New Mexico Geological Society Annual Spring Meeting — Abstracts

The Pemada Canyon dike (PCD) is an isolated dike that is situated close to the center of the San Juan basin (SJB) in the southeastern Colorado Plateau, New Mexico. It has evaded any prior attempts to understand its provenance and role in what it potentially preserves about the region's geologic past. Knowledge of the PCD is limited to the facts that it is a lamprophyric dike that intrudes siliciclastic sedimentary rocks of the Eocene San Jose Formation and that preliminary geochronologic analyses suggest that it dates back to the Miocene. Other preliminary results yielded that the PCD is composed of ultramafic material, with a low silica content (SiO₂ 27.8-37.7%) and higher than normal alkaline content (Na₂O 0.313-1.72%, K₂O 0.453-2.02%) for an ultramafic lamprophyre; thin section analyses demonstrated a trachytic, fine-grained matrix of kalsilite, clinopyroxene, magnetite ± ilmenite, calcite, and phlogopite. In addition, 1–2 cm grains of coarse faceted calcite, euhedral clinopyroxene, phlogopite, and sparse kalsilite (±nepheline) appear, with olivine being noticeably absent. What we could acquire from conducting research on the PCD could offer a glimpse into an understudied episode that may have occurred throughout the SJB’s geologic history.

This project intends to address some of its unknown constituents, particularly by mapping out its extent, attempting to constrain the time of emplacement, note its mineral modal abundance and composition, determine its magmatic genesis, and ascertain if there is a relationship between other dikes in the region. Additionally, further research involves scoping out and logging its physical extent, analyzing its stress regime/joints, settling a correlation between the dike and the stresses occurring throughout the basin, and ultimately, resolve if the PCD was a single event or if it was episodic and if the latter, the temporal and/or compositional separation between emplacement events. Field research involves the collection of an appropriate amount of rock samples, recording geographic coordinates, and scaling the feasible length of the PCD. Laboratory analyses entail ⁴⁰Ar/³⁹Ar dating, bulk-chemical, major and trace elemental analyses and thin section microscopy. Mapping will be conducted with ArcGIS Pro, following USGS guidelines. Research into the PCD wouldn’t just yield information regarding itself and the SJB, rather, its status as a lamprophyre warrants additional investigations for economic potential.