Mantle is betweenMoho surfaceandGutenberg discontinuity The thickness is more than 2800 km, the average density is 4.59 g/cm ³, the volume accounts for 82.26% of the earth's volume, and the mass of the mantle accounts for about 67.0% of the earth's total mass, which largely affects the total composition of the earth's material.The lateral variation of the mantle is relatively uniform, according toSeismic wave velocityThe 1000 km surge zone is taken as the interface (Leipoti surface) to further divide the upper mantle and the lower mantle into two secondary layers.[1]
The crust is the surface of the earth above the Moho.Its thickness varies between 5-70km.The thickness of the continental area is relatively large, with an average of about 33km;The thickness of the ocean region is relatively small, with an average of about 7km;The overall average thickness is about 16km, accounting for about 1/400 of the earth's radius, 1.55% of the earth's total volume, and 0.8% of the earth's total mass.The density of crustal materials is generally 2.6-2.9g/cm ³, and the density of its upper part is relatively small, but it increases towards the lower part: the crust is composed of solid rocks, including sedimentary rocks, magmatic rocks and metamorphic rocksgeophysics, geography and other disciplines, therefore, the details will be further introduced in the next section.
（2） Mantle
The mantle is the middle part of the earth below the Moho surface and above the Gutenberg surface (2885km deep).Its thickness is about 2850km, accounting for 82.3% of the total volume and 67.8% of the total mass of the earth. It is the main part of the earth.Seen from the fact that the whole mantle passes through seismic shear waves, it is mainly composed of solid materials.According to the secondary discontinuity of seismic waves, the mantle can be divided into two secondary spheres, the upper mantle and the lower mantle, with a depth of 650km as the boundary.
1. Upper mantle
The average density of the upper mantle is 3.5g/cm ³, which is equivalent to that of meteorites, suggesting that it may have similar material composition to meteorites.According to the deep materials brought out from the upper mantle by volcanic eruption and tectonic movement, they are also ultrabasic rocks.In recent yearsHigh temperature and high pressure testWhen simulating the properties of mantle rocks, it is found that the mixture of 55% peridotite, 35% pyroxene and 10% garnet is used as the sample (the mineral composition is equivalent to ultrabasic rocks), and its wave velocity and density are measured under the temperature and pressure conditions equivalent to the upper mantle, and the results are basically consistent with those of the upper mantle.According to the above reasons, it is speculated that the upper mantle is composed of materials equivalent to ultrabasic rocks, the main mineral composition of which may be olivine, and some of which are pyroxene and garnet. This speculated mantle material is called mantle rock.
There is an asthenosphere in the upper part of the upper mantle, extending from about 70km to about 250km, which is characterized by the presence of low velocity zones of seismic waves.Physical experiments show that the decrease of wave velocity may be caused by the partial melting of asthenospheric material, which reduces its strength.According to the estimation of the temperature in the earth, the temperature of the asthenosphere can reach 700-1300 ℃, which is close to the melting point temperature of ultrabasic rocks under this pressure. Therefore, some fusible components or components with low melting point can begin to melt.According to the calculation, the melt in the asthenosphere may only account for 1% - 10%, and the melt is scattered among the solid materials, which greatly reduces the strength and makes the asthenosphere have strong plasticity or fluidity.As the asthenospheric material has approached the critical state of melting, it has become an important source of magma.
2. Lower mantle
The average density of the lower mantle is 5.1 g/cm ³. Because of the strong internal pressure, olivine and other minerals in the upper mantle are decomposed into FeO, MgO, SiOtwoAnd AltwoOthree, and other simple oxides.Compared with the upper mantle, the change of chemical composition of its material may be mainly manifested by the relative increase of iron content (or the increase of the proportion of Fe/Mg).As the pressure increases with the depth, the density of the material and the wave velocity gradually increase.
（3） Geonucleus
The core is the part from Gutenberg surface to the center of the earth inside the earth. Its volume accounts for 16.2% of the total volume of the earth, but its mass accounts for 31.3% of the total mass wall of the earth. The density of the core is 9.98-12.5 g/cm ³.According to the propagation characteristics of seismic waves, the core can be further divided into three layers: the outer core (depth 2885-4170km), the transition layer (4170-5155km) and the core (5155km to the core).In the outer core, according to the fact that the shear wave cannot pass through and the longitudinal wave has a large attenuation, it is inferred that it is liquid;In the core, the shear wave reappears, indicating that it becomes solid again;The transition layer is a liquid solid transition state.
