Plate Tectonic Theory

Home , Arabian Plate, Indian Plate, Iranian Plate, North American Plate

PLATE TECTONIC THEORY

Department of Geography Jawaharlal Nehru College, Pasighat • The Earth’s crust and upper mantle (i.e lithosphere)are broken into sections called plates.

TECTONIC PLATES/ LITHOSPHERIC PLATES These are massive, irregularly-shaped slab of solid rock, generally composed of both continental and oceanic lithosphere

The crust and part of the upper mantle = lithosphere 5-100 km thick in oceanic areas  200 km thickness in continental areas

Less dense Department than the of material Geography below it, so it “floats” Jawaharlal Nehru College, Pasighat What is the Asthenoshere?

• The plastic/ductile layer below the lithosphere = asthenosphere • The plates of the lithosphere float on the asthenosphere

Department of Geography Jawaharlal Nehru College, Pasighat LITHOSPHERE

ASTHENOSPHERE

MESOSPHERE

• The Earth is composed of a mosaic of thin rigid plates (pieces of lithosphere) that move horizontally with respect to one another • Plates interact with each other along their plate boundaries • Plate boundaries associated with tectonic activity (mountain building, earthquakes, active volcanoes)

Department of Geography Jawaharlal Nehru College, Pasighat 2 Types of Plates

• Oceanic plates - plates below the oceans • Continental plates - plates below the continents

Department of Geography Jawaharlal Nehru College, Pasighat Department of Geography Jawaharlal Nehru College, Pasighat Major tectonic plates

• Antarctica and the surrounding oceanic plate • North American plate • South American plate • Pacific plate • India-Australia-New Zealand plate • Africa with the eastern Atlantic floor plate • Eurasia and the adjacent oceanic plate

Department of Geography Jawaharlal Nehru College, Pasighat Minor tectonic plates • Cocos plate: Between Central America and Pacific plate • Nazca plate: Between South America and Pacific plate • Arabian plate: Mostly the Saudi Arabian landmass • Philippine plate: Between the Asiatic and Pacific plate • Caroline plate: Between the Philippine and Indian plate (North of New Guinea) • Fuji plate: North-east of Australia. • Turkish plate, • Aegean plate (Mediterranean region), • Caribbean plate, • Juan de Fuca plate (between Pacific and North American plates) Department of Geography • Iranian plate.Jawaharlal Nehru College, Pasighat

• 1. Divergent

• 2. Convergent

• 3. Transform fault Department of Geography Jawaharlal Nehru College, Pasighat Department of Geography Jawaharlal Nehru College, Pasighat Department of Geography Jawaharlal Nehru College, Pasighat Features of Divergent Boundaries • Mid- ocean ridges • rift valleys • fissure volcanoes

Department of Geography Jawaharlal Nehru College, Pasighat Divergent plate boundaries

• The Mid- Atlantic Ridge is a divergent plate boundary where sea floor spreading occurs

Department of Geography Jawaharlal Nehru College, Pasighat • Formation of an ocean basin by rifting and sea floor spreading

Department of Geography Jawaharlal Nehru College, Pasighat Department of Geography Jawaharlal Nehru College, Pasighat Department of Geography Jawaharlal Nehru College, Pasighat Department of Geography Jawaharlal Nehru College, Pasighat Department of Geography Jawaharlal Nehru College, Pasighat Department of Geography Jawaharlal Nehru College, Pasighat Department of Geography Jawaharlal Nehru College, Pasighat Department of Geography Jawaharlal Nehru College, Pasighat

Convection Currents

• Hot magma in the Earth moves toward the surface, cools, then sinks again. • Creates convection currents beneath the plates that cause the plates to move.

Department of Geography Jawaharlal Nehru College, Pasighat Department of Geography Jawaharlal Nehru College, Pasighat Comparison: Continental Drift – See Floor Spreading – Plate Tectonics

Continental Drift See Floor Spreading Plate Tectonics

Explained Alfred Wegener in Arthur Holmes explains In 1967, McKenzie and by 1920s Convectional Current Theory Parker suggested the theory in 1930s. of plate tectonics. The Based on convectional theory was later outlined by current theory. Harry Hess Morgan in 1968 explains Sea Floor Spreading in 1940s

Theory Explains Movement Explains Movement of Explains Movement of of Continents only Oceanic Plates only Lithospheric plates that include both continents and oceans.

Buoyancy, gravity, Convection currents in Convection currents in Forces for Department of Geography pole fleeingJawaharlal force, tidal Nehru the mantle College, drag crustalPasighat the mantle drag crustal movement currents, tides, plates plates Contd...

Apparent affinity of Ocean bottom Ocean bottom relief, physical features, botanical relief, Paleomagnetic rocks, evidence, fossil evidence, Paleomagnetic distribution of Evidences Tillite deposits, placer rocks, earthquakes and deposits, rocks of same age distribution of volcanoes, gravitational across different continents earthquakes and anomalies at trenches, etc. volcanoes etc. etc.

Too general with silly and Doesn’t explain Drawbacks sometimes illogical the movement of ——————— evidences. continental plates

Acceptance Totally discarded Not complete Most widely accepted

Helped in the evolution of Helped in the Helped understand convectional current theory Usefulness Department ofevolution Geography of plate various geographical and seeJawaharlal floor spreading Nehru College, Pasighat tectonics theory features. theory