Abstract
Magmatism's role in continental rupture and ocean formation remains a critical question in Earth Sciences. The Red Sea, where Arabia is rifting from Nubia, offers an ideal setting to explore this process. This study analyses geochemical and isotopic data from gabbros and basaltic dikes in the Tihama Asir complex, formed during early Red Sea rifting (Late Oligocene). The results show that asthenospheric melts assimilated ancient lower crust before rising into shallow magma chambers with minimal upper crustal contamination. Rising asthenosphere driven by the Afar plume and by extensional stresses thermally weakened the lower crust, allowing it to decouple from the mantle, causing depth-dependent deformation. The generated asthenospheric melts underplated and intruded the thinning continental crust protracting continental rifting by re-thickening of the crust and accommodating extension. This study provides the evidence of tholeiitic underplating beneath thick continental crust during early rifting, substantially postponing the onset of seafloor spreading.