The density of the core is so large that only some metal materials can compare with it from the surface materials. The most common metal on the surface is iron, with a density of 8g/cm ³, which can completely reach the density of the core under ultra-high pressure.The density of the core is close to that of iron meteorite, which also indicates that the core may be mainly composed of iron and nickel.The earth has a magnetic field mainly caused by internal materials, which means that there must be a certain sphere with highly magnetic iron and nickel materials in the earth's interior, but it does not exist in the crust and mantle, so it should exist in the core.In addition, people use the instantaneous ultrahigh pressure provided by the blasting shock wave to simulate the strict state of the earth core, and measure the wave velocity and density of some elements under the instantaneous ultrahigh pressure. It is found that the wave velocity and density of the earth core are close to those of iron and nickel.It is inferred from many aspects that the core should be mainly composed of iron and nickel.Further research in recent years has also found that the density of pure iron and nickel is slightly higher under the high pressure of the core. It is speculated that the most reasonable material composition of the core should be an alloy composed of iron, nickel and a small amount of silicon, sulfur and other light elements.[2]
The structure of the earth's internal spheres and the main geophysical data of each sphere
Earth sphere name
depth
(km)
earthquake
Longitudinal wave velocity
(km/s)
earthquake
Shear wave velocity
(km/s)
Density (g/cm3)
material
state
class a
layered
second level
layered
tradition
layered
Outside
The Ball
Crust
Crust
0-33
5.6-7.0
3.4-4.2
2.6-2.9
Solid matter
Outside
too
Ferry
layer
Outer transition layer
(I)
upper mantle
33-980
8.1-10.1
4.4-5.4
3.2-3.6
part
Molten material
Outer transition layer
(B)
Lower mantle
980-2900
12.8-13.5
6.9-7.2
5.1-5.6
Liquid solid substance
liquid
state
layer
Liquid layer
Field nuclear
2900-4700
8.0-8.2
Unable to pass
10.0-11.4
Liquid substance
within
The Ball
Introgression
Degree layer
Transition layer
4700-5100
9.5-10.3
twelve point three
Liquid solid substance
earth 's core
Inland nuclear
5100-6371
10.9-11.2
twelve point five
Solid matter
Division basis
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(1) According to the density andSeismic wave velocityIt can be inferred by comparing with relevant properties of surface rocks or minerals.
(2) According to the pressure and temperature of each layer, it is speculated through high-temperature and high-pressure simulation experiments.
(3) Inference is based on materials from deep underground.Volcanic eruptions and tectonic movements can sometimes bring materials from deep underground (such as mantle) to the surface, providing a basis for our understanding of deep materials.
(4) Compare with the results of meteorite research.
Meteorites are fragments of celestial bodies from the space of the solar system. From the perspective of a large number of meteorites obtained, they can be divided into three categories according to their composition:
Meteorite(stonemeteorite)olivine、pyroxeneThe mineral composition (silicate of iron and magnesium) is about equivalent to the ultrabasic rock seen on the surface, with little iron and nickel in the metal state and a density of 3-3.5g/cm ³ or more.
Iron meteorite(ironmeteorite) Natural alloy mainly composed of iron and nickel in metal state, with a density of 8-8.5g/cm ³ or more;
The iron meteorite is a transitional type of the above two types of meteorites, in which the iron, magnesium silicate minerals and the iron and nickel components in the metal state account for a part respectively.
