When the subducting slab broke off ( slab breakoff, slab pull ) and fell away, the subducted crust began moving up.

When seismic research is combined with insights from gravitational research and mantle tomography the subducting slab of the European plate can be mapped.

A trench marks the position at which the flexed, subducting slab begins to descend beneath another lithospheric slab.

These areas are subject to many earthquakes, which are caused by the interactions between the subducting slab and the mantle, the volcanoes, and ( when applicable ) the mountain-building related to island arc collisions.

The down-going slab — the subducting plate — is overridden by the leading edge of the other plate.

The arc magmatism occurs 100 – 200 km away from the trench and ~ 100 km from the subducting slab.

This depth of arc magma generation is the consequence of the interaction between fluids, released from the subducting slab, and the arc mantle wedge that is hot enough to generate hydrous melting.

Earthquakes mainly propagate in the cold subducting slab and define the Wadati-Benioff zone.

* Flat-slab subduction (< 30 °): occurs when subducting lithosphere, called a slab, subducts horizontally or nearly-horizontally.

The conditions within the subducting slab as it plunges toward the mantle in a subduction zone also produce regional metamorphic effects.

The process of subduction creates metamorphism in the subducting slab.

This implies that the thick plume-derived oceanic crust reached an intraoceanic convergent plate boundary and was intruded and overlain by felsic melts coming from both a subducting slab and an overlying mantle wedge.

Another force, that for some plates exceeds ridge-push, is slab pull, where the weight of a subducting slab pulls the plate at the surface along.

This loss of water is due to the destabilization of the mineral chlorite at approximately 40 – 60 km depth .< ref > Grove, T. L., N. Chatterjee, S. W. Parman, and E. Médard ( 2006 ), The Influence of H < sub > 2 </ sub > O on Mantle Wedge Melting, Earth and Planetary Science Letters, 249, 74-89 .</ ref > This is the reason for island arc volcanism at consistent distances from the subducting slab: because the temperature-pressure conditions for flux-melting volcanism due to chlorite destabilization will always occur at the same depth, the distance from the trench to the arc volcanoes is determined only by the dip angle of the subducting slab.

The hypocenters of earthquakes at this location outline a Benioff zone indicating that the Philippine Sea Plate is subducting at an angle of about 45 ° beneath the Eurasian plate in this area ; it should be noted that the dip of the slab changes dramatically from one end of the trench to the other as noted in the next section.

It is the surface expression of melting within and above the plunging subducting slab.

This buoyant region prevents the slab ( subducting tectonic plate ) from diving deep into the mantle, where the heat and pressure would destabilize the mineral chlorite, releasing water that would in turn cause melting and volcanism.

The blue blob in the cutaway section is the seismically imaged Farallon Plate, which is subducting beneath North America.

The Philippine Sea Plate is subducting under the Philippine Mobile Belt at the rate of about 16 cm per year.

Although trenches would seem to be positionally stable over time, it is hypothesized that some trenches, particularly those associated with subduction zones where two oceanic plates converge, retrograde, that is, they move backward into the plate which is subducting, akin to a backward-moving wave.

The plateau is, like the islands, generally believed to be less than 5 million years old, although one hypothesis has the plateau ( not the islands ) as being significantly older and having a mirror image, the Inca Plateau, subducting under northern Peru.

The opposite occurs when a ridge linked to a subducting plate, where all the lithosphere ( new sea floor ) being created by the ridge is being subducted, or swallowed up, by the subduction zone.

In a subduction zone, the subducting plate, which is normally a plate with oceanic crust, moves beneath the other plate, which can be made of either oceanic or continental crust.

Denali National Park and Preserve is located in an area of intense tectonic activity: the Pacific Plate is subducting under the North American plate, creating the Denali fault system, which is a right-lateral strike-slip fault over 720 miles long.

Although there is evidence to suggest that the subducting oceanic crust may also melt during this process, the relative contribution of the three components ( crust, sediment, and wedge ) to the generated basalts is still a matter of debate.

Heat from these subducting plates have fed scores of volcanoes in California, Oregon, Washington and British Columbia over at least the past 30 million years ( see Geology of the Pacific Northwest ) and is also responsible for activities in the Lassen volcanic area.

In the context of mantle plumes, the near-surface material is postulated to have been transported down to the core-mantle boundary by subducting slabs, and to have been transported back up to the surface by plumes.

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 downgoing and overriding plates.

This trench is created by the gravitational pull of the relatively dense subducting plate pulling the leading edge of the plate downward.

The Juan de Fuca Plate is a tectonic plate generated from the Juan de Fuca Ridge and is currently subducting under the northerly portion of the western side of the North American Plate at the Cascadia subduction zone.

One of these compounds is water ; its addition to the mantle wedge formed between the subducting and overriding plates lowers the melting point enough to allow magma to form.

Melts generated in the mantle wedge are of basaltic composition, but they have a distinctive enrichment of soluble elements ( e. g. potassium ( K ), barium ( Ba ), and lead ( Pb )) which are contributed from sediment that lies at the top of the subducting plate.

Magmatism in island arc regions ( i. e., active oceanic margins ) comes from the interplay of the subducting plate and the mantle wedge, the wedge-shaped region between the subducting and overriding plates.

The longest earthquake ruptures on strike-slip faults, like the San Andreas Fault ( 1857, 1906 ), the North Anatolian Fault in Turkey ( 1939 ) and the Denali Fault in Alaska ( 2002 ), are about half to one third as long as the lengths along subducting plate margins, and those along normal faults are even shorter.

On this diagram, subducting Slab ( geology ) | slabs are in blue, and continental margins and a few plate boundaries are in red.

Water released from the subducting plate lowers the melting temperature of the overlying mantle wedge, creating magma.

The subducting plate bends and forms a fore-arc basin in front of the overriding plate — an elongated, deep asymmetric basin.

This subduction system therefore shows the southern plates of African affinity subducting below the northern plates of European affinity.

The driver for seafloor spreading in plates with active margins the weight of the cool, dense, subducting slabs that pull them along.

Orogenesis, or mountain-building, occurs when large pieces of material on the subducting plate ( such as island arcs ) are pressed into the overriding plate.

The subducting basalt and sediment are normally rich in hydrous minerals and clays.

Volcanoes near plate boundaries and mid-ocean ridges are built by decompression melting of rock in the mantle that then floats up to the surface, while volcanoes formed near subducting zones are created because the subducting plate adds volatiles to the rising plate that raise its melting point.

Lava flows from mid-ocean ridge and plate boundary seamounts are mostly basaltic ( both tholeiitic and alkalic ), whereas flows from subducting ridge volcanoes are mostly calc-alkaline lavas.