Use of stereoscopic satellite imagery for 3D mapping of bedrock structure in West Antarctica: An example from the northern Ford Ranges

In coastal West Antarctica, crustal-scale faults have been minimally mapped using traditional ground-based methods but regional scale structures are inferred mainly on the basis of low resolution potential fields data from airborne geophysical surveys (15 km flightline spacing). We use a new approach to detailed mapping of faults, shear zones, and intrusive relationships using panchromatic and multispectral imagery draped upon a digital elevation model (DEM). Our work focuses on the Fosdick Mountains, a culmination of lower middle crustal rocks exhumed at c. 100 Ma by dextral oblique detachment faulting. Ground truth exists for extensive areas visited during field studies in 2005-2011, providing a basis for spectral analysis of 8-band WorldView-02 imagery for detailed mapping of complex granite- migmatite relationships on the north side of the Fosdick range. A primary aim is the creation of a 3D geological map using the results of spectral analysis merged with a DEM computed from a stereographic pair of high resolution panchromatic images (sequential scenes, acquired 45 seconds apart). DEMs were computed using ERDAS Imagine™ LPS eATE, refined by MATLAB-based interpolation scripts to remove artifacts in the terrain model according to procedures developed by the Polar Geospatial Center (U. Minnesota). Orthorectified satellite imagery that covers the area of the DEMs was subjected to principal component analysis in ESRI ArcGIS™ 10.1, then the different rock types were identified using various combinations of spectral bands in order to map the geology of rock exposures that could not be accessed directly from the ground. Renderings in 3D of the satellite scenes draped upon the DEMs were created using Global Mapper™. The 3D perspective views reveal structural and geological features that are not observed in either the DEM nor the satellite imagery alone. The detailed map is crucial for an ongoing petrological / geochemical investigation of Cretaceous crustal differentiation on the margin of the Gondwana supercontinent, but the methods that we here employ are broadly applicable for a wide variety of rock types in remote and inaccessible localities in the polar regions. A further use of the DEMs + imagery are for mapping of regional-scale subglacial bedrock faults and geological contacts in the region, of potential significance for interpretation of GPS and seismic data being recorded at Mt. Carbone in the ANET/POLEnet array. Prior research identified a lithospheric-scale fault that separates the Fosdick Mountains from Mt Carbone in the Phillips range. The pronounced contrast in rock type and cooling history, steep magnetic and gravity gradients, and the presence of the west-flowing Balchen Glacier provide evidence for the fault, which is concealed by glacier ice. Accurate determination of the fault location and lateral extent may be important for interpretation of regional patterns of post-glacial response and/or neotectonics based on GPS+seismic data being collected by ANET/POLEnet in West Antarctica.