Horizontal shortening of the Laramide Zuni Arch, west-central New Mexico: A preliminary study
— Jacob O. Thacker
The Zuni Mountains are an anticlinal Laramide arch with marked asymmetry along its southwestern forelimb (Nutria monocline), a low-elevation basement-involved range crest, and a gentle northeast-dipping backlimb (Chaco Slope). However, the range exhibits considerable along-strike complexity at odds with this simplistic framework. In the northwest Zuni arch, folds are southwest vergent, and the two dominant reverse faults, the Stinking Springs and McGaffey faults, strike north to northwest and exhibit east to northeast dips. In the southeast Zuni arch, the dominant fold pattern is northeast vergent and the Sedgwick reverse fault is largely north-northwest striking and exhibits a west to southwest dip. Minor fault data (strike-slip, conjugate strike-slip, and thrust) from these northwest and southeast domains show that early horizontal shortening preceded significant folding and faulting, as suggested by restoring bedding to horizontal, and both domains share similar geometric and kinematic results despite opposing fault polarities and variably-striking (i.e., E-W or N-S) beds from which minor faults are documented. Similarly, both domains and the range record WSW-ENE directed shortening (051–073° azimuth; 061° mean azimuth) that is consistent with estimates of shortening on numerous other Laramide arches in the Colorado Plateau and Rocky Mountains. Comparable shortening azimuths suggest that deformational processes between the Colorado Plateau and Rocky Mountain regions during the Late Cretaceous–Paleogene were similar, and therefore ENE horizontal shortening is the likely means by which the Zuni arch deformed during Laramide orogenesis. These results and interpretations are not in accord with previously suggested models for Zuni arch formation by mass transfer and/or Eurasian-style extrusion tectonics.
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- Thacker, Jacob O., 2021, Horizontal shortening of the Laramide Zuni Arch, west-central New Mexico: A preliminary study, in: New Mexico Geological Society, 71st Annual Fall Field Conference, September 2021, Geology of Mount Taylor, Frey, Bonnie A.; Kelley, Shari A.; Zeigler, Kate E.; McLemore, Virginia T.; Goff, Fraser; Ulmer-Scholle, Dana S., New Mexico Geological Society, Guidebook, pp. 281-290. https://doi.org/10.56577/FFC-71.281