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
Labrador Trough Labrador Trough The Labrador Trough or the New Quebec Orogen is a long and wide geologic belt in Canada, extending south-southeast from Ungava Bay through Quebec and Labrador. The trough is a linear belt of sedimentary and volcanic rocks which developed in an Early Proterozoic rift basin. To the west is the Archean Superior Craton. To the east are the rocks of the Archean Rae Craton. The sedimentary rocks and volcanics of the Labrador Trough were intensely deformed and subjected to high grade metamorphism along with the Churchill terrain during the Trans-Hudson orogeny. It is a northeast extension of the