Senior Project Advisor
Volcano, Eruption, Cinder Cone, Reaction Rim, Geology
Cinder Cone is a monogenetic cinder cone volcano located in Lassen National Volcanic Park, California. It erupted in 1666 CE and had three eruptive phases, each producing tephra and lava flows that ranged in style from Hawaiian (low explosivity) to Strombolian (moderate to high explosivity). This eruptive style variability at Cinder Cone was not caused by viscosity or volatile differences, and ascent rate has been proposed as a causal factor in the observed explosivity difference between phases. Ubiquitous quartz crystals are entrained within tephra and lava and were likely sourced from the assimilation of a granitic basement rock underlying the eruptive deposits. Most quartz xenocrysts from Cinder Cone are enveloped by a pyroxene reaction rim. This thesis aims to investigate the efficacy of pyroxene reaction rims as an ascent rate chronometer, and use geochemical data from pyroxenes and melts (now quenched as volcanic glass) to better understand the processes and timescales of the crystallization of reaction rims.
Reaction rim thickness does not vary between units and suggests that the reaction rim thicknesses are not indicative of ascent rate variability between units. Geochemical analyses of clinopyroxenes in tephra samples all plot as augite to diopside regardless of quartz proximity, indicating that all pyroxenes likely formed after the introduction of quartz to the magma. Major element chemistry plots of weight% SiO2 to TiO2 and FeO to MgO for melt lenses between quartz xenocrysts and surrounding pyroxene rims suggest that small scale mixing between quartz melt and matrix melt played a role in the formation of reaction rims. This study determined that while reaction rims surrounding quartz cannot be used as an ascent rate chronometer, they do allow for further constraint of the assimilation to eruption timescale of >24 hours to ~6 years.
Carozza, Annabelle, "An Analysis of Clinopyroxene Reaction Rims as Assimilation Chronometers at Cinder Cone Volcano, Lassen National Volcanic Park, California" (2023). WWU Honors College Senior Projects. 766.
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