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

Fredrik Sahlström, Valentin R. Troll, Sabina Strmić Palinkaš, Ellen Kooijman, Xin Yuan Zheng

Research output: Contribution to journalArticlepeer-review

Abstract

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°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‰) to the δ56Fe signature of dissolved iron released from TAG into the North Atlantic Ocean. Texturally distinct types of pyrite, in turn, preserve a δ56Fe range from −1.27 to +0.56‰ 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.

Original languageEnglish (US)
Article number193
JournalCommunications Earth and Environment
Volume3
Issue number1
DOIs
StatePublished - Dec 2022

Bibliographical note

Funding Information:
The authors would like to thank Karin Wallner and Melanie Kielman-Schmitt for assistance during iron isotope analysis at Vegacenter. Keiko Hattori, Jeff Hedenquist, and Antonio Arribas gave helpful advice on sample preparation methods. We further thank the International Ocean Discovery Program (IODP) for providing the TAG drill core samples. Generous funding from Equinor (Akademiaavtale project A31687) and Vetenskapsrådet (grant number 2020-03789) is gratefully acknowledged. This is Vegacenter publication #056.

Funding Information:
The authors would like to thank Karin Wallner and Melanie Kielman-Schmitt for assistance during iron isotope analysis at Vegacenter. Keiko Hattori, Jeff Hedenquist, and Antonio Arribas gave helpful advice on sample preparation methods. We further thank the International Ocean Discovery Program (IODP) for providing the TAG drill core samples. Generous funding from Equinor (Akademiaavtale project A31687) and Vetenskapsrådet (grant number 2020-03789) is gratefully acknowledged. This is Vegacenter publication #056.

Publisher Copyright:
© 2022, The Author(s).

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