Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.t12a..08h&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #T12A-08
Physics
[8120] Tectonophysics / Dynamics Of Lithosphere And Mantle: General, [8147] Tectonophysics / Planetary Interiors, [8149] Tectonophysics / Planetary Tectonics
Scientific paper
Plate tectonics, which in our solar system is unique to Earth, represents a convective regime in which convective motions reach the surface allowing the strong upper rock layer, the lithosphere, to be mobile. Motivated by a seismically observed low-velocity zone (LVZ) it has been suspected since the discovery of plate tectonics, but never demonstrated, that a low viscosity layer beneath plates may play a central role in facilitating their motions. Using three-dimensional spherical mantle convection simulations we show that a thin low-viscosity asthenosphere as on Earth, compared to a thicker upper mantle of low viscosity inherent to all terrestrial planets, increases the stress at the base of the lithosphere and thereby facilitates plate tectonics. In the absence of a thin asthenosphere, stress levels fall below the strength of the lithosphere and a stagnant-lid mode of convection results, i.e. a single plate planet. As well as elucidating the role of the asthenosphere for plate tectonics on Earth, our results also provide insights into differences between the Earth and its sister planet Venus, which lacks evidence for an asthenosphere and for active plate tectonics. Furthermore, the prediction that stress increases with decreasing asthenospheric thickness provides a step toward resolving the discrepancy between the very low values of yield stress needed to generate plate like behavior in previous mantle convection simulations and the values determined from laboratory experiments on the strength of rock. Finally, the need for a relatively thin low viscosity layer on Earth suggests that water is fundamentally involved in the LVZ's origin.
Höink Tobias
Lenardic Adrian
Richards Anita M.
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