German meteorologist and geologist Wei Gena first put forward the theory of continental drift. He believes that in Precambrian, there was a unified continent on the earth: Pan-continent. Later, through the process of separation and integration, in the early Mesozoic, the unified ancient land was divided into Laoyasia in the north and Gondor 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 huge ocean such as the Indian Ocean and the Atlantic Ocean. In Cenozoic, because India drifted northward to the southern edge of Eurasia, the two collided, and the Qinghai-Tibet Plateau uplifted, forming a grand 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 the Cenozoic position. So the basic outline of land and sea developed into the scale of Cenozoic.
Due to the limitation of scientific and technological level and understanding at that time, the theory of continental drift failed to correctly explain the dynamic mechanism of continental drift and provided the best scheme for continental splicing. The theory of continental drift caused great controversy in academic circles at that time. Soon after it was put forward, it was considered an absurd guess. Because Wei Gena himself devoted himself to the scientific exploration of Greenland snowfield, the theory of continental drift was once silent.
19 15, Wei Gena put forward the concept of continental drift in his book The Origin of the Continent and the Ocean. However, the evidence he presented 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.
Because it is related to the state around the Pacific plate called "Pacific Rim", earthquakes, deep earthquakes and volcanic activities in this area are very active. Due to the collision between the Indian Ocean plate and the Eurasian plate, the Himalayas and the Qinghai-Tibet Plateau were formed. Under the boundary of convergent plates where continental plates collide with each other, the conflict zone between continents is formed, and large folded mountains are also created.
In 1960s, seafloor spreading and plate tectonics brought new vitality to the early continental drift theory. A great deal of evidence obtained before 20 15 shows that the basic viewpoint of continental drift in Wei Gena is correct.
In the early 1960s, American seismologist R. Dietz (196 1) put forward the concept of "submarine expansion". Then, Hess (1962) elaborated in depth.
Dietz pointed out that the heat generated by the decay of radioactive elements in the mantle causes large-scale thermal circulation of mantle materials at a speed of several centimeters per year, forming convection circles, which act on the lithosphere and become the main force to promote crustal movement. The formation of oceanic crust is related to mantle convection. The ocean floor is the top of the convection circle, which is formed in the discrete zone of the ocean floor and slowly expands to the convergence zone. Generally speaking, the structure of the ocean floor is a direct reflection of mantle convection, the ridge is the upwelling part of mantle material, and the trench is the descending part of mantle material.
Howe believes that the mid-ocean ridge is a place where mantle convection rises, from which mantle materials are constantly pouring out, and islands and trenches distributed around the Pacific Ocean, continental margin mountains, volcanoes and earthquakes are all formed in this way.
Due to the development of plate tectonic theory, most of the earth activities that have been regarded as mysteries so far have been explained. Since 1970s, the world-scale earth observation aimed at confirming the theory of plate tectonics has developed vigorously. Through these observations, the age distribution of the seabed is determined in detail, and the plate movement process in previous geological periods is clarified. Moreover, due to the development of space observation technology, even the plate movement of one centimeter per year can be observed for several years.
In 1950s, the development of ocean exploration confirmed that the rocks on the seabed were thin and young (200-300 million years at most, while there were billions of years of rocks on land). In addition, the seabed magnetization measurement since 1956 shows that the geomagnetic anomalies on both sides of the mid-ocean ridge are symmetrical. On this basis, the American scholar H.H.Hess put forward the theory of submarine expansion, arguing that the convective rise of mantle asthenosphere material made new rocks form in Hailing area, and pushed the whole submarine to expand to both sides, and finally dive below the continental crust in the trench area.
It is the dynamic support of seafloor spreading theory and new evidence (paleomagnetism research, etc.). ) The supporting continent is really likely to drift, so the revived continental drift theory (plate tectonic theory is also called the new continent drift theory) began to form.
Because of the evidence provided by the "pole shift curve" and submarine expansion, continental drift is indeed a fact that is happening. In 1965, scientists used computers to put together the continents on the earth according to their existing shapes. Moreover, the seabed topography, earthquake location, volcanic activity and other active parts are all connected into strips, so the revolutionary viewpoint of "plate tectonics" has emerged.
