Mathematics – Logic
Scientific paper
Mar 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993lpi....24.1319s&link_type=abstract
In Lunar and Planetary Inst., Twenty-Fourth Lunar and Planetary Science Conference. Part 3: N-Z p 1319-1320 (SEE N94-20636 05-91
Mathematics
Logic
Boundary Layers, Gravitational Fields, Magellan Project (Nasa), Morphology, Planetary Crusts, Plates (Tectonics), Tectonics, Topography, Venus (Planet), Convection, Gravitation, Highlands, Lithosphere, Thermal Boundary Layer, Thickness
Scientific paper
The long wavelength correlation of the gravity and topography and the large apparent depths of compensation (approximately 150-300 km) for large highland regions on Venus require significant differences between the interior structure of Earth and Venus. The morphology, geologic history, and large apparent depths of compensation for many highlands have been interpreted to indicate areas of mantle upwelling. A large apparent depth of compensation at a mantle upwelling is generally interpreted to indicate the base of the thermal boundary layer of convection. A boundary layer thickness of 150-300 km implies that the interior of Venus is presently much colder than Earth and thus tectonically less active. The recent Magellan mission has provided contradictory evidence regarding the present level of tectonic activity on Venus, prompting considerable debate. In this study, we investigate the possibility that a chemical boundary layer acts together with a thermal boundary layer to produce large apparent depths of compensation, or equivalently, large geoid-to-topography-ratios (GTR's). The crust of a planet forms through partial melting of mantle materials. Both the melt and the residuum are lower in density than unmelted (or undepleted) mantle. In the absence of vigorous plate tectonics, a thick layer of buoyant residuum, or depleted mantle, may collect beneath the lithosphere. In this scenario, the thermal lithosphere does not need to be thick and cold to match the GTR's. Cooling of the depleted layer may lead to overturn of the upper mantle and episodic resurfacing with time scales on the order of 300-500 MY, consistent with the resurfacing age of Venus.
Parmentier Marc E.
Smrekar Suzanne E.
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