Laramide thin-skinned deformation in Permian rocks, Fra Cristobal Range, south-central New Mexico
Eric P. Nelson and James C. Hunter
The Fra Cristobal Range is a horst along the east edge of the southern Rio Grande rift near Truth or Consequences. The west-central portion of the range exposes Permian strata which have been affected by Laramide(?) thin-skinned deformation. Structures are concentrated in, but not limited to, the Meseta Blanca and Los Vallos Members of the Yeso Formation. Meso- and megascopic folds are upright, mostly subhorizontal, and north-trending ( ± 45°). Cylindrical, box, recumbent, and disharmonic geometries are present. Folds generally are restricted to particular stratigraphic intervals in plates bounded by thrust faults forming complicated duplex structures. Mesoscopic thrust faults show decollement and ramp geometries. Fold vergence and thrustplane slickenside lineations suggest both east (dominant) and west tectonic transport. No penetrative planar or linear fabrics have been observed, indicating a fairly brittle deformational environment.
East of a rift-related normal fault (Double Peak fault), Permian strata are undeformed, suggesting that the zone of deformation either climbs section eastward (to a now-eroded level), or dies out eastward. This fault may represent a Laramide ramp or a Laramide deformation front. The thin-skinned structural style probably was controlled by the presence of mechanically weak evaporites in the Permian section. The deformation is related to development of a basement-cored uplift. The structures developed in response to either crustal shortening or to gravity sliding off the steep limb of the uplift.
- Nelson, Eric P.; Hunter, James C., 1986, Laramide thin-skinned deformation in Permian rocks, Fra Cristobal Range, south-central New Mexico, in: Truth or Consequences region, Clemons, R. E.; King, W. E.; Mack, G. H., New Mexico Geological Society, Guidebook, 37th Field Conference, pp. 115-121.