1. Plate Tectonics Dr. G. Madhavi Latha Dept. of Civil Engineering
CE 244-GML
Plate Tectonics
Dr. G. Madhavi Latha
Dept. of Civil Engineering
Indian Institute of Science

2. Origin of Universe
Big Bang model (Hubble, 1929) - The universe began with an explosive expansion of matter, which later became what we know as stars, planets, moons, etc. This event is thought to have occurred billion yrs ago.
Nebular Hypothesis (Kant, Laplace 1796) - Earth and the other bodies of our solar system (Sun, moons, etc.) formed from a “vast cloud of dust and gases” called a nebula.

3. Big bang theory
There was a big bang some 15 billion years ago, when the size of the universe was zero and the temperature was infinite. The universe then started expanding at near light speed.
At about 10,000 years after the Big Bang, the temperature had fallen to such an extent that the energy density of the Universe began to be dominated by massive particles, rather than the light and other radiation which had predominated earlier. This explains the formation of galaxies and other large-scale structures observed in universe today.

4. Nebular Hypothesis
According to this hypothesis, the nebular cloud consisted of H and He, and a small percentage of the heavier elements we find in the solar system
Within the rotating disk, the rocky material and gases began to nucleate and accrete into protoplanets

5. Formation of Earth’s Interior
As Earth was formed, it was extremely hot from the bombardment of space debris, radioactive decay, and high internal pressures.
These processes caused Earth’s interior to melt, and then to differentiate into regions of chemical and physical differences as it cooled.

6. Layers of the Earth Crust: Continental crust (25-40 km)
Oceanic crust (~6 km)
Mantle
Upper mantle (650 km)
Lower mantle (2235 km)
Core
Outer core: liquid (2270 km)
Inner core: solid (1216 km)
 Values in brackets represent the approximate thickness of each layer

7. Layers of the Earth
The earth is divided into four main layers: Inner core, outer core, mantle and crust.
The core is composed mostly of iron (Fe) and is so hot that the outer core is molten, with about 10% sulphur (S). The inner core is under such extreme pressure that it remains solid.
Most of the Earth's mass is in the mantle, which is composed of iron (Fe), magnesium (Mg), aluminum (Al), silicon (Si), and oxygen (O) silicate compounds. At over 1000 degrees C, the mantle is solid but can deform slowly in a plastic manner.
The crust is much thinner than any of the other layers, and is composed of the least dense calcium (Ca) and sodium (Na) aluminum-silicate minerals. Being relatively cold, the crust is rocky and brittle, so it can fracture in earthquakes.

8. Continental drift Alfred Wegener
Theory that continents and plates move on the surface of the Earth proposed by Alfred Wegener in 1915.
Alfred Wegener

9. Maps by Wegener (1915), showing continental drift

10. Theory of continental drift

11. Evidence for continental drift
Matching coastlines
Matching mountains
Matching rock types and rock ages
Matching glacier deposits
Matching fossils

12. Evidence for continental drift
Matching
coastlines

13. Evidence for continental drift
Matching
mountain
ranges

14. Evidence for continental drift
Matching rock types and ages of rocks

15. Evidence for continental drift
Matching glacier
deposits 300
million years
ago

16. Evidence for continental drift
Fossils of of Mesosaurus (aquatic reptile) found on both sides of Atlantic

17. Theory of Plate tectonics
The theory of Plate tectonics was proposed in 1960s based on the theory of continental drift.
This is the Unifying theory that explains the formation and deformation of the Earth’s surface.
According to this theory, continents are carried along on huge slabs (plates) on the Earth’s outermost layer (Lithosphere).
Earth’s outermost layer is divided into 12 major Tectonic Plates (~80 km deep). These plates move relative to each other a few centimeters per year.

18. Earth’s magnetic field
Basic Data used in formulating plate tectonics:
Magnetic stripes on the sea-floor. Magnetic field of Earth reverses on semi-regular basis. Minerals act like compass needles and point towards magnetic north. “Hot” rocks record the direction of the magnetic field as they cool.

19. Tectonic plates of Earth

20. Types of plate boundaries
Divergent plate boundaries: where plates move apart
Convergent Plate boundaries: where plates come together
Transform plate boundaries: where plates slide past each other

21. Types of plate boundaries
Divergent (Tension)
Convergent (Compression)
Transform (shearing)

22. Types of plate boundaries

23. Divergent Plate Boundaries
Plates move away from each other (tension)
New lithosphere is formed
normal faults
Causes volcanism
not very explosive

24. Convergent Plate Boundary
Plates move toward each other (compression)
lithosphere is consumed
reverse/thrust faults
and folds
Mountain building
explosive volcanism

25. Ocean- Continent convergent margin
Ocean-continent plates collide
Ocean plate subducts below continent
Forms a subduction zone
Earthquakes and volcanoes

26. Ocean-ocean convergent margin
2 oceanic plates collide
One plate dives (subducts) beneath other
Forms subduction zone
Earthquakes and volcanoes

27. Continent-continent convergent margin
2 continental plates collide
Neither plate wants to subduct
Collision zone forms high mountains
Earthquakes, no volcanoes
example: Himalayas

28. Himalayas: Continents collide
Millions of years ago India and an ancient ocean called the Tethys Ocean were sat on a tectonic plate. This plate was moving northwards towards Asia at a rate of 10 centimeters per year. The Tethys oceanic crust was being subducted under the Asian Continent. The ocean got progressively smaller until about 55 milion years ago when India 'hit' Asia. Because both these continental landmasses have about the same rock density, one plate could not be subducted under the other. The pressure of the impinging plates could only be relieved by thrusting skyward, contorting the collision zone, and forming the jagged Himalayan peaks

29. Transform plate margin
Two plates slide past each other
strike slip faults.
Lithosphere is neither consumed nor destroyed.
Earthquakes, no volcanoes
Responsible for most of the earthquakes

30. What drives plate movement?
Ultimately: heat transported from core and mantle to surface
Heat transported by convection
Core is ~5,000°C and surface is ~0°C
Where mantle rises: rifting
Where mantle dives: subduction zones