SUBDUCTION

Reporters:Alconera, P.P.Villacampa, E.

Mangaway, Cris

A scientific theory which describes the large scale motions of Earth's lithosphere.

Plate tectonics is the study of how the Earth's plates are driven and shaped by geological forces that keep them in constant motion.

Plate Tectonic Theory states that the Earth's outer layer is fragmented into plates that are in constant motion.

Plate tectonics

Key words

• Slab pull• Ridge push• Convection

Slab pull and ridge push

Model of convection in the Earth's mantle.

Types of plate boundaries

• Transform• Convergent• Divergent

Subduction

Subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge.

Subduction• Subduction zones mark sites of convective downwelling of

the Earth's lithosphere .• Subduction zones exist at convergent plate boundaries where

one plate of oceanic lithosphere converges with another plate.

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

• The slab sinks at an angle of approximately 25 to 45 degrees to the surface of the Earth.

Effects

Volcanic activity

Earthquakes and tsunamis

The strains caused by plate convergence in subduction zones cause at least three different types of earthquakes. Earthquakes mainly propagate in the cold subducting slab and define the Wadati-Benioff zone.

Orogeny

Orogeny refers to forces and events leading to a severe structural deformation of the Earth's crust due to the engagement of tectonic plates

its the primary mechanism by which mountains are built on continents.

Mountain Building

Importance

Subduction Zone Physics: Sinking of the oceanic lithosphere (sediments + crust + mantle),

•The cold and old lithosphere and the hot asthenospheric mantle wedge, is the strongest force.

• Needed to drive plate motion and is the dominant mode of mantle convection.

Subduction zones are important for several reasons:

Importance

Subduction Zone Chemistry:

The subducted sediments and crust dehydrate and release water-rich (aqueous) fluids into the overlying mantle, causing mantle melting and fractionation of elements between surface and deep mantle reservoirs, producing island arcs and continental crust.

Importance

Subduction zones drag down subducted oceanic sediments, oceanic crust, and mantle lithosphere that interact with the hot asthenospheric mantle from the overriding plate to produce calc-alkaline series melts, ore deposits, and continental crust.

Tectonic plate interactions occurring in Phils.

•The Philippine Sea Plate is subducting under the Philippine Mobile Belt forming the Philippine Trench and the East Luzon Trench.

•The Eurasian Plate is subducting under the Philippine Mobile Belt at the Manila Trench.

•The Sunda Plate is subducting under the Philippine Mobile Belt at the Negros Trench and the Cotobato Trench

Conclusion

Additional facts

Subduction zones have also been considered as possible disposal sites for nuclear waste.

•But this method of disposal is currently banned by international agreement.

Many thanks…