SUBDUCTION
Reporters:
Alconera, P.P.
Villacampa, E.
Mangaway, Cris
Plate tectonics
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.
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 zones are important for several reasons:
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.
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
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…