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
Rockall Basin 55 million years ago, a continental fragment formed between Greenland and Europe when the ancient continent of Laurasia was split apart by plate tectonics. The Rockall Islet is the highest point of the plateau, rising 21 m above sealevel. It is made of a type of peralkaline granite. The petroleum and natural gas resources in the area have been the source of political tensions between the governments of the United Kingdom, Ireland, Iceland and the Faroe Islands (a possession of Denmark). The area supports cold water coral colonies and carbonate mound fields such as the Logachev Mounds; the trough supports