A Study of Magma Dynamics Using Short-Lived Radionuclides

知识价值：将分析来自弧形、大洋岛屿和大洋中脊的熔岩，以在238U和232Th衰变系列中分析短期核素，以调查导致火山喷发的数十年、数年和数周内发生的岩浆过程的时间尺度。该项目的一个主要目标是绘制由于构造环境、初始水含量和氧逸度的不同而导致的岩浆之间脱气和结晶模式的差异。该项目将提供圣海伦斯山(MSH)和基拉韦厄火山持续活动的喷发产物的时间序列分析，这反过来将有助于了解岩浆系统动力学，以及充电和储存历史。这些信息将导致对这些火山过去的行为和未来活动的更现实的模型。第一项研究旨在根据2004年10月以来喷发的熔岩和特弗利夫岩样本，了解MSH的岩浆室过程。通过阿尔法光谱分析对这些样品进行210Po的重复分析，可以确定最初的210Po和210Pb活度。~(214)Pb和~(228)Ac的活度将用伽马能谱测定，并作为~(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，后者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。关于基质物质的初步数据限制了岩浆脱气的深度和时间，斜长石矿物的初步数据提供了关于这些矿物生长历史的信息。其他分析将勾勒出新旧斜长石的比例，并测试岩浆室发育和结晶的模型。第二个项目是合作研究从Pu‘u O’o及其附近的基拉韦厄喷口喷发的熔岩中的210Po-210Pb-226Ra不平衡。这个项目的目标是绘制基拉韦岛玄武岩喷发前脱气的持续时间和时间图。还将确定储存在浅层地壳中并在1980年代初和1997年期间喷发的岩浆的地壳停留时间。更广泛的影响。这项研究将加强来自各种构造环境和分馏程度的不同熔岩中短寿命U系列核素的数据库。这将使我们更好地了解火山喷发后一个世纪内发生的挥发性熔融和结晶的性质，并提供有关岩浆储集层的深度和体积、岩浆粘度和爆炸性如何随时间变化以及是什么触发岩浆从深室系统向地表迁移的信息。这项研究还将寻找喷发活动变化的地球化学前兆。它将继续爱荷华大学、圣海伦斯山工作组和美国其他一些机构的研究人员之间的国际合作。爱荷华大学的本科生和研究生水平的研究将得到这个项目的支持。

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.