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
Svecofennian orogeny rocks and the emplacement of the Jormua and Outokumpu ophiolites about 1950 million years ago. In the later stages of the Lapland-Savo orogeny an island arc, the Knaften arc, accreted to the Keitele-Karelia-Norrbotten collage. The stage to the Fennian orogeny was set by a collision between Keitele and Karelia about 1920–1910 million years ago which resulted in a reorganization of the local plate tectonics. As concequence the Bergslagen microcontinents collided with the Keitele–Karelia collage starting the Fennian orogeny. The until then linear Fennian orogen was "buckled" from 1870 million years ago onwards due to an orthogonal change in tectonic compressive