NEW TECHNIQUES IN FIELD GEOLOGY: THE ULTIMATE DIGITAL MAPPING TOOLBOX FOR OUTCROP-SCALE GEOLOGIC MAPPING

Outcrop-scale geologic mapping in coastal Maine exposures as part of a field training program has been targeting features that are often overlooked due to their intermediate scale range; too big to grasp while standing on the outcrop, yet too small to be visible in available aerial imagery. Outcrop-scale mapping has the potential to reveal new never-before-seen structures that can lead to new analyses and interpretations of geologic relationships. Important tools and resources for outcrop-scale digital mapping include: geographic information system (GIS) software (ArcMap 9.3); a GPS base station to establish a field datum linked to the aerial imagery; RTK GPS rovers and optical total stations for precision surveying of geologic features at 1-2 cm precisions; handheld GPS for positioned structural orientation measurements at 1 m precisions; high resolution georeferenced aerial imagery with 15 cm ground distance pixel sizes; high resolution low elevation aerial imagery georeferenced to survey control points using a 5-15 m digital camera pole for single photos and simple mosaics or new GPS-guided unmanned aerial vehicles equipped with remote viewing digital cameras for extensive mosaic coverages; new airborne LiDAR precision elevation data and derived digital elevation models (DEMs); and GPS-enabled handheld touch screen computers or geopads running ArcPad software for digitizing visible features in georeferenced aerial imagery and DEMs. This style of integrated digital outcrop-scale mapping tied to an image-based field datum in GIS has revealed the geometry and distribution of syntectonic granites in coastal Maine where crosscutting granite dikes were emplaced by strain partitioning and deformed by continued regional shearing related to the Late Paleozoic-age Norumbega fault and shear zone system. A 30 km-wide mid-coast domain of pure shear-dominated layer-normal flattening (with folding of crosscutting dikes) was found to be flanked by zones of simple shear-dominated layer-parallel shearing (with rotation and boudinage of crosscutting dikes) with opposing strike-slip shear sense. This structural pattern is best explained by transpressional deformation during regional shearing with a period of lateral extrusion of the mid-coast block out of a restraining bend section of the Norumbega fault zone.