Characteristics of the Earth's mantle
A sphere in the bowels of the Earth between the lower boundary of the Earth's crust, the so-called Mohorovichich gap (at an average depth of about 35 km) and the upper surface of the Earth's core
(at a depth of 2900 km).
The Earth's mantle is the most massive part of our globe (about 68% by mass).
Both longitudinal and transverse seismic waves propagate in the Earth's mantle, which allows us to conclude that the Earth's mantle behaves like a solid body under short-term elastic deformations, although it has plastic properties under the influence of forces acting on the age scale, and therefore convection currents can occur.
The density of the Earth's mantle ranges from 3300 kg/m3 (under the Mokhorovichi rupture) to 5500 kg/m3 (at the lower limit), the temperature (at the lower limit) is about 3000 ° C, the velocity of longitudinal seismic waves is 8.1–13.6 km / s; the pressure at the base of the Earth's mantle is about 13.1012 P.
It is assumed that the Earth's mantle consists of a material similar in composition to peridotite, and also, possibly, to eclogite under the continents. At great depths, this material probably contains impurities of chromium, nickel, metallic iron, possibly sulfides and metal oxides.
There are several seismic ruptures inside the mantle, the most important of which is the boundary at a depth of about 670 km. The mantle above this boundary is called the upper mantle,
and below it the lower mantle.
The Earth's crust and the uppermost part of the upper mantle are quite cold and form a mechanically stable layer known as the lithosphere. The thickness of the lithosphere varies and depends on the temperature distribution. It is located a few kilometers under the mid-ocean ridges, about 50-60 km from them, and it is even thicker (about 100-120 km) under the continents. Below the lithosphere is the asthenosphere, characterized by a decrease in the propagation velocity of seismic waves, especially transverse waves, which indicates that it is relatively low-viscosity and more susceptible to deformation than the adjacent spheres.
The temperature of asthenospheric rocks is close to their melting point, so they deform easily. Thus, although these rocks are solid from the point of view of physics, they can be considered as liquid on a geological time scale. Reservoirs of molten matter (magma) make up a small percentage of the volume of the asthenosphere and are located only below volcanic zones. The lower boundary of the asthenosphere is not strictly defined. Due to the increase in pressure with depth, rocks become less and less susceptible to residual deformation.
Nevertheless, the entire mantle beneath the lithosphere exhibits liquid properties, given the slow geological processes over millions of years. The liquid properties of the mantle make it possible to form convection currents in it, which are the main driving force of tectonic processes on Earth. For fast processes such as short-term associated deformations
during the passage of a seismic wave, mantle rocks behave like an elastic body.
The rocks of the upper mantle contain about 60% olivine, 30% pyroxenes and 10% garnets. At a depth of about 670 km, the phase transition of olivines and garnets leads to the formation of the MgSiO3 mineral in the perovskite structure.
The lower mantle (mesosphere) is probably quite homogeneous; the speed of seismic waves and their density continuously increase with depth to the so-called "D" layer.
The "D" layer varies in thickness depending on the location (on average about 100 km). Despite the high temperature, due to significant pressure, the rock material of the lower mantle is in a solid state. aposta-1.bet
(at a depth of 2900 km).
The Earth's mantle is the most massive part of our globe (about 68% by mass).
Both longitudinal and transverse seismic waves propagate in the Earth's mantle, which allows us to conclude that the Earth's mantle behaves like a solid body under short-term elastic deformations, although it has plastic properties under the influence of forces acting on the age scale, and therefore convection currents can occur.
The density of the Earth's mantle ranges from 3300 kg/m3 (under the Mokhorovichi rupture) to 5500 kg/m3 (at the lower limit), the temperature (at the lower limit) is about 3000 ° C, the velocity of longitudinal seismic waves is 8.1–13.6 km / s; the pressure at the base of the Earth's mantle is about 13.1012 P.
It is assumed that the Earth's mantle consists of a material similar in composition to peridotite, and also, possibly, to eclogite under the continents. At great depths, this material probably contains impurities of chromium, nickel, metallic iron, possibly sulfides and metal oxides.
There are several seismic ruptures inside the mantle, the most important of which is the boundary at a depth of about 670 km. The mantle above this boundary is called the upper mantle,
and below it the lower mantle.
The Earth's crust and the uppermost part of the upper mantle are quite cold and form a mechanically stable layer known as the lithosphere. The thickness of the lithosphere varies and depends on the temperature distribution. It is located a few kilometers under the mid-ocean ridges, about 50-60 km from them, and it is even thicker (about 100-120 km) under the continents. Below the lithosphere is the asthenosphere, characterized by a decrease in the propagation velocity of seismic waves, especially transverse waves, which indicates that it is relatively low-viscosity and more susceptible to deformation than the adjacent spheres.
The temperature of asthenospheric rocks is close to their melting point, so they deform easily. Thus, although these rocks are solid from the point of view of physics, they can be considered as liquid on a geological time scale. Reservoirs of molten matter (magma) make up a small percentage of the volume of the asthenosphere and are located only below volcanic zones. The lower boundary of the asthenosphere is not strictly defined. Due to the increase in pressure with depth, rocks become less and less susceptible to residual deformation.
Nevertheless, the entire mantle beneath the lithosphere exhibits liquid properties, given the slow geological processes over millions of years. The liquid properties of the mantle make it possible to form convection currents in it, which are the main driving force of tectonic processes on Earth. For fast processes such as short-term associated deformations
during the passage of a seismic wave, mantle rocks behave like an elastic body.
The rocks of the upper mantle contain about 60% olivine, 30% pyroxenes and 10% garnets. At a depth of about 670 km, the phase transition of olivines and garnets leads to the formation of the MgSiO3 mineral in the perovskite structure.
The lower mantle (mesosphere) is probably quite homogeneous; the speed of seismic waves and their density continuously increase with depth to the so-called "D" layer.
The "D" layer varies in thickness depending on the location (on average about 100 km). Despite the high temperature, due to significant pressure, the rock material of the lower mantle is in a solid state. aposta-1.bet