New Mexico Geological Society Annual Spring Meeting — Abstracts

From a surface perspective the architecture of the Albuquerque (ABQ) geohydrologic basin is deceptively simple. It comprises three major physiographic subdivisions of the Rio Grande rift (RGR) tectonic province Santo Domingo, Central ABQ, and Belen Basins that are linked by the Middle Rio Grande Valley between Cochiti Dam and San Acacia. Combined surface and subsurface geological and geophysical information, however, reveal that the internal architecture of these basins is much more complicated in terms of not only basin-till stratigraphic and lithofacies composition, but also structural fabric and centers of RGR-related igneous activity (see reviews in Keller and Cather, 1994, GSA Special Paper 291). The linked structural units, here designated the Albuquerque Basin Complex (ABC), comprise five distinct RGR depressions (each with two or more subbasin components) and three well-defined inter-depression structural highs that, for the most part, are deeply buried. From north to south, linked structural depressions are designated Cochiti-Bernalillo, Metro-Area, Wind Mesa, Lunas-Bernardo, and Lower Puerco. The major interdepression highs comprise the Ziana-Sandia Pueblo and Westland-Mountain view dividing "ridges", as well as the Tijeras-Gabaldon "accommodation zone" (Hawley, 1996, NMBMMR, Open-file Report 402-0). All these features form significant geohydrologic subunits that need to be characterized in much more detail as (conceptual-numerical) models of the ABC's groundwater-flow system continue to be developed and improved.

The emphasis of this poster session is on external and internal basin-boundaries between tilted fault-block structures produced by RGR basin extension during the past 25 Ma. A major conclusion of our collective studies in the region, which span a period of more than 35 years, is that the ABQ geohydrologic basin is not isolated geohydrologically from the Espanola Basin to the northeast, the "Valles-Toledo" basin to the north, or the Socorro-La Jencia (Popotosa) basin to the south. Our work to date suggests that the best definition of major basin boundaries is obtained when a variety of surface and subsurface geophysical survey techniques (e.g., gravity, seismic, magneto-telluric, and electromagnetic) are combined with geologic mapping, deep-borehole logging, geochemical and petrographic studies, and potentiometric-surface characterization. Deep drilling, seismic and electromagnetic surveys for hydrocarbon and geothermal resource evaluation all provide localized views of basin-boundaries and internal structural complexity (e.g. Russell and Snelson, and May and Russell, 1994, GSA Special Paper 291, pp. 83-112, 113-123). On a basin-wide scale, however, the best available tools for understanding major boundary elements of the ABC's hydrogeologic framework are published maps and profiles of Bouguer and isostatic-residual gravity anomalies (e.g. Cordell, 1978, GSA Bull., v. 89, p. 1073-1090; 1979, Geology, v. 7, p. 201-205; Birch, 1982, Geophysics, v. 47, p. 11851197; Keller and Cordell, 1983, NMSU Energy Institute, Geothermal Res. of NM, Scientific Map Series; and Heywood, 1992, USGS, WRI Report 91-4065).