The early opening of the Red Sea rift is accompanied by tholeiitic magmatism stretching at least 1700 km along the western coast of Saudi Arabia, and consisting of thick gabbroic dykes, dense dyke swarms, plutons and discrete lava flows. Whereas the conventional K-Ar measurements have furnished a wide variety of ages, the 40Ar/39Ar analyses presented here (giving 17 plateau-ages) display a pronounced cluster of ages from 24 to 21 Ma. Such a short-lived magmatic event has been suggested for other continental rifts. ¿ American Geophysical Union 1991