Lunar crustal analysis of Mare Orientale from topographic and gravity correlations

Abstract

Abstract. We investigated the use of spectral correlation analysis for modeling the crustal features of Mare Orientale from lunar 70th degree spherical harmonic topographic and gravity field models derived from Clernentine satellite and earlier investigations. The analysis considered a 64ø-by-64 ø region of the Moon centered roughly on Mare Orientale at an altitude of 100 kin. The topography of the study region, which includes over 11 krn of relief, was modeled for its gravity effects in lunar spherical 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 gravity anomalies that seriously limit the utility of simple Bouguer gravity anomalies for subsurface studies. Using the wavenumber correlation spectrum between the two data sets, we designed correlation filters to extract the common features. Possible interpretations for the terrain-correlated free-air gravity anomalies include isostatic crustal mass irnbalances that may be equilibrated by radial adjustments of the Moho of up to 44 kin, assuming Airy-Heiskanen compensation and a mantle density contrast of 0.5 g/crn 3 with the crust. These Moho adjustments define mass variations that account for most of the rnascon and flanking negative free-air gravity anomalies. Furthermore, their remarkable correlation with the topographic rings of Mare Orientale points to the possible influence of a strong local stress field of the crust in the development of the ring structures. Subtracting the terrain-correlated free-air ar•ornalies from the free-air gravity anomalies and terrain gravity effects yielded terrain-decorrelated free-air and isostatically compensated terrain gravity anomalies, respectively, that show zero correlation. 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 thickness of about 17 kin. Corresponding terrain-decorrelated free-air gravity anomalies of Mare Orientale may be related to a central cone-shaped 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/crn 3 density contrast that may extend about 7 km below the surface. 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 rernelting of the rocks about the impact site may have occurred.

Comprehensive mass modeling of the Moon from spectrally correlated free‐air and terrain gravity data

“…Hence to the degree that the terrain effects have been accurately modeled, the existence of an annihilating anomaly field can be inferred. Assuming that the lunar topography may be compensated by thickness variations of the crust [e.g., Bowin et al , 1975; Bratt et al , 1985; Zuber et al , 1994; Neumann et al , 1996; von Frese et al , 1997b; Wieczorek and Phillips , 1997], the annihilating effects can be analyzed for mantle topography and crustal thickness variations.…”

“…For lunar crustal modeling we estimate the gravity effects of the topography (i.e., terrain gravity effects) and analyze their correlations with the free‐air gravity anomalies [ von Frese et al , 1997a, 1997b]. Terrain gravity effects are readily determined in lunar spherical coordinates by Gauss‐Legendre quadrature integration to accuracies that are commensurate with the accuracies of the elevation and related density data [ von Frese et al , 1981].…”

“…This approach was initially developed for the crustal analysis of the Mare Orientale basin [ von Frese et al , 1997b, 1998]. It was tested and validated in crustal studies of East Asia [ Tan and von Frese , 1997] and the Antarctic [ von Frese et al , 1999], where the gravity estimated Moho depths were found to be well within 10% of depths inferred by large offset seismic studies.…”

Crustal modeling of the North Atlantic from spectrally correlated free-air and terrain gravity

“…We also used this methodology for crustal analyses of the Moon (Potts and von Frese, 2003;von Frese et al, 1998) and its Mare Orientale Basin (von Frese et al, 1997b), Venus (Leftwich et al, 1999), Greenland (Roman, 1999), and Ohio . For our continental studies of the Earth, however, the gravity Moho estimates correlated well with the seismic estimates except in the thermally active areas of the ocean basins where temperature related mantle density reductions were involved.…”

Crustal properties of Mercury by morphometric analysis of multi‐ring basins on the Moon and Mars

“…For Mars, we compared, also at 100 kIn altitude, gravity data from the Mars Global Surveyor (Lemoine et al, 2001) with the gravity effects ofthe topography mapped by the Mars Orbiter laser altimeter (Smith et al, 1999). In both cases, the gravity effects of the topography were computed in spherical coordinates at satellite altitudes using Gauss-Legendre quadrature integration (von Frese et al, 1981(von Frese et al, , 1997b) and 2.8 g/cm-' terrain density.…”