Collaborative Research: Constraining the flux of magma and magmatic CO2 during early-stage rifting in East Africa

合作研究：限制东非早期裂谷期间岩浆和岩浆二氧化碳的通量

• 批准号: 1836651
• 负责人: Josef Dufek
• 金额: $ 6.71万
• 依托单位: University of Oregon Eugene
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-05-16 至 2021-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1836651&HistoricalAwards=false
• 关键词: Collaborative; Research; Constraining; flux; magma

Identifying and quantifying the key ingredients for rift initiation and evolution is fundamental to our understanding of plate tectonic theory, revealing how extensional plate boundaries initiate and develop in order to break apart continents. Two of these ingredients, magma and magmatic volatiles, play not only a critical role in continent break up, but also the growth of continental crust and atmospheric evolution. Critically, rates of magmatism and related magmatic degassing are poorly constrained for continental rifts on Earth, and thus the primary focus of this study is to quantify the flux of magma and magmatic volatiles during the initial stages of continental rifting. In addition to constraining these fundamental parameters, outcomes of this project will include refining annual estimates of natural carbon dioxide emissions, quantifying rates of magma recharge into hazardous volcanoes, and advancing our understanding of subsurface fluid movement in areas of geothermal energy potential. The outcomes of this project can also inform earthquake models by better constraining processes of fluid movements along faults, potentially leading to advances in earthquake hazard forecasts. To answer these questions, new measurements of field-based gas flux and carbon isotopes analyses of magmatic CO2 will be collected along and across the rift axis of the East African Rift. Target areas include the Manyara, Natron, and Magadi rift basins near the Kenya-Tanzania border, which range in age from 1 to 7 Ma. By comparing rift basins of different ages, we will illuminate along-axis changes in volatile degassing at different stages of rift development through time. An important goal is to place these findings in context with existing observations (e.g., geophysical, geochemical, geodetic) of key rifting processes to identify spatial links between volatile flux, tectonic deformation, magma intrusion, and volcanism. Field, geochemical, and geophysical observations will then be compared and contrasted with thermal-petrographic model simulations of tectonic extension and magmatic processes (e.g., intrusion, cooling, crystallization, and degassing). Numerical modeling scenarios will be constrained by, and tested against, the full range of observational datasets in the region, including: (1) newly acquired CO2 data, (2) sub-crustal magma bodies inferred from existing 2-D and 3-D geophysical models, (3) chemistry and phase equilibria of erupted products, (4) thermal state of the crust, and (5) crustal thinning. Comparisons between observations and modeling results will allow us to constrain, for the first time, the plausible range of magma fluxes at various locations and stages of rift development at this type locality for active magmatic rifting.

确定和量化裂谷形成和演化的关键因素是我们理解板块构造理论的基础，揭示了伸展板块边界如何形成和发展，以分裂大陆。岩浆和岩浆挥发分不仅在大陆裂解过程中起着重要作用，而且在陆壳生长和大气演化过程中也起着重要作用。关键是，岩浆活动和相关的岩浆脱气率在地球上的大陆裂谷中受到很大的限制，因此本研究的主要重点是量化大陆裂谷初始阶段的岩浆和岩浆挥发物的通量。除了限制这些基本参数外，该项目的成果还将包括改进天然二氧化碳排放量的年度估计，量化岩浆向危险火山的补给率，并提高我们对地热能潜力地区地下流体运动的理解。该项目的成果还可以通过更好地约束沿沿着的流体运动过程来为地震模型提供信息，从而可能导致地震灾害预测的进步。为了回答这些问题，将收集沿着和横跨东非裂谷的裂谷轴的新的基于场的气体通量测量和岩浆CO2的碳同位素分析。目标区域包括肯尼亚-坦桑尼亚边界附近的马尼亚拉、纳特龙和马加迪裂谷盆地，这些盆地的年龄范围为1 - 7 Ma。通过对不同时代裂谷盆地的对比，阐明了裂谷发展不同阶段挥发分脱气作用随时间的轴向变化。一个重要目标是将这些发现与现有观察结果结合起来（例如，地球物理学、地球化学、大地测量学），以确定挥发性通量、构造变形、岩浆侵入和火山活动之间的空间联系。然后，将实地、地球化学和地球物理观测结果与构造伸展和岩浆过程的热岩相模型模拟进行比较和对比（例如，侵入、冷却、结晶和脱气）。数值模拟方案将受到该地区所有观测数据集的约束，并根据这些数据集进行测试，这些数据集包括：（1）新获得的二氧化碳数据，（2）从现有二维和三维地球物理模型推断的地壳下岩浆体，（3）喷发产物的化学和相平衡，（4）地壳的热状态，以及（5）地壳减薄。观测和建模结果之间的比较将使我们能够约束，第一次，合理的范围内的岩浆通量在不同的位置和阶段的裂谷发展在这种类型的地方活跃的岩浆裂谷。

项目成果

Displaced cratonic mantle concentrates deep carbon during continental rifting

• DOI: 10.1038/s41586-020-2328-3
• 发表时间: 2020-06
• 期刊: Nature
• 影响因子: 64.8
• 作者: J. Muirhead;T. Fischer;S. Oliva;A. Laizer;J. V. van Wijk;C. Currie;Hyunwoo Lee;E. Judd;E. Kazimoto;Y. Sano;N. Takahata;C. Tiberi;S. Foley;J. Dufek;M. Reiss;C. Ebinger