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

Plate TectonicsPlate Tectonics

Dr. G. Madhavi LathaDr. G. Madhavi LathaDept. of Civil EngineeringDept. of Civil Engineering

Indian Institute of ScienceIndian Institute of Science

CE 244-GML

Origin of UniverseOrigin of Universe Big Bang modelBig Bang model (Hubble, 1929) - The (Hubble, 1929) - The

universe began with an explosive universe began with an explosive expansion of matter, which later expansion of matter, which later became what we know as stars, became what we know as stars, planets, moons, etc. This event is planets, moons, etc. This event is thought to have occurred 10 - 15 thought to have occurred 10 - 15 billion yrs ago. 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.

•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.

Big bang theoryBig bang theory

•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

Nebular HypothesisNebular Hypothesis

Formation of Earth’s Formation of Earth’s InteriorInterior

•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.

Layers of the EarthLayers of the Earth

Crust: Crust: Continental crust (25-40 kmContinental crust (25-40 km)) Oceanic crust (~6 km)Oceanic crust (~6 km)

MantleMantle Upper mantle (650 km)Upper mantle (650 km) Lower mantle (2235 km)Lower mantle (2235 km)

CoreCore Outer core: liquid (2270 km)Outer core: liquid (2270 km) Inner core: solid (1216 km)Inner core: solid (1216 km)

Values in brackets represent the approximate thickness of each layer

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.

Layers of the EarthLayers of the Earth

Alfred WegenerAlfred Wegener

Continental driftContinental driftTheory that continents and plates Theory that continents and plates move on the surface of the Earth move on the surface of the Earth proposed by Alfred Wegener in proposed by Alfred Wegener in 1915.1915.

Maps by Wegener (1915), Maps by Wegener (1915), showing continental driftshowing continental drift

Theory of continental driftTheory of continental drift

Evidence for continental Evidence for continental driftdrift

Matching coastlinesMatching coastlines Matching mountainsMatching mountains Matching rock types and rock agesMatching rock types and rock ages Matching glacier depositsMatching glacier deposits Matching fossilsMatching fossils


Matching coastlines


Matching mountainranges


Matching rock types and ages of rocks


Matching glacierdeposits 300million yearsago


Fossils of of Mesosaurus (aquatic reptile) found on both sides of Atlantic

Theory of Plate tectonicsTheory of Plate tectonics The theory of Plate tectonics was proposed The theory of Plate tectonics was proposed

in 1960s based on the theory of continental in 1960s based on the theory of continental drift.drift.

This is the Unifying theory that explains the This is the Unifying theory that explains the formation and deformation of the Earth’s formation and deformation of the Earth’s surface. surface.

According to this theory, continents are According to this theory, continents are carried along on huge slabs (plates) on the carried along on huge slabs (plates) on the Earth’s outermost layer (Lithosphere).Earth’s outermost layer (Lithosphere).

Earth’s outermost layer is divided into 12 Earth’s outermost layer is divided into 12 major Tectonic Plates (~80 km deep). major Tectonic Plates (~80 km deep). These plates move relative to each other a These plates move relative to each other a few centimeters per year.few centimeters per year.

Earth’s magnetic fieldEarth’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.

Tectonic plates of EarthTectonic plates of Earth

Types of plate Types of plate boundariesboundaries

Divergent plate boundariesDivergent plate boundaries: : where where plates move apart plates move apart

Convergent Plate boundariesConvergent Plate boundaries: : where where plates come togetherplates come together

Transform plate boundariesTransform plate boundaries: : where where plates slide past each other plates slide past each other

Divergent (Tension)Divergent (Tension)

Convergent (Compression)Convergent (Compression)

Transform (shearing)Transform (shearing)



Divergent Plate Divergent Plate BoundariesBoundaries

Plates move away Plates move away from each other from each other (tension)(tension)

New lithosphere is New lithosphere is formedformed

normal faultsnormal faults Causes volcanismCauses volcanism not very explosivenot very explosive

Convergent Plate Convergent Plate BoundaryBoundary

Plates move toward Plates move toward each other each other (compression)(compression)

lithosphere is lithosphere is consumedconsumed

reverse/thrust reverse/thrust faultsfaults

and foldsand folds Mountain buildingMountain building explosive volcanismexplosive volcanism

Ocean-continent Ocean-continent plates collideplates collide

Ocean plate Ocean plate subducts below subducts below continentcontinent

Forms a Forms a subduction zonesubduction zone

Earthquakes and Earthquakes and volcanoesvolcanoes

Ocean- Continent Ocean- Continent convergent marginconvergent margin

Ocean-ocean convergent Ocean-ocean convergent marginmargin

2 oceanic plates 2 oceanic plates collidecollide

One plate dives One plate dives (subducts) beneath (subducts) beneath otherother

Forms subduction Forms subduction zonezone

Earthquakes and Earthquakes and volcanoesvolcanoes

Continent-continent Continent-continent convergent marginconvergent margin

2 continental 2 continental plates collideplates collide

Neither plate Neither plate wants to wants to subductsubduct

Collision zone Collision zone forms high forms high mountainsmountains

Earthquakes, Earthquakes, no volcanoesno volcanoes

example: Himalayasexample: Himalayas

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

Himalayas: Continents Himalayas: Continents collidecollide

Two plates slide Two plates slide past each otherpast each other

strike slip faults. strike slip faults. Lithosphere is Lithosphere is

neither consumed neither consumed nor destroyed.nor destroyed.

Earthquakes, no Earthquakes, no volcanoesvolcanoes

Responsible for Responsible for most of the most of the earthquakesearthquakes

Transform plate marginTransform plate margin

What drives plate What drives plate movement?movement?

Ultimately: heat transported from Ultimately: heat transported from core and mantle to surfacecore and mantle to surface

Heat transported by convectionHeat transported by convection Core is ~5,000°C and surface is Core is ~5,000°C and surface is

~0°C~0°C Where mantle rises: riftingWhere mantle rises: rifting Where mantle dives: subduction Where mantle dives: subduction

zoneszones

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