Constraining Sulfur Isotope Fractionation During Volcanic Degassing Through the Study of an Open-system Basaltic Volcano

通过开放系统玄武岩火山的研究限制火山脱气过程中的硫同位素分馏

• 批准号: 1049891
• 负责人: Tobias Fischer
• 金额: $ 10.13万
• 依托单位: University of New Mexico
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-03-01 至 2014-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1049891&HistoricalAwards=false
• 关键词: Constraining; Sulfur; Isotope; Fractionation; During

This project is being supported by the Petrology and Geochemistry program (Division of Earth Sciences) and the Africa, Near East & South Asia Program (Office of International Science and Engineering).Sulfur (S) is one of the most abundant constituents of volcanic gases and is an important component of magmas. Sulfur is the most important volcanic gas in terms of climate impact due to the oxidation of sulfur to sulfate aerosols in the atmosphere. Large eruptions like the one at Pinatubo, Philippines in 1991, caused global temperatures to drop by two degrees over a period of two years. Sulfur has recently received a lot of attention due to ideas of geo-engineering where scientists propose to inject large quantities of sulfur into the stratosphere to counterbalance global warming. Therefore, understanding how and in what quantities sulfur degases naturally from magmas at volcanoes is a critical step in evaluating the global sulfur cycle with implications for climate impact as well as evaluating potential consequences of human impacts on the Earth's sulfur budget. In this proposed work, the team aims to investigate sulfur degassing from a persistently active lava lake. The lava lake that is best suited for this project is that of the Erta Ale volcano in Ethiopia. This lake is the Earth's longest-lived lava lake and has been persistently active for over 100 years. It degases large quantities of sulfur from a basaltic magma. They will collect samples of the active lava lake, the degassing sulfur, and the sulfate aerosol formed in the atmosphere. The isotopic composition of the sulfur in the lava, gas, and aerosols will be analyzed to understand the nature of the sulfur cycle. The ultimate goal of this study is to develop a consistent model for how sulfur degases from magmas in volcanoes worldwide. Fluxes of sulfur dioxide can be measured because their atmospheric concentrations are easily detectable due to its absorption of ultraviolet light. The H2S/SO2 ratio of primary magmatic gases is pressure dependent and therefore can be used as a proxy for depth of degassing. Therefore, degassing of S provides useful insights into volcanic degassing processes, can be used as an indication of increasing or decreasing volcanic activity, and is routinely used in volcano monitoring. Sulfur isotopes provide a powerful tool for studying sources of sulfur, degassing processes and pre-eruptive volatile contents of magmas. The proposed study is a quantitative, robustly constrained evaluation of sulfur isotope fractionation during volcanic degassing that will allow assessment of currently employed isotope fractionation models and fractionation factors. The study will measure S abundances in gas and melt, speciation of S in the melt and gas phases, isotope compositions of all S species, and use measured constraints on degassing conditions such as temperature and the fugacity of oxygen (fO2). The study will also assess disequilibrium fractionation during degassing. All data will be obtained from the consistently degassing basaltic lava lake of Erta Ale, Ethiopia. Erta Ale is ideal for this study because it has a relatively reduced magma (fO2 ~ QFM), high, consistent SO2 flux and high S content in the gases. Erta Ale provides a reduced end-member for terrestrial S degassing. The results from this study will be compared with an oxidizing end-member (QFM +1.6 and high S flux) represented by volcano Masaya that is located in a subduction zone setting.

该项目得到了岩石学和地球化学计划（地球科学系）和非洲近东亚和南亚计划（国际科学与工程办公室）的支持。Sulfur（S）是火山气体最丰富的组成部分之一，并且是岩浆的重要组成部分。在气候影响方面，硫是最重要的火山气体，这是由于大气中硫酸盐气溶胶的氧化而导致的。 1991年在菲律宾Pinatubo的大型喷发爆发导致全球温度在两年内下降了两个度。由于地理工程的想法，科学家建议将大量的硫注入平流层以平衡全球变暖，因此硫磺最近引起了很多关注。因此，了解火山岩浆自然含量和含量的数量是什么是评估全球硫周期的关键步骤，对气候影响的影响以及评估人类对地球硫预算的影响的潜在后果。在这项拟议的工作中，该团队旨在调查持续活跃的熔岩湖中的硫脱水。最适合该项目的熔岩湖是埃塞俄比亚的Erta Ale火山。这个湖是地球最长的熔岩湖，已经活跃了100多年。它从玄武岩岩浆中分发出大量的硫。他们将收集活跃的熔岩湖，脱气的硫和大气中形成的硫酸盐气溶胶的样品。将分析熔岩，气体和气溶胶中硫的同位素组成，以了解硫循环的性质。 这项研究的最终目的是开发一个一致的模型，以了解全球火山中岩浆的硫德能够。可以测量二氧化硫的通量，因为由于其吸收紫外线，它们的大气浓度很容易被检测到。原代岩浆气体的H2S/SO2比是压力依赖性的，因此可以用作脱气深度的代理。因此，S的脱气为火山脱水过程提供了有用的见解，可以用作增加或减少火山活动的指示，并通常用于火山监测中。 硫同位素为研究岩浆的硫，脱气过程和爆发前的挥发性含量提供了强大的工具。拟议的研究是对火山脱水过程中硫同位素分馏的定量，牢固约束的评估，它将允许评估当前使用的同位素分馏模型和分级因子。该研究将测量气体和熔体的体重，熔体和气相中的S形成，所有S物种的同位素组成，并在脱气条件（例如温度和氧气的散发性）上使用测得的约束（FO2）。该研究还将评估脱气过程中的不平衡分馏。所有数据将从埃塞俄比亚Erta Ale的一贯脱气的玄武岩熔岩湖中获得。 ERTA ALE是这项研究的理想选择，因为它具有相对降低的岩浆（FO2〜QFM），高，一致的SO2通量和气体中高S含量。 Erta Ale提供了减少陆地脱胶的末端成员。这项研究的结果将与位于俯冲区设置中的火山泥层代表的氧化末端成员（QFM +1.6和高S磁通）进行比较。