Topographic setting of the Rio Grande rift, New Mexico: Assessing the role of flexural "rift-flank uplift" in the Sandia Mountains
Mousumi Roy, Karl E. Karlstrom, Shari Kelley, Frank Pazzaglia, and Steve Cather


The Rio Grande rift is a north-trending system of grabens that formed as a result of Neogene extension along the eastern margin of the Colorado Plateau. The location of the rift coincides with the eastern edge of a zone of crustal thickening and high topography during the Laramide (Late Cretaceous–Eocene) orogeny. Following Laramide crustal thickening, the region may have undergone broad, epeirogenic uplift during mid-Tertiary time. This paper analyzes the topographic setting of the Rio Grande rift in order to the address the relative importance of Laramide shortening, mid-Tertiary epeirogeny, and Neogene extension in generating high topography and observed topographic variability along the rift. Flexural modeling of topography and gravity data within the Sandia Mountains suggests that much of the present-day short-wavelength topography of this mountain belt can be attributed to flexural footwall uplift in response to Neogene extension. Topographically high rift-flanks also exist, however, within hanging-wall blocks. These are not easily attributed to extension and, based on apatite fission-track dates, apparently reflect the combined effects of Laramide crustal thickening and mid-Tertiary regional denudation. Based on flexural modeling, together with geologic and geomorphologic arguments, we propose that extensional processes may have only locally modified topography along the Rio Grande rift. In particular, we argue that the broad, long-wave length (>1000 km) topographic high at the eastern margin of the Colorado Plateau (Alvarado ridge) probably post-dates Laramide crustal thickening and pre-dates the formation of the Rio Grande rift.


  1. Roy, Mousumi; Karlstrom, Karl E.; Kelley, Shari; Pazzaglia, Frank; Cather, Steve, 1999, Topographic setting of the Rio Grande rift, New Mexico: Assessing the role of flexural "rift-flank uplift" in the Sandia Mountains, in: Albuquerque Country, Pazzaglia, Frank J.; Lucas, S. G.; Austin, G. S., New Mexico Geological Society, Guidebook, 50th Field Conference, pp. 167-174.

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