A MAPPING, PETROGRAPHY, AND GEOCHEMISTRY-BASED STUDY OF VOLCANIC UNITS IN THE SOUTHERN OREGON CASCADES

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 flows between these cones, particularly in the dominantly-mafic southern Oregon Cascades. This study features recent mapping of volcanic features in the 1:24,000 USGS quadrangles near Mt. McLoughlin, Oregon: Willow Lake, Rustler Peak, Big Butte Springs, Prospect South, and Imnaha Creek.

The definition of geologic unit extents was jointly based upon macroscopic descriptions, and the geochemistry and petrography of samples collected over multiple field seasons. Formal maps were drafted using ArcGIS, allowing for a clearer determination of relative flow ages and edifice volumes. Crystallization textures observed in some of the more-expansive of these flows have suggested potential patterns relating post-eruptive crystal growth to flow volumes and distance traveled.