Basic content 1968, D.P.Mckenzin and R.L.Parker of Cambridge University, W.J.Man of Princeton University and X.Lepichon of lamont Observatory jointly put forward a new theory of continental drift-plate tectonics, namely submarine expansion.
The theory of plate tectonics is based on the theory of continental drift and submarine spreading, combined with a large number of marine geology, geophysics, submarine topography and other data, and put forward after comprehensive analysis. Therefore, some people call continental drift theory, submarine expansion theory and plate tectonics the trilogy of the development of global tectonic theory. Plate tectonics is the most popular global tectonic theory in modern times. According to this theory, the earth's lithosphere is not a whole, but divided into many tectonic units by the growth boundary of the crust (such as herring and transform fault) and the extinction boundary of the crust (such as trenches, orogenic belts and ground suture lines). These structural units are called plates. The global lithosphere is divided into six plates: Eurasia plate, Africa plate, America plate, Pacific plate, Indian Ocean plate and Antarctic plate. Among them, the Pacific plate is almost entirely in the ocean, and the other five plates include a large land and a large ocean. A big board can also be divided into several sub-boards. These plates float on the "asthenosphere" and keep moving. Generally speaking, the crust inside plates is relatively stable, and the boundary between plates is a relatively active zone, and the crust is unstable. The basic features of the earth's surface are formed by the collision and stretching of relatively moving plates. Rifts and oceans are usually formed in areas where plates are cracked, such as the Great Rift Valley in East Africa and the Atlantic Ocean. Mountains are usually formed in areas where plates collide and compress. When the ocean plate collides with the continental plate, the ocean plate dives under the continental plate because of its high density and low position, and a trench is often formed here, which becomes the deepest place in the ocean. Continental plates are squeezed into arches and rise into island arcs and coastal mountains. The deep trench and island arc chain in the western Pacific Ocean are formed by the collision between the Pacific plate and the Eurasian plate. Where two continental plates collide, huge mountains usually form. The Himalayas were produced during the collision between the Indian plate and the Eurasian plate. Plate tectonic theory has been used to explain the formation and distribution of volcanoes and earthquakes, as well as the formation and distribution of minerals. However, there are still different opinions on what drives the plate to carry out large-scale and sustained movement.
This theory has successfully explained many geographical phenomena, such as the contours of both sides of the Atlantic; In Africa and South America, the same paleontological fossils are found to be related to modern organisms; Similar moraines have been found in Antarctica, Africa and Australia. Coal seams formed in warm conditions have been found in Antarctica and other places. But it has a fatal weakness: motivation. According to Wei Gena, physicists at that time immediately began to calculate the quality of land by using its volume and density. Then according to the friction between aluminosilicate rock (granite layer) and siliceous magnesium rock (basalt layer), how much force is needed to make the continent move. Physicists found that the gravity of the sun and the moon and the tidal force were too small to push the vast continent. Therefore, the theory of continental drift gradually disappeared after more than ten years of prosperity.
Plate tectonics Plate tectonics, also known as global tectonics. The so-called plate refers to the lithospheric plate, including the whole crust and the top of the upper mantle below Moho.
The top of the mantle above the crust and asthenosphere. According to the new global tectonic theory, large-scale horizontal movement has occurred and continues to occur in continental and marine crust. However, this horizontal movement does not occur between Si-Al layer and Si-Mg layer as envisaged by continental drift theory, but the lithospheric plate moves on the whole mantle asthenosphere like a conveyor belt, and the mainland is just a "passenger" on the conveyor belt.
The earth is the only planet suitable for plate tectonics.
The giant earth-like planet found outside the solar system was named "Super Earth". "Super Earth" has aroused scientists' keen interest in studying what the earth might look like. 20 14 scientists from Harvard university pointed out that these terrestrial planets are also suitable for plate tectonic theory. The theory of plate tectonics refers to the movement theory of huge plates that constitute the earth's solid crust. Plate movements often lead to earthquakes, volcanic eruptions and other major geological events. Basically, plates determine the geological history of the earth. The earth is the only known planet suitable for plate tectonics theory. The movement of the earth's plates is considered to be a necessary condition for the evolution of life.
"Super Earth" also applies to planets suitable for plate tectonics.
