CONTRIBUTIONS MADE BY UNDERGRADUATE RESEARCH IN THE ABSAROKA VOLCANIC PROVINCE

Undergraduate research projects focused on the geology exposed in the Absaroka Mountains have added knowledge through petrologic descriptions of textures and minerals, X-ray diffraction for mineralogy, and geochemical signatures of major and trace elements. Initial characterization of the volcanic province in these projects started with a literature review and comparison of igneous rocks in the Absaroka Mountains with those from the Yellowstone Caldera. Although adjacent, these two volcanic provinces are vastly different from one another. Volcanic units of the Absaroka Mountains are distinctly intermediate to mafic in composition and are dominated by volcanoclastic rocks whereas the Yellowstone units are typically more felsic and fine-grained. Volcanoclastic units in the Absarokas include brecciated and conglomeratic textures with a wide variety of igneous lithologies exhibited in the clasts. Clasts in the breccias are commonly porphyritic basaltic lava and are variable in size and shape. Comparatively, clasts in the volcanoclastic conglomerates are rounded, often cobble-sized and have lithologies ranging from porphyritic dacite to basaltic lava flows. The volcanoclastic units are separated by and sometimes contain lava flows of intermediate to mafic composition. Previous studies have utilized these lava flows and dike intrusions in the area to determine the timing of igneous activity during the Tertiary. Dike intrusions into these volcanic units have also been used to delineate several volcanic centers across the province. Geochemical signatures of the igneous rocks in the province have SiO₂ compositions of 50.8-65.6% indicating the overall intermediate composition of the province. Some of the samples have unusually high K₂O compositions given the silica content while others indicate some minor enrichment of Cu. The geochemical signatures and petrographic observations are verified with data from X-ray diffraction indicating feldspathoid minerals and alteration products where K₂O compositions were high and feldspar varieties that are congruent with Na and Ca compositions. Together, these undergraduate research projects of rock units in the Absaroka Mountains have provided pieces of information that can be used to build on the existing knowledge base in the area.