PRELIMINARY STRUCTURAL AND GEOPHYSICAL INVESTIGATION OF POSSIBLE CENOZOIC INTRUSIVE EVENTS ALONG THE NE UNCOMPAHGRE PLATEAU IN WESTERN COLORADO

A preliminary research conducted along the northeastern slope of the Uncompahgre Plateau near Grand Junction, Colorado, indicates the likely presence of a shallow, but unexposed, igneous intrusion that could be a Precambrian gabbroic intrusion or an Oligocene porphyritic diorite intrusion in origin. Elsewhere in the vicinity of the research area, similar igneous rocks of Precambrian or Oligocene age have been identified; thus, it is possible that analogous intrusive features may exist in the study area. A local magnetic high was observed along the Redlands Fault Zone, which indicates these types of sources in the subsurface. The igneous intrusion may be one viable explanation for the initially observed magnetic anomalies since fault-displaced basement rock may also cause a measurable magnetic signature. The application of ground-based, high-resolution magnetic surveying coupled with forward modeling of likely subsurface geometries may be instrumental in identifying undiscovered intrusions or bedrock faulting. Multiple strike and dip measurements of fractures were conducted to determine the orientation of local stress fields. The data shows uplift events have produced large oblique strike-slip faults, such as the Redlands Fault Zone. Previous studies have found that faults along the Colorado Plateau display deformation kinematics that are consistent with two uplift periods: the Permo-Pennsylvanian Ancestral Rockies Orogeny and the Late Cretaceous-Paleogene Laramide Orogeny. Seismic tomography maps representing “fast” and “slow” seismic propagation velocities are used in this research to elucidate the potential deep-seated origin of the intrusions into the Uncompahgre Plateau. The high-magnetic anomaly, structural analysis, and tomography data all indicate a possible porphyritic diorite intrusion that is Oligocene in age within the northwestern slope of the Uncompahgre Plateau.