INTEGRATED GEOPHYSICAL MODELING OF THE ALBUQUERQUE BASIN RAISES QUESTIONS ABOUT THE MIOCENE DEVELOPMENT OF THE CENTRAL RIO GRANDE RIFT, NEW MEXICO

A 3D model of rift-fill thickness developed for the Albuquerque Basin (Grauch and Connell, 2013) shows a view of basin geometry that differs substantially from a previous, popular paradigm. The 3D model represents the integration of diverse geophysical data sets, borehole information, and geologic mapping. A major objective of the modeling effort was to reconcile apparent conflicts between gravity, seismic-reflection, and borehole constraints on basin-fill thickness from previous interpretations. Dr. Randy Keller and his students were involved in the initial stages of this work. Eventually, apparent conflicts were reconciled through reanalysis and reinterpretation of all the data sets.

The main elements of the 3D model are three, 3-5-km-deep, inter-connected structural depressions that increase southward in size, complexity, and segmentation. These subbasins, as well as smaller structural segments within the southern subbasin, are separated by antiformal or synformal structures. Four half-graben elements are recognized, three of which tilt east. The floor of the fourth, in the southwest corner of the basin, tilts west to southwest. Independent information suggests that this and two of the east-tilted half-grabens in the north-central and central parts of the basin actively subsided between 20-10 Ma, concomitant with rapid uplift of the northeastern and southwestern rift flanks. Miocene synrift strata were involved in tilting associated with formation of antiformal and synformal structures and at least one low-angle normal fault toward the end of this period. High-angle normal faults accommodate the greatest vertical displacement in the east-tilted half-grabens. A low-angle normal fault, down to the east-northeast, may have accompanied basin subsidence in the southwestern half-graben, but the evidence is equivocal. The synchronous formation of these diverse structures raises questions about how to interpret structural linkages and strain accommodation among these subbasins during rift development.