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The asthenosphere is a part of the upper mantle just below the lithosphere that is involved in plate tectonic movement and isostatic adjustments. It is composed of peridotite, a rock containing mostly the minerals olivine and pyroxene. [2] The lithosphere-asthenosphere boundary is conventionally taken at the 1,300 °C (2,370 °F) isotherm.
The lithosphere–asthenosphere boundary lies between Earth's cooler, rigid lithosphere and the warmer, ductile asthenosphere. The actual depth of the boundary is still a topic of debate and study, although it is known to vary according to the environment. [1]
It is bounded by the surface and the lithosphere-asthenosphere boundary. Lithospheric processes accommodate mountain formation in the lithosphere. Lithospheric processes which operate across mountain belts include those related to the theory of plate tectonics (e.g. tectonic plate convergence, folding, faulting, exhumation).
Below the asthenosphere, the mantle is again relatively rigid. The Earth's mantle is divided into three major layers defined by sudden changes in seismic velocity: [ 6 ] the upper mantle (starting at the Moho, or base of the crust around 7 to 35 km [4.3 to 21.7 mi] downward to 410 km [250 mi]) [ 7 ]
Earth's crust and mantle, Moho discontinuity between bottom of crust and solid uppermost mantle. The Mohorovičić discontinuity (/ ˌ m oʊ h ə ˈ r oʊ v ɪ tʃ ɪ tʃ / MOH-hə-ROH-vih-chitch; Croatian: [moxorôʋiːtʃitɕ]) [1] – usually called the Moho discontinuity, Moho boundary, or just Moho – is the boundary between the crust and the mantle of Earth.
The lowest part of the mantle next to the core-mantle boundary is known as the D″ (D-double-prime) layer. [23] The pressure at the bottom of the mantle is ≈140 G Pa (1.4 M atm ). [ 24 ] The mantle is composed of silicate rocks richer in iron and magnesium than the overlying crust. [ 25 ]
In 2016, a geophysical study was published on the possible presence of a layer of buoyant material between the Earth's lithosphere and the asthenosphere under the Juan de Fuca plate. The study extends the theory of partial melt in the lithosphere-asthenosphere boundary to subduction zones, specifically in the convergent margins. [12]
The low-velocity zone (LVZ) occurs close to the boundary between the lithosphere and the asthenosphere in the upper mantle. It is characterized by unusually low seismic shear wave velocity compared to the surrounding depth intervals. This range of depths also corresponds to anomalously high electrical conductivity.