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

位于东非裂谷的尼拉贡戈火山和尼亚穆拉吉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威胁。许多对大量人口构成巨大威胁的火山都得到了很好的研究和科学仪器的高度监测，但对尼拉贡戈火山和尼亚穆拉吉拉火山系统的许多基本方面仍然缺乏根本性的了解。这次调查将通过关注(1)岩浆如何在两座火山下形成，(2)火山爆发前岩浆在火山下储存的深度和时间，(3)是什么触发了火山侧翼、人口稠密地区及其附近的喷发，以及(4)岩浆在喷发期间向地表移动的速度有多快，以及人们在喷发前有多少预警时间，来提高我们对这些系统的理解。除了这些侧重于危害的方面，该项目还将调查这些火山以二氧化碳的形式释放的碳的来源。大量的碳可能储存在地球内部的固体矿物中，在东非这样的厚而古老的大陆地壳下，当地壳像东非裂谷那样被撕裂时，碳有助于岩浆的形成。尼拉贡戈火山是世界上最大的二氧化碳排放火山之一，更好地了解火山下矿物中的碳和岩浆形成之间的联系将有助于我们更好地了解地球深处的碳循环。这个项目的大部分研究将由俄勒冈大学和怀俄明大学的研究生进行，作为他们科学训练的一部分。与刚果民主共和国戈马火山观测站的科学家的合作将包括定期召开视频会议，以分享对火山灾害监测很重要的研究成果。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观众的关于尼拉贡戈和尼亚穆拉吉拉火山危害以及火山释放二氧化碳的短篇文章。具体来说，该项目的主要目标是：(1)了解岩石圈交代作用对尼拉贡戈火山和尼亚穆拉吉拉火山岩浆生成的时间整合效应；(2)将结果作为这些火山从源头到地表的管道系统、岩浆储存时间尺度、喷发触发过程和岩浆上升速率研究的起点。虽然这些火山相距只有15公里，但它们的喷发行为和喷发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作为岩浆源的作用，我们将利用现有的主微量元素和同位素数据，以及橄榄石为主的熔融包裹体挥发性含量的新数据，建立母熔体成分和源岩性。我们的数据和建模方法也将为每个火山的母岩浆CO2和S浓度以及岩浆通量提供重要的约束。我们提出的工作将使用现有的火山和熔岩样本，并将重点放在尼拉贡戈火山和尼亚穆拉吉拉火山两侧的许多寄生锥和凝灰岩环上，因为这些火山喷发出的成分比火山中心的喷口更原始。为了研究管道系统，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停留时间，(3)矿物分带和扩散时线来确定可能触发喷发并产生前兆地震信号的补给和混合过程，以及(4)熔体包裹体的扩散损失来推断喷发期间岩浆上升速率，这可能影响爆炸性。我们的首要目标是提供地质基础良好、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，从而改进危害评估模型。该奖项反映了美国国家科学基金会的法定使命，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.