study presents in situ zircon Hf–O isotope analyses of Late Mesozoic Nansha (Group I, ca. 154–159 Ma) and Qiongnan (Group II, ca. 95–101 Ma) granites. Both groups result from variable mantle–crust mixing, with Group I having greater mantle input. Their two‐stage Hf model ages (1300–1100 Ma) coincide with the Grenvillian orogeny, indicating primary crust formation then, with Late Mesozoic magmatism representing reworking, not net accretion. Shared Grenvillian T DM2 ages suggest a common crustal affinity of the Nansha and Qiongnan blocks along the Rodinia margin, though original continuity remains unproven. Their isotopic differences reflect multiple factors—spatial position, temporal evolution, and crustal heterogeneity—rather than a single control. These findings constrain the pre‐drift setting, crustal reworking, and magmatic evolution of the SCS region.