A Study of Magma Dynamics Using Short-Lived Radionuclides

智力优势：火山弧，海洋岛屿和洋中脊的熔岩将被分析为短寿命的核素在238 U和232 Th衰变系列调查的时间尺度ofmagmatic过程发生在几十年，几年，几周导致火山爆发。该项目的一个主要目标是绘制由构造环境、初始水含量和氧逸度的差异引起的岩浆之间脱气和结晶模式的差异。该项目将对圣海伦斯火山和基拉韦厄火山正在进行的活动的喷发产物进行时间序列分析，这反过来将有助于了解岩浆系统动力学以及再循环和储存历史。 这些信息将为这些火山过去的行为和未来的活动提供更现实的模型。第一项研究的目的是了解岩浆房的过程中MSH的熔岩和火山岩喷发的样品为基础，自2004年10月。通过α光谱法对这些样品进行210 Po的重复分析将允许确定初始210 Po和210 Pb活性。214 Pb和228 Ac的活度将用γ能谱仪测定，并用作226 Ra和228 Ra的替代物。这些数据将与MSH工作组合作进行解释，该工作组正在收集相同样品的其他主要元素，微量元素，同位素和矿物成分数据。基块物质的初步数据提供了对岩浆脱气深度和时间的限制，斜长石矿物的初始数据提供了这些矿物生长历史的信息。其他分析将描绘新老斜长石的比例，以及岩浆房发展和结晶的测试模型。第二个项目是合作研究Pu 'u O 'o和附近基拉韦厄火山口喷发的熔岩中210 Po-210 Pb-226 Ra不平衡。这个项目的目标是绘制出基劳亚玄武岩喷发前脱气的持续性和时间。还将确定1980年代初和1997年期间储存在地壳浅层并喷发的岩浆的地壳驻留时间。更广泛的影响。这项研究将加强数据库的短寿命U系列核素在各种熔岩从广泛的构造环境和分馏程度。这将导致更好地了解挥发性流动和结晶的性质，发生在一个世纪的火山爆发，并提供有关岩浆库的深度和体积的信息，岩浆粘度和爆炸性如何随时间变化，以及什么触发岩浆从深室系统向地表迁移。本研究还将寻找喷发活动变化的地球化学前兆。它将继续与爱荷华州大学、圣海伦斯山工作组和美国其他一些机构的研究人员进行国际合作，并监督。该项目将支持爱荷华州大学的本科生和研究生水平的研究。

Intellectual Merit: Lavas from arcs, ocean islands, and mid-ocean ridges will be analyzed for shortlived nuclides in the 238U and 232Th decay series to investigate the time-scales ofmagmatic processes occurring over the decades, years, and weeks leading to volcanic eruptions. A primary goal of the project is to chart differences in degassing andcrystallization patterns between magmas resulting from differences in tectonic settings, initial water contents, and oxygen fugacities. This project will provide time series analysis of eruptive products from ongoing activity at Mount St. Helens (MSH) and Kilauea volcanos, that in turn will help understand magma system dynamics, and recgharge and storage histories. Such information will lead to more realistic models for past behavior and future activity at these volcanoes.. The first study aims to understand magma chamber processes at MSH based on samples of lavas and tephras erupted since October, 2004. Repeat analyses of these samples for 210Po by alpha spectrometry will allow initial 210Po and 210Pb activities to be determined. Activities of 214Pb and 228Ac will be determined by gamma spectrometery and used as proxies for 226Ra and 228Ra. These data will be interpreted in collaboration with the MSH working group, who are collecting other major element, trace element, isotope, and mineral composition data on the same samples. Preliminary data on groundmass material provide constraints on depths and timing of magma degassing, and initial data for plagioclase mineral provide information on the growth history of these minerals. Additional analyses will delineate the proportions of old and new plagioclase and test models of magma chamber development and crystallization. The second project is a collaborative study of 210Po-210Pb-226Ra disequilibrium in lavas erupted from Pu'u O'o and nearby vents at Kilauea. The goal of this project is to chart the persistence and timing of degassing for Kilauean basalts before they erupt. The crustal residence times of magmas that were stored in the shallow crust and erupted during the early 1980s and during the 1997 also will be determined. Broader Impacts. This study will enhance the database for short-lived U-series nuclides in diverse lavas from a wide array of tectonic settings and degrees of fractionation. This will lead to a greater understanding of the nature of volatile fluxing and crystallization that occurs within a century of volcanic eruptions, and also provide information about the depth and volumes of magma reservoirs, how magma viscosity and explosivity changes with time, and what triggers of magma migration from deep chamber systems toward the surface. This study also will look for geochemical predecessors of change in eruption activity. It will continue an international collaboration between the University of Iowa, the Mount St. Helens working group, and researchers from a number of other institutions in the USA and oversees. Undergraduate- and graduate-level research at the University of Iowa will be supported by this project.