Sandia Mountains and Rio Grande rift: Ancestry of structures and history of deformation
Karl E. Karlstrom, S. M. Cather, M. T. Heizler, F. J. Pazzaglia, and M. Roy
The Sandia Mountains and other rift flanks of the Rio Grande rift are, in large part, the product of both Laramide contraction and Neogene extension superimposed upon an already segmented crust. Rio Grande rift extension represents tectonic inversion (extensional collapse) of Laramide Rocky Mountain structures. Laramide structures were strongly influenced by older NE (1.65 and 1.4 Ga), NW (1.1 Ga), and N–S (0.8 Ga) structural grains.The Sandia Mountain area is important for interpretation of the relative importance of Laramide versus Miocene structures. Reverse faults along the eastern flank of the mountains suggest the Sandia Mountains were a northern extension of the Montosa uplift that resembled a mirror image of the Nacimiento uplift. However, apatite fission-track data indicate that cooling of Proterozoic basement through 60-120o C did not take place until after 30 Ma. Hence, we infer a mildly positive Laramide uplift (hundreds of meters, not kilometers, of structural relief). Normal faulting in the Placitas fault system, at the northern end of the Sandias, began during Laramide time in a releasing bend step between the dextral Rincon and San Francisco faults. Neogene uplift of the Sandia footwall due to tectonic denudation on these faults resulted in northward tilting of beds at the northern end of the Sandias and increase in dips of normal faults of the Placitas fault system. Our interpretation suggests a multistage uplift history for the Sandia Mountain block.
- Karlstrom, Karl E.; Cather, S. M.; Heizler, M. T.; Pazzaglia, F. J.; Roy, M., 1999, Sandia Mountains and Rio Grande rift: Ancestry of structures and history of deformation, in: Albuquerque Country, Pazzaglia, Frank J.; Lucas, S. G.; Austin, G. S., New Mexico Geological Society, Guidebook, 50th Field Conference, pp. 155-165.