A Polyextreme Hydrothermal System Controlled by Iron: The Case of Dallol at the Afar Triangle Kotopoulou, Electra Delgado Huertas, Antonio García Ruiz, Juan Manuel Domínguez Vera, José Manuel López García, José María Guerra Tschuschke, Isabel Iron oxidation Hyperacidic Hydrothermal Polyextreme One of the latest volcanic features of the Erta Ale range at the Afar Triangle (NE Ethiopia) has created a polyextreme hydrothermal system located at the Danakil depression on top of a protovolcano known as the dome of Dallol. The interaction of the underlying basaltic magma with the evaporitic salts of the Danakil depression has generated a unique, high-temperature (108 °C), hypersaline (NaCl supersaturated), hyperacidic (pH values from 0.1 to −1.7), oxygen-free hydrothermal site containing up to 150 g/L of iron. We find that the colorful brine pools and mineral patterns of Dallol derive from the slow oxygen diffusion and progressive oxidation of the dissolved ferrous iron, the iron-chlorine/-sulfate complexation, and the evaporation. These inorganic processes induce the precipitation of nanoscale jarosite-group minerals and iron(III)- oxyhydroxides over a vast deposition of halite displaying complex architectures. Our results suggest that life, if present under such conditions, does not play a dominant role in the geochemical cycling and mineral precipitation at Dallol as opposed to other hydrothermal sites. Dallol, a hydrothermal system controlled by iron, is a present-day laboratory for studying the precipitation and progressive oxidation of iron minerals, relevant for geochemical processes occurring at early Earth and Martian environments 2020-02-06T09:57:11Z 2020-02-06T09:57:11Z 2019 journal article Kotopoulou, E., Delgado Huertas, A., Garcia-Ruiz, J. M., Dominguez-Vera, J. M., Lopez-Garcia, J. M., Guerra-Tschuschke, I., & Rull, F. (2018). A Polyextreme hydrothermal system controlled by iron: the case of Dallol at the Afar triangle. ACS Earth and Space Chemistry, 3(1), 90-99. http://hdl.handle.net/10481/59480 10.1021/acsearthspacechem.8b00141 eng http://creativecommons.org/licenses/by/3.0/es/ open access Atribución 3.0 España American Chemical Society