The research of modern astronomy and astrogeology shows that: ① These meteorites should come from celestial bodies or asteroids in the solar system. When they enter the earth's gravitational field, they are attracted by the earth, and a considerable part of them are rubbed and burned by the atmosphere, and their debris falls to the surface as meteorites.The possibility of materials outside the solar system entering the earth through remote space is extremely small. ②The material composition, formation and evolution in the solar system are unified, especially the fact that humans landed on the moon and got some rocks on the surface of the moon similar to some rocks on the surface of the earth, which further established the belief in the material unity of the solar system.Therefore, the characteristics of meteorites can be used to infer the material state of the earth's interior.[5]
Upper mantle rocks
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The basement structure of the upper mantle is composed of refractory peridotite with different thickness, which transits downward to mantle rock (Figure 5-1).The main characteristic of rocks close to the composition of mantle rocks is that they can be crystallized by the following four different mineral combinations (Ringwood, 1962 a, b; Green and Ringwood, 1963):
Mineral assemblage of mantle rocks and density and P-wave velocity of dunite and peridotite under atmospheric temperature and pressure[3]
Olivine amphibole olivine+aluminum poor pyroxene+plagioclase plagioclase mantle rock
The different physical properties of these mineral assemblages (see the table on the right) clearly indicate their different P-T-PH2O conditions during crystallization and equilibrium.This raises the possibility that there may be huge mineral zoning in the upper mantle controlled by the stable zone of these mineral assemblages.[3]
research findings
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Mantle endmember
In the early stage of the earth's development and evolution, the mantle continuously undergoes partial melting, and a considerable number of elements that are easy to enter the liquid phase move out of the mantle source area and into magma with melting, thus making the mantle lose the above components and forming a chemically depleted mantle.Such as Si, AL, Ca, Na, K, etc.If the above elements are added to the mantle, the enriched mantle will be formed.
According to the isotopic and trace element composition, it has been divided into the following six types of mantle end members or reservoirs in geochemistry. Through the extensive mixing of these mantle end members, the isotopic and trace element composition of all observed mantle derived magmatic rocks can be explained.(Different academic schools have different division schemes)
（1）DMdepleted mantle Is the main component of the mid ocean ridge basalt source area, which is characterized by low Rb/Sr and high Sm/Nd;143Nd/144Nd ratio is high, 87Sr/86Sr ratio is low, and its&Nd (t) is a high positive value, and&Sr (t) is a negative value.
（2）EMIType I enriched mantle, characterized by high Rb/Sr ratio and low Sm/Nd ratio;The ratio of Ba/Th and Ba/La is high, and the ratio of 87Sr/86Sr changes greatly;The 143Nd/144Nd ratio is low.For a given 206Pb/204Pb, the ratio of 207Pb/204Pb and 208Pb/204Pb is high.
(3) EMI II type II enriched mantle is characterized by high Rb/Sr ratio, low Sm/Nd ratio, and high Th/Nd K/Nb and Th/La ratios.The ratios of 143Nd/144Nd and 87Sr/86Sr are higher than EMI.EMII is of metasomatic origin associated with crust and mantle.EMII is related to the upper continental crust, which may representterrigenous sedimentary rock Continental crust altered oceanic crust orOcean island basaltThe recycling effect ofsubcontinentThe lithosphere enters the mantle and mixes with it.
(4) U and Th are enriched relative to Pb in the mantle with high U/Pb ratio of HIMUThe cause of HIMU may be that the altered oceanic crust enters the mantle and mixes with it, the lost lead enters the core, and the metasomatic fluid in the mantle causes the loss of Pb and Rb.
(5) PREMA precious mantleUniversal mantle, which is the common mantle composition frequently observed.The 206Pb/204Pb is 18.2-18.5, higher than DM and EMI, and lower than EMI and HIMU mantle;87Sr/86Sr is lower than EMI and EMI, higher than DM.143Nd/144Nd, higher than EMI and EMI, and lower than DM.
（6）FOZOMantle concentration zone。It is at the bottom of the triangle formed by DM-EMI-HIMU. It is a mixture of DM and HIMU, which may be derived fromLower mantle, which originated from the core mantle boundaryMantle plumeCapture.
Mantle chording
origin
mantle
The earth is not a solid ball, but a very active one composed of multiple concentric spheresplanet。Due to the revolution and tilt rotation of the earth and the existence of celestial gravity, the concentric spherical layers of each layer have their own movements, includingHydrosphere, atmosphere, liquidOuter nucleus, solid shelltideExercise.The tilt rotation of the earth makes the tide direction of the liquid outer core tilt, which leads to the "tilt of the differential production of the upper lithosphere (mantle chord)". The result of the mantle chord is:;The main reason for frequent earthquakes is that the two poles of the earth's crust and the earth's crust are transposed in the tilt differential velocity, so that the linear velocity of the plate changes.Scientists found that the rotation speed of the earth's core is 0.3 to 0.5 degrees faster than that of the mantle and crust every year, that is, the earth's core is faster than the earthSurface textureThe plate moves 50000 times faster, and the new discovery helps scientists to explainGeomagnetic fieldHow did it come about.U.S.AUniversity of Illinois Professor Song Xiaodong, a geophysicist, is the person in charge of this research. Their achievements were published in the American journal Science on August 26, 2005.The new discovery also ended a 9-year debate.Song Xiaodong said, "We believe that we have obtained conclusive evidence."
