Delamination (geology)

Delamination (geology)

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In geophysics
Geophysics
Geophysics is the physics of the Earth and its environment in space; also the study of the Earth using quantitative physical methods. The term geophysics sometimes refers only to the geological applications: Earth's shape; its gravitational and magnetic fields; its internal structure and...

, delamination refers to the loss and sinking of the portion of the lowermost lithosphere
Lithosphere
The lithosphere is the rigid outermost shell of a rocky planet. On Earth, it comprises the crust and the portion of the upper mantle that behaves elastically on time scales of thousands of years or greater.- Earth's lithosphere :...

 from the tectonic plate to which it was attached.

This can occur when the lower portion of the lithosphere becomes more dense than the surrounding mantle
Mantle (geology)
The mantle is a part of a terrestrial planet or other rocky body large enough to have differentiation by density. The interior of the Earth, similar to the other terrestrial planets, is chemically divided into layers. The mantle is a highly viscous layer between the crust and the outer core....

. Because of the instability of higher density
Density
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...

 material atop lower density material, the lower lithosphere separates from the tectonic plate and sinks into the mantle.

Delamination is of two basic types: brittle or ductile. In the brittle type, the lower crust metamorphoses to the denser eclogite
Eclogite
Eclogite is a mafic metamorphic rock. Eclogite is of special interest for at least two reasons. First, it forms at pressures greater than those typical of the crust of the Earth...

, causing a density inversion, which then may detach (rip away) and sink.

The second type, ductile delamination, is related to convective instabilities. The convection
Convection
Convection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....

 can simply peel away the lower crust. Or, in a different scenario, a Rayleigh-Taylor instability
Rayleigh-Taylor instability
The Rayleigh–Taylor instability, or RT instability , is an instability of an interface between two fluids of different densities, which occurs when the lighter fluid is pushing the heavier fluid....

 is created. Due to the instability in a local area, the base of the lithosphere breaks up into descending blobs fed by an enlarging region of thinning lithosphere. The space left by departing lithosphere is filled by an asthenosphere
Asthenosphere
The asthenosphere is the highly viscous, mechanically weak and ductilely-deforming region of the upper mantle of the Earth...

 upwelling.

Delamination of the lithosphere has two major geologic effects. First, because a large portion of dense material is removed, the remaining portion of the crust and lithosphere undergo rapid uplift
Tectonic uplift
Tectonic uplift is a geological process most often caused by plate tectonics which increases elevation. The opposite of uplift is subsidence, which results in a decrease in elevation. Uplift may be orogenic or isostatic.-Orogenic uplift:...

 to form mountain ranges. Second, flow of hot mantle material encounters the base of the thin lithosphere and often results in melting and a new phase of volcanism
Volcanism
Volcanism is the phenomenon connected with volcanoes and volcanic activity. It includes all phenomena resulting from and causing magma within the crust or mantle of a planet to rise through the crust and form volcanic rocks on the surface....

. Delamination may thus account for some volcanic regions that have been attributed to mantle plumes in the past.

One example of the effects of lithosphere delamination is the Sierra Nevada mountains in the western USA.

See also

  • Mountain building
  • Orogeny
    Orogeny
    Orogeny refers to forces and events leading to a severe structural deformation of the Earth's crust due to the engagement of tectonic plates. Response to such engagement results in the formation of long tracts of highly deformed rock called orogens or orogenic belts...

  • Epeirogeny
  • Plate tectonics
    Plate tectonics
    Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...

  • Mantle convection
    Mantle convection
    Mantle convection is the slow creeping motion of Earth's rocky mantle caused by convection currents carrying heat from the interior of the Earth to the surface. The Earth's surface lithosphere, which rides atop the asthenosphere , is divided into a number of plates that are continuously being...

  • Plating (geology)
    Plating (geology)
    In geology, plating is a hypothesized process whereby asthenospheric mantle hardens beneath crustal material, thereby becoming attached to it and thereafter moving together with the crustal material as part of the lithosphere....