Collaborative Research: Volatile sources, eruption triggers, and magma ascent rates for mafic alkaline magmas at Nyiragongo and Nyamulagira volcanoes, DR Congo, East African Rift

位于东非大裂谷的尼拉贡戈火山和尼亚穆拉吉拉火山是世界上最活跃的两座火山，它们对居住在附近的大量人口构成了重大危险。许多火山对大量人口构成巨大风险，已得到科学仪器的充分研究和高度监测，但对尼拉贡戈和尼亚穆拉吉拉火山系统的许多基本方面仍然缺乏基本了解。这项调查将通过关注以下问题来提高我们对这些系统的理解：（1）岩浆如何在两座火山下方形成;（2）火山爆发前岩浆在火山下方储存的深度和时间;（3）是什么触发了火山侧翼、人口稠密地区及其附近的火山爆发，（4）火山爆发时岩浆向地表移动的速度，以及人们在火山爆发前有多少预警时间。除了这些方面的危害，该项目将调查这些火山释放的二氧化碳的碳源。大量的碳可能储存在地球内部的固体矿物中，在像东非那样的厚而古老的大陆地壳之下，当地壳被东非裂谷那样的裂谷拉开时，碳有助于岩浆的形成。尼拉贡戈火山是世界上二氧化碳气体排放量最大的火山之一，更好地了解矿物中的碳与火山下岩浆形成之间的联系将有助于我们更好地了解地球深部的碳循环。该项目的大部分研究将由俄勒冈州大学和怀俄明州大学的研究生进行，作为他们科学培训的一部分。与刚果民主共和国戈马火山观测站的科学家合作将包括定期举行视频会议，分享对火山灾害监测十分重要的研究成果。公众参与将包括一个国家地理探险家的博客和几篇针对普通读者的关于尼拉贡戈和尼亚穆拉吉拉火山危险和火山释放二氧化碳的短文。详细地说，这个项目的主要目标是（1）了解岩石圈交代作用对尼拉贡戈和尼亚穆拉吉拉地下岩浆生成的时间综合影响，以及（2）使用这些结果作为起点，对这些火山的管道系统、岩浆储存时间尺度、喷发触发过程和岩浆上升速率进行源到表面的调查。虽然这些火山相距仅15公里，但它们的喷发行为和喷出的熔岩类型却截然不同，尼拉贡戈火山喷发的熔岩类型是地球上任何地方都能找到的最不寻常的熔岩类型。为了了解岩石圈地幔和交代脉岩浆源的作用，我们将使用现有的主要和微量元素和同位素数据，以及新的数据的挥发性含量的橄榄石托管熔融包裹体，以建立母熔体成分和源岩性。我们的数据和建模方法也将提供重要的约束母岩浆CO2和S浓度和岩浆通量为每个火山。我们拟议的工作将使用现有的火山灰和熔岩样本，并将重点放在尼拉贡戈和Nyamulagira侧翼的许多寄生锥和凝灰岩环上，因为这些火山喷发的成分比火山的中央喷口更原始。为了调查管道系统，我们将使用（1）熔体包裹体挥发性数据来确定结晶深度，（2）U系列矿物等时线来确定晶体和岩浆的停留时间，（3）矿物分区和扩散计时法来确定可能引发喷发并产生间接地震信号的补给和混合过程，（4）熔融包裹体中H的扩散损失，推测喷发过程中岩浆的上升速率，可能影响爆炸性。我们的首要目标是提供地质学上有充分依据的、最先进的地球化学和岩石学数据，以提高我们对这些火山系统的理解，从而改进灾害评估模型。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Nyiragongo and Nyamulagira, in the East African Rift, are two of the most active volcanoes in the world, and they pose major hazards to large populations living nearby. Many volcanoes that pose great risks to large populations are well studied and highly monitored with scientific instruments, but there is still a fundamental lack of understanding of many basic aspects of the Nyiragongo and Nyamulagira systems. This investigation will improve our understanding of these systems by focusing on (1) how magma forms beneath the two volcanoes, (2) how deeply and for how long magma is stored beneath the volcanoes before eruption, (3) what triggers eruptions to occur on the flanks of the volcanoes, in and near populated areas, and (4) how fast magma moves towards the surface during an eruption and how much warning time people would have in advance of an eruption. In addition to these aspects focused on hazards, this project will investigate the source of the carbon that is released as carbon dioxide by these volcanoes. Large amounts of carbon are likely stored in solid minerals inside the Earth beneath thick, old continental crust like that in East Africa, and when the crust gets pulled apart by rifting as in the East African Rift, the carbon contributes to magma formation. Nyiragongo is one of the largest emitters of carbon dioxide gas of any volcano worldwide, and better understanding the connection between carbon in minerals and magma formation beneath this volcano will help us better understand the Earth’s deep carbon cycle. Much of the research for this project will be conducted by graduate students at the University of Oregon and University of Wyoming as part of their scientific training. Collaboration with scientists at the Goma Volcano Observatory in the Democratic Republic of the Congo will include periodic videoconferences to share research results important for volcanic hazards monitoring. Public engagement will include a National Geographic Explorer’s Blog and several short articles for a general audience on volcanic hazards at Nyiragongo and Nyamulagira and release of carbon dioxide from volcanoes.In detail, the primary goals of this project are (1) to understand the time-integrated effects of lithospheric metasomatism on magma generation beneath Nyiragongo and Nyamulagira, and (2) to use the results as the starting point for a source-to-surface investigation of the plumbing systems, magma storage timescales, eruption triggering processes, and magma ascent rates for these volcanoes. Although these volcanoes are only 15 km apart, their eruption behavior and the types of lava they emit are profoundly different, with Nyiragongo erupting some of the most unusual lava types found anywhere on Earth. To understand the roles of lithospheric mantle and metasomatic veins as magma sources, we will use existing major and trace element and isotopic data together with new data on volatile contents of olivine-hosted melt inclusions to establish parental melt compositions and source lithologies. Our data and modeling approach will also provide important constraints on parental magma CO2 and S concentrations and magma fluxes for each volcano. Our proposed work will use existing tephra and lava samples and will focus on the many parasitic cones and tuff rings on the flanks of Nyiragongo and Nyamulagira, as these erupt more primitive compositions than the volcanoes’ central vents. For investigating the plumbing systems, we will use (1) melt inclusion volatile data to determine crystallization depths, (2) U-series mineral isochrons to determine crystal and magma residence times, (3) mineral zoning and diffusion chronometry to identify recharge and mixing processes that may trigger eruptions and yield precursory seismic signals, and (4) diffusive loss of H from melt inclusions to infer magma ascent rates during eruption, which likely influence explosivity. Our overarching goal is to produce geologically well-grounded, state-of-the-art geochemical and petrological data that improves our understanding of these volcanic systems and thereby improves hazard assessment models.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.