A GIS BASED STUDY OF MAFIC DIKE ORIENTATION IN SOUTHEAST UTAH

The Navajo volcanic field is comprised of ~25 Ma minette diatremes, plugs, and numerous dikes. The magmatism and geochemistry of rocks in this field have been studied extensively, but questions remain regarding structural controls on their emplacement. Previous work establishes that dominant trends of dikes in the NVF is ~020^o east of this study area associated with extension, and secondary northwest trends associated with reactivated basement structures. Characterizing the structural controls on emplacement of the dikes in this area is important because it enriches the established data of the NVF. Here we explore three potential structural controls; the Late Cretaceous Laramide Comb Ridge structure, Rio Grande Rift related extension, and magmatic dynamics at the time of emplacement.

In this study, minette dikes in the NVF south of Bluff, Utah were investigated to compare with regional data. Twenty-six dike segments were identified in the study area using GIS aerial imagery. Dike orientations range from 349 ^o to 010 ^o with an average of 003 ^o. Previous work documents that fracture sets associated with Comb Ridge have two dominant orientations (N-S and NNE-SSW ), Rio Grande Rift extensional features have ENE-WSW orientations, while magmatic emplacement not related to the previous two mechanisms is more random.

Due to timing constraints, the observed trends documented in NVF dikes in the study area are most consistent with both magmatic factors and Rio Grande Rift extension. The interplay of magmatism and tectonics south of Bluff and the implications for dike emplacement are discussed thoroughly in this report.