Senior Project Advisor

Kristina Walowski

Document Type

Project

Publication Date

Fall 2023

Keywords

Volcano, Eruption, Cinder Cone, Reaction Rim, Geology

Abstract

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.

Department

Geology

Subjects - Topical (LCSH)

Volcanoes--California--Lassen Volcanic National Park; Volcanic eruptions--California--Lassen Volcanic National Park; Geology--California--Lassen Volcanic National Park

Geographic Coverage

Lassen Volcanic National Park (Calif.)

Type

Text

Rights

Copying of this document in whole or in part is allowable only for scholarly purposes. It is understood, however, that any copying or publication of this document for commercial purposes, or for financial gain, shall not be allowed without the author’s written permission.

Language

English

Format

application/pdf

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Included in

Geology Commons

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