Orogenèse acadienne

The Acadian orogeny is a long-lasting mountain building event which began in the Middle Devonian, reaching a climax in the early Late Devonian. It was active for approximately 50 million years, beginning roughly around 375 million years ago, with deformational, plutonic, and metamorphic events extending into the Early Mississippian. The Acadian orogeny is the third of the four orogenies that formed the Appalachian orogen and subsequent basin. The preceding orogenies consisted of the Potomac and Taconic orogeny, which followed a rift/drift stage in the Late Neoproterozoic. The Acadian orogeny involved the collision of a series of Avalonian continental fragments with the Laurasian continent. Geographically, the Acadian orogeny extended from the Canadian Maritime provinces migrating in a southwesterly direction toward Alabama. However, the Northern Appalachian region, from New England northeastward into Gaspé region of Canada, was the most greatly affected region by the collision. It was roughly contemporaneous with the Bretonic phase of the Variscan orogeny of Europe, with metamorphic events in southwestern Texas and northern Mexico, and with the Antler orogeny of the Great Basin. During the time of the Acadian orogeny, Middle Devonian (385 Ma), the paleolatitude of the Laurentia was in the southern hemisphere near the equator, between 0° to 30°S latitude. Laurentia did not change much with respect to paleolatitude during the Devonian. Gondwana, on the other hand, traveled a large distance, such that in the Ordovician the South pole was located in northern Africa, where it then moved west of southern Chile during the Silurian, and moved back to central Africa during the Devonian. However, more recent research, from Scotese & McKerrow, suggests that in Late Devonian, the South Pole was in north-central Argentina rather than Northern Africa, which was supported with paleoclimatic evidence. The paleolatitude of Gondwana during the Middle to Late Devonian resided around intermediate latitudes of about 50°S.