The Archean Earth as constrained by stable isotopes of transition metal (Zn, Fe)

• Main Author: Pons, Marie-Laure
• Other Authors: Laboratoire de Géologie de Lyon - Terre, Planètes, Environnement (LGL-TPE), École normale supérieure de Lyon (ENS de Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Institut national des sciences de l'Univers (INSU - CNRS)-Université Jean Monnet - Saint-Étienne (UJM)-Centre National de la Recherche Scientifique (CNRS), Ecole normale supérieure de lyon - ENS LYON, Francis Albarède
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2011
• Subjects: Geochemistry; Stable isotopes; Archean; Early Earth; Early life; Zinc; Serpentinites; Isua; Banded iron formations; Géochimie; Isotopes stables; Archéen; Terre primitive; Vie primitive; Serpentinite; Formations de fer rubané; [SDU.STU]Sciences of the Universe [physics]/Earth Sciences; Greenland
• Online Access: https://theses.hal.science/tel-00682665; https://theses.hal.science/tel-00682665/document; https://theses.hal.science/tel-00682665/file/PONS_MarieLaure_2011_These.pdf

During the Archean (4 to 2.5 Ga ago), the Earth experienced the biggest changes in terms of geological and biological settings – continental growth, transition from sagduction towards purely horizontal plate tectonics, emergence of life, … The purpose of the present study is to better understand the archean earth environment by measuring the isotopic composition of transition metals – Zn, Fe – of archean rocks. Most of the samples belong to the Isua supracrustal belt, in Greenland, dated 3.8 Ga. The chemical extraction protocol of Fe, Cu, Zn was adapted to our Fe-rich samples and isotopic analyses were conducted by multicollection inductively coupled plasma mass spectrometry. The serpentinization of the oceanic crust produces fuels for life (CH 4 , H 2 ) and mackinawite, which catalyses formation of complex organic compounds. Serpentinization may thus provide a suitable environment for the emergence of the first biomolecules. We analysed the oldest known serpentinites from Isua (3.81-3.70 Ga) to comprehend the archean serpentinization process. The isotopic compositions of zinc reported in this samples and in modern serpentinites attest to a strong similarity between Isua and the Mariana serpentinite mud volcanoes. We identified Isua as an oceanic forearc environment permeated by high-pH (9-12) hydrothermal solutions at medium temperature (100-300°C). We show that such an environment could have fostered the emergence of early life. We also analyzed several banded iron formations (BIF), which are sediments limited to the Archean and Proterozoic. The temporal evolution of these samples' isotopic composition shows a close relationship with the continental freeboard. Our results support the continental emersion starting 2.9 Ga ago. Besides, we identified the life colonization of continents at 2.6 Ga together with pedogenesis of archean soils with an organic horizon. L’Archéen, de 4 à 2,5 Ga, est la période qui a connu les plus grands bouleversements géologiques et biologiques de l’histoire de la Terre : formation ...