Mechanisms of nitrogen isotope fractionation at an ancient black smoker in the 2.7 Ga Abitibi greenstone belt, Canada

verfasst von

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 δ¹⁵N_bulk values as high as +23%o are associated with Cu-Zn mineralization, whereas unmineralized organic-rich shales exhibit much lower δ¹⁵N_bulk and δ¹⁵N_kerogen values. Moreover, we find a large offset between δ¹⁵N_bulk and δ¹⁵N_kerogen 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.

Organisationseinheit(en)

Institut für Mineralogie
AG Geochemie

Externe Organisation(en)

University of St. Andrews
Universität zu Köln
Oakland University
Technische Universität Kaiserslautern

Typ

Artikel

Journal

GEOLOGY

Band

52

Seiten

181-186

Anzahl der Seiten

6

ISSN

0091-7613

Publikationsdatum

01.03.2024

Publikationsstatus

Veröffentlicht

Peer-reviewed

Ja

ASJC Scopus Sachgebiete

Geologie

Ziele für nachhaltige Entwicklung

SDG 14 – Lebensraum Wasser

Elektronische Version(en)

https://doi.org/10.1130/G51689.1 (Zugang: Offen)