Accreted Terranes

A terrane in geology in full a tectonostratigraphic terrane is a fragment of crustal material formed on or broken off from one tectonic plate and accreted or sutured to crust lying on another plate the crustal block or fragment preserves its own distinctive geologic history which is different from that of the surrounding areas hence the term exotic terrane.

Accreted terranes. Most continents are composed of multiple accreted terranes pieces of low density continental crust with different origins. As with the other accreted terranes discussed so far most of these terranes originated as island arcs and sections of oceanic crust. However based on the composition of volcanic and sedimentary rocks the accreted terrane in idaho is not related to the wrangellia terrane. Accreted terranes may be called exotic terranes suspect terranes or tectonostratigraphic terranes.

The volcanic arc terranes are similar to the accreted island arc terranes termed wrangellia that lie between alaska and vancouver island. 1 9 available at course canvas site. Accreted terranes upsc ias a more recent discovery has helped explain the often confusing juxtaposition of different types of rock seen along the margins of some continents. The word terrane with its distinctive spelling is technically a tectonostratigraphic terrane a piece of the earth s crust or lithosphere that has been accreted to the edge of one tectonic plate from another tectonic plate.

A broad swath of the present continental margin is underlain by rocks of these accreted terranes that have diverse origins as paleozoic mesozoic crustal fragments from the ancestral pacific. There is a significant tectonic history seen in most mountain belts that occurs before final ocean basin closure with the collision of two continents and that can t be explained by simple subduction processes. Accreted terranes isolated or in fields or collages assemblages in diameter sizes of between 50 and 500 km occupy an estimated third of the known and mapped cordilleran provinces on coherent cratonic lithosphere hillhouse 1989. Introduction of howell jones schermer 1985 tectonostratigraphic terranes of the circum pacific region p.

For example north america is made up of multiple accreted terranes that collided with the laurentian proto continent such as the proterozoic yavapai mazatzal and grenville province terranes. A terrane is a small to medium mass of lithosphere bounded on all sides by faults that may have been carried a long distance by a moving plate eventually to converge with the edge of another plate. The western side of idaho preserves some of these tectonic fragments the blue mountains terranes and the collision zone along which they were sutured to the north american continent in late mesozoic time.