Formation of Intra-oceanic island arcs with example

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When tectonic plates converge or slide past each other the continental margins are called Active margins/Pacific type margins(as they are common around Pacific ocean's rim).Active margin is divided into 2 sub-types:-

1)Steady-state margins;&

2)Collision-state margins.
Subduction is deemed to create steady-state margins in the sense that oceanic crust is subducted indefinitely while a continent or island arc resists subduction.Steady-state margins produce 2 major landforms:-

a)Intra-oceanic island arcs;&
b)Continental magin orogens.

Intra-oceanic island arcs result from the oceanic lithosphere being subducted beneath another oceanic plate.The subducted portion of that plate starts getting heated up & melts,as we know temperature decreases with depth.Subduction causes fracture.

The molten portion of the subducted plate causes pressure inside the crust which is equated & released when volcanic eruption occurs through the fracture followed by other thermal activity.thus,the relief of the arcs is formed by volcanic eruptions & igneous rock intrusions.Deep trench often forms ahead of the arc at the point where the oceanic lithosphere starts plunging into the mantle(Eg.-Marina trench).Currently,there are about 20 intra-oceanic island arcs sitting at subduction zones.Most of these lie in western Pacific ocean & include the Aleutian arc,Tonga Arc,Colebes Arc etc.

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