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Spatially Variable CO 2 Degassing in the Main Ethiopian Rift: Implications for Magma Storage, Volatile Transport, and Rift‐Related Emissions

2017; Wiley; Volume: 18; Issue: 10 Linguagem: Inglês

10.1002/2017gc006975

1525-2027

Jonathan A. Hunt, A. Zafu, Tamsin A. Mather, David M. Pyle, Peter H. Barry,

earthquake and tectonic studies

Abstract Deep carbon emissions from historically inactive volcanoes, hydrothermal, and tectonic structures are among the greatest unknowns in the long‐term (∼Myr) carbon cycle. Recent estimates of diffuse CO 2 flux from the Eastern Rift of the East African Rift System (EARS) suggest this could equal emissions from the entire mid‐ocean ridge system. We report new CO 2 surveys from the Main Ethiopian Rift (MER, northernmost EARS), and reassess the rift‐related CO 2 flux. Since degassing in the MER is concentrated in discrete areas of volcanic and off‐edifice activity, characterization of such areas is important for extrapolation to a rift‐scale budget. Locations of hot springs and fumaroles along the rift show numerous geothermal areas away from volcanic edifices. With these new data, we estimate total CO 2 emissions from the central and northern MER as 0.52–4.36 Mt yr −1 . Our extrapolated flux from the Eastern Rift is 3.9–32.7 Mt yr −1 CO 2 , overlapping with lower end of the range presented in recent estimates. By scaling, we suggest that 6–18 Mt yr −1 CO 2 flux can be accounted for by magmatic extension, which implies an important role for volatile‐enriched lithosphere, crustal assimilation, and/or additional magmatic intrusion to account for the upper range of flux estimates. Our results also have implications for the nature of volcanism in the MER. Many geothermal areas are found >10 km from the nearest volcanic center, suggesting ongoing hazards associated with regional volcanism.