Tectonic, hydrothermal and geomorphic controls on alteration scar formation near Questa, New Mexico
Jeff Meyer and Robert Leonardson
Alteration scars are iron-oxide and clay-rich areas of badlands topography that form by processes of landsliding, stumpage, rockfall and direct erosion by water. Scars form in regions of high slope angle where the rock has been weakened by hypogene (primary) and supergene (secondary) alteration, and rift-related tectonic events. Low-angle fault zones related to Oligocene extension were preferentially pyritized by meteorichydrothermal systems related to subjacent magmatic activity. Late-Miocene to present uplift of the eastern margin of the Rio Grande rift exposed these tectonically weakened, high pyrite zones, resulting in the formation of alteration scars. High slope angles form: (I) in headwater portions of tributary drainages, (2) at a slope break in the cross-canyon profiles caused by later entrenchment of the canyon and (3) along the rift-front escarpment. Mudflows that emanate from the scars pose significant geologic hazards and strongly influence the down-canyon profile of the Red River drainage.
- Meyer, Jeff; Leonardson, Robert, 1990, Tectonic, hydrothermal and geomorphic controls on alteration scar formation near Questa, New Mexico, in: Tectonic development of the southern Sangre de Cristo Mountains, New Mexico, Bauer, Paul W.; Lucas, Spencer G.; Mawer, Christopher K.; McIntosh, William C., New Mexico Geological Society, Guidebook, 41st Field Conference, pp. 417-422.