Massive and prolonged deep carbon emissions associated with continental rifting

TLDR: In this paper, the authors use measurements of diffuse soil CO2, combined with carbon isotopic analyses, to quantify the flux of CO2 through fault systems away from active volcanoes in the East African Rift system.

Abstract: Transfer of CO2 from Earth’s interior to the atmosphere happens largely by volcanic degassing. Measurements of CO2 emissions from faults in the East African Rift system imply that tectonic degassing is also important for deep carbon release. Carbon from Earth’s interior is thought to be released to the atmosphere mostly via degassing of CO2 from active volcanoes1,2,3,4. CO2 can also escape along faults away from active volcanic centres, but such tectonic degassing is poorly constrained1. Here we use measurements of diffuse soil CO2, combined with carbon isotopic analyses to quantify the flux of CO2 through fault systems away from active volcanoes in the East African Rift system. We find that about 4 Mt yr−1 of mantle-derived CO2 is released in the Magadi–Natron Basin, at the border between Kenya and Tanzania. Seismicity at depths of 15–30 km implies that extensional faults in this region may penetrate the lower crust. We therefore suggest that CO2 is transferred from upper-mantle or lower-crustal magma bodies along these deep faults. Extrapolation of our measurements to the entire Eastern rift of the rift system implies a CO2 flux on the order of tens of megatonnes per year, comparable to emissions from the entire mid-ocean ridge system2,3 of 53–97 Mt yr−1. We conclude that widespread continental rifting and super-continent breakup could produce massive, long-term CO2 emissions and contribute to prolonged greenhouse conditions like those of the Cretaceous.