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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]
Also called Indianite. A mineral from the lime-rich end of the plagioclase group of minerals. Anorthites are usually silicates of calcium and aluminium occurring in some basic igneous rocks, typically those produced by the contact metamorphism of impure calcareous sediments. anticline An arched fold in which the layers usually dip away from the fold axis. Contrast syncline. aphanic Having the ...
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 ]
The intrusion of more buoyant asthenosphere making contact with the crust and replacing dense lower lithosphere must occur. The metamorphic transition from mafic granulite facies to the denser eclogite facies in the lower portion of the crust is the main mechanism responsible for creating negative buoyancy of the lower lithosphere. [ 3 ]
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.
Geology portal; Asthenosphere – Highly viscous, ductile, and mechanically weak region of Earth's mantle; Continent – Large geographical region identified by convention; Craton – Old and stable part of the continental lithosphere Platform – A continental area covered by relatively flat or gently tilted, mainly sedimentary strata
The lithosphere–asthenosphere boundary is defined by a difference in response to stress. The lithosphere remains rigid for very long periods of geologic time in which it deforms elastically and through brittle failure, while the asthenosphere deforms viscously and accommodates strain through plastic deformation. [citation needed]