The Mokholovich discontinuity is usually called the Moho interface, or M interface for short, which refers to the interface dividing the crust and mantle.It is a sudden boundary, which marks a change in chemical composition and crystal structure, rather than a sudden change in the state of matter from hard to soft.
The Mokholovich discontinuity depth map is of great significance to the study of crustal structure, crustal isostasy and natural seismicity.For oil exploration, the gravity effect of Moho is often removed as a deep influence.[1]
Chinese name
Mohorovich discontinuity
Foreign name
Mohoroviic discontinuity,Moho
Abbreviation
Moho, Moho, or Moho
Representation method
Represented by M, also called M discontinuity or MInterface
Depth
Different from place to place, averageoceanLighter
Abbreviation of Mohorovich discontinuityMoho surface, Mohs surface orMoho interface。Commonly used M, also called M discontinuity or M interface, refers toCrustAndupper mantleThe interface of.[2]
A brief history of research
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On October 8, 1909,YugoslaviaSeismologist, meteorologistMohorovich(Andreja Mohorovic)CroatiaDomesticZagrebAfter about 40 km of seismic records, it was found that:P-waveThen there is an obvious wave group P, which he believes is caused by the rapid change of material at a depth of 50km below the surface, so that the propagation speed of the lower longitudinal wave is greater than that of the upper longitudinal wave.according toTime distance curveThe P-wave velocity (vP) surges from 7 to 6 km/s to 8.0 to 82 km/s, and the S-wave velocity (vS) surges from 38 km/s to 44 to 46 km/s.Later, the observation confirmed that this discontinuity exists not only in Europe, but also in the world.So in order to commemorate the contribution of Mohorovich to earthquake research, people named the discontinuity discovered by Mohorovich as the Mohorovich discontinuity.The material above the interface is called the crust, and the material below the interface is calledmantle。[3]
The Mokholovich discontinuity is a sudden boundary, which marks a change in chemical composition and crystal structure, rather than a sudden change of substance from hard to soft.Therefore, in recent years, some scholars have proposed that the Moho interface is crustalgabbro（basalt）Andupper mantleIntrinsically chemically equivalentEclogiteThe boundary hypothesis of facies between rocks holds that this assumption can explain the tectonic problems: deep underground, changes in pressure and temperature in such facies conversion areas will cause the rise or subsidence of the earth surface.[4]
Since the 1950s, scientists have studied the relatively fine structure of the crust and upper mantle through the deep detection method of artificial source earthquakes, and found that the structure of the Mokholovich discontinuity in some areas is relatively complex, and the first level discontinuity is only one of the possible cases.It is generally explained that the Mohorovich discontinuity is aTransition zone, in bandSeismic wave velocityIt increases with depth, that is, a positive velocity gradient layer, or a layer composed of several uniform thin layers with gradually increasing velocities.Another explanation is that Moho transition zone is a thin interbedded structure with multiple high and low velocities.Because the Mohorovich discontinuity in the mainland area is deeply buried, people can not directly observe its true appearance.The Mokholovic discontinuity in the marine area is much shallower than that in the continental area, so scientists have put forward the "Mohole Plan", that is, drill holes in the deep ocean where the crust is thin, drill through the Mokholovic discontinuity all the time, and directly observe the fine structure of the Mokholovic discontinuity through the drill core.This idea undoubtedly has great attraction for earth scientists.[5]
features
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Magma in this layer of Mohorovich discontinuity can flow, and the continent moves very slowly in a certain direction on these magmas, which is called plate drift.The temperature of magma is about 1100 ℃SurfaceIt forms lava, and after cooling, it solidifies intorock, this process continues,LavaIt is formed by continuous coolingvolcano。[6]
The depth of the Mohalovich discontinuity varies from place to place. Generally, the ocean is shallow, ranging from 5 to 15 kilometers; the Atlantic Ocean and Indian Ocean are 10 to 15 kilometers;The central part of the Pacific Ocean is only 5 kilometers;The island arc area is 20-30 kilometers.The mainland is generally 30-40 kilometers deep, with the deepest mountain area, and 60-80 kilometers deep in the Tibetan Plateau and Tianshan Mountains in China.[3]
The Mohorovich discontinuity is aseismic waveThe strong reflection surface of the Mohorovich discontinuity can be observed on both the natural earthquake and the artificial seismic bathymetry record map, and the strong reflected longitudinal wave and reflected transverse wave can be observed generally, and the refracted longitudinal wave below the Mohorovich discontinuity can also be observed.Using this information, the structure of the interface can be inverted.The Mohorovich discontinuity obtained from the early study of natural seismic data is a simple primary discontinuity, namelySeismic wave propagationThe discontinuity where the velocity changes abruptly on both sides of the interface.
The Mohorovich discontinuity is also the interface of rock properties.Seismological observation and high-temperature and high-pressure test results of laboratory rock samples have proved that the lower crust above the Mohorovich discontinuity is mainly composed of basic granulite, while the upper mantle is composed ofolivineDominantHyperbasicityMantle rock orEclogiteas well asLherzolite。[5]
Application and significance
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① Since the 1970s, a large number of deep seismic exploration studies have been carried out in North China and Northeast China.Many researchers have discussed the depth and variation of Moho in this area and its influenceGeodynamicssignificance.The results show that the deepest Moho in North China occurs in the Inner Mongolia fold belt, and the shallowest Moho occurs in the Bohai Bay Basin.The deepest Moho in Northeast China occurs in the Great Khingan Mountains, and the shallowest Moho occurs in the Yilan Yitong fault zone;The Great Khingan Mountains Taihang Mountains gravity gradient belt is an important steep change zone of Moho. The Moho in the west is generally more than 40km, and the Moho in the east is generally less than 36km. In the Tanlu fault zone and its northern extension Yilan Yitong fault zone, there are uplifts along the Moho, but the amplitude is different.Bohaiwan basin and Fangzheng fault depression (located in Yilan Yitong fault zone) have obvious Moho uplift, while Dunmi fault zone has Moho fault;In the block where ancient crystalline basement rocks are exposed, the Moho depth is deeper than that of adjacent basins;The depth of Moho in front of Taihang Mountains and Yanshan Mountains increased significantly.These characteristics indicate that North China and Northeast China have experienced the influence of the Pacific tectonic movement together after joining together, while the Great Khingan Taihang Mountains gradient zone limits the influence scope of the Pacific tectonic domain. The front edge of the Pacific plate's westward subduction may be located to the east of the Taihang Mountains and the west of the Tanlu fault zone.[7]
② The observation of Moho changes by near vertical deep seismic reflection profiles strongly shows that the complex characteristics of continental Moho record the tectonic history of the lithosphere.The deep seismic reflection profile across the foreland of the Dabie orogenic belt is about 140km long, recording time is up to 30s, and the detection depth is up tolithosphereMantle.The deep seismic reflection profile reveals the fine structure of the lithosphere, clear Moho and its variation characteristics at the junction of the Yangtze landmass and the Dabie orogenic belt.[8]
