Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmdi43a1942a&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #DI43A-1942
Physics
[1200] Geodesy And Gravity, [5420] Planetary Sciences: Solid Surface Planets / Impact Phenomena, Cratering, [5430] Planetary Sciences: Solid Surface Planets / Interiors
Scientific paper
The topography and crustal structure of the Moon are dominated by the signatures of impact basins, yet the process of basin formation and modification remains poorly understood. The subsurface structure of the basins provides an important constraint on the basin formation process. Models of the relief along the crust-mantle interface, or Moho, and the resulting crustal thickness can be generated from gravity and topography data. We modify the standard approach of computing crustal thickness from the gravity and topography in order to take advantage of the inherent symmetry of the basins and amplify the signal to noise ratio in the gravity data, thereby improving the stability of the downward continuation of the Bouguer anomaly to the mean Moho depth. The resolution of the resulting crustal thickness models is significantly improved, revealing new details of the subsurface structure. The new models fully resolve the uplifted mantle plug beneath the basins, allowing improved constraints on the diameters of the excavation cavities. The majority of the basins, including Orientale, are found to be underlain by approximately cylindrical plugs of uplifted mantle, rather than the parabolic Moho uplifts found in lower resolution models. The quasi-cylindrical mantle plug and approximately uniform crustal thickness beneath the basin floor do not likely reflect the initial geometry of the excavation cavity. Rather, we interpret these as resulting from the basin modification stage. Lateral flow and isostatic adjustment of either an intra-basin melt pond or the acoustically fluidized sub-basin crust would result in a uniform crustal thickness beneath the basin floor. For the larger basins, excavation of the entire crust followed by solidification of the intra-basin melt pond would have the same result, with the non-zero crustal thickness beneath the basin resulting from differentiation of the impact melt pond. For Orientale, the basin ring structures are resolved in the gravity field, but are not prominently expressed at the Moho. A substantial crustal thickening is observed exterior to the basin. However, this crustal thickening occurs at the base of the crust, rather than at the surface as would be expected for impact ejecta. We suggest that this annulus of thickened crust is a result of deep crustal processes involved in the basin modification and ring formation stages. As numerical models of basin formation and modification advance, the crustal structure of the basins will provide an important constraint against which the model predictions can be compared.
Andrews-Hanna Jeffrey C.
Krahenbuhl Richard A.
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