STRUCTURAL MAPPING OF THE UPPER NUTRIA QUADRANGLE, WESTERN ZUNI MOUNTAINS, NEW MEXICO: IMPLICATIONS FOR GROUNDWATER FLOW

The Zuni Mountains of west-central New Mexico comprise one of the classic basement-cored anticlinal arches (Zuni Arch) of the Colorado Plateau. The overall structure of the Zuni Arch is an asymmetric anticline with a sinuous axis. This structural complexity has led to multiple hypotheses of its kinematic evolution, including extrusion tectonics, two-stage uplift, and a single phase of regionally pervasive horizontal shortening. The purpose of this study is to evaluate these models via detailed bedrock geologic mapping. We report the preliminary results of 1:10,000 scale structural mapping and fault kinematic analysis in the Upper Nutria Quadrangle, New Mexico. Four major structural features are present within the map area: the Nutria monocline, the Stinking Springs fault, the Oso Ridge fold, and the McGaffey fault. The north-south trending west-verging Nutria monocline folds Triassic-Cretaceous rocks into a steeply-dipping to locally-overturned hogback that defines the western edge of the Zuni Arch. The Stinking Springs fault is a broadly north-striking arcuate reverse fault that cross-cuts the Nutria monocline and thrusts mid-Permian strata over Triassic through Jurassic sedimentary rocks. The Oso Ridge fold is a north-trending inclined west-verging anticline-syncline pair. The McGaffey fault is a north-striking reverse fault that cross-cuts the Oso Ridge fold and juxtaposes mid-Permian sedimentary rocks in its hanging wall against upper Triassic rocks in its footwall. Fault geometric and kinematic data were collected from minor structures near these map-scale features and restored to horizontal about the axes of the Nutria and Oso Ridge folds. Restored structural data were then used to calculate paleostrain axes using FaultKin. Shortening directions estimated from the minor faults indicate horizontal NE-SW contraction and are permissible with formation of these structures during horizontal shortening. Active and historic springs are concentrated along map-scale faults and folds, suggesting that these structures are conduits to groundwater flow. Microstructural, porosity, and fracture density analysis of rock samples within and between major structures is underway.