SGER: The 2007 - 2008 Explosive Eruption of the World's Only Active Carbonatite Volcano: Gas Emissions From Oldoinyo Lengai, Tanzania

这项探索性研究的小额赠款(SGER)是由国际科学与工程办公室和地球科学部的岩石学和地球化学计划共同发起的。这项研究将探讨世界上唯一一座目前活跃的碳酸盐岩火山Oldoinyo Lengai的岩浆和火山气体最近的地球化学变化。其喷发活动以喷流为主，喷发出极低粘度和低温(~540°C)的熔岩流。自2007年9月以来，奥多尼约伦盖进入了以剧烈爆炸为特征的新一轮火山活动。这样的爆炸性事件大约每50年才会发生一次。该项目是与坦桑尼亚科学家的全面合作，他们已经能够从这些喷发中获得样本。这些样品的成分与通常在火山喷发期间流出的熔岩有很大的不同：它含有大约20%的二氧化硅。这次SGER的结果将与2005年7月至2006年5月发生的前一次喷发事件的结果进行比较，当时该小组收集了来自Oldoinyo Lengai的火山气体，这些气体没有受到严重的空气污染。尽管熔岩与大洋中脊玄武岩(MORB)非常不同，而且赋存于远离洋脊的环境中，但气体在化学和同位素上与上地幔、大洋中脊气体难以区分。火山目前的活动将提供第一次机会来检验关于这一特定系统的一些假设。例如，有人提议测试世界上唯一的碳酸盐岩活火山现在是否正在向高硅岩浆喷发过渡，这种过渡是否伴随着来自地幔熔体的二氧化硫通量的增加并以高度爆炸性喷发为特征，以及这种过渡是否由上地幔化学和同位素组成所特有的气体排放引起。Oldoinyo Lengai是坦桑尼亚的一个主要旅游景点，因为它靠近恩戈罗陨石坑、塞伦盖蒂野生动物保护区和纳特龙湖。几个马赛村位于火山底部。每年有数百名游客攀登火山口，其中许多人在活火山的火山口露营。通过描述和更好地了解火山的爆发活动，可以更好地评估对游客和当地人口的危害，并可能更好地了解光标前的活动，就像目前的情况一样。该提案还将支持一名研究生，并进一步加强P.I.与达累斯萨拉姆大学的坦桑尼亚科学家的合作。

This Small Grant for Exploratory Research (SGER) is co-sponsored by the Office of International Science and Engineering, and the Petrology and Geochemistry program of the Division of Earth Sciences. The study will address the recent geochemical variations of magmas and volcanic gases in Oldoinyo Lengai, the only currently active carbonatite volcano in the world. Its eruptive activity is dominated by effusive eruptions that emit very low viscosity and low temperature (~540°C) lava flows. Since September 2007, Oldoinyo Lengai has entered a new episode of volcanic activity that is characterized by violent explosions. Such explosive episodes occur only about every 50 years. The project is a full collaboration with Tanzanian scientists that have been able to obtain samples from these eruptions. The composition of these samples is quite different from the lavas usually discharged during the effusive periods of the volcano: it contains approximately 20% SiO2. The results from this SGER will be compared to those of a prior eruption episode that took place between July 2005 and May 2006, when the team collected volcanic gases emanating from Oldoinyo Lengai that were not severely air contaminated. Gases are chemically and isotopically indistinguishable from upper mantle, mid-ocean-ridge gases, despite the fact that lavas are very different from mid-ocean-ridge basalts (MORB) and occur in a setting far removed from oceanic ridges. The current activity of the volcano will provide the first opportunity to test a number of hypotheses about this particular system. For instance, it is proposed to test if the world's only active carbonatite volcano is now transitioning to erupting higher-silica magmas, and if this transition is accompanied by an increase in SO2 flux from mantle-derived melts and characterized by highly explosive eruptions, and if such transition is caused by gas emissions that are characteristic of upper mantle chemical and isotopic compositions. Oldoinyo Lengai is a major tourist attraction in Tanzania as it is located close to Ngorongoro Crater, the Serengeti wildlife reserve and lake Natron. Several Massai villages are located on the base of the volcano. Hundreds of tourists climb the crater each year many of them camp in the crater of the active volcano. By characterizing and better understanding the explosive activity of the volcano, hazards to tourists and the local population can be better assessed and pre-cursor activity may be better understood as is currently the case. The proposal will also support a graduate student and further strengthen collaboration of the P.I. with Tanzanian scientists based at the University of Dar Es Salaam.