CAREER: Stable Isotope (18O/16O and D/H) Studies of Continental Arc Magmatism

Montana State University, Bozeman MT

Investigators

Abstract

Feeley 9983769 Stable isotope ratios can provide important constraints on the origins of the magmatic and volatile sources of igneous rocks and the differentiation processes by which they evolve. However, traditional whole-rock isotopic measurements of glassy volcanic rocks may not reflect magmatic values because of modification during eruptive and post-eruptive degassing and alteration. In contrast, analyses of phenocrysts provides an accurate and precise means of determining isotopic variations resulting from magmatic processes. This Career research will examine variations in stable isotope compositions (18O/16O and D/H) of phenocrysts from subduction-related volcanic rocks, emphasizing (but not restricted to) intermediate lavas that provide information on the petrologic mass balance and shallow crustal degassing processes at calc-alkaline stratovolcanoes. The proposed Research Plan involves two parts: (1) detailed study of oxygen isotope variations for magmatic products erupted at the Lassen volcanic center during individual eruptive cycles and over the prolonged magmatic history of the center and (2) study of hydrogen isotope compositions of hydrous phenocrysts in rocks from Lassen and Mount St. Helens. The Education Plan involves three levels of instruction: 1) new course development; 2) traditional graduate student training, and 3) specialized undergraduate research training. The new courses created will be a lower-division, service-learning course focusing on volcanic hazards in southwest Montana, and an upper-division course in isotope geochemistry. The purpose of the undergraduate training program is to provide talented students, especially those planning on a research-oriented career, with one-on-one training in field, laboratory, and dissemination skills.