LUNAR CRUSTAL ANALYSIS OF MARE-ORIENTALE FROM TOPOGRAPHIC AND GRAVITYCORRELATIONS

We investigated the use of spectral correlation analysis for modeling the crustal features of Mare Orientale from lunar 70th degree spherica l harmonic topographic and gravity field models derived from Clementin e satellite and earlier investigations. The analysis considered a 64(0 )-by-64(0) region of the Moon centered roughly on Mare Orientale at an altitude of 100 km. The topography of the study region, which include s over 11 km of relief, was modeled for its gravity effects in lunar s pherical coordinates by Gauss-Legendre quadrature integration assuming a terrain density of 2.8 g/cm(3) We observed substantial positive and negative correlations between terrain gravity effects and free-air gr avity anomalies that seriously limit the utility of simple Bouguer gra vity anomalies for subsurface studies. Using the wavenumber correlatio n spectrum between the two data sets, we designed correlation filters to extract the common features. Possible interpretations for the terra in-correlated free-air gravity anomalies include isostatic crustal mas s imbalances that may be equilibrated by radial adjustments of the Moh o of up to 44 km, assuming Airy-Heiskanen compensation and a mantle de nsity contrast of 0.5 g/cm(3) with the crust. These Moho adjustments d efine mass variations that account for most of the mascon and flanking negative free-air gravity anomalies. Furthermore, their remarkable co rrelation with the topographic rings of Mare Orientale points to the p ossible influence of a strong local stress field of the crust in the d evelopment of the ring structures. Subtracting the terrain-correlated free-air anomalies from the free-air gravity anomalies and terrain gra vity effects yielded terrain-decorrelated free-air and isostatically c ompensated terrain gravity anomalies, respectively, that show zero cor relation. This lack of correlation may be interpreted for a Moho that involves over 100 km of relief assuming Airy-Heiskanen compensation of the crust. Beneath Mare Orientale, we observed a minimum crustal thic kness of about 17 km. Corresponding terrain-decorrelated free-air grav ity anomalies of Mare Orientale may be related to a central cone-shape d body of 0.5 g/cm(3) density contrast with apex extending nearly 5 km below the surface, which is surrounded by a ringed-shaped body of -0. 5 g/cm(3) density contrast that may extend about 7 km below the surfac e. These bodies resulted possibly from meteorite impact that produced a roughly circular region of breccia and highly fractured crust with a higher density core where some remelting of the rocks about the impac t site may have occurred.