Rheic Ocean - Geodynamic Evolution

Geodynamic Evolution

At the beginning of the Paleozoic Era, about 540 million years ago, most of the continental mass on Earth was clustered around the south pole as the paleocontinent Gondwana. The exception was formed by a number of smaller continents, such as Laurentia and Baltica. The Paleozoic ocean between Gondwana, Laurentia and Baltica is called the Iapetus Ocean. The northern edge of Gondwana had been dominated by the Cadomian orogeny during the Ediacaran period. This orogeny formed a cordillera-type volcanic arc where oceanic crust subducted below Gondwana. When a mid-oceanic ridge subducted under an oblique angle, extensional basins developed along the northern margin of Gondwana. During the late Cambrian to Early Ordovician these extensional basins had evolved a rift running along the northern edge of Gondwana. The rift in its turn evolved into a mid-oceanic ridge that separated small continental fragments such as Avalonia and Carolina from the main Gondwanan land mass.

Avalonia drifted north from Gondwana, the Rheic Ocean grew. The northward movement of Avalonia made the Iapetus Ocean shrink during the Middle Ordovician to Late Silurian. For much of the Late Ordovician, the Rheic Ocean appears to have widened as fast as today's East Pacific Rise (at 17 cm/year). Meanwhile, Avalonia collided with Baltica and Laurentia in the Late Silurian to form Laurussia during the Caledonian orogeny. The Rheic Ocean itself began to close in the Devonian when Gondwana, probably preceded by terranes that had broken off, drifted towards Laurussia. By the Late Devonian, the Rheic Ocean had become a narrow ocean that was then sutured between Gondwana and Laurussia. The ocean closed from east to west, first in what is presently central Europe (the Hercynian orogeny), then the northeast of North America (Alleghenian orogeny) and northwest of Africa and finally in the southeast of North America (Ouachita orogeny) and north of South America.