Mechanisms of nitrogen isotope fractionation at an ancient black smoker in the 2.7 Ga Abitibi greenstone belt, Canada
- authored by
- A. N. Martin, E. E. Stüeken, J. A.S. Michaud, C. Münker, S. Weyer, E. H.P. van Hees, M. M. Gehringer
- Abstract
The biological nitrogen (N) cycle on early Earth is enigmatic because of limited data from Archean (meta-)sediments and the potential alteration of primary biotic signatures. Here we further investigate unusual 15N enrichments reported in 2.7 Ga meta-sediments from the Abitibi greenstone belt, Canada, purportedly related to a 15N-enriched Archean atmosphere. Given that sediments from this region are contemporaneous with large-scale volcanogenic massive sulfide deposits, we utilize Cu and Zn contents to trace the effects of hydrothermal circulation on N isotope fractionation. We show that high δ15Nbulk values as high as +23%o are associated with Cu-Zn mineralization, whereas unmineralized organic-rich shales exhibit much lower δ15Nbulk and δ15Nkerogen values. Moreover, we find a large offset between δ15Nbulk and δ15Nkerogen of as much as 17%o and relate this to the addition of organic-bound N during the late-stage emplacement of organic-rich veins. We conclude that the previously reported high δ15N values are most parsimoniously explained by biotic and abiotic mechanisms rather than a 15N-enriched atmosphere. Crucially, both mechanisms require the presence of NH4+ in hydrothermal fluids, supporting the hypothesis that hydrothermal discharge was an important nutrient source for Neoarchean marine life.
- Organisation(s)
-
Institute of Mineralogy
Geochemistry
- External Organisation(s)
-
University of St. Andrews
University of Cologne
Oakland University
University of Kaiserslautern
- Type
- Article
- Journal
- GEOLOGY
- Volume
- 52
- Pages
- 181-186
- No. of pages
- 6
- ISSN
- 0091-7613
- Publication date
- 01.03.2024
- Publication status
- Published
- Peer reviewed
- Yes
- ASJC Scopus subject areas
- Geology
- Sustainable Development Goals
- SDG 14 - Life Below Water
- Electronic version(s)
-
https://doi.org/10.1130/G51689.1 (Access:
Open)