However, a paper published in Astrophysics by Diana Valencia, a planetary scientist at Harvard University, and her colleagues predicted that the "super earth" (whose mass is one to ten times that of the Earth) will also provide one of the necessary conditions for sustaining life through plate tectonics. Valencia, the author of the paper, said, "Some of these super-earths may also be in the' habitable zone' of their solar system, which means that they are just at the right distance from their parent star and there is liquid water, so there will be life. Although only the thermal and chemical evolution of these planets can ultimately determine whether they are suitable for living, these thermal and chemical characteristics are extremely dependent on plate tectonic theory. " By comprehensively simulating the internal structure of these super-earths with large land area, Valencia and his research team discovered the relationship between the mass of the "super-earth" and its plate and plate stress. Some of these stress values change the earth's mantle very slowly. Stress value is the driving force of plate deformation and subduction (one plate sinks under another plate). Because these "super earths" are more massive than the earth, this driving force is also much greater than the earth.
The research team found that as the mass of the planet increases, the shear force will increase and the thickness of the plate will decrease. These two factors weaken the plate and reduce the plate, which is the key part of plate tectonic theory. Therefore, scientists say that "super earth" can easily meet the conditions needed for plate deformation and subduction. Their research results show that the plate tectonic theory is especially suitable for the massive super earth. Valencia said, "People's research has proved that there is plate tectonic movement in the' super earth', even if there is no water on these planets." In the future, people can use NASA's Earth-like Planet Detector or European Space Agency's Darwin Project to verify these conclusions. The Darwin project of the European Space Agency will consist of three astronomical telescopes, aiming at finding Earth-like planets.
The structure is divided into six plates. Le Pixiong divided the global crust into six plates in 1968. Pacific plate, Asia-Europe plate, Africa plate, America plate, Indian Ocean plate (including Australia) and Antarctica plate. Except for the Pacific plate, which is almost entirely ocean, the other five plates have both continents and oceans. In addition, the plate can be divided into several sub-plates. For example, the American plate can be divided into South America and North America, and the Philippines, Arabian Peninsula and Turkey can also be used as independent small plates. The boundaries between plates are mid-ocean ridge or ocean ridge, deep trench, transform fault and ground suture. The ridge here generally refers to the mountains at the bottom of the ocean.
The seabed topography has an active ocean ridge between the Atlantic Ocean and the Indian Ocean, also known as the mid-ridge, which consists of two parallel ridge peaks and a middle canyon. There is also an earthquake ridge in the Pacific Ocean, but not in the middle of the ocean, but in the east. It is not very rugged, and there are no two rows of ridge peaks separated by the middle canyon. It is often called the rise of the central Pacific. The oceanic ridge is actually an area where the submarine splits to produce a new crust. Transform fault is a mid-ocean ridge cut into small segments by many transverse faults. It is not a simple translation fault, but a fault with one side split and the other side horizontally dislocated. Wilson called it transform fault. When two plates collide, the contact zone is squeezed and deformed, forming a folded mountain range, which sews up the originally separated two continents, which is called ground fissure. Generally speaking, within the plates, the crust is relatively stable, and the boundary between plates is a relatively active zone of the crust. Volcanic and seismic activities, faults, compressional folds, magma rising and crustal subduction occur frequently.
