Subduction Zones

Where 2 tectonic key converge, if one or both of the key is oceanic lithosphere, a subduction zone will form. An oceanic plate will sink earlier into the mantle. Remember, oceanic key are developed from mantle product at midocean ridges. Young oceanic lithosphere is hot and buoyant (low density) as soon as it creates at a midocean ridge. Yet as that spreads far from the ridge and also cools and contracts (becomse denser) that is able to sink right into the hotter basic mantle. There is a deep s trench whereby the oceanic bowl bends downward.

Volcanic Arcs: The basaltic s crust has hydrous minerals choose amphiboles, few of which developed by hydrothermal modification as seawater seeped through hot, fractured, young ocean crust in ~ the midocean ridge. Together the ocean crust sink deeper into the mantle the pressure boosts (the temperature that the ocean crust rocks increases an ext slowly because rocks are negative conductors that heat). At depths of roughly 100 kilometres beneath the surface, the push is good enough because that the hydrous minerals to undergo metamorphism. The result minerals room denser and also they don"t save on computer the bonded water. This metamorphic dewatering process liberates water native the descending crust. The water progressively seeps upward into the overlying wedge of hot mantle. The enhancement of water to the currently hot mantle rocks lowers their melting temperature resulting in partial melting of ultramafic mantle rocks to productivity mafic magma. Melting aided through the enhancement of water or other fluid is dubbed flux melting. The is somewhat more complex than this, but metamorphic dewatering the suducting crust and also flux melt of the mantle wedge appears to account for most of the magma in ~ subduction zones.

Magma formed over a subducting plate gradually rise right into the overriding crust and finally come the surface creating a volcanic arc, a chain of active volcanoes i m sorry parallels the deep ocean trench. In ~ the energetic volcanic arc lie intrusive igneous rocks created from magma that didn"t make it all the means to the surface prior to crystallizing. The volcano arcs might be volcanic island arcs (e.g., Aleutians, Mariannas), whereby one oceanic plate subducts beneath an additional oceanic plate, or continental volcano arcs (e.g., Andes, Cascades), whereby oceanic plates subduct under a continental plate. The most abundant igneous rock created at volcanic arcs is andesite (or intrusive diorite), despite volcanic arc rocks may selection in composition from basalt to rhyolite (mafic come felsic).


Benioff Zones: Earthquakes in and also around deep s trenches are principally produced by activities on thrust faults, describe compression (converging plates). A aircraft of earthquake focci descend native the area roughly the trench under the overriding plate. The farther indigenous the trench, the deeper the earthquakes are. This earthquakes that the Benioff Zone (or Wadati-Benioff Zone) happen near the upper surface of the descending plate (or slab).

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They occur down to depths of around 670 kilometres at part subduction zones. Note: the volcanic arc lies wherein the Benioff region earthquakes are around 100 km beneath the surface however Benioff ar earthquakes continue past this, landward down to 60 km; because of this the slab has not melted away!