Convergent boundary

[2] These convection cells bring hot mantle material to the surface along spreading centers creating new crust.

[3] As the relatively cool subducting slab sinks deeper into the mantle, it is heated, causing hydrous minerals to break down.

As the slab sinks deeper into the mantle, it releases water from dehydration of hydrous minerals in the oceanic crust.

Partial melt will travel up through the asthenosphere, eventually, reach the surface, and form volcanic island arcs.

Volcanic arcs form on continental lithosphere as the result of partial melting due to dehydration of the hydrous minerals of the subducting slab.

[7] Evidence of this continental rebound includes ultrahigh pressure metamorphic rocks, which form at depths of 90 to 125 km (56 to 78 mi), that are exposed at the surface.

[8] Seismic records have been used to map the torn slabs beneath the Caucasus continental – continental convergence zone,[9] and seismic tomography has mapped detached slabs beneath the Tethyan suture zone (the Alps – Zagros – Himalaya mountain belt).

During subduction, oceanic lithosphere is heated and metamorphosed, causing breakdown of these hydrous minerals, which releases water into the asthenosphere.

Partial melting allows the rise of more buoyant, hot material and can lead to volcanism at the surface and emplacement of plutons in the subsurface.

The more oxidized calc-alkaline series, which is moderately enriched in potassium and incompatible elements, is characteristic of continental volcanic arcs.

[14][15] Back-arc basins form behind a volcanic arc and are associated with extensional tectonics and high heat flow, often being home to seafloor spreading centers.

Opening of back-arc basins may arise from movement of hot asthenosphere into lithosphere, causing extension.

[17] Oceanic trenches are narrow topographic lows that mark convergent boundaries or subduction zones.

A region of high earthquake activity, the Wadati–Benioff zone, generally dips 45° and marks the subducting plate.

Tensional or normal faulting occurs on the outer wall of the trench, likely due to bending of the downgoing slab.

[18] A megathrust earthquake can produce sudden vertical displacement of a large area of ocean floor.