The evolution of impact basins: Viscous relaxation of topographic relief

• Main Authors: Sean C. Solomon, Robeat, P. Comeit, James W. Head
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 1982
• Subjects: South Pole; Aitken; South pole
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.564.9222; http://www.planetary.brown.edu/pdfs/436.pdf

We evaluate the hypothesis that viscous relaxation has been an important process for modifying the topographic profiles of ancient large impact basins on the moon. We adopt a representative topographic profile of the Orientale basin, the youngest large impact basin on the moon, as an estimate of th e initial topography of older basins of similar horizontal dimensions, and we predict the topographic profiles that would result from viscous relaxation according to a number of simple analytical representations of the rheological response of the moon to surface topography. At wavelengths greater than the thickness of a high-viscosity lithosphere, both a decrease in viscosity with depth and the partial to complete isostatic compensation of topographic relief have pronounced effects on the wavelength-dependent relaxation times and must be considered in modeling viscous relaxation for features as large as impact basins. The effect of a decrease in viscosity with depth is to enhance the rate of viscous relaxation at long wavelengths, while the rate of relaxation decreases substantially for the fraction of long-wavelength topography which is isostatically compensated as an initial condition. TheSe models are applied to two pre-Nectarian basins on the moon, the Tranquillitatis basin on the lunar nearside and the much larger and older South Pole-Aitken basin on the farside. The topographic profile of Tranquillitatis, after correcting for the effect of mare basalt fill, is consistent with