According to Hess's theory of seafloor spreading, it is considered that the mid-ocean ridge is the place where mantle convection rises, and mantle material keeps pouring out from here, cooling and solidifying into a new ocean crust. Later, the heat flow from the mid-ocean ridge pushed the previously formed oceanic crust outward, expanding from the mid-ocean ridge to both sides at a rate of 0.5~5 cm per year, constantly adding new strips to the oceanic crust. Therefore, the age of submarine rocks gets older with the distance from the mid-ridge. When the moving oceanic crust meets the continental crust, it dives into the mantle, and in the subduction zone, a deep trench is formed due to drag. When the ocean crust is squeezed and bent beyond a certain limit, it will break, which will lead to earthquakes. Finally, the ocean crust is squeezed below 700 kilometers and absorbed and assimilated by mantle materials in a state of high temperature melting. The uplifted continental crust edge is extruded and uplifted into island arcs or mountains, which are generally related to trenches. Islands, trenches, continental margin mountains, volcanoes and earthquakes distributed around the Pacific Ocean are formed in this way. Therefore, the marine crust was born in the mid-ocean ridge and disappeared in the trench island arc zone, and it is constantly updated, and it will be updated every 200-300 million years. Therefore, the seabed rocks are very young, generally less than 200 million years old, with an average thickness of about 5~6 kilometers, mainly composed of basalt and other substances. Rocks 3.7 billion years ago have been found in the continental crust, with an average thickness of about 35 kilometers and a maximum thickness of more than 70 kilometers. Except sedimentary rocks, it is mainly composed of granite. Convective rise of mantle materials also takes place in the depths of the mainland, and the continental crust will rupture where the upwelling gushes out. For example, the Great Rift Valley in East Africa, which is more than 6,000 kilometers long, is a manifestation of the convection of mantle materials prompting the African continent to start cracking.
Structural analysis of plate tectonic theory According to plate theory, the ocean also has its birth and death, from scratch to small. Can also be from big to small, from small to nothing. The development of the ocean can be divided into embryonic period (such as the Great Rift Valley in East Africa), juvenile period (such as the Red Sea and the Gulf of Aden), adult period (such as the Atlantic Ocean), declining period (such as the Pacific Ocean) and terminal period (such as the Mediterranean Sea).
The theory of moving plate tectonics 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.
Schematic diagram of plate structure. Their differences are mainly as follows:
(1) Wei Gena and others put the mainland only containing continental silicon-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. Continental drift theory holds that the continent passes through silicon and magnesium under the crust.
Drifting from one floor to another; 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.
German meteorologist Wei Gena Wei Gena and others think that the Si-Al layer in the mainland is completely different from the Si-Mg layer in the mantle. 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.
Plate motion With the motion of asthenosphere, each plate will also move horizontally. According to geologists' estimation, the large plate can move a distance of 1-6 cm every year.
Although this speed is very small, after hundreds of millions of years, the land and sea of the earth will change greatly: when the two plates are gradually separated, new depressions and oceans will appear at the separation; The Atlantic and East African Rift Valley were formed when the two plates separated. When two large plates collide near each other, high and steep mountains will be squeezed out where they collide. The Himalayas, located in the southwest frontier of China, were formed by the collision and extrusion of the Indian plate in the south and the Eurasian plate in the north more than 30 million years ago. Sometimes there will be another situation: when two hard plates collide, the rock strata in the contact part have not had time to bend and deform, and one of them has been deeply inserted into the bottom of the other plate. Due to the strong collision force and deep insertion, the old rock layers on the original plate were brought to the high temperature mantle and eventually melted. Deep trenches are formed where the plates are deeply embedded in the earth's crust. In this way, some trenches on the seabed of the western Pacific Ocean have been formed.
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 period (such as the Rift Valley in East Africa), childhood period (such as the Red Sea and Gulf of Aden), recession period (such as the Atlantic Ocean), recession period (such as the Pacific Ocean) and final period (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 continues to advance northward, and the western part of the ancient Mediterranean gradually shrinks to a new 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 a new location. So the basic outline of land and sea developed into scale.
Earthquakes at the plate boundary are almost all distributed on the plate boundary, and volcanoes are especially close to the boundary. Others, such as tension, magma rising, heat flux increasing and large-scale horizontal dislocation, also occur on the boundary, and crustal subduction is one of the important signs of collision boundary division. It can be seen that the plate boundary is an extremely unstable zone of the crust.
Driving mechanism for problem board
Although various possible ideas have been put forward, such as mantle convection, plate pushing outward from mid-ocean ridge, trench traction, mantle drag and sliding from mid-ocean ridge to both sides under the action of gravity, no one can verify exactly what forces are driving plate movement. Therefore, whether the driving mechanism can be solved perfectly may be the key to the ultimate success or failure of plate tectonics theory.
vertical motion
According to the theory of plate tectonics, the horizontal movement of lithospheric plates is the main tectonic movement of the earth, which can only be transformed into oblique and vertical movements at the convergence of plates. Therefore, vertical movement and oblique tectonic movement in the lithosphere can not be regarded as independent main movements for this theory, but can only be regarded as components of horizontal movement. If so, the theory can't explain the crustal movements that represent the direct vertical reflection of physical and chemical actions in the underlying mantle—for example, the uplift and depression of the whole continent or part of it. Some people think that the vertical movement of the lithosphere is at least as important as the horizontal movement, if not more important. Therefore, in order to find out how and where the basic horizontal movement of the plate may be related to the vertical movement, it is necessary to further clarify the plate tectonic theory.
