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

稳定同位素比值对火成岩的岩浆岩和挥发性烃源的成因及其演化的分异过程具有重要的约束作用。然而，由于火山喷发和喷发后脱气蚀变的改变，玻璃质火山岩的传统全岩同位素测量可能不能反映岩浆值。相比之下，对斑晶的分析提供了一种准确而精确的方法来确定岩浆过程引起的同位素变化。本职业研究将研究俯冲相关火山岩中斑晶的稳定同位素组成（18O/16O和D/H）的变化，强调（但不限于）中间熔岩，它提供了钙碱性层状火山岩石学质量平衡和浅层地壳脱气过程的信息。提出的研究计划包括两个部分：(1)详细研究拉森火山中心在个别喷发周期和中心岩浆历史长河中喷发的岩浆产物的氧同位素变化；(2)研究拉森火山和圣海伦火山岩石中含水斑晶的氢同位素组成。教育计划包括三个层面的教学：1)新课程开发；2)传统的研究生训练，3)专门的本科生科研训练。新开设的课程将是一个低级别的服务学习课程，侧重于蒙大拿州西南部的火山灾害，以及一个高级别的同位素地球化学课程。本科培训计划的目的是为有才华的学生，特别是那些计划从事研究型职业的学生，提供一对一的实地、实验室和传播技能培训。

Feeley9983769Stable 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.