Why is it the asthenosphere in the upper layer of the mantle that melts, but not in the lower layer

The asthenosphere refers to the low-velocity layer of the upper mantle about 100 kilometers below the earth's surface, which was first proposed by Gutenberg in 1926, called the asthenosphere, which is located in the upper part of the upper mantle, below the lithosphere (lithosohere). Below the ocean floor, it lies below a depth of about 60 km; On the mainland, it is located below a depth of about 120 kilometres, with an average depth of about 60,250 kilometres. Modern observations and studies have confirmed the existence of this asthenosphere.

The asthenosphere is a weak layer that is prone to peristaltic deformation and slow movement, and because it contains 1%-10% liquid substance, the material in this area is relatively soft and prone to plastic flow.

We know that as the depth increases, the temperature of the Earth's interior gradually increases, but the melting point of minerals also increases as the pressure increases. At the depth at which the asthenosphere is located, its temperature is higher than the melting point of some minerals, and the phenomenon of partial melting occurs. Scientists believe that

The weakening of the asthenosphere comes from a sudden decrease in the solubility of water in orthorhombite, one of the constituent minerals of the mantle, resulting in more water being retained in olivine, which produces partial melting, making the asthenosphere less viscous than the rest of the mantle, and more prone to deformation and flow.

It is generally accepted that the formation of the asthenosphere requires high temperature conditions, as well as the addition of water and volatile components. The temperature of the earth's interior increases with the increase of depth, generally to a depth of 100 km, the temperature is close to the solidus temperature of the mantle (mantle) to begin to melt, and at this time, with the participation of water and volatile components, selective melting begins to occur, and a solid-fluid asthenosphere is gradually formed.

The mantle under the asthenosphere, due to the high pressure, causes the melting point of the mineral to be too high, and the temperature of its position is higher, that is to say, the melting point grows faster than the temperature increases, and partial melting cannot occur, so it is in a rigid state. And in the lower mantle, the amount of orthorhombic pyroxene will gradually decrease, which is also one of the reasons.

The substance there is lighter, the melting point is lower, and most importantly, the temperature is just right.

The soft flow is between 60 km and 250 km below ground and is the upper part of the upper mantle.

Upper mantle: Moho surface to 1000 km

Lower mantle: 1000 km to 2900 km

Asthenosphere: The upper part of the upper mantle (the material is in a molten state, which is the source of magma) lithosphere = crust + top of the upper mantle (above the asthenosphere).

a. The above Moho interface is the earth's crust, so it does not conform to the topic;

b. The mantle is divided into the upper mantle and the lower mantle, and the asthenosphere is mainly located in the upper part of the upper mantle, so it is correct;

c. The mantle is divided into the upper mantle and the lower mantle, and the asthenosphere is mainly located in the upper part of the upper mantle, so it does not conform to the theme;

d. The asthenosphere is located in the upper part of the mantle rather than the bottom of the mantle, so it does not fit the <> of the topic

In general, the asthenosphere is at the top of the upper mantle, but there is a very thin layer of mantle above the asthenosphere, which is divided according to geophysics - the distribution of the lithosphere asthenosphere has obvious regional differences, and the general rule is that the position below the ocean is higher (generally less than 60 km), and the position below the continent is deeper (the depth is less than 120 km).

The top-bottom interface of the asthenosphere is not very certain, there is no obvious interface with the lithosphere, and it has the characteristics of gradual transition, but in general, the asthenosphere is at the top of the upper mantle, but there is a very thin layer of mantle division according to geophysics above the asthenosphere - the lithospheric mantle. Lithospheric mantle + crust above asthenosphere = lithosphere, direct transition between the crust and the lithospheric mantle, only the difference of ** waves.

Location of the asthenosphereWhat is the location of the asthenosphere in the inner sphere of the earth.

a. The asthenosphere is located in the mantle, so it does not fit the topic;

b. There is a Moho interface between the earth's crust and the mantle, so it does not conform to the topic;

c. The asthenosphere is located in the upper part of the mantle and is composed of plastic materials, so it is correct;

d. The asthenosphere is located in the mantle, so it does not fit the topic

Therefore, c

The Earth is divided into three layers: the central layer is the core, the middle layer is the mantle, and the outer layer is the crust.

The average radius of the Earth is about 6,370 kilometers, and the thickness of the earth's crust is about 35 kilometers, and most of the destructive ** occurs within the earth's crust.

But it happens not only in the earth's crust, but also in the asthenosphere.

According to the department, deep sources generally occur 300-700 kilometers underground. So far, the deepest known epicenter is 720 km.

From this point of view, the traditional theory of plate extrusion stratigraphic fault does not reasonably explain the deep source**, because there is no solid material at a depth of 720 km. Scientists envision drawing a map of the earth's rocks, which is of great help to ****.

There is also a part of the mantle between the earth's crust and the asthenosphere, so the earth's crust cannot "drift above the asthenosphere, it should be the lithosphere" drifting above the asthenosphere Therefore, b

The asthenosphere, also known as the asthenosphere, is located below the lithosphere in the upper upper mantle, with a depth of 80-400 km, and is a basically globally distributed inner sphere.

The asthenosphere is generally considered to be the main source of magma. The distribution of the asthenosphere has obvious regional differences, and the general rule is that the position below the ocean is higher (generally less than 60 km) and the lower position is deeper below the continent (below 120 km). The top-bottom interface of the asthenosphere is not very certain, and there is no obvious interface with the lithosphere, which has the characteristics of gradual transition.

It occurs not only in the Earth's crust, but also in the asthenosphere of the Earth's interior.

The asthenosphere, also known as the asthenosphere, is located in the upper part of the upper mantle, below the lithosphere, and is an inner layer that is basically distributed globally.

From the inside of the earth to the outside, the inner part of the earth is the core, the mantle, and the crust, and the outer layer of the earth is the crust.

**Also known as ground motion, ground vibration, is a natural phenomenon that causes vibration in the process of rapid release of energy in front of the earth's crust, during which ** waves will be generated.

The place where it begins to occur is called the epicenter, the ground directly above the epicenter is called the epicenter, and the place where the most destructive ground vibration is most intense is called the extreme earthquake area, and the extreme earthquake area is often the area where the epicenter is located.

a. The location of the asthenosphere is located in the upper part of the mantle but not at the very top, so the trace banquet does not conform to the topic;

b. The asthenosphere is composed of plastic materials, which is generally considered to be the birthplace of magma in a molten state, so it does not conform to the topic; Exciting state virtuality.

c. The soft open flame layer is composed of plastic substances, which is in a molten state, just like viscous and soft glass, so both transverse and longitudinal waves can pass through, so it is correct;

d. The lithosphere refers to the part of the mantle above the asthenosphere and the entire crust, so it does not conform to the topic