Intellectual merit. Arc magmatism is a major process whereby continents form, and caldera-forming eruptions can have substantial impact on global climate. Crater Lake is a representative example of arc-related calderas and is very well studied in terms of the geologic history and nature of eruptive products. However, such caldera-style eruptions seldom occurred at other Cascades volcanoes, and this study aims to understand why this is the case. This project aims to increase understanding of two aspects of arc magmatism: [1] the role of the lower crust, and particularly young mafic crust, in moderating and attenuating the ascent of magmas; and [2] the rate at which large magma bodies develop in the upper crust. Feedbacks between lower and upper crustal magmatic processes will be explored at Mt. Mazama (Crater Lake), with the goal of understanding differences in magmatic evolution at Mazama viz a viz other Cascades stratovolcanoes. Research will follow three approaches: [1] Use of U-Th and Re-Os isotopes, coupled with Sr-Nd-Pb isotopes and trace elements, to evaluate magma interactions with mafic lower crust. This approach is sensitive to involvement of garnet and can help constrain thermal and compositional characteristics of the lower crust. [2] Use of U-Th and O isotopic data to evaluate young volcanic deposits erupted in the last ~100 kyr. U series data are sensitive to hydrothermal processes, and will be used to constrain the size of the hydrothermal system associated with the pre-climactic magma chamber. [3] Use of U-Th isotopes to determine residence times of the crystal cargo in evolved eruptive units associated with the climactic caldera-forming eruption. These approaches will be used to estimate overall dimensions of the magma chamber that fed the climactic eruption at Mt. Mazama and formed the summit caldera, and to better understand the plumbing system and magmatic processes operating at this volcano.
Broader impacts. The proposed work will foster collaborations between UW-Madison, USGS, Carnegie-DTM, and US National Park Service on a volcanic system that potentially poses significant geologic risk. Outreach activities will include K-12 teacher workshops at Crater Lake National Park.
