DEFORMATION AND METAMORPHISM OF NAVAJO SANDSTONE ADJACENT TO A DIKE WITHIN THE HENRY MOUNTAINS IGNEOUS COMPLEX, SOUTHERN UTAH

We examined the deformation mechanisms and effects of contact metamorphism in the Navajo sandstone along a traverse oriented perpendicular to the dike. Samples were collected in 7 cm increments to help better understand deformation dissimilarities moving away from the intrusion. Thin sections were studied using a petrographic microscope. Petrographic analysis indicates that the sandstone within the first 7 cm from the dike exhibit features that indicate the most intense deformation of the sandstone and the highest degree of thermal effects. Deformation and metamorphism decrease gradually over a distance of two meters from the dike and then more rapidly diminish to background levels over the next 9 meters.

The intense zone of deformation and metamorphism is characterized by the absence of porosity. Grains seem to have mobilized by grain boundary sliding assisted by fracturing, intense brecciation, and pressure solution. The fracturing has allowed for fragments to slide into pores and locally the very fine grain products of brecciation fills pore space. Many fractures are barely visible and seem at least partly healed. All grain-grain contacts are tightly fitting and are interpreted to be the effects of pressure solution. Some grain boundaries seem to be slightly sutured and therefore hint at the possible effects of grain boundary migration. In addition, planar zones of intense brecciation cross the rock. The porosity of samples increases moving away from the intrusion; ranging from no porosity to highly porous sandstone. The deformation of these rocks quickly deteriorates within 2 meters of the intrusion. At 10 meters, the sandstone appears un-deformed. Our next step is to use cathodoluminescence to examine the evolution of grain boundaries.