What do the convergent boundaries ( collision zone) do colloids, separate or past each other?

When two oceanic plates collide one oceanic plate is eventually subducted under the other. Where one plate slides under the other is referred to as the 'subduction zone'. As the subducting plate descends into the mantle where it is being gradually heated a benioff zone is formed. This benioff zone is a zone of shallow,intermediate and deep focused earthquakes. Some deep focused earthquakes that occur at ocean ocean- collision boundaries can be as deep as 670 kilometres. As the subducted plate descends into the mantle it is gradually heated allowing the formation of magma. The magma that forms is andesitic in composition and begins to form when the subducted plate reaches a depth of 100 kilometres. This andesitic magma is formed from the partial melting  of the asthenosphere just above the subduction zone. This partial melting of the subducting plate is due to the loss of water as it descends into the mantle. The andesitic magma is now less dense than the surrounding material so it rises through the crust and erupts to form an arc of volcanoes called an island arc. The distance between the trench and the island arc depends greatly upon where the subducting plate reaches the 100 kilometer depth. If the subduction angle is steep then the distance between the arc and the trench will be short.If the suduction angle is shallow the distance is longer. The main features are indicated in the diagram below. The swell is seen by a bulge in the in the downgoing plate where it is subducted into the mantle.where the plate subducts into the mantle is known as the trench.the forearc ridge contains highly deformed sedimentary and metemorphic rock. The backarc region is located behind the arc and can be compressed or extended.

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