Late Oligocene volcanism and extension in the southern Red Sea Hills, Sudan

Abstract

The temporal and spatial relationships between Cenozoic extension in the Red Sea and flood basalt volcanism in the Ethiopian plateau region were poorly understood along the Red Sea Hills region of Sudan. Rift basins in the Red Sea area developed in terranes accreted in Pan-African time, and it is believed that some of these ancient sutures controlled later Red Sea rifting. The objectives of field, remote sensing and geochronological studies of the southern Red Sea Hills near the Sudan–Eritrea border were to constrain the geometry and kinematics of extension, the timing of volcanism, and the structural relationship between Cenozoic and Pan-African faults. Basaltic volcanism began at about 31 Ma in the Derudeb region, coincident with the widespread flood basaltic volcanism in Ethiopia and Yemen associated with the Afar plume, suggesting a causal link. Felsic lavas erupted onto a faulted erosional surface at about 29 Ma, based on 40 Ar/ 39 Ar step heating results on feldspar separates. The original form of these basins has been modified by subsequent faulting, Red Sea rift flank uplift, and erosion. Structural patterns indicate that extension increases eastward toward the Red Sea, with stratal dips of up to 35° in the Adar Ribad region, but most of this fault block rotation post-dates the rhyolite eruptions. The location of the Odi and Adar Ribad basins, and the reactivation of segments of Pan-African shear zones of the Baraka suture suggest that the development of these basins was influenced by pre-existing crustal shear zones, although some faults and dykes cross-cut other basement structures.