| 英文摘要: | 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. |