NEW PERSPECTIVES ON RIFT BASIN STRUCTURE IN NEW MEXICO BASED ON SEISMIC REFLECTION AND GRAVITY DATA

Understanding the geometry of the basins associated with the Rio Grande rift helps efforts to understand the overall tectonic history of the region as well as efforts to evaluate natural resources. In order to advance our understanding of the Rio Grande rift, we have targeted the Albuquerque basin and the basins in the southern Rio Grande rift (Hueco, Mesilla, and Jornada del Muerto). We have focused on seismic reflection data by reanalyzing 200 km of published data in the Albuquerque basin and 400 km of newly released data in the southern Rio Grande rift. We also used a number of updated data sets in our analysis including well log information; remote sensing data; and gravity and magnetic data. The Albuquerque basin has been defined as consisting of 2 subbasins divided by a fault zone called the Tijeras Transfer Zone. We offer an alternative interpretation to this simple model since our integrated gravity and seismic models do not show evidence for this zone. In agreement with our earlier gravity work done in collaboration with V. J. S. Grauch, our interpretations suggest slightly deeper Cenozoic basin fill than earlier work, 3 major sub-basins, and the possibility of pre-Mesozoic salt in the central part of the basin. We also found evidence for significant amounts of upper crustal intrusion in the southern part of the basin. By re-interpreting and modeling the seismic lines integrated with gravity data, we derived an improved interpretation of the geometry of this basin. Our new seismic data in the southern rift area provide a significant new perspective on the deep structure in this area. Although our interpretations are still preliminary, the pre-rift volcanics and the Love Ranch Formation are often thicker than previously thought. Several basement structures including the Laramide Rio Grande uplift are clear in these data. Deep reflectivity suggests thick Paleozoic and/or Precambrian strata are present in some areas.