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: 1654433
• 负责人: Tobias Fischer
• 金额: $ 9.55万
• 依托单位: University of New Mexico
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-07-01 至 2022-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1654433&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.

识别和量化裂谷起始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起始和发展以分裂大陆。其中两种成分，岩浆和岩浆挥发物，不仅在大陆破裂中发挥着关键作用，而且在大陆地壳的生长和大气演化中发挥着关键作用。至关重要的是，地球上大陆裂谷的岩浆活动和相关岩浆脱气速率受到的限制很少，因此本研究的主要重点是量化大陆裂谷初始阶段的岩浆通量和岩浆挥发物。除了限制这些基本参数外，该项目的成果还将包括完善对自然二氧化碳排放量的年度估计，量化危险火山的岩浆补给率，以及增进我们对地热能潜力区域地下流体运动的了解。该项目的成果还可以通过更好地约束沿断层的流体运动过程来为地震模型提供信息，从而有可能推动地震灾害预测的进步。为了回答这些问题，将沿着东非裂谷的裂谷轴收集现场气体通量的新测量数据和岩浆二氧化碳的碳同位素分析。目标区域包括肯尼亚-坦桑尼亚边境附近的曼雅拉、纳特龙和马加迪裂谷盆地，其年龄范围为 1 至 7 Ma。通过比较不同年代的裂谷盆地，我们将阐明裂谷发育不同阶段挥发分脱气随时间的沿轴变化。一个重要的目标是将这些发现与关键裂谷过程的现有观测（例如地球物理、地球化学、大地测量）结合起来，以确定挥发通量、构造变形、岩浆侵入和火山活动之间的空间联系。然后将现场、地球化学和地球物理观测与构造伸展和岩浆过程（例如侵入、冷却、结晶和脱气）的热岩模型模拟进行比较和对比。数值建模方案将受到该地区全方位观测数据集的约束和测试，包括：(1) 新获取的二氧化碳数据，(2) 从现有 2-D 和 3-D 推断的地壳下岩浆体地球物理模型，（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。观测结果和模拟结果之间的比较将使我们能够首次限制这种活跃岩浆裂谷类型地点不同位置和裂谷发育阶段的岩浆通量的合理范围。

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

Earth’s Volatile Balancing Act

地球的波动平衡法

• DOI: 10.1029/2021eo155887
• 发表时间: 2021
• 期刊: Eos
• 作者: Muirhead, James;Naif, Samer;Fischer, Tobias;Shillington, D.
• 通讯作者: Shillington, D.

Focussed degassing of stored continental deep carbon

大陆深部碳的集中脱气

• 发表时间: 2019
• 期刊: American Geophysical Union Fall meeting
• 作者: FISCHER, T;MUIRHEAD, J;SANO, Y;TAKAHATA, N.;LAIZER, A.;KAZIMOTO, E.;OLIVA, S.;EBINGER, C.;VAN WIJK, WERNER;AIUPPA, A.
• 通讯作者: AIUPPA, A.