Discontinuity (geology)

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A geological or geophysical discontinuity is a metrologically detectable separation area within rock bodies close to the surface or in deeper regions of the earth's crust and mantle . The name means an interruption within the regular structure ( continuum ) of a rock or other solid and was coined by geophysicists. In the deeper layers of the earth, discontinuities can also occur in plastic fluids .

geophysics

The geophysical discontinuities include those in the internal structure of the earth . Above all, there are zones of discontinuity in the large-scale shell structure of the earth's interior , which are caused by strong changes in physical properties as a result of changed chemical composition, mineralogical structure or the state of aggregation . The seismology and applied seismology can discontinuities by changing the speed of propagation of seismic waves to determine which changes in the elastic modulus or the rock density display. Some of these interfaces can also be determined by gravimetric methods - the more precisely the more inclined the density interfaces are. In 2003 G. Papp investigated the Pannonian Plain by means of gravimetry and vertical deviations and determined the exact depth profile of the Moho surface .

Global and regional discontinuities

Discontinuities, which are characteristic of the structure of the entire earth body , are called global , while small-scale, limited changes in the structural structure of the earth are characterized by local or regional discontinuities. Since the underlying changes often take place over a larger depth interval, most of the discontinuities are, strictly speaking, transitional areas . Boundary layers with an abrupt change in seismic velocity are called zero-order discontinuities.

Noticeable discontinuities

Well-known discontinuities are - from top to bottom:

Further discontinuities caused by phase transformations of mantle minerals are named after their average depth. The most important phase transitions are those of olivine . They mark the transition from the upper to the lower mantle (mantle transition zone ) and are located at depths of 410 , 520 and 660 km .

There are further discontinuities, some of which are regionally observed and often controversial

geology

For geology, interfaces of different materials are of particular interest, which run through compact rock bodies or the structure of a mountain range . This includes tectonic dividing areas of greater extent such as some geological faults , which can sometimes extend over hundreds of kilometers and separate different types of rock , as well as parts of rift zones where the subsidence has brought various rocks into contact, as in the Upper Rhine Rift . Local phenomena such as relay fractures in geological fracture zones or sedimentary basins can also be discontinuities, but are not always referred to as such. On a small scale, crevices filled with foreign rock in rocks close to the surface should be mentioned, as well as visible or measurable boundaries within a stratification or foliation .

literature

  • László Egyed : Solid Earth Physics , 370 p., Akadémiai Kiadó, Budapest 1969
  • NMS Rock: Numerical Geology . Lecture Notes in Earth Sciences Volume 18, 430 p., Springer-Verlag Berlin,… New York, Tokyo 1988