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形成和发展，以分裂大陆。其中两种成分，岩浆和岩浆挥发物，不仅在大陆分裂中起着关键作用，而且对大陆地壳的生长和大气演化也起着重要作用。重要的是，地球上的大陆裂谷对岩浆活动和相关岩浆脱气速率的限制很差，因此本研究的主要重点是量化大陆裂谷初始阶段岩浆和岩浆挥发物的通量。除了限制这些基本参数外，该项目的成果将包括改进自然二氧化碳排放量的年度估计，量化岩浆重新进入危险火山的速度，并提高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，从而可能导致地震危险预测的进步。为了回答这些问题，将沿着东非裂谷的裂谷轴收集新的野外气体通量测量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Manyara、Natron和Magadi裂谷盆地，年龄范围为1 - 7 Ma。通过对不同时代裂谷盆地的对比，阐明裂谷发育不同阶段挥发性脱气的沿轴变化规律。一个重要的目标是将这些发现与关键裂陷过程的现有观测（例如地球物理、地球化学、大地测量）结合起来，以确定挥发性通量、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）的热岩相模型模拟进行比较和对比。数值模拟情景将受到该地区全部观测数据集的约束和检验，包括：(1)新获得的CO2数据，(2)从现有的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)地壳热状态，以及(5)地壳变薄。将观测结果与模拟结果进行比较，将使我们第一次能够限制在这种类型地区的活跃岩浆裂谷的不同位置和裂谷发育阶段的岩浆通量的合理范围。

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.