In our Previous articles, we discussed the major theories proposed at different times regarding the distribution of Oceans and Continents. Continuing the discussion we will learn about Plate Tectonics Theory
Plate Tectonics Theory
The basic concept of plate tectonics involves the movement of lithospheric plates and the geological activity associated with them, which helps us to understand the dynamic processes that shape the Earth’s surface, including the formation of continents, ocean basins, mountains, earthquakes, and volcanic activity.
The solid upper layer of the mantle is hot and behaves like plastic and can flow. The earth’s crust (oceanic + continental) together with the upper layer of the mantle constitutes the lithosphere. The lithosphere rides on the asthenosphere.
The rigid lithosphere is capable of moving bodily over the asthenosphere and is disjoined into large segments or blocks extensively by faults or thrusts. The blocks are known as “lithospheric plates” which are in motion relative to each other.
A tectonic plate may be a continental plate or an oceanic plate. The Earth’s lithosphere is divided into 7 major plates and some minor plates.
The Pacific plate
The North American plate
The South American plate
The Indian-Australian-New Zealand plate
The African with eastern Atlantic floor plate
The Eurasian plate
The Antarctic plate
Some important minor plates include:
Cocos plate- between Central America and the Pacific plate
Nasca plate- between South America and the Pacific plate
Arabian plate- mostly Saudi Arabian landmass
Philippine plate- between Asiatic and Pacific plate
Caroline plate- between the Philippine and Indian plate
Fuji plate- Northeast of Australia
Juan De Fuca plate- South-East of North American plate
A plate is a large, rigid slab of rock that moves slowly over the asthenosphere. The thickness of the plate is from 0 to 10 kms at ridges and 100-150kms elsewhere.
Nearly all seismic, volcanic, and tectonic activities are localized around the plate margins and are associated with differential motions between adjacent plates.
Plates move with velocities ranging from 1 to 6cm/year; plates move away from one another, slide past one another, or towards one another
Where two plates diverge, we find extensional features, typically the ocean ridges symmetrical about the vertical axis. Where two plates converge and one is thrust beneath the other, we find island arcs-the huge asymmetric features which are the sites of greatest earthquakes, explosive volcanism, great topographic relief, and many other distinctive features.
Where two plates slide past each other, there occurs transcurrent faults i.e. the large strike-slip faults joining segments of ocean ridges or arcs.
