title: Clues from Fe isotope variations on the origin of early Archean BIFs from Greenland.
abstract: Archean rocks may provide a record of early Earth environments. However, such rocks have often been metamorphosed by high pressure and temperature, which can overprint the signatures of their original formation. Here, we show that the early Archean banded rocks from Isua, Akilia, and Innersuartuut, Greenland, are enriched in heavy iron isotopes by 0.1 to 0.5 per mil per atomic mass unit relative to igneous rocks worldwide. The observed enrichments are compatible with the transport, oxidation, and subsequent precipitation of ferrous iron emanating from hydrothermal vents and thus suggest that the original rocks were banded iron formations (BIFs). These variations therefore support a sedimentary origin for the Akilia banded rocks, which represent one of the oldest known occurrences of water-laid deposits on Earth.
authors.affiliation: Origins Laboratory, Department of the Geophysical Sciences, and Enrico Fermi Institute, University of Chicago, 5734 South Ellis Avenue, Chicago, IL 60637, USA. dauphas@uchicago.edu
authors.forename: Nicolas
authors.initials: N
authors.lastname: Dauphas
authors.forename: Mark
authors.initials: M
authors.lastname: van Zuilen
authors.forename: Meenakshi
authors.initials: M
authors.lastname: Wadhwa
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Davis
authors.forename: Bernard
authors.initials: B
authors.lastname: Marty
authors.forename: Philip E
authors.initials: PE
authors.lastname: Janney