Mathematics – Logic
Scientific paper
May 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agusm.p21a..06v&link_type=abstract
American Geophysical Union, Spring Meeting 2002, abstract #P21A-06
Mathematics
Logic
3210 Modeling, 3230 Numerical Solutions, 5430 Interiors (8147), 6295 Venus, 8121 Dynamics, Convection Currents And Mantle Plumes
Scientific paper
Recent evidence suggests that the Beta Regio equatorial highland, generally considered to be a plume-related structure, was emplaced over a relatively short period of time in the recent Venus history (100-400 m.y.). We perform numerical simulations which use this evidence as a new constraint on geodynamic models. The best results are obtained for the model with exponential viscosity law and the viscosity contrast of 104. This model predicts correct gravity and topography anomalies and fast uplift rates for Beta Regio, ~500 million years, consistent with geological constraints. It also suggests that the uplift continues at present times. However, it is difficult to reconcile the small viscosity of the upper lithosphere and the crust with experimental data on the rheology of rocks. A similar model but with a strong upper crust gives the uplift time of about 1.2 b.y. which is only marginally acceptable from both geological and geodynamical points of view. A model with original Arrhenius viscosity law gives a factor of 2 longer uplift time than those obtained with the exponential viscosity, which is inconsistent with geological constraints unless we assume extremely low values of the activation enthalpy. Pressure-dependent viscosity does not affect much the uplift rate for the pressure-induced viscosity contrast of up to 100. In any case, the rapid uplift of Beta Regio suggests a strong plume coming from great depth, perhaps, from the core-mantle boundary and to satisfy the geological constraints on the uplift rate, the lithosphere or at least its lower part must be ``softer'' than expected at subsolidus temperatures. Partial melting is the primary candidate responsible for lithospheric weakening.
Basilevsky Alexander T.
Head James W.
Moresi L.-N.
Solomatov S. S.
Vezolainen Alexei V.
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