Gravity field of Benue Trough, Nigeria

The Benue Trough, located at the Gulf of Guinea re-entrant on the West African coast (Fig. 1), is a unique Cretaceous rift whose origin is related to the opening of the South Atlantic and the continental separation of Africa from South America. The trough extends northeastwards for ~700 km from the Niger Delta to the Chad Basin and is filled with an estimated 5,000 m of Cretaceous sediments and volcanic rocks. Studies on the origin and tectonic evolution of the Benue Trough have been based so far principally on surface geological and geochemical evidence^1-5. Gravity measurements by Cratchley and Jones⁶ in the middle Benue area are of limited significance because they were aimed mainly at resolving the then controversy between the tensional and compressional⁸ hypotheses. New and more extensive gravity data presented here indicate rifting in the upper and middle sections of the trough whereas the complex field over the lower section could be due to an `unsuccessful' attempt to open into an ocean during the late Cretaceous.