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They are formed by flexing of the oceanic lithosphere, developing on the ocean side of island arcs. Back-arc basin: They are also referred to as marginal seas and are formed in the inner, concave side of island arcs bounded by back-arc ridges. They develop in response to tensional tectonics due to rifting of an existing island arc.
A volcanic arc (also known as a magmatic arc [1]: 6.2 ) is a belt of volcanoes formed above a subducting oceanic tectonic plate, [2] with the belt arranged in an arc shape as seen from above. Volcanic arcs typically parallel an oceanic trench , with the arc located further from the subducting plate than the trench.
Oceanic-continental convergence and creation of accretionary wedge Stages of accretion through time with accretionary wedge and volcanic island arc. In geology, accretion is a process by which material is added to a tectonic plate at a subduction zone, frequently on the edge of existing continental landmasses.
Most of the material in the accretionary wedge consists of marine sediments scraped off from the downgoing slab of oceanic crust, but in some cases the wedge includes the erosional products of volcanic island arcs formed on the overriding plate. An accretionary complex is a current (in modern use) or former accretionary wedge.
The Aleutian Trench, formed by the subduction of the Pacific plate under the North American plate, sits south of the island arc. [2] A forearc basin reaching depths of 7 km occupies the space between the trench and the island arc and leads up to the Aleutian Ridge, the north side of which being the area where the most volcanic activity occurs. [2]
The resulting feature is a 180-degree island arc, which is more than 1,000 kilometres (620 miles) long. Geographically, it stretches across eastern Indonesia, and is delimited by an active inner volcanic arc. The outer arc contains numerous islands, and its internal geologic structure contains young oceanic crust exclusively. [8]
It is classified as a "marginal trench" in the east as it runs along the margin of the continent. The subduction along the trench gives rise to the Aleutian Arc, a volcanic island arc, where it runs through the open sea west of the Alaska Peninsula. As a convergent plate boundary, the trench forms part of the boundary between two tectonic plates.
The islands formed by subduction and melting of the Farallon Plate along a fragment (or microplate) upon which they rose called the Insular Plate. They were bounded by the Panthalassic Ocean to the west and the Bridge River Ocean to the east. They probably formed as a composite of several volcanic chains near the equator, offshore of ...