Mathematics – Logic
Scientific paper
May 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agusm...p21a01p&link_type=abstract
American Geophysical Union, Spring Meeting 2001, abstract #P21A-01
Mathematics
Logic
5420 Impact Phenomena (Includes Cratering), 5430 Interiors (8147), 5475 Tectonics (8149)
Scientific paper
A lunar crustal model for the region +/- 64° latitude was developed using gravity components evaluated from available spherical harmonic gravity and topographic field models that include Lunar Prospector, Clementine, and earlier satellite observations. Terrain gravity effects were computed at 100-km altitude in spherical coordinates from 1° topography (GLTM-2) by Gauss-Legendre quadrature integration using a terrain density of 2.8 g/cm3 Corresponding free-air gravity anomalies (LP75G) were spectrally correlated with the terrain effects to differentiate the terrain-correlated and -decorrelated free-air components. The terrain-correlated free-air gravity anomalies may then be subtracted from the terrain gravity effects to estimate compensated terrain effects. The lack of correlation between the compensated terrain gravity effects and the terrain-decorrelated free-air components was interpreted for a Moho that may involve over 120 km of relief assuming the lunar crust was mainly compensated by its thickness variations with a density contrast of -0.5 g/cm3 relative to the mantle. Related crustal thicknesses beneath many of the major nearside basins are largely consistent with pre-Lunar Prospector estimates. However, for many farside basins, quite large disparaties are evident that may reflect differences in accounting for the strong gravity effects of the relatively rugged terrain. The terrain-decorrelated anomalies were differentiated further into crustal and subcrustal components on the basis of their correlation spectrum with the free-air anomalies. Terrain-decorrelated crustal maxima over lunar central basins predicted mare fill thicknesses ranging from several hundred meters to a few kilometers assuming a density increase of 0.5 g/cm3 for the mare fill relative to nonmare crust. These results are much more consistent with the thinner estimates from photogeologic and remote sensing studies than the inflated predictions of previous gravity investigations that invoke intrusions of high-density mare fill beneath the central basins. Terrain-correlated free-air anomaly components were investigated for uncompensated crustal mass variations of the major central basins. In general, nearly all nearside multi-ring basins appear to be marked by mascon gravity anomalies reflecting mass concentrations from superisostatic mantle plugs plus mare fill. Farside basins, by contrast, mostly involve maslite gravity anomalies from mass deficiencies due to subisostatic mantle plugs with marginal or no mare fill. The preponderance of maslites on the farside is consistent with crust that responded more rigidly to impacts than the nearside crust, which had a higher thermal gradient due to enhanced abundances of radioactive elements in the nearside mantle and crust. However, the extended thermal evolution of the lunar lithosphere also may have promoted the development of interfering mascon and maslite effects for tectonically complicated regions like the farside Freundlich-Sharonov basin.
Potts Laramie V.
von Frese Ralph R.
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