GEOLOGIC MAPPING, GEOCHEMISTRY, AND GEOCHRONOLOGY OF THE SILVER ISLAND MOUNTAINS OF WESTERN UTAH

Geologic mapping and analysis of a study area in the central Silver Island Mountains, located in western Utah, was completed as part of an undergraduate research experience in the capstone Field Methods course at Weber State University. Rocks exposed in the area include Upper Paleozoic strata, intrusive igneous rocks with possible Jurassic and/or Paleogene ages, various volcanic rocks with likely Neogene ages, and basin fill of the Salt Lake Group. Ages, geochemistry, and tectonic significance of igneous rocks, as well as the nature of metamorphism and structural evolution of the study area, however, were incompletely understood. The project included making a detailed geologic map and cross section of the area, and collecting samples for geochemical and geochronologic analyses. The nature of contact metamorphism adjacent to a complex intrusive body and dike system, and potential presence of economic minerals were also evaluated. Major, minor, and trace element contents of igneous rock samples were determined using a combination of X-ray fluorescence spectrometry and inductively-coupled optical-emission spectroscopy. Mineralogy and semi-quantitative mineral compositions were determined using petrographic and scanning electron microscopy. Igneous rocks included older intrusive diorite, and rhyolite vitrophyre, tuffs, and volcanic breccias, which show different major and trace element geochemical patterns. U-Pb geochronology of zircons from intrusive and volcanic rocks is underway and will provide further information on the timing of various tectonic events in the Great Basin. By combining detailed mapping with multiple analytical techniques, we have developed a more complete understanding of the geologic history of the Silver Island Mountains of western Utah.