RETHINKING AN ARCHETYPE OF RIFT HALF-GRABEN FORMATION—A REVISED MODEL OF BASIN GEOMETRY FOR THE ALBUQUERQUE SEGMENT OF THE RIO GRANDE RIFT, NEW MEXICO
A model of basin-fill thickness constructed from gravity data supports a different picture of basin geometry, primarily for the southern half of the Albuquerque basin. The thickness model is constrained by well information, allows for variable density, matches new structural cross-sections, and is supported by limited re-interpretation of seismic-reflection data. In the new model, the northern sub-basin generally consists of an ENE-facing half-graben, differing primarily from the earlier model by its farther extent to the east. A northwest-trending structural high rather than a southwest-trending transfer zone separates the northern and southern parts of the Albuquerque basin. Dominating the southern half of the basin is a sub-basin that generally deepens to the east, modified by several north-trending structural highs. In sharp contrast to the earlier structural model, the areas of west-tilted strata are confined to a 15- to 30-km wide zone along the southwestern margin of the basin. The divide between the oppositely tilted regions is a crooked, south- to southeast-trending structural high. The new model suggests that the entire Albuquerque basin predominantly tilts eastward, with only a marginal region of westward tilting and no scissor-like transfer zone. The restricted region of westward tilting may have resulted from a brief change in subsidence history, the influence of pre-rift structure, or accommodation that occurs as a double-sided hinge rather than as a scissor-like slip zone.