Lithospheric plates: theory of lithospheric plates

The theory of lithospheric plates is one of the most interesting in geographic science. The hypothesis of mobilism (once-the drift of the continents), once forgotten, has now been revived again, thanks to the discovery of the poles of magnetic anomalies with a variable sign that are symmetrical to the mid-oceanic ridges (their axes), the primary magnetization, and the time variation of the position of the magnetic poles.

Repeated confirmation of the idea of an expansion of the ocean floor along the axes of the mid-oceanic ridges to peripheral regions was obtained in the course of many years of research and also as a result of deep-sea drilling. A significant contribution to the study 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 zones of seismic activity on the whole surface of the Earth. It turned out that these zones are extended, but rather narrow: they pass near the main arcs, along the fringes of the continents and the mid-ocean ridges.

Tectonics of lithospheric plates

This hypothesis of mobilism was called "tectonics of lithospheric plates." They are not so many - only eight large and with a dozen small. 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 slabs have a continental-type crust. The lithospheric plates have different boundaries (edges) and move very slowly over the entire surface of the planet. When the lithospheric plates diverge, the edges become divergent: diverging, the plates form a rift zone (a crack) into which the mantle substance enters. On the surface of the bottom it freezes, and the oceanic crust builds up. All new and new mantle material entering the rift zone expands it and causes the plates to move. Where they move apart, an ocean forms and its dimensions are constantly growing. This type of boundaries is now found along the axes of the mid-ocean ridges and is fixed by rift cracks.

Convergent boundaries are formed when the lithospheric plates converge. When they come closer in the areas of contact, rather complex processes occur, among which two basic scientists stand out. The first of these is that when a continental plate collides with an oceanic one, one of them is immersed in the mantle, and this is accompanied by breaking and warping. A deep-focus earthquake occurs in the collision zone. After the plate enters the mantle, it is partially melted: its lightest components after melting again rise to the surface, becoming volcanic eruptions. And the denser components, gradually plunging into the mantle, drop down to the core boundaries. This is how the Pacific Ring of Fire was formed .

The impact of two continental plates is hummocking. This can be observed when ice drifts, when ice floes, colliding and approaching each other, become irritated. When lithospheric plates collide, they shrink, and on the edges large mountain structures are formed.

The theory of lithospheric plates

Thanks to long-term and numerous observations, geophysicists have established average speeds of movement of lithospheric plates. In the region of the Hindustan and African plates formed with the Eurasian plate of the Alpine-Himalayan compression belt, the rate of convergence between them is up to 0.6 cm / year in the Himalayas and Pamir regions and 0.5 cm / year in the Gibraltar region.

The theory of lithospheric plates has established that now Europe departs from North America at a speed of about 5 cm / year. But Australia "sails" from Antarctica at a speed of about 14 cm / year. The highest speeds for oceanic plates - they are 4-7 times higher than the speeds of continental ones. The fastest is the Pacific plate, and the slowest is the Eurasian one.