| Abstract |
In this study, we looked at the petrographic and geochemical aspects of small rhyolite breccia plutons that formed by volcanic explosions in the Black Hills region. These intrusions are roughly 58-50Ma (Eocene) and are the result of shallow level magma explosions. In this region we can see a wide variety of different intrusive bodies such as dikes, sills, laccoliths, diatremes, and breccia pipes. Each of the 18 samples we looked at plotted in the rhyolite field. According to Lockrem (1980), there are four possibilities for origins of breccia: igneous intrusion breccia, pyroclastic volcanic breccia, meteorite breccia, and breccia pipe origin. Based on the textural evidence like clasts within a fine-grained igneous matrix, with the clasts being composed mainly of quartz and feldspar, and evidence that both the clasts and the matrix are highly altered we can conclude that our samples are breccia pipe in origin (Lockrem, 1980). References: Lockrem, T.M., “Petrographic Analysis of an Early Cenozoic Breccia from the Tinto Area, Northern Black Hills, South Dakota” (1980). Undergraduate theses and senior Projects. 76. https://commons.und.edu/senior-projects/76
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| Modified Abstract |
In this study, we are looking at the petrographic and geochemical aspects of small rhyolite breccia plutons that formed by volcanic explosions in the Black Hills region. These intrusions are roughly 58-50 Ma and are the result of shallow level magma explosions. In this region we can see a wide variety of different intrusive bodies. The 18 samples that we examined using SEM, XRD, and thin section analysis plotted in the rhyolite field. They contained a fine-grained igneous matrix with clasts that were quartz and feldspar dominated. This allowed us to conclude that these samples are breccia pipe in origin.
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