Karlstrom, K.E., Cather, S. M., Kelley, S.A. , Heizler, M.T., Pazzaglia, F.J., and Roy, M.
New Mexico Geological Society Guidebook, F.J. Pazzaglia and S. Lucas (eds.), 50th Field Conference, Albuquerque Geology, 1999.
Abstract: The Sandia Mountains and other rift flanks of the Rio Grande rift are, in large part, the product of Laramide contractional and Miocene extensional deformations superimposed upon an already segmented crust. This paper examines the ancestry of faults and fault systems in the Sandia Mountain region. We conclude that Rio Grande rift extension represents tectonic inversion (extensional collapse) of Laramide Rocky Mountain structures. Laramide structures were, in turn, influenced by older NE (1.65 and 1.4 Ga), NW (1.1 Ga), and N-S (0.8 Ga) lineaments and structural grains. The Sandia Mountains is an important area for interpretations of the relative importance of Laramide versus Miocene structures. Reverse faults in the east flank of the mountains suggests this feature may have been a mildly positive, northern extension of the Montosa uplift that resembled a mirror image of the Nacimiento uplift. However, uplift was insufficient to cause cooling of Proterozoic basement through 60-120º C until 30 Ma, hence we infer hundreds of meters, not kilometers, of structural relief. Normal faulting in the Placitas fault system, at the north 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 block due to tectonic denudation on these faults caused northward tilting of the ramp area and rotation of normal faults of the Placitas fault system to very steep dips. Our interpretation suggests a multistage uplift history for the Sandia Mountain block.