Geochronology of the Navajo-Hopi Diatremes, Four Corners Area

Abstract

Accessory minerals from Precambrian xenoliths found in the diatremes and dikes of the Four Corners area of the Colorado Plateau were dated by means of fission tracks. Apatite from inclusions in four diatremes and two dikes in the Navajo intrusive field was completely annealed before or during intrusion. Sphene and zircon from these same inclusions were completely to partly annealed. The average age for the four kimberlitic diatremes (Buell Park, Garnet Ridge. Moses Rock, and Mule Ear) is 31.3±0.9 m.y., and the average age for the two minette dikes (Mitten Rock and Ship Rock) is 31.5±1.4 m.y. The Coliseum and Hoskietso monchiquite diatremes in the Hopi Buttes volcanic field have ages of 2.1±0.2 m.y. and 5.5±1.1 m.y., respectively. Discordant sphene and zircon ages from different xenoliths at the Garnet Ridge diatreme suggest that the annealing was due to burial rather than the initial temperatures of the diatreme.