Errors and problems problems and errors 1:
Where is the original crust?
According to the plate growth and extinction map drawn by plate theory, both the Atlantic Ocean and the Indian Ocean expand eastward and westward. In the southern part of the Atlantic Ocean, the Atlantic Ocean extends more than 3000 kilometers eastward from the mid-ridge, because the width of the Atlantic Ocean is more than 6000 kilometers. The Indian Ocean has expanded westward for more than 3,000 kilometers. The two add up to more than 6000 kilometers. Where is the original 6000 km wide crust?
The expansion of the Indian Ocean and the Pacific Ocean to the south has moved the Antarctic plate to the present Antarctic position, so where did the original Antarctic crust go?
Question and error 2:
How to explain the contradiction between the direction of ridge expansion and the direction of plate collision?
The Indian Ocean Ridge is Ru-shaped, the Beiyang Ridge is north-south, and there are two secondary north-south ridges distributed in parallel. The ocean expands from the ridge to both sides, that is, the North Indian Ocean expands in the east-west direction.
So, how did the Indian Ocean plate collide with the Eurasian plate northward? How did the Qinghai-Tibet Plateau uplift form?
Question and error 3:
How to explain the mismatch between seabed topography and seabed expansion?
The view of plate theory is that the oceanic crust is formed by the mid-ocean ridge spreading to both sides. The formed ridge topography will not disappear, but will expand and move to both sides as the ridge expands to both sides. According to this theory, the seabed topography should be all ridges.
Through the submarine map, it is clearly indicated that the mid-ocean ridge is located in ocean centre, and there are ocean basins on both sides of the mid-ocean ridge. How did the ocean basin form? Ocean topography negates plate theory.
Question and error 4:
How does the intersection of two mid-ocean ridges expand?
The mid-Atlantic ridge and the mid-Indian ridge are connected in a ⊥ shape, and the outward expansion direction of the two mid-oceanic ridges is in a ⊥ confrontation ⊥ shape. How to expand?
In the Indian Ocean, the mid-ocean ridges are connected in an "inner" shape, and the outward expansion directions of the two mid-ocean ridges are also "opposite".
How to expand outward?
Question and error 5:
There are two trenches under the Atlantic Ocean. How do you explain it?
Puerto Rico Trench in the Atlantic Ocean: the deepest point is 9219m, and it is located in the northern Atlantic Ocean 9218km north of Puerto Rico Island, with a length of about1550km and an average width of120km.
The New Hebrides Trench in the Atlantic Ocean: the deepest point is 9174m, which is located at the edge of the Coral Sea between Wanadu Island (New Hebrides Island) and New Caledonia Island. It is about 1200 km long and has an average width of 70 km.
The viewpoint of plate theory is that the oceanic plate was born from the mid-ocean ridge, then spread and proliferated to both sides, and then dived under the continental plate at the trench and disappeared.
With the mid-Atlantic ridge as the boundary, the western Atlantic is divided into the American plate together with North America and South America. How do you explain the two trenches in the Atlantic?
Question and error 6:
How can there be convection at the intersection of two mid-ocean ridges?
The plate movement mechanism of plate theory is thermal convection, and the diagram of convection mechanism can be drawn on a mid-ocean ridge. So how do you convection at the intersection of two mid-ocean ridges?
Plate theory explains that the heat energy of thermal convection comes from the heat of transformation of radioactive elements. The question is, where did so many radioactive elements come from? The radioactive element deposits found now are rocks with high radioactive elements, not solids. In addition, if the heat generated by the transformation of radioactive elements forms magma and produces convection, then the elements generated by the transformation should be in magma, and the magma ejected from the mid-ocean ridge should contain these metamorphic elements. I didn't see the relevant report.