Benue Trough the Central African Shear Zone and for the volcanic island of St. Helena in the Atlantic ocean. Three periods of magmatic activity (volcanic action) have been identified, 147–106 Ma, 97–81 Ma and 68–49 Ma. The first is prominent in the north of the trough, and contemporary with magmatism in Brazil, probably occurring during a period of crustal extension before the Atlantic started to open. The second is found only in the south of the trough, and may belong to a period when the extension of the Atlantic had slowed down, ending with a period of compression. The third and last
Cayman Trough and extends offshore under the Pacific Ocean, where it intersects the Middle America Trench subduction zone. The relatively narrow trough trends east-northeast to west-southwest and has a maximum depth of . Within the trough is a slowly spreading north-south ridge which may be the result of an offset or gap of approximately along the main fault trace. The Cayman spreading ridge shows a long-term opening rate of The eastern section of the trough has been named the Gonâve Microplate. The Gonâve plate extends from the spreading ridge east to the island of Hispaniola. It is bounded on the north by