PETROLOGICAL COMPARISON BETWEEN THE SUNLIGHT AND THOROFARE CREEK GROUPS IN THE ABSAROKA MOUNTAINS, WYOMING

The purpose of this undergraduate research project is to compare and contrast the petrological, geochemical and mineralogic data between the Sunlight and Thorofare Creek Groups in the Absaroka Mountains. These formations are found within the Absaroka Volcanic Province but are related to separate volcanic structures that formed at different times. These volcanic formations consist of volcaniclastic rocks and lava flows. Breccias, volcanoclastic conglomerates, lava flows, and clasts of granite were collected, powdered, and thin sectioned for analysis. Some of the powdered samples were sent off-site for chemical analysis and the remainder used for X-ray Defraction. These samples are being utilized to better understand the textural and mineralogical differences between the Sunlight Group and the Thorofare Creek Group. These textural and mineralogical differences are evident in the field, hand sample, and in thin section. For example, samples from the Sunlight Group are more mafic in composition and have more frequently brecciated textures that are later intruded by dikes. In comparison, the Thorofare Creek Group ranges from mafic to felsic in composition and typically contains rounded clasts with evidence earlier igneous activity. These differences are helpful in unraveling the processes that formed the volcanic centers. The primary onset of the Absaroka Mountains was during the Eocene and is related to the Tertiary Laramide orogeny the affected northwestern Wyoming. This provides the control of depositional, tectonic and volcanic processes for the Absaroka Mountains.