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 Rockall Basin The Rockall Basin (also known as the Hatton Rockall Basin) is a large (c. 800 km by 150 km) sedimentary basin that lies to the west of Ireland and the United Kingdom beneath the major deepwater area known as the Rockall Trough. It is named after Rockall, a rocky islet lying 301.4 km west of St Kilda. The nature of the crust beneath the Rockall Trough has long been a matter of debate. Originally thought to be oceanic crust it is now generally considered to be highly stretched continental crust, although some groups of researchers continue to favour