a curved linear chain of volcanoes above a subduction zone is called a volcanic arc.
a curved linear chain of volcanoes above a subduction zone is called a volcanic arc.
what is a curved linear chain of volcanoes above a subduction zone called?
a volcanic arc
the canadian portion of the pacific northwest began forming during the early jurassic period when a group of active volcanic islands collided against a pre-existing continental margin and coastline of western canada. these volcanic islands, known as the intermontane islands by geoscientists, were formed on a pre-existing tectonic plate called the intermontane plate about 245 million years ago by subduction of the former insular plate to its west during the triassic period. this subduction zone records another subduction zone called the intermontane trench under an ancient ocean between the intermontane islands and the former continental margin of western canada called the slide mountain ocean. this arrangement of two parallel subduction zones is unusual in that very few twin subduction zones exist on earth; the philippine mobile belt off the eastern coast of asia is an example of a modern twin subduction zone. as the intermontane plate drew closer to the pre-existing continental margin by ongoing subduction under the slide mountain ocean, the intermontane islands drew closer to the former continental margin and coastline of western canada, supporting a volcanic arc on the former continental margin of western canada. as the north american plate drifted west and the intermontane plate continued to drift east to the ancient continental margin of western canada, the slide mountain ocean began to close by ongoing subduction under the slide mountain ocean. this subduction zone eventually jammed and shut down completely about 180 million years ago, ending the arc volcanism on the ancient continental margin of western canada and the intermontane islands collided, forming a long chain of deformed volcanic and sedimentary rock called the intermontane belt, which consists of deeply cut valleys, high plateaus, and rolling uplands. this collision also crushed and folded sedimentary and igneous rocks, creating a mountain range called the kootenay fold belt which existed in far eastern british columbia.
volcanology of canada
bullet::::- flat-slab subduction (subducting angle less than 30°) occurs when subducting lithosphere, called a slab, subducts nearly horizontally. the relatively flat slab can extend for hundreds of kilometers. that is abnormal, as the dense slab typically sinks at a much steeper angle directly at the subduction zone. because subduction of slabs to depth is necessary to drive subduction zone volcanism (through the destabilization and dewatering of minerals and the resultant flux melting of the mantle wedge), flat-slab subduction can be invoked to explain volcanic gaps. flat-slab subduction is ongoing beneath part of the andes causing segmentation of the andean volcanic belt into four zones. the flat-slab subduction in northern peru and norte chico region of chile is believed to be the result of the subduction of two buoyant aseismic ridges, the nazca ridge and the juan fernández ridge respectively. around taitao peninsula flat-slab subduction is attributed to the subduction of the chile rise, a spreading ridge. the laramide orogeny in the rocky mountains of united states is attributed to flat-slab subduction. then, a broad volcanic gap appeared at the southwestern margin of north america, and deformation occurred much farther inland; it was during this time that the basement-cored mountain ranges of colorado, utah, wyoming, south dakota, and new mexico came into being. the most massive subduction zone earthquakes, so-called "megaquakes", have been found to occur in flat-slab subduction zones.
subduction