title: Early Archean serpentine mud volcanoes at Isua, Greenland, as a niche for early life.
abstract: The Isua Supracrustal Belt, Greenland, of Early Archean age (3.81-3.70 Ga) represents the oldest crustal segment on Earth. Its complex lithology comprises an ophiolite-like unit and volcanic rocks reminiscent of boninites, which tie Isua supracrustals to an island arc environment. We here present zinc (Zn) isotope compositions measured on serpentinites and other rocks from the Isua supracrustal sequence and on serpentinites from modern ophiolites, midocean ridges, and the Mariana forearc. In stark contrast to modern midocean ridge and ophiolite serpentinites, Zn in Isua and Mariana serpentinites is markedly depleted in heavy isotopes with respect to the igneous average. Based on recent results of Zn isotope fractionation between coexisting species in solution, the Isua serpentinites were permeated by carbonate-rich, high-pH hydrothermal solutions at medium temperature (100-300 °C). Zinc isotopes therefore stand out as a pH meter for fossil hydrothermal solutions. The geochemical features of the Isua fluids resemble the interstitial fluids sampled in the mud volcano serpentinites of the Mariana forearc. The reduced character and the high pH inferred for these fluids make Archean serpentine mud volcanoes a particularly favorable setting for the early stabilization of amino acids.
authors: Ecole Normale Supérieure, Université Claude Bernard Lyon 1, and Centre National de la Recherche Scientifique, 69007 Lyon, France.
authors: Marie-Laure
authors: ML
authors: Pons
authors: Ghylaine
authors: G
authors: Quitté
authors: Toshiyuki
authors: T
authors: Fujii
authors: Minik T
authors: MT
authors: Rosing
authors: Bruno
authors: B
authors: Reynard
authors: Frederic
authors: F
authors: Moynier
authors: Chantal
authors: C
authors: Douchet
authors: Francis
authors: F
authors: Albarède
mesh_terms: D000596:Amino Acids; D005591:Chemical Fractionation; D006116:Greenland; D049690:History, Ancient; D006863:Hydrogen-Ion Concentration; D058085:Iron Compounds / Q000737:chemistry; D017633:Magnesium Silicates / Q000737:chemistry; D008854:Microscopy, Electron; D012987:Soil / Q000737:chemistry*; D018707:Volcanic Eruptions / Q000266:history*; D015033:Zinc Isotopes / Q000737:chemistry
chemical_list: D000596:Amino Acids; D058085:Iron Compounds; D017633:Magnesium Silicates; D012987:Soil; D015033:Zinc Isotopes