GRAVITY MODELS OF THE ALBUQUERQUE BASIN AND TULAROSA BASIN IN THE RIO GRANDE RIFT, NEW MEXICO

The Rio Grande Rift is a major Cenozoic continental rift zone that extends south from southern Colorado through north-central New Mexico. North of central New Mexico the rift is a narrow chain of extensional grabens within the southern Rocky Mountains. South of central New Mexico the rift widens significantly, forming multiple, laterally adjacent basins and eventually merges with the southern Basin and Range province. The Albuquerque Basin is located in the narrow section of the rift. The Tularosa Basin, east of the San Andres and Oscura Mountains, is located in the wider region of the rift. Gravity and seismic models published in 1998 show the Albuquerque Basin as a deep (10 km) asymmetric graben with the major basin-bounding fault located along the base of the Sandia Mountains on the eastern edge of the rift. New gravity data, available as part of the Pan American Center for Earth and Environmental Studies (PACES) gravity compilation, is used to refine these existing models of the Albuquerque Basin. Our models are consistent with a deep basin, but show a gravity high in the middle of the basin, indicating either a mafic intrusion, or basin fault geometry that brings higher density basement rock closer to the surface. Gravity models using the PACES gravity compilation and density data from wells were also constructed along NW to SE profiles across the SE flank of the Oscura Mountains into the Northern Tularosa Basin. These models constrain the presence of two normal faults along the northwestern edge of the basin as well as the subsurface geometry of the basin. Models along an east-west profile across north central Tularosa Basin show a subsurface horst-graben series within the basin. The lack of seismic constraints on crustal density and structure in the Tularosa Basin limits independent validation of our models, but we present ideas regarding the nature of the inferred structures in relation to the known tectonic history of the Rio Grande Rift region.