theory
University of CaliforniaGary Grazmire, a professor of earth science at Santa Cruz University, said: "This is a meaningful discovery. It reduces the uncertainty in a field, and you can learn something new from it."《science》The magazine specially distributed review articles for this discovery. The New York Times《National Geography》The discovery was reported in detail by the magazine and the UK's Physics World.National Science FoundationandNational Natural Science Foundation of ChinaFunding was provided for this work.
The Earth's core is composed of solid metal, which includes a solid core with a diameter of 2400 kilometers, which is the size of the moon, and a liquid outer core with a diameter of 7000 kilometers.Scientists believe that the core of the earth's magnetic fieldGeodynamicsFrom geodynamicselectromagnetic torque This causes the core to rotate relative to the mantle and crust.
As early as 1996,Song XiaodongandPaul Richards stillColumbia University, New YorkSeismologists from Lamont Doherty Earth Observation Station put forward the view that the rotation speed of the earth's core is faster than that of other parts for the first time through the analysis of seismic waves passing through the earth.But this was quite controversial at that time, and some seismologists suspected that the data derived from the results were wrong or false;Some scientists have tried to prove thatMovement speedNot faster than other parts;Some scientists say that although the core is rotating, its speed is higher thanColumbiaThe speed proposed by scholars is much slower;Others say they have found no evidence that the core rotates faster than the rest of the earth.Later, Song Xiaodong arrivedUniversity of Illinois As a professor in the Department of Geology, he andColumbia UniversityRichard, who co led a new study, will dispel any doubt about this conclusion.
Song XiaodongSaid: "Although the rotation speed of the core cannot be measured accurately, our paper shows that this speed cannot be zero." The earth rotates once a day, or 360 degrees. New research shows that the rotation speed of the core of the earth is 0.3 to 0.5 degrees faster than other parts every year.This more accurate discovery is 1.1 degrees faster and a little slower than what they proposed in 1996.
By comparing the data of seismic waves passing through the earth's liquid core and solid core in history, Song Xiaodong and others have found convincing evidence that the earth's solid core is indeed rotating at different speeds.From the South Sandwich Islands in the Atlantic toSouthern United StatesAlong the coastline, they observed 18 similar earthquakes.Similar earthquakes are also calledwave formThe waveform of a pair of earthquakes recorded at the same station is exactly the same, indicating that the two earthquakes occurred at the same place.Song Xiaodong and others found that these earthquakes had a negative impact onAlaska58 seismic stations nearby have records, and the interval of earthquake pairs spans 0 to 35 years, so that researchers can observe the changes of seismic waves with time.
Song Xiaodong said, "When the time interval between the two events of the earthquake is more than a few years, the similarity across the earth's coreseismic waveThere are systematic changes in travel time and waveform.The only credible explanation is the movement of the kernel. "Why does the Earth's core rotate at different speeds?Song Xiaodong believes that the most likely explanation is electromagnetic couplingOuter nucleusLayer generatedMagnetosphereIt diffuses to the core layer, where it generates current.Current vsmagnetic fieldThe interaction of the causes the core to rotate, just as the armature rotates in the motor.
Related disciplines
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Mantle petrology is a kind of petrology that takes the mantle as the object. Its research contents include the composition of the upper mantle (rocks, minerals, geochemistry) and its vertical and horizontal heterogeneity;The role of melting magma in the upper mantle and its chemical reservoir;upperMantle rheologyAnd dynamic characteristics;Upper mantle thermal state;The evolution of the mantle and other geological processes (such as metasomatism) occurring in the mantle.On the surface, from kimberlite andAlkaline basaltThe upper mantle samples were obtained from the upper mantle xenoliths, the Alpine type intrusive rocks and the metamorphic peridotites in the ophiolite suite in order to provide compositional information.But in order to build a complete modelgeophysicsPhysical ChemistryExperimental petrologyThe mutual penetration of can provide more constraints.[4]
