asthenosphere

(ass-th'en -ŏ-sfeer) See Earth.

Collins Dictionary of Astronomy © Market House Books Ltd, 2006

asthenosphere

[as′then·ə‚sfir]

(geology)

That portion of the upper mantle beneath the rigid lithosphere which is plastic enough for rock flowage to occur; extends from a depth of 30-60 miles (50-100 kilometers) to about 240 miles (400 kilometers) and is seismically equivalent to the low velocity zone.

The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Asthenosphere

a layer of low hardness, strength, and viscosity in the earth’s upper mantle. It is identical to Gutenberg’s layer. It is found at depths of about 100 km under the continents and about 50 km under the ocean floor; the lower boundary occurs at 250 to 350 km. The layer may not be continuous. Seismic studies have shown that the rate of propagation of transverse and possibly longitudinal seismic waves within the asthenosphere is somewhat slower than in the covering and underlying layers of the upper mantle. The viscosity of the substance of the asthenosphere is 10¹⁹ to 10²³ poises, whereas below and above the boundaries of the asthenosphere it is at least 10²³ poises. It is conjectured that there is a slow overflow of masses in a horizontal direction within the asthenosphere because of the low yield point. The overflow is caused by uneven stress from the earth’s crust.

The presence of the asthenosphere is explained by the high geothermal gradient, the high temperature of the substance of the asthenosphere (close to the melting point), and processes of relaxation. Volcanic materials usually originate in the asthenosphere, and the subcrustal masses that accomany the main tectonic processes are displaced. The term “asthenosphere” was introduced in 1914 by the American geologist J. Barrell.

V. A. MAGNITSKII

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References in periodicals archive

Slab pull: Relatively cool and dense oceanic plates (slabs) have negative buoyancy after subducting at ocean trenches and sink into the ductile, less dense asthenosphere, pulling the rest of the tectonic plate along behind it.

An evidence-based approach to teaching plate tectonics in high school

These seismic and electrical signatures are supposed to characterize the oceanic asthenosphere below the high-velocity and more resistive lithosphere.

Electromagnetic exploration of the oceanic mantle

"Our analysis supports the prevailing view that most of the heat is generated in the asthenosphere, but we found that volcanic activity is located 30 to 60 degrees East from where we expect it to be," said Christopher Hamilton of the University of Maryland, College Park.

Volcanoes in Jupiter's moon Io located 30 to 60 degrees East from where they were predicted

Blame the asthenosphere. When it rises from below, this less-dense layer infiltrates the stiffer crust above and then freezes, weakening the lithosphere and eventually chiseling chunks of rock away.

Grand Canyon's high surroundings may be product of continental lift: 'drip' deep within Earth possibly buoyed Colorado Plateau

[2] Bath M., 1957, Shadow zone, travel times and energies of longitudinal seismic waves in the presence of an asthenosphere low-velocity layer, Trans.

Dispersion of G type seismic waves in low velocity layer

Beneath the earth's thin outer skin (called the lithosphere), mantle rocks creep plastically in a layer known as the asthenosphere, where temperatures stay near the rocks' melting point.

Hitting the hotspots

The theory of plate tectonics holds that the Earth's geological processes, from earthquakes and volcanoes to mountain-building and continent formation, are the result of the slow movements of a dozen or so gigantic slabs that shift over the asthenosphere, a molten region of the upper mantle.

Mapping Earth's unseen region

It floats on a layer called the asthenosphere - a silly putty like plastic material which is directly below it and a few 100 miles in thickness.

The Missing Element In Earth's Core

A tectonomagmatic model is proposed wherebyEoceneNisai intrusions have been generated through processes of subduction-related flux melting and localized extension through plate flexure, providing necessary deep melting of the upper asthenosphere.

Geochemistry and petrogenesis of igneous intrusions within the Eocene Nisai Formation of the Muslim Bagh-Khanozai Region, NW Pakistan

The other is the lower-crustal channel flow model, which proposes the existence of a low-viscosity asthenosphere in the lower crust of the QTP's eastern margin.

Deep physical structure and geotectonic implications of the eastern margin of the Qinghai--Tibet Plateau