Alleghanian orogeny Alleghanian orogeny The Alleghanian orogeny or Appalachian orogeny is one of the geological mountain-forming events that formed the Appalachian Mountains and Allegheny Mountains. The term and spelling Alleghany orogeny was originally proposed by H.P. Woodward in 1957. The Alleghanian orogeny occurred approximately 325 million to 260 million years ago over at least five deformation events in the Carboniferous to Permian period. The orogeny was caused by Africa colliding with North America. At the time, these continents did not exist in their current forms: North America was part of the Euramerica super-continent, while Africa was part of Gondwana. This collision formed
East African Orogeny supercontinent (today known as Rodinia), a process that eventually culminated in the relatively short-lived Gondwanan supercontinent. Two partly incomparable scenarios have been proposed for this assembly. In one model, the EAO evolved from an accretionary orogeny involving the amalgamation of arcs and evolved into a collisional orogeny when the Neoproterozoic continent Azania collided with the Congo-Tanzania-Bangweulu Block at . In another model, the assembly of East Gondwana was a multiphase process which included two main periods of orogenesis: the older EAO ( ) and the younger Kuunga Orogeny ( ). In the former scenario the Kuunga Orogeny of the latter