Island arc

Most island arcs originate on oceanic crust and have resulted from the descent of the lithosphere into the mantle along the subduction zone.

They also possess a distinct curved form, a chain of active or recently extinct volcanoes, a deep-sea trench, and a large negative Bouguer anomaly on the convex side of the volcanic arc.

[3] If the oceanic part of the plate is represented by the ocean floor on the convex side of the arc, and if the zone of flexing occurs beneath the submarine trench, then the deflected part of the plate coincides approximately with the Benioff zone beneath most arcs.

[6] It is now believed that water acts as the primary agent that drives partial melting beneath arcs.

It has been shown that the amount of water present in the down-going slab is related to the melting temperature of the mantle.

On the subducting side of the island arc is a deep and narrow oceanic trench, which is the trace at the Earth's surface of the boundary between the down-going and overriding plates.

Multiple earthquakes occur along this subduction boundary with the seismic hypocenters located at increasing depth under the island arc: these quakes define the Benioff zone.

Movement between two lithospheric plates explains the major features of active island arcs.

The calc-alkaline and alkaline series are seen in mature subduction zones, and are related to magma of greater depths.

[15] Several processes are involved in arc magmatism which gives rise to the great spectrum of rock composition encountered.

These processes are, but not limited to, magma mixing, fractionation, variations in the depth and degree of partial melting and assimilation.

Therefore, the three volcanic series results in a wide range of rock composition and do not correspond to absolute magma types or source regions.