A rare rock type known as a shonkinite was found in the Adel Mountain range of Southwest Montana near the Missouri River and we set out to determine its crystallization history and magmatic evolution. As a first step towards this research goal, thin sections were made, and a petrographic analysis was conducted to determine composition and modal mineralogy. The rock was found to consist of mostly groundmass and augite (clinopyroxene) with lesser amounts of plagioclase, oxides, olivine, and orthopyroxene. Zoned plagioclases were found, and elemental composition tests were run on the crystals. Future research will seek to do more thorough analyses of crystallization history and run radiometric dating on the zircon inclusions found in the zoned plagioclase.
Author: Kevin J. Woeste
Advisor: Claire McLeod, Geology & Environmental Earth Science
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