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Continental Drift - Coggle Diagram
Continental Drift
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Plate Tectonics Theory
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lithospheric plates
Major plates:
- Antarctica and surrounding oceanic plate
- North American plate(with western Atlantic floor separated from the South American plate along the Caribbean islands)
- South American plate(with western Atlantic floor separated from the North American plate along the Caribbean islands)
- India-Australia-New Zealand plate.
- Africa with the eastern Atlantic floor plate
- Eurasia and the adjacent oceanic plate.
Notable Minor plates:
- Cocos plate between Central America and Pacific plate
- Nazca plate between south America and pacific plate
- Arabian plate that covers the Arabian Peninsula
- Philippine plate between the Asiatic and Pacific plate
- Caroline plate between Philippine and Indian plate(North of New Guinea)
- Fuji plate in the North east of Australia.
Indian Plate
- The Indian plate includes peninsular India and the Australian continental portions.
- The subduction zone along the Himalayas forms the northern plate boundary in the form of continent-continent convergence
8 In the east, it extends through Rakinyoma Mountains of Myanmar towards the island arc along Java Trench. The eastern margin is a spreading site lying to the east of Australia in the form of oceanic ridge in SW Pacific.
- The western margin follows Kirthar Mountain of Pakistan. It further extends along Makrana coast and joins the Red sea rift southeastward along Chagos archipelago.
- The boundary between India and the Antarctic plate is also marked by oceanic ridge running in roughly W-E direction and merging into the spreading site, a little south of New Zealand.
Movement of Indian Plate
- India was a large island situated of Australian coast, in a vast ocean. The Tethys sea separated it from the Asian continent till about 225 million years ago. India is supposed to have started her northward journey about 200 million years ago at the time when Pangaea broke.
Formation of Himalayas and Deccan plateau
- Himalayas formed as the result of Indian plate collided with Asian plate about 40-50 million years ago.
- About 140 million years before the present, the subcontinent was located as south as 50°S latitude, with Tethys sea separating Indian and Asian landmass. During the movement of the Indian plate towards the Asiatic plate, massive lava outpouring over the Indian plate, leading to the formation of Deccan traps.
- Himalayas started forming 40 million years after the formation of Deccan traps, and the process still continues.
Movement of plates
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- The plates have been constantly moving over the globe throughout the history of the earth, also will keep moving on in the future as well.
- The Continents are part of the plate, hence it is the plates that are moving instead of continents against the Continental drift theory proposed by Alfred Wegener.
- Pangaea was a result of converging of different continental masses that were parts of one or the other plates.
- Scientists using the palaeomagnetic data, have determined the positions held by each of the present continental landmass in different geological periods.
- Position of the Indian sub-continent is traced with the help of the rocks analysed from the Nagpur area.
- The strips of normal and reverse magnetic field that parallel the mid oceanic ridges help scientists determine the rates of plate movement.
- Arctic Ridge has the slowet rate with less than 2.5 cm/year. The east Pacific rise near the Easter island, in the South Pacific about 3,400 km west of Chile, has the fastest rate, with more than 15 cm/year.
Force for movement of Plate movement:
- The heat within the earth comes from two main sources: radio active decay and residual heat.
- The slow movement of hot, softened mantle that lies below the rigid plates is the driving force behind the plate movement.
- The mobile rock beneath the rigid plates is believed to be moving in a circular manner. The heated material rises to the surface, spreads and begins to cool, and then sinks back into deeper depths. This cycle is repeated over and over to generate a convection cell or convection flow
- McKenzie, Parker and Morgan collected the available ideas and came out with the Concept of Plate Tectonics in 1967.
- A Tectonic plate or a lithospheric plate is a massive irregularly shaped slab of solid rock, generally composed of both continental and oceanic lithosphere.
- Plates move horizontally over the asthenosphere as rigid unit.
- A plate may be referred to as continental plate or oceanic plate depending on which of the two occupy a larger portion of the plate.
Sea floor spreading
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- The concept of Sea floor spreading was proposed by Harold Hess and Robert Deitz.
- Hess argues the constant eruptions at the crest of the oceanic ridges cause the rupture of the oceanic crust and the new lava wedges into it, pushing the oceanic crust on the either side, and thus the ocean floor spreads.
- It further states that, the ocean floor that gets pushed due to volcanic eruptions at the crest, sinks down at the oceanic trenches and gets consumed.
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- Alfred Wegener, a German meteorologist who put forth a comprehensive argument in the form of 'continental drift theory' in 1912.
- According to Wegener, all the continents formed a single continental mass(Pangea), a mega ocean surrounded by the same(Panthalassa).
- He argues around 200 Millions years ago, Pangea began to split, breaking into two large continental masses; Laurasia and Gondwanaland forming the northern and southern components respectively. Subsequently, Laurasia and Gondwanaland continued to break into various smaller continents that exist today.
