Antarctic crustal modeling from the spectral correlation of free-air gravity anomalies with the terrain

We investigated the use of enhanced spectral correlation theory for modelin g the crustal features of the Antarctic from regional observations of gravi ty and terrain. The analysis considered 1 degrees-gridded free-air gravity anomalies and topographic rock, ice, and water components for the region so uth of 60 degrees S. We modeled terrain gravity effects at 150-km altitude by Gauss-Legendre quadrature (GLQ) integration assuming densities of 2800 k g/m(3) for rock, 900 kg/m(3) for ice, and 1030 kg/m(3) for seawater. These effects are substantial relative to the free-air anomalies and must be comp ensated by the effects of subsurface density variations. Significant terrai n-correlated free-air anomalies were revealed by the wavenumber correlation spectrum between the free-air anomalies and the modeled terrain gravity ef fects, which we interpreted mostly to reflect possible isostatic imbalances of the crust. Subtracting the terrain-correlated free-air anomalies from t he total free-air anomalies and topographic gravity effects yielded terrain -decorrelated free-air anomalies and the gravity effects of isostatically c ompensated terrain features, respectively, which are uncorrelated with each other. The compensating effects that annihilate the latter were attributed to undulations of the Moho, which we estimated by inversion using GLQ inte gration and a mantle-to-crust density contrast of 400 kg/m(3) The inversion produced a Moho map with nearly 40 km of total relief that agrees very wel l with deep seismic refraction soundings. For East Antarctica, a bimodal va riation in crustal thickness was found: the crustal wedge between the easte rn Weddell Sea (similar or equal to 330 degrees E) and the eastern flank of the Gamburtsev Subglacial Mountains (similar or equal to 90 degrees E) has a mean thickness of about 37 km, whereas the mean crustal thickness is nea r 32 km for the northern half of the rest of East Antarctica up to the west ern flank of the Transantarctic Mountains (similar or equal to 150 degrees E). For West Antarctica and the oceanic regions, mean crustal thicknesses o f about 30 km and 14 km, respectively, are inferred. The terrain-decorrelat ed free-air anomalies may be related to long-wavelength, large-amplitude su bcrustal density variations and to much shorter-wavelength, smaller-amplitu de intracrustal density variations.