New Mexico Geological Society Annual Spring Meeting — Abstracts

The regional aeromagnetic cup of north-central New Mexico was cut along prominent structural trends, then reassembled by rematching aeromagnetic anomalies and by restoring shortening along major contractile structures of Ancestral Rocky Mountain (ARM) and Laramide age. This reconstruction indicates dextral separations on the Picuris-Pecos fault (?40 km) and the Tusas-Picuris fault (?15 km) that are compatible with previous studies. About 22 km of dextral slip on the Nacimiento fault system, restored subparallel to the Gallina fault, rematches aeromagnetic patterns and predicts ?7 km of shortening along the front of the Nacimiento-Penasco uplift, similar to that proposed by Pollock et al. (2004, NMBGMR Bull. 160). About 12 km of shortening in the Sangre de Cristo uplift is balanced by dextral slip on the Tijeras-Canoncito fault. The latter fault serves to transfer slip northeastward from the Montosa and Paloma faults. Dextral components on the thrust fault of the eastern Sangre de Cristo Mountains may range between ?5-10 km, depending on the obliquity of shortening. This simplistic model predicts ?22 k of shortening in the southern Rockies near the latitude of Santa Fe. At least ?55 km and as much as ?90 km of dextral separation may be present on north-striking faults. Net Dextral separation thus may be two to four times greater than contraction in north-central New Mexico. Dextral separation probably results mostly from ARM and Laramide tectonism, as no other known Proterozoic or Phanerozoic deformation can be inferred to have produced major dextral slip.