Sonoma orogeny Sonoma orogeny The Sonoma orogeny was a period of mountain building in western North America. The exact age and structure of the Sonoma orogeny is controversial. The orogeny is generally thought to have occurred during the Permian / Triassic transition, around 250 million years ago, following the Late Devonian Antler orogeny. The Sonoma orogeny was one of a sequence of accretionary events along the Cordilleran margin, possibly caused by the closure of the basin between the island arc of Sonomia and the North American continent. Evidence of this event has been reported throughout western North America, but most distinctly in
Svecofennian orogeny broad terms, regardless of details, it has been proposed that the Svecofennian orogeny involved more-less continuous subduction with subduction zones progressively migrating to the southwest. An alternative model postulates subduction included alternating extension and compression cycles, with the orogenic activity ceasing after the collision between the Fennoscandian Craton and the Sarmatian Craton. Prior to the onset of orogeny the Archean-aged craton of what is today northeastern Fennoscandia rifted creating an ocean basin, the "pre-Svecofennian Ocean", that then closed during the Svecofennian orogeny. The closure of this basin was indebted to subduction and resulted thus both in the formation of igneous