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

The temporal and spatial relationships between Cenozoic extension in the Re d Sea and flood basalt volcanism in the Ethiopian plateau region were poorl y understood along the Red Sea Hills region of Sudan. Rift basins in the Re d Sea area developed in terranes accreted in Pan-African time, and it is be lieved that some of these ancient sutures controlled later Red Sea rifting. The objectives of field, remote sensing and geochronological studies of th e southern Red Sea Hills near the Sudan-Eritrea border were to constrain th e geometry and kinematics of extension, the timing of volcanism, and the st ructural relationship between Cenozoic and Pan-African faults. Basaltic vol canism began at about 31 Ma in the Derudeb region, coincident with the wide spread flood basaltic volcanism in Ethiopia and Yemen associated with the A far plume, suggesting a causal link. Felsic lavas erupted onto a faulted er osional surface at about 29 Ma, based on Ar-40/Ar-39 step heating results o n feldspar separates. The original form of these basins has been modified b y subsequent faulting, Red Sea rift Bank uplift, and erosion. Structural pa tterns indicate that extension increases eastward toward the Red Sea, with stratal dips of up to 35 degrees in the Adar Ribad region, but most of this fault block rotation post-dates the rhyolite eruptions. The location of th e Odi and Adar Ribad basins, and the reactivation of segments of Pan-Africa n shear zones of the Baraka suture suggest that the development of these ba sins was influenced by pre-existing crustal shear zones, although some faul ts and dykes cross-cut other basement structures.