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  Encyclopedia of Keywords > Time > Events > Earthquakes > Plate Tectonics > Asthenosphere   Michael Charnine

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  1. The asthenosphere is a part of the upper mantle that exhibits plastic properties.
  2. Asthenosphere: The hot, slowly flowing layer of upper mantle below the lithosphere (700 km thick).
  3. Asthenosphere - A zone in the upper mantle of the Earth, consisting of hot, plastic rock, that underlies the stronger lithosphere.
  4. The asthenosphere is a layer of solid rock that is near its melting point.
  5. Asthenosphere is a "weak" region beneath the lithosphere.

Tectonic Plates

  1. The lithosphere essentially floats on the asthenosphere and is broken up into what are called tectonic plates.
  2. The key principle of plate tectonics is that the lithosphere exists as separate and distinct tectonic plates, which "float" on the fluid-like asthenosphere.

Different Directions

  1. The relative fluidity of the asthenosphere allows the tectonic plates to undergo motion in different directions.
  2. Due to convective currents in the asthenosphere, the tectonic plates undergo motion in different directions.
  3. Plate boundaries As the rock of the asthenosphere moves in different directions, it carries the plates of the lithosphere along with it.


  1. In the theory of plate tectonics the outermost part of the Earth 's interior is made up of two layers, the outer lithosphere and the inner asthenosphere.
  2. The lithosphere is cooler and more rigid, whilst the asthenosphere is hotter and mechanically weaker.
  3. Below the lithosphere lies the asthenosphere.
  4. Tectonic plates are able to move because of the relative density of oceanic lithosphere and the relative weakness of the asthenosphere.
  5. This bulge is thought to be caused by upward convective forces in the asthenosphere pushing the oceanic crust and lithosphere.


  1. The deeper mantle below the asthenosphere is more rigid again.
  2. In the mantle layer called the asthenosphere, mantle rock melts to make magma.
  3. Within the crust and upper mantle there is also an inferred mechanical layering distinguishing lithosphere, asthenosphere and mesosphere.
  4. The upper mantle which underlies the lithosphere to a depth of 200 km is the asthenosphere.
  5. The molten magma, typically of basaltic composition, rises up through the asthenosphere, the mantle portion of the lithosphere, and into the lower crust.


  1. Geologists later discovered that radioactive decay provided a heat source within Earth's interior that made the asthenosphere plasticine (semi-solid).
  2. Also, the lithosphere loses heat by conduction whereas asthenosphere transfers heat by convection and has a nearly adiabatic temperature gradient.

Lithospheric Plates

  1. The lithospheric plates ride on the asthenosphere.
  2. Lithospheric plates on the scales of continents and oceans move at rates of centimeters per year in response to movement in the asthenosphere.


  1. They may originate within the asthenosphere or even deeper within the earth at the boundary between the mantle and the core.
  2. Ultramafic rocks with 1-10 percent magma occur in (A) the crust, (B) the lithosphere, (C) the asthenosphere, or (D) the outer core.

Plates Move

  1. The underlying, partially molten part of the mantle, on which the plates slide, is called the asthenosphere.
  2. Pressure on the asthenosphere may also be reduced in zones of divergence, where two plates are separating from each other.
  3. In this case, the lighter of the colliding plates slides upward and over the heavier of the plates, which dives down into the asthenosphere.
  4. Sources of plate motion As noted above, the plates are able to move because of the relative weakness of the asthenosphere.
  5. Others view the asthenosphere as the driving force or means of conveyance for the plates.


  1. Although solid, the asthenosphere has relatively low viscosity and shear strength and can flow like a liquid on geological time scales.
  2. The asthenosphere is solid even though it is at very hot temperatures of about 1600 degrees Celsius due to the high pressure from above.

Km Depth

  1. By 220km depth the asthenosphere comes to an end and the mantle goes back to a less flexible state.
  2. Beneath continents the asthenosphere appears at around 150km depth, while under oceans it can be as shallow as 60km.


  1. As the plates separate along the boundary, the block between the faults cracks and drops down into the soft, plastic interior (the asthenosphere).
  2. The outermost layer of the earth is called the lithosphere (100-200km deep); it is followed by a plastic asthenosphere (150-400km deep).


  1. This mechanism could explain the widespread range of E-W fast anisotropy presumably in the asthenosphere without a need for complicated models.
  2. In that case, the pressure exerted on the asthenosphere beneath it is reduced, melting begins to occur, and asthenospheric materials begin to flow upward.
  3. No. Eventually Earth will cool to the point that the asthenosphere will not be sufficiently ductile.
  4. McGeary and Plummer (1998) say that these findings cast doubt on the original, simple lithosphere-asthenosphere model of plate behavior.
  5. There is a suggestion that convection at the Hawaiian plume is more complicated than a parabolic pancake spread of dragged asthenosphere.


  1. Time > Events > Earthquakes > Plate Tectonics
  2. Encyclopedia of Keywords > Places > Earth
  3. Glossaries > Glossary of Plate Tectonics /
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  Originally created: March 24, 2008.
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