Paleozoic Structures of the Sacramento Mountains, Otero County, New Mexico and Implications for Ancestral Rocky Mountain Tectonics

A. W. Howell
Colorado State University, Department of Earth Resources, Fort Collins, CO

The Sacramento Mountains, Otero County, New Mexico, provide an ideal location for testing Ancestral Rocky Mountain tectonic hypotheses. Several well-exposed Pennsylvanian faults and folds within the Sacramento Escarpment are unconformably overlain by undeformed Permian strata and this offers an excellent opportunity for analyzing the Ancestral Rockies structures. Ancestral Rocky Mountain tectonic hypotheses predict conflicting fault patterns. Formation related to the Ouachita-Marathon orogen predicts northwestsoutheast compression (Kluth, 1986), whereas northeast-southwest compression is predicted by formation related to a possible Andeantype margin to the southwest (Ye et al., 1996). In the northern Sacramento Mountains, the association of high-angle faults and overlying subparallel folds suggests strike-slip movement on faults, as opposed to the normal slip hypothesized by early workers in the area (Cather, 2000). Thus the faults and folds of the Sacramento Mountains are ideal for testing conflicting hypotheses because their northsouth orientations would result in opposite shear sense that would reflect compression direction. Left-lateral slip would support the Ouachita-Marathon hypothesis whereas right-lateral movement would suggest compression from the southwest.

This research will provide detailed field data, analyses and interpretation of Paleozoic structures exposed in the Sacramento Mountains. Fieldwork will include mapping of exposed faults and offset strata in canyons cuffing the Sacramento Mountains Escarpment. Collection of fault data including slickenline orientations, presence of Riedel fractures, possible lateral displacement of rock units, and analysis of thin sections will test tectonic models. Construction of balanced cross-sections and three-dimensional models based on field data, thin sections and analysis of fault kinematics will provide an integrated test of hypotheses.

AAPG Search and Discovery Article #90902©2001 AAPG Foundation Grants-in-Aid