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

识别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开始和发展以分裂大陆。其中两种成分，岩浆和岩浆挥发分，不仅在大陆解体中起着关键作用，而且在大陆地壳的生长和大气演化中也起着关键作用。重要的是，地球上的大陆裂谷对岩浆作用和相关的岩浆脱气速率的约束很差，因此这项研究的主要重点是量化大陆裂谷初期阶段的岩浆和岩浆挥发分的流动。除了限制这些基本参数外，该项目的成果还将包括改进对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速度，并促进我们对地热能源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断层的流体运动过程来为地震模型提供信息，有可能导致地震危险预测的进步。为了回答这些问题，将沿着东非裂谷轴线和横跨东非裂谷轴线收集新的现场气体流量测量和岩浆二氧化碳碳同位素分析。目标地区包括肯尼亚-坦桑尼亚边境附近的曼亚拉、纳特龙和马加迪裂谷盆地，其年龄从1 Ma到7 Ma不等。通过对不同时代裂谷盆地的对比，揭示裂谷发育不同阶段挥发分脱气的轴向变化。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)联系起来，以确定挥发通量、构造变形、岩浆侵入和火山作用之间的空间联系。然后，将野外、地球化学和地球物理观测与构造伸展和岩浆过程(如侵入、冷却、结晶和脱气)的热-岩石模型模拟进行比较和对比。数值模拟情景将受到该区域各种观测数据集的约束和测试，这些数据集包括：(1)新获得的二氧化碳数据，(2)从现有的2-D和3-D地球物理模型推断的次地壳岩浆体，(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。观测结果和模拟结果的比较将使我们能够第一次限制在这种类型的裂谷发育的不同位置和阶段的岩浆流量的合理范围，以进行岩浆裂谷活动。

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.