Computer Science
Scientific paper
Feb 1991
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1991phdt........59k&link_type=abstract
Thesis (PH.D.)--CALIFORNIA INSTITUTE OF TECHNOLOGY, 1991.Source: Dissertation Abstracts International, Volume: 51-10, Section: B
Computer Science
1
Scientific paper
The Equatorial Highlands of Venus, including Atla Regio, Beta Regio, Ovda Regio, and Thetis Regio, are quasi -circular regions with peak elevations of 4 to 5 km, large positive geoid anomalies, extensional tectonism, and shield volcanism. Isostatic processes can not plausibly account for the observed geoid and topography of these regions. The Equatorial Highlands are probably the surface expression of hot, rising plumes in the mantle of Venus. A similar process can explain terrestrial hotspot swells such as Hawaii and Cape Verde. In order for the plume model to explain the observed geoid and topography in the Equatorial Highlands, Venus must lack an Earth-like low viscosity layer in its upper mantle. The absence of a low viscosity zone on Venus is also consistent with the shape of the admittance spectrum and the slope of the geoid spectrum. Even trace amounts of water substantially lower the viscosity of silicates; the absence of a low viscosity zone on Venus may indicate that its mantle is dry. The Ishtar Terra region of Venus consists of a 3.5 km high central plateau surrounded on three sides by 6 to 10 km high mountain belts of an apparently compressive origin. A mantle plume model can not explain the observed tectonic structures or the high mountain belt topography. Ishtar is probably a region of thickened crust formed by crustal convergence over a region of mantle downwelling. A simple model of crustal flow driven by pressure gradients and by convective flow in the underlying mantle shows that if the crustal convergence hypothesis is correct, then the the plains surrounding Ishtar must be less than 25 km thick.
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