Iron isotopes constrain sub-seafloor hydrothermal processes at the Trans-Atlantic Geotraverse (TAG) active sulfide mound

• Published in: Communications Earth & Environment
• Main Authors: Sahlström, Fredrik, Troll, Valentin R., Palinkas, Sabina Strmic, Kooijman, Ellen, Zheng, Xin-Yuan
• Format: Article in Journal/Newspaper
• Language: English
• Published: Uppsala universitet, Naturresurser och hållbar utveckling 2022
• Subjects: Oceanography; Hydrology and Water Resources; Oceanografi; hydrologi och vattenresurser; Geology; Geologi; Mid-Atlantic Ridge; North Atlantic
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-484212; https://doi.org/10.1038/s43247-022-00518-2

Iron isotopic equilibration at the Trans-Atlantic Geotraverse hydrothermal field takes place over tens of thousands of years, with variable degrees of hydrothermal maturation throughout the active mound, according to iron isotope analyses of sulfide minerals. Sub-seafloor hydrothermal processes along volcanically active plate boundaries are integral to the formation of seafloor massive sulfide deposits and to oceanic iron cycling, yet the nature of their relationship is poorly understood. Here we apply iron isotope analysis to sulfide minerals from the Trans-Atlantic Geotraverse (TAG) mound and underlying stockwork, 26 degrees N Mid-Atlantic Ridge, to trace hydrothermal processes inside an actively-forming sulfide deposit in a sediment-free mid-ocean ridge setting. We show that data for recently formed chalcopyrite imply hydrothermal fluid-mound interactions cause small negative shifts (<-0.1 parts per thousand) to the delta Fe-56 signature of dissolved iron released from TAG into the North Atlantic Ocean. Texturally distinct types of pyrite, in turn, preserve a delta Fe-56 range from -1.27 to +0.56 parts per thousand that reflects contrasting precipitation mechanisms (hydrothermal fluid-seawater mixing vs. conductive cooling) and variable degrees of progressive hydrothermal maturation during the >20 kyr evolution of the TAG complex. The identified processes may explain iron isotope variations found in fossil onshore sulfide deposits.