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Types of Tectonic Plates
Plate is a rigid lithospheric slate (earth’s solid outer layer that includes the crust and the uppermost mantle) that glides over the earth’s mantle. Below the lithosphere is the viscous layer called the asthenosphere that lubricates the earth’s tectonic plates, responsible for the movement of the lithospheric plates.
Types of Plates
Based on their size, plates are classified into major (relatively larger) and minor plates (relatively smaller).
Major Plates
There are a total of seven major tectonic plates that make up our planet. They are as follows
Pacific plate − The pacific major plate is the oceanic plate and the largest among the major plates that underlie the Pacific Ocean completely. It is surrounded by the North American plate in the east, the Eurasian Plate in the west, the Indo-Australian Plate in the south west, and the Antarctic plate in the south. It is home to most of the pacific ring of fire, which is prone to catastrophic calamities like earthquakes and volcanic eruptions.
North American Plate − It's an oceanic-continental plate. This plate is surrounded by the Eurasian plate in the east, the African plate in the south-east and the Pacific plate in the west. The North American plate extends over the north pole, and it contains Siberia and the Kuril Islands of Russia.
Eurasian Plate − The Eurasian major plate is a continental plate bordered by the North American plate, the African plate, and the Indo-Australian plate on the north, west, and south sides, respectively. This plate consists of Europe, major parts of Asia.
African Plate − The African Plate is an Oceanic-Continental Plate which contains the whole continent of Africa and part of the Atlantic Ocean. It is surrounded by the Eurasian plate on the north, the North American plate on the north-west, the South American plate on the west, and the Antarctic plate on the south.
Antarctic Plate − The Antarctic Plate is an Oceanic-Continental Plate which contains the entire continent of Antarctica and the Antarctic Ocean. It encompasses African, Indo-Australian, Pacific and South American plates.
Indo-Australia Plate − It is an oceanic-continental plate which stretches from Australia to India, including the oceanic crust of the Indian Ocean. It is bordered by the Eurasian plate in the north, the Pacific plate in the east, and the Antarctic plate in the south.
South American Plate − The South American plate is the smallest among the major plates. It is an Oceanic-Continental Plate which includes the whole of South America and parts of the Atlantic Ocean. It is surrounded by the African plate in the east, the North American plate in the north, and the Antarctic plate in the south.
Minor Plates
There are more than 20 minor plates that lie in between the major plates. Nazca plate, Cocos plate, Arabian plate, Philippines plate, Caroline plate, Fuji Plate, Caribbean plate, Scotia plate, Anatonian plate, Rivera plate, Iranian plate are some of the significant minor plates of the earth.
Factors affecting the movements of plates
Rotation of the earth
The Thermal Convective Current
Basal Drag (Friction) − The friction between the rigid lithosphere and the thermal convective current in the underlying asthenosphere results in movement of the Earth’s tectonic plate.
Slab Suction (Gravity) − Due to the effect of local thermal convective currents, the plate experiences a downward pull in the subduction zone at ocean trenches.
The inverse relationship between the temperature and density of the plates results in their movement.
Tidal force / drag exerted on the crust of the earth due to the gravitational force of the moon and the sun makes the plates to move.
Shear strain is experienced by the earth due to the north-south compression associated with the earth’s rotation.
Pole flight force − Equatorial drift due to rotation and centrifugal effects drives the plates to move equatorward from the poles.
Changes in the rotational axis of the earth with respect to its crust cause deformation of the geoid.
Conclusion
The theory of plate tectonics revolutionized the earth sciences by explaining how the movement of geologic plates causes mountain building, volcanoes, earthquakes and of course the present locations of different plates.
Frequently Asked Questions
What are Tectonic plates?
Tectonic plates are the gigantic lithospheric structures that moves under the influence of the endogenetic forces which are broken into several major and minor plates.
List some of the minor plates in the world?
There are more than 20 minor plates that lie in between the major plates. Nazca plate, Cocos plate, Arabian plate, Philippines plate, Caroline plate, Fuji Plate, Caribbean plate, Scotia plate, Anatonian plate, Rivera plate, Iranian plate are some of the significant minor plates of the earth.
What is Basal Drag and Slab Suction?
Basal Drag (Friction) − The friction between the rigid lithosphere and the thermal convective current in the underlying asthenosphere results in movement of the Earth’s tectonic plate.
Slab Suction (Gravity) − Due to the effect of local thermal convective currents, the plate experiences a downward pull in the subduction zone at ocean trenches.
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