What is the theory of plate tectonics?

The global coastal lithosphere is divided into six plates: Asia-Europe plate, Africa plate, America plate, Pacific plate, Indian Ocean plate and Antarctica plate. Plate Tectonic Theory 19 15 Wei Gena put forward the concept of continental drift in his book The Origin of the Continent and the Ocean, but their evidence failed to convince geologists of the authenticity of continental drift. In the early 1960s, H.Hess put forward the concept of seafloor spreading, which was supported by a series of new evidences such as paleomagnetism, geochronology, marine geology and geophysics. Three different phenomena: the age of magnetic polarity turning in lava sequence; The depth of the residual magnetization circle in the deep sea core and the width of the linear magnetic anomaly parallel to the mid-ocean ridge all change at the same rate, which is caused by the migration of the crust from the mid-ocean ridge. Geologists generally accepted the viewpoint of activity theory and gradually formed the theory of plate movement. Plate tectonic theory divides the earth's surface into several rigid lithospheric plates, including subduction zone, collision zone, mid-ocean ridge, transform fault and other active zones. According to the theory of plate tectonics, the movement of the earth's surface is mainly completed by fault activities between plates, and the deformation of wide blocks between plate boundaries is very small, which can be ignored in the global scope, that is, plates can be considered as rigid. Plate movement holds that the thin plate of rigid lithosphere (including continental and oceanic crust) moves on the asthenosphere with less viscosity in the upper mantle. It is developed from the continental drift theory, but it is different from the continental drift theory. Their differences are mainly as follows: (1) Wei Gena and others regard the mainland as containing only continental silicon and aluminum layers; In plate theory, lithospheric plate includes lithosphere (lithospheric mantle) and asthenosphere above the crust. (2) Wei Gena and others regard the continent as an active unit in plate theory, while the continent is passive. The continental drift theory holds that the continental drift passes through the silicon-magnesium layer under the crust; Plate theory introduces the concept of passive continent, just like being put on a conveyor belt. Because of its low component density, it is usually buoyant, which can escape the fate of being shrunk and become a stable passive floating block on the conveyor belt. (3) Wei Gena and others think that the continental Si-Al layer is completely different from the mantle Si-Mg layer; According to plate theory, land is a chemical product of mantle differentiation and floating, and land is connected with a part of its underlying mantle. Plate tectonics provides space for the development of mantle convection theory. Lithosphere includes lithosphere (lithospheric mantle) and asthenosphere above the earth's crust. From a thermodynamic point of view, it is equivalent to the part above the solid line of rock. From a mechanical point of view, it is an earth watch case that can withstand long-term pressure. Plate theory is gradually recognized in the field of geography. It seems simple, but in fact it has profound truth. Plate tectonics, also known as seam block tectonics, exists in various structures on the earth's surface. Even in the most severely deformed collision zone in Taiwan Province Province, steep folds are composed of a series of relatively complete limestone blocks and their faults. From the point of view of tectonic physics, due to the nonlinear rheological properties of rocks, crustal deformation is mainly concentrated in some narrow zones, while the vast areas between these active zones only bear small deformation. These vast areas are blocks, and the long and narrow active zones are the boundaries between blocks. The nonlinearity of rheological constitutive relation is mainly manifested in the exponent n of stress term in the relationship between strain rate and stress. The greater the n, the stronger the nonlinearity and the narrower the active band. It is this rheological basis that determines the geometry of plate tectonics, which is manifested in structures of various scales. According to the plate theory, the ocean also has its birth and death, from scratch, from small to large; Can also be from big to small, from small to nothing. The development of the ocean can be divided into embryonic stage (such as the Great Rift Valley in East Africa), juvenile stage (such as the Red Sea and Gulf of Aden), adult stage (such as the Atlantic Ocean now), declining stage (such as the Pacific Ocean) and terminal stage (such as the Mediterranean Sea). The development of the ocean and the division of the mainland complement each other. In Precambrian, there was a pan-continent on the earth. Later, after the process of separation and integration, in the early Mesozoic, Pangea was divided into two ancient lands, namely, the Laoya ancient land in the north and Gondwana ancient land in the south. By the end of Triassic, the two ancient lands were further separated and drifted away, and gradually developed from a narrow strait to a modern huge ocean such as the Indian Ocean and the Atlantic Ocean. In Cenozoic, as India drifted northward to the southern edge of Eurasia, the two collided, and the Qinghai-Tibet Plateau rose, forming a magnificent Himalayan mountain system, and the eastern part of the ancient Mediterranean completely disappeared. Africa continued to advance northward, and the western part of the ancient Mediterranean gradually shrank to its present scale; Southern Europe was pushed into the Alps. During the westward drift of South America and North America, their front edges were squeezed by the Pacific crust and lifted to the Cordillera-Andes system. At the same time, the two Americas met again in the isthmus of Panama. The Australian mainland left Antarctica and drifted northeast to its present position. So the basic outline of land and sea has developed to the present scale.