INSIGHT INTO THE ORIGIN AND EVOLUTION OF VOLATILES IN MINETTE DIKES OF THE NAVAJO VOLCANIC FIELD

The diatreme-dike centers in the Oligocene Navajo volcanic field (NVF) are an important part of the geologic history and evolution of the Colorado Plateau. Although a number of previous studies have focused on the generation and evolution of magmas associated with the NVF, the origin and evolution of volatile species during magma formation and emplacement are not well understood.

Detailed petrographic studies on selected samples from fluorine-rich dikes located in the Carrizo Mountains near Ship Rock indicate high concentrations of zoned volatile-bearing minerals (phlogopite and apatite). Some studies dealing with the emplacement of diatremes in the NVF have argued that a major portion of volatiles was derived from crustal reservoirs as mantle magmas interacted with them during transport. Late-stage crystallization of calcite and fluorite in the breccia zones in some diatremes and dikes in the northeastern NVF, however, hint that volatiles rich in CO2 H2O, and F were liberated from magmas associated with these events. New data from electron microprobe studies on phenocryst phases will be presented as a test of these hypotheses. These data will constrain the concentrations and changes in volatile species (Cl, F) and selected lithophile elements (B, Be, Li, Rb, Sr), to insight into the nature and role of volatiles in the creation, transport, and emplacement of NVF magmas.