Abstract: The formation and geodynamic setting of Mesozoic-Cenozoic volcanic rocks in the basins along the South China coast remain controversial, traditionally attributed to either Paleo-Pacific subduction or South China Sea spreading. Focusing on NE-trending fissure-erupted basalts from the Heyuan Basin, this study uses ⁴⁰Ar/³⁹Ar dating to constrain their eruption ages to (67.29 ±1.78) Ma and (66.48 ±2.53) Ma. These ages coincide with the Cretaceous-Paleogene (K-Pg) boundary. Geochemically, the basalts exhibit sodic subalkaline tholeiitic characteristics (SiO₂ = 47.43-52.67 wt.%), with low Mg, K, and Ti but high Na and Al contents. Their rare earth element (REE) patterns indicate slight light REE (LREE) enrichment (ΣREE = 77-85 ppm; (La/Yb)N = 4.48-6.68), lacking significant Eu, Ce, Nb, Ta, or Ti anomalies, but displaying positive Ba, Th, and U anomalies and a negative P anomaly. Key elemental ratios (Th/Yb = 1.72-1.15, Th/Nb = 0.20-0.21, Nb/La = 1.07-1.08, Hf/Th = 1.13-1.35) suggest derivation from a depleted lithospheric mantle source with crustal contamination, formed in a continental rift setting. The Sr-Nd isotopic compositions indicate that the Heyuan basalts originated from a mixture of depleted mantle and enriched lithospheric mantle components. Regional comparisons with coeval basalts from the Nanxiong (79-69 Ma), Lianping, and Sanshui (61-54 Ma) basins reveal a NE-SW trending continental rift system along the northern South China margin during the Late Cretaceous to early Paleogene (79-54 Ma). This rifting episode likely responded to back-arc extension triggered by Paleo-Pacific plate rollback. Our findings provide critical constraints on the Mesozoic-Cenozoic tectonic evolution of South China and the incipient rifting stage of South China Sea.