Core complex type structures are common in continental margins. Recent studies have proposed exhumation of deeper crustal and mantle levels during extension of the continental margin along the Northern South China Sea (NSCS) in a core complex mode. Here, we present high‐resolution seismic profiles across different sections of the NSCS that allow us to observe two types of core complex systems. The Kaiping Rift and eastern Baiyun Rift are characterized by a sub‐horizontal Moho and exhumation of ductile deeper crust beneath an extremely thinned brittle upper crust. The central Baiyun Rift in contrast is marked by homogeneous thinning of the entire crust that is floored by mantle unroofing with a concave‐down Moho geometry. While the former type, referred to as crustal core complexes, coincides with relatively intense syn‐rift magmatism, the latter, referred to as mantle core complexes, is marked by limited magmatism. Consistently, basin subsidence rates are lower over crustal core complexes than mantle core complexes. Compared to mantle core complexes at the magma‐poor Iberian margin, the widely distributed crustal core complexes in the NSCS indicate higher geotherms and more intense magmatism during extension of the continental lithosphere. We propose that the continental core complexes observed at the NSCS represent a typical outcome of extension of a gravitationally unstable lithosphere.

Crustal thinning and hyperextension have been clearly imaged and well‐documented in the Qiongdongnan Basin (QDNB), located in the NW South China Sea. Integrated analysis of newly acquired 3D seismic data, covering the majority of the QDNB, reveals the presence of two distinct fault systems: a NE‐trending set and an E‐W‐trending set, both of which played significant roles in controlling sedimentation patterns and crustal deformation during Cenozoic rifting. The NE‐trending faults were primarily active during a first stage (∼42.5–33.9 Ma) and led to crustal stretching. In contrast, the E‐W‐trending faults developed during a second stage (∼33.9–25.5 Ma) and induced crustal necking and hyperextension, resulting in the formation of metamorphic core complexes and associated detachment faults. Kinematic restoration of seismic profiles indicates that detachment fault activity and crustal thinning progressed through a gradual westward migration during the second stage. This evolution followed a core complex necking model, wherein ductile lower crustal material flowed into the footwall region beneath the detachment fault, thereby expanding the exhumation domain until the lower crust in the hanging wall was fully attenuated. Subsequently, fault deformation transitioned from decoupled to coupled behavior, with strain progressively localizing within the brittle upper crust of the hanging wall, ultimately resulting in the formation of a hyperextended crustal architecture.

Magmatic intrusions and extrusions significantly influence the architecture of sedimentary basins, yet their genetic mechanisms in hyper-extended rifted margins remain debated. Using basin-wide 3D seismic data, we investigated magmatism in the central depression belt of the Qiongdongnan Basin (QDNB), northern South China Sea. We identified a complex igneous province comprising diverse intrusive bodies (sills, dykes, laccoliths) and 24 volcanic edifices, defined 13 volcanic architectural elements, and classified five conduit types. Detachment faulting thinned the crust to 5–10 km, and the resulting weak zones facilitated melt ascent. We propose a “Lithospheric Decompression Melting–Mantle Plume Upwelling Dual Dynamic Control Model,” in which Cenozoic magmatism was governed by three coupled factors: (1) hyper-extension weak zones that provided inherited pathways for melt ascent; (2) thermal anomalies from the Hainan Mantle Plume; and (3) southward–southeastward migration of the South China Block relative to the plume axis. This interaction produced a “tectonic conveyor belt” effect, explaining two magmatic pulses: a late Oligocene–Pliocene pulse centered in the QDNB and a Pliocene–Quaternary pulse in the Leiqiong area. This study provides a typical case of lithosphere–mantle interaction, with implications for hydrocarbon exploration and geothermal assessment in igneous-rich deep-water basins.