Late Paleozoic Orogenies in western Africa and eastern North America: The diachronous closure of Theic Ocean

Abstract

The Carboniferous evolution in western Morocco, southeastern Canada, and New England was dominated by intracontinental processes: the subsidence of pull‐apart sedimentary basins, and their subsequent deformation during middle Carboniferous to Early Permian times, with the development of autochthonous structures and mainly low‐ to medium‐grade metamorphism. On the other hand, the structural style of the late Carboniferous deformation in the southern Appalachians, and to a substantial degree also in New England, that is related to a continental collision is characterized by deep‐seated northwest‐vergent thrusts and medium‐ to high‐grade metamorphism. The Mauritanides structures are symmetrically east‐vergent thrusts. This pattern is explained by the diachronous closure of the Theic ocean that separated the Avalon and Carolina microcontinental blocks from paleo‐Gondwana. The closure of the Theic ocean occurred during Devonian times between the northern Appalachians and the northwestern edge of paleo‐Gondwana (Morocco), whereas it was achieved only at the end of Carboniferous times between the southern Appalachians and western Africa (Mauritania‐Senegal). The Late Devonian to early Carboniferous counterclockwise rotation of Gondwana induced the opening of the pull‐apart basins of Canada, New England, and Morocco as well as, later, the oblique collision in the southern Appalachians and the generalized late Paleozoic dextral transcurrent faulting along the northern edge of paleo‐Gondwana.