Convection in Io's asthenosphere: Redistribution of nonuniform tidal heating by mean flows

Three-Dimensional Simulations of Mantle Convection in Io

“…This exponent is close to the value of −0.2 obtained in a related study in Cartesian geometry (Tackley 2001). Exponents for the base-oflithosphere lines are −0.107 for the rms variation and 0.001 for the peak-to-peak variation, with an average of all six lines being −0.144.…”

Formation of mountains on Io: Variable volcanism and thermal stresses

“…The models in Tackley (2001) and Tackley et al (2001), however advanced in 3-D geometry or high Ra achieved, still represent conventional convective approaches. Heat is transported by fluid convection in an internally heated mantle, and then conducted through a thin, immobile lithosphere.…”

“…The concept of mantle diapirs makes the most sense in terms of a cooling mantle with an unstable lower thermal boundary layer, such as the Earth's mantle (Davies, 1999;Sleep, 2006). For a mantle strongly tidally heated from within there are no plumes per se; there are thermal instabilities, but these diminish in strength (temperature contrast and physical extent) as the Rayleigh number, Ra (the dimensionless measure of convective vigor) increases (e.g., Tackley, 2001). Furthermore, for internally heated convection at high Ra the thermal instabilities are downwellings that peel off from the upper boundary layer, not upwellings (Tackley, 2001, Plate 1).…”

“…Unfortunately, the broad-scale convective stresses that are called upon to cause these effects are, as above, simply too small. In order to convectively transport Io's tidal heat, asthenospheric viscosities in Tackley's (2001) convective calculations are relatively low (10 10 Pa-s is a nominal value). Even though the maximum horizontal flow velocities are relatively large (∼500 m yr −1 ), one can integrate the resulting shear stress of this "magma wind" along the base of Io's lithosphere or crust, and the resulting maximum lithospheric stresses are only a few kPa, give or take an order of magnitude.…”

“…Based upon the evidence for an anticorrelation, Schenk et al (2001) and Tackley (2001) advanced a scenario where stresses from a bimodal global mantle convection pattern imposed by a spatial tidal heating function (Tackley, 2001;Tackley et al, 2001) are superimposed on the subsidence stress. Global mantle upwellings then, in principle, impose tensional stresses due to crustal thinning and stretching that reduce the magnitude of compressional stresses, producing a region with more volcanism.…”