THE APPLICATION OF GIS, GEOCHEMISTRY, AND PETROLOGY TO MAP VOLCANIC FIELDS AND DEFINE MAGMATIC HISTORIES AROUND MT. MCLOUGHLIN, OREGON

In-depth geologic mapping and petrological studies have been completed on many of the large stratovolcanoes throughout the Cascades, such as Mts. Rainier, Mazama, and Shasta. Only limited analysis has been completed, however, on the smaller edifices and flows between these cones. In this study, the volcanic features in two 1:24000 USGS quadrangles adjacent to Mt. McLoughlin, Oregon were mapped: Willow Lake and Rustler Peak, updating and revising work completed in these areas in 2013.

The accuracy and precision of the field mapping was enhanced by the use of GPS technology, used in concert with hard-copy maps. The subsequent definition of geologic unit extents, based upon sample geochemistry and petrography, was completed using GIS technology, allowing for a clearer determination of relative flow ages and edifice volumes. Through an application of previously-published regional eruption ages, this in turn allowed for a first-order determination of cone-building rates from these smaller, peripheral vents. Crystallization textures observed in these flows were also correlated with distance from eruptive centers. This allowed for the determination of patterns relating post-eruptive crystal growth to flow volumes and distance travelled.