{"id":207,"date":"2019-05-21T10:14:25","date_gmt":"2019-05-21T10:14:25","guid":{"rendered":"http:\/\/geop11.epgpbooks.inflibnet.ac.in\/?post_type=chapter&p=207"},"modified":"2019-05-21T10:27:18","modified_gmt":"2019-05-21T10:27:18","slug":"plate-tectonics","status":"publish","type":"chapter","link":"https:\/\/ebooks.inflibnet.ac.in\/geop11\/chapter\/plate-tectonics\/","title":{"rendered":"Plate Tectonics"},"content":{"raw":"
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\r\n\r\n\u00a0 \u00a0 In the present module we are going to discus about following aspects of Plate Tectonics:<\/strong>\r\n\r\n \r\n\r\n1.\u00a0 Historical Background\r\n\r\n2.\u00a0 Assumptions of the theory\r\n\r\n3.\u00a0 Evidences\r\n\r\n4.\u00a0 What is a plate?\r\n\r\n5.\u00a0 Distribution of major and Minor Plates\r\n\r\n6.\u00a0 Why Plate Moves?\r\n\r\n7.\u00a0 Types of Plate Boundaries\r\n\r\n8.\u00a0 Features formed\r\n\r\n \r\n\r\n1. Historical Background<\/strong>\r\n\r\n \r\n

You must be having a fair idea about continental drift theory given by Alfred Lothar Wegener-a 32 year old lecturer in meteorology and astronomy in Germany. Wegener delivered a lecture on \u201cThe Formation of the major Features of the Earth\u2019s Crust (Continents and Oceans)\u201d<\/em> at Frankfurt in an eminent Geological Association. In his lecture he suggested that continents had once been combined in the form of original single sialic land-mass and had afterward broken apart and drifted to their present positions.<\/p>\r\n\r\n<\/div>\r\n\"\"\r\n\r\n\"\"\r\n

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\u00a0 \u00a0His theory attracted little notice by the scientific community of his day. Geologists considered his theory as an impossible hypothesis. He gave his theory in 1912 and humankind reached on moon on 16 July 1969 (Apollo 11).<\/p>\r\n \r\n\r\n<\/div>\r\n\"\"\r\n

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\u00a0 \u00a0 During 1915 to 1960 in general scientific community overlooked that \u201cSouth America and Africa appear to fit together\u201d which was infact a reality. It was no less than revolution in science and paradigm in geoscience to recognize that land under you and me is not static rather it is moving at a rate of 2.5 to more than 15 centimeters per year. A famous historian of science Thomas J. Kuhn (1970) said \u201cParadigms gain their status because they are more successful<\/em> than their competitors in solving a few problems that the group of practitioners has come to recognize as acute\u201d<\/em>. Wegner was right that continents are moving but since at his time there was a little information about the secrets of the Ocean floor. Wegner was also not able to convince geologists what moved the continents.<\/p>\r\n \r\n

Now we know that continents are like cargo containers on a ship i.e., ship transports the cargo containers. On the planet the ship can be considered as plate. Tuzo Wilson was first to introduce the moving-plates idea in the year 1965 but his purpose was to explain the transform<\/em> faults <\/em>which later became an important feature to delineate the plate boundary. Dan P. McKenzie an English geophysicist and his colleague, Robert L. Parker (1967) studied the Wilson\u2019s transform fault and moving plate idea. They identified steady direction of plate movement by analyzing the occurrence of earthquakes around the Pacific Ocean. A Princeton geophysicist W. Jason Morgan was also working on the same theme of plate movement. He picked up the idea of \u201csea floor spreading\u201d coined by Robert Dietz and explained by Harry Hess (1962) of Princeton University and applied the Leonhard Euler\u2019s (French Mathematician of 18th Century) theorem to calculate the movements of the plate on the earth with reference to axis of rotation of the plate.<\/p>\r\n\r\n<\/div>\r\n\"\"\r\n

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\u00a0 \u00a0 \u00a0In this way Morgan prepared a world map showing about six large and 12 small \u201csubplates\u201d. He published his findings in Journal of Geophysical Research<\/em> in March 1968. Later in September 1968 i.e., five months after the publication of Morgan\u2019s paper, three seismologists at Lamont-Bryan Isacks, Jack Oliver and Lynn Sykes published their article in the same journal and said that seismological evidences like occurrences of shallow foci earthquakes along the transform fault and deep earthquakes along the destructive plate boundaries support the moving plate hypothesis. They also prepared a very beautiful wall sized map hung at Lamont showing epicenters of the earthquakes (1961-1967) in and around the Mid-Ocean Ridges of the world. It is noteworthy that Isacks, Oliver and Sykes were the one who first proposed the term \u201c new global tectonics\u201d (Greek \u201ctecton\u201d meaning builder<\/em>). The \u201cnew global tectonics\u201d is now popurlar as \u201c Plate Tectonics\u201d. Let us now discuss the plate tectonic theory in detail.<\/p>\r\n \r\n\r\n2.\u00a0 <\/strong>Assumptions of the Theory<\/strong>\r\n