Presentation on Plate Tectonics.

1. NAME : ANURAG MISHRA
DEPARTMENT : RPEG
YEAR : 1ST YEAR
SUBJECT : GEOGRAPHY
TOPIC : PLATE TECTONICS AND ASSOCIATED CONCEPTS

2. CONCEPT OF PLATE TECTONICS AND VULCANICITY,
EARTHQUAKES AND EVOLUTION OF MOUNTAINS

4. • It refers to the process through which the gases and the molten rocks are either
extruded on the earth”s surface or intruded into the earth’s crust.
• At times, the magma solidifies beneath the earth’s surface before emerging onto
the earth’s surface.
• Volcanoes are absent when the two continental crusts converge as subduction is not
present and doubling of Earth’s crust takes place.
• When the continental and the oceanic crust converges, subduction takes place and
the oceanic plate melts in the Asthenosphere and the rise in magma tries to escape
on the Earth’s surface.
• In the oceanic-oceanic convergence, the relatively denser plate subducts and
magma escapes onto the oceanic floor and solidifies.
• Over the period of time, a layer upon layer of lava gets accumulated and emerges
above water forming an island. Eg: Iceland
VULCANICITY

7. PLATE TECTONIC THEORY
• WHAT ARE PLATES ?
• WORLD PLATES (MAJOR/MINOR)
• WHAT DOES PLATE TECTONICS MEAN ?
• TYPES OF PLATE BOUNDARIES
• VULCANICITY
• EARTHQUAKES
• EVOLUTION OF MOUNTAINS

8. WHAT ARE PLATES ?
• Rigid slabs of lithosphere
• Float atop a region of partially melted
asthenosphere
• Plates can be oceanic, continental or both.
• They are of different sizes and densities

10. The theory of plate tectonics states that the
Earth's solid outer crust, the lithosphere,
is separated into plates that move over the
asthenosphere, the molten upper portion
of the mantle.
Due to which different reliefs are formed
over the Earth’s surface.
WHAT IS MEANT BY PLATE TECTONICS ?

12. Due to the hot convection currents
present in the asthenosphere, these plates
move and this determines the type of
boundary like convergent, divergent and
transform.
TYPES OF PLATE BOUNDARIES

14. • When one limb of convectional current comes toward the other
limb, this causes plates to move towards each other.
• The two plates collide and the denser [oceanic plate is denser
than the continental plate] plate slides below the lighter plate.
• This forms a zone of subduction or Benioff zone.
CONVERGENT PLATE BOUNDARY

15. TYPES OF CONVERGENT
PLATE BOUNDARY

16. CONTINENTAL-CONTINENTAL
COLLISION
• When two continental plates converge towards each other the
relatively denser plate slides below the less denser plate or the
plate of more velocity slides below the other.
• Subduction is absent
• Crustal doubling takes place
• Volcanoes are absent
• Trenches are absent
• Earthquakes take place around the plate margin.
• Fold mountains

17. OCEANIC-OCEANIC COLLISION
• When two oceanic plate converges, the relatively
denser plate subducts.
• Deep trenches would be formed on the plate margin
• Volcanoes will be present
• Earthquakes will be present
• Island arcs will be formed

18. OCEANIC-CONTINENTAL COLLISION
• In this collision the heavier oceanic plate subducts
below the lighter continental plate.
• As the oceanic plate will melt, the magma formed would
erupt violently.
• Fold mountains will be present on the plate margins.
• Trenches will be present.
• Volcanoes will be present
• Earthquakes will be present.

21. • When limbs of convectional currents after witnessing the thin oceanic crust diverges, the
oceanic crust breaks and moves along the direction of currents.
• The hot basaltic magma emerges from the gap and solidifies quickly to form a mid oceanic
ridge; a continuous mountain system under the ocean.
• Along side the ridge mountains are formed.
• New crust is formed near the MOR and gets destroyed around the trenches.
• Shallow focus intense earthquakes are caused
• Fissure type of eruptions
• Age of the crust is newer around the ridges and gets older away from the ridges.
• Magentic polarity is seen
• This is a diastrophic process
• Due to erosion the mountains away from the ridges keep getting shorter in height.

23. • In this plate boundary the two plates slide past each other.
• A plate is neither created nor destroyed in this case.
• A large amount of stress is released as the plates move against each other.
• Release of stress leads to shallow focus intense earthquakes.
• Example San Andreas faulting California, USA
• Rift valley would be formed
• Example Great African Rift Valley
TRANSFORM/CONSERVATIVE PLATE
BOUNDARY

27. SAN ANDREAS FAULT

28. • It is the sudden shaking of the ground caused by the passage of seismic waves
through Earth’s rocks.
• Seismic waves are produced when some form of energy stored in Earth’s crust is
suddenly released.

29. EARTHQUAKES AT CONVERGENT PLATE
BOUNDARY
Earthquakes occurring along the Convergent plate boundary take place due to
subduction.
1.Reverse Fault refers to the breaking of the rocks due to
compression under subduction.
Shallow-focus earthquakes are caused due to reverse faults.
2. Normal fault refers to the fault in which the hanging wall has
moved downward relative to the footwall.
These faults result in Intermediate-focus earthquake.
3. Reverse (thrust) fault is a dip-slip fault in which the upper block,
above the fault plane, moves up and over the lower block.
Deep Focus earthquakes take place in this case.

30. EARTHQUAKES AT AND
PLATE BOUNDARY
• Earthquakes at divergent plate boundary occur due to separation/divergence
of two plates.
Shallow Focus intense Earthquakes are caused.
• At the Transform Plate boundary, a large amount of stress is released as the
plates move against each other.
This leads to Shallow Focus intense Earthquakes.

31. EVOLUTION OF MOUNTAINS
• During convergence, the sediments of both the plate get folded along the margins
resulting into formation of fold mountains.
• In continental-continental collision, doubling of Earth’s crust takes place, thus
mountains are of great heights like Himalayas and volcanism is absent.
• In oceanic-continental collision, the oceanic plate subducts and sediments are folded
resulting in fold mountains of volcanic origin.
• In oceanic-oceanic collision, the plate subducts and Island arcs are formed.

32. THANK YOU !