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δ2H of water from fluid inclusions in Proterozoic halite: Evidence for a deuterium-depleted hydrosphere?

Authors :
Lécuyer, Christophe
Fourel, François
Blamey, Nigel
Brand, Uwe
