Plate tectonics
Published on 31 Jan 2025
Developed by McKenzie, Parker and Morgan. It rejected the idea of SIALic continents floating over SIMAtic oceans.
Floating lithospheric plates: It is not the continents that moves as believed by Wegener. Continents and oceans are part lithospheric plate and what moves is the plate horizontally over the asthenosphere.
Convectional current: Movement of plates are driven by convectional currents in the earth’s mantle.
Nature of lithospheric plate: The lithospheric plates may be entirely oceanic or continental, but mostly are both.
Major and minor plates: Earth’s lithosphere is divided into seven major plates and some minor plates
Example: Major plates – Antarctica, North America, South America, Pacific
Minor plates – Cocos, Nazca, Arabian, Caroline etc.
Other crustal features: Young Fold Mountains, ridges, trenches and faults surround these major plates.
Earth’s geological activities takes place in these boundaries. There are three types of boundaries.
Divergent boundaries
Convergent boundaries
Transform boundaries
Plate interactions and consequent landforms
Divergent plate boundaries
Here plates move away from each other and it’s a zone of continuous upwelling of lava and results in the creation of new ocean floors.
Resulting land forms
Mid Oceanic Ridges: Formed at divergent boundaries as magma comes out and solidifies to form MOR
Example: mid Atlantic ridge
Rift valleys: When plates pull apart, causing crustal stretching, block faulting, subsidence, and eventual seafloor spreading.
Example: East African ridge
Fissure volcanoes: Plates separate, causing magma to intrude through cracks, leading to multiple surface eruptions.
Convergent plate boundaries
It’s a tectonic boundary where two plates are moving toward each other and collide making new landforms.
OCEAN-OCEAN COLLISION
Here two or more lithospheric ocean plates collide with each other. Plate with denser oceanic crust will subduct below the other plate.
Resulting landforms
Trenches: When denser oceanic crust subduct under the lighter one.
Example: Japanese trench, Mariana trench.
Archipelagos and islands: Formed due to volcanism of the subducted plate
Example: Indonesia and Philippines
Island arcs: Formed when one oceanic plate subducts beneath another, creating magma that erupts to build volcanic islands.
Example: Aleutians, Kuril
OCEAN–CONTINENT COLLISION
Here a continental plate collides with an oceanic plate. Denser oceanic crust get consumed under less dense continental crust.
Resulting landforms
Volcanoes: Formed by the consuming of oceanic plate under lighter continental plate.
Example: Mt.Chimborazo, Mt. Cotopaxi, Ojos del salados of Andes mountains etc.
Fold Mountains: Formed from the sediments and compressive force.
Example: Andes, Rockies, Atlas, Great Dividing Range, Kjollen mountains etc.
Trenches: Formed by the subduction of oceanic plate.
Example: Mariana trench – formed when pacific plate subducts under less dense Philippine plate.
CONTINENT-CONTINENT COLLISION
Occurs when two continental plates move towards each other. There is no subduction in continent - continent collision since continents are lighter and buoyant. There for no volcanism and trench formation. Results in creation of larger land mass.
Resulting landforms
Fold mountains: By the compression created by the moving Indian plate towards European plate.
Example: Himalayas
Transform plate boundary
Here two plates are slipping past one another. The two plates are in contact along a vertical fracture called transform fault.
Example: The San Andreas fault in California