INTEGRATING 2D GEOLOGIC DATA WITH GEOPHYICS TO GENERATE A 3D GEOLOGIC MAP OF THE ROSILLOS MOUNTAINS IN BIG BEND NATIONAL PARK, TX

The Rosillos Mountains, located in the northern portion of Big Bend National Park, are comprised of a Teriary aged fayalite-bearing, granitic laccolith the base of which is bounded by the Upper Cretaceous lower Aguja Formation. The laccolith is semicircular in shape (10.5 km by 7.5 km) with its long axis striking NNW. The laccolith is >600 m thick. The Tertiary aged normal Chalk Draw fault trending NNW dipping NE, cuts and offsets the eastern edge of the Rosillos laccolith resulting in the down-dropping of an eastern flank. Numerous Oligocene aged intrusive bodies of varying composition surround the Rosillos Mountains.

This study integrates and interprets numerous geospatial data sets covering the Rosillos Mountains in order to construct a 3-dimensional geologic map of the region and refine the surficial geologic map. Each data set has been processed to derive unique geologic information that is used to define the geology in three dimensions. The one meter resolution color aerial photography is useful for delineating geologic contacts at a high resolution. The Landsat ETM image is useful for differentiating surficial lithologic units that are not obvious in the color aerial photography, as well as providing a general description of the geologic material. Aeromagnetic data are useful for differentiating intrusive bodies, as well as modeling the vertical and lateral extent of the intrusions. Gravimetric data are useful for constraining the vertical extent of the intrusive bodies. Radiometric data are useful for differentiating intrusive bodies and provides clues to surficial rock types as well as weathering processes.

A geographic information system (GIS) is capable of integrating the various derivative products and provides the architectural framework for building the interpreted three dimensional geologic model. This study demonstrates the usefulness of applying basic processing to a variety of geospatial data to extract surficial geologic information and extrapolate this information into the subsurface to build a three dimensional geologic model.