The theory of lithospheric plates is one of the mostinteresting in geographical science. The hypothesis of mobilism (otherwise - continental drift), once forgotten, is now revived, thanks to the discovery of magnetic anomalies with variable sign poles, which are symmetrical to the mid-ocean ridges (their axes), the primary magnetization, and also the position of magnetic poles change with time.
Repeated confirmation of the idea ofthe expansion of the ocean floor along the axes of the mid-ocean ridges to the peripheral areas was obtained through many years of research, as well as by deep-sea drilling. A significant contribution to the research and development of the idea of continental drift (mobilism) was made by seismologists. Thanks to their research, it was possible to clarify the order of distribution of seismic activity zones over the entire surface of the Earth. It turned out that these zones are extensive, but rather narrow: they pass near the main arcs, along the edges of the continents and mid-ocean ridges.
Tectonics of lithospheric plates
This mobilism hypothesis is called"Tectonics of lithospheric plates". There are not so many of them - only eight large ones and about a dozen small ones. The latter are also called microplates. The largest plates are located within the Pacific Ocean, they are a thin, easily permeable oceanic crust. The Indo-Australian, Antarctic, African, South American, North American and Eurasian plates are of the continental type. Lithospheric plates have different borders (edges) and very slowly move across the entire surface of the planet. When the lithospheric plates diverge, the edges become divergent: diverging, the plates form a rift zone (crack) into which the mantle substance enters. On the bottom surface, it freezes, and the oceanic crust builds up. All new and new mantle matter entering the rift zone expands it and makes the plates move Where they move apart, the ocean forms, and its size constantly grows. This type of boundaries today exists along the axes of the middle oceanic ridges and is fixed by rift cracks.
Convergent boundaries are formed whenlithospheric plates converge. With their approaching in the areas of contact, quite complex processes take place, among which two main scientists are distinguished. The first of these is that when a collision occurs between the continental plate and the oceanic one, one of them plunges into the mantle, and this is accompanied by breaking and warping. A deep-earthquake occurs in the collision zone. After the slab enters the mantle, it partially melts: its lightest components after melting again rise to the surface, becoming volcanic eruptions. And the more dense components, gradually plunging into the mantle, descend down to the borders of the core. This is how the Pacific Ring of Fire was formed.
When two continental plates collidehumming occurs. This can be observed during the ice drift, when the ice floes, colliding and approaching each other, are crushed. When lithospheric plates collide, they contract, and large mountain structures form at the edges.
Theory of lithospheric plates
Thanks to many yearsObservations, geophysicists have established the average speed of movement of lithospheric plates. In the area of the Alpine-Himalayan compression belt formed during the collision of the Indian and African plates with the Eurasian plate, the rate of convergence between them amounts to 0.6 cm / year in the Himalayan and Pamir regions and 0.5 cm / year in the Gibraltar region.
The theory of lithospheric plates has established that nowEurope departs from North America at a rate of about 5 cm / year. But Australia "sails" from Antarctica at a speed of about 14 cm / year. Oceanographic plates have the highest speeds - they are 4-7 times higher than continental speeds. The fastest is the Pacific Plate, and the slowest is the Eurasian Plate.
