Plate Tectonics Theory
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
Principles of plate tectonics
• 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)
Types of Plates
• Oceanic plates - plates below the oceans
• Continental plates - plates below the
continents
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
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)
• Iranian plate.
The 3 types of plate boundaries
• 1. Divergent
• 2. Convergent
• 3. Transform fault
Causes of Plate Tectonics
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.
Important contributions to Plate Tectonics theory:
1596 Recognition of the plates having moved
1858 Correlating rock type and fossils across the continents
1872 Mapping the Atlantic Mid-ocean Ridge
1896 Discovery of radioactivity (Earth's interior is hot)
1897–1911 Delineating Earth's layered interior
1912 Alfred Wegner proposes "Continental Drift"
1927 Convection of mantle could drive the plates
1953 Marie Tharpe recognizes mid-ocean ridge spreading
1962 Harry Hess names "Spreading ridges"
1963 Magnetic striping of ocean floor gives relative ages
1963 Hot spots defined; transform faults.
1960s defined the driving forces of plate tectonics
(a) Plate tectonics(from the Late Latin tectonicus, from the Greek: τεκτονικός “pertaining to building”)is a scientific theory describing the large-scale motion of 7 large plates and the movements of a larger number of smaller plates of the Earth‘s lithosphere, over the last hundreds of millions of years.
(b) The theoretical model builds on the concept of continental drift developed during the first few decades of the 20th century. The geo scientific community accepted plate-tectonic theory after seafloor spreading was validated in the late 1950s and early 1960s.
(c) The lithosphere, which is the rigid outermost shell of a planet (the crust and upper mantle), is broken up into tectonic plates. The Earth’s lithosphere is composed of seven or eight major plates (depending on how they are defined) and many minor plates.
(d) Where the plates meet, their relative motion determines the type of boundary: convergent, divergent, or transform.
(e) Earthquakes, volcanic activity, mountain-building, and oceanic trench formation occur along these plate boundaries. The relative movement of the plates typically ranges from zero to 100 mm annually.
(f) Tectonic plates are composed of oceanic lithosphere and thicker continental lithosphere, each topped by its own kind of crust.
(g) Along convergent boundaries, subduction carries plates into the mantle; the material lost is roughly balanced by the formation of new (oceanic) crust along divergent margins by seafloor spreading.
(h) In this way, the total surface of the lithosphere remains the same. This prediction of plate tectonics is also referred to as the conveyor belt principle. Earlier theories, since disproven, proposed gradual shrinking (contraction) or gradual expansion of the globe.
(i) Tectonic plates are able to move because the Earth’s lithosphere has greater strength than the underlying asthenoshere.
(j) Lateral density variations in the mantle result in convection.
(k) Plate movement is thought to be driven by a combination of the motion of the seafloor away from the spreading ridge (due to variations in topography and density of the crust, which result in differences in gravitational forces) and drag, with downward suction, at the subduction zones.
(l) Another explanation lies in the different forces generated by tidal forces of the Sun and Moon.
(m) The relative importance of each of these factors and their relationship to each other is unclear, and still the subject of much debate.
Significance of plate tectonic theory
Plate tectonics explains the distribution of continents and oceans, the formation of mountain ranges, the opening and closing of ocean basins, and the generation of geological hazards such as earthquakes and volcanic eruptions.
(a) Plate tectonics is responsible for creating almost all significant landforms.
(b) Magmatic eruptions cause the core to spew out new materials.
(c) Minerals with high economic value, such as copper and uranium, are located close to plate borders.
(d) The future shape of landmasses can be anticipated using the current understanding of crustal plate movement.
(e) For instance, North and South America will split if current patterns continue. The east coast of Africa will split off into a new region. Australia will approach Asia.
Conclusion
The great unifying theory of geosciences that describes how continents move is called plate tectonics. Most significant landforms on Earth’s surface, such as mountains, mid-ocean ridges, and the production of the new lithosphere are caused by volcanism and earthquakes.
The plate tectonic theory has revolutionized our understanding of the Earth’s geology and has become a unifying principle in the field of earth sciences.
It provides a framework for explaining the dynamic processes that have shaped the Earth’s surface over millions of years and continue to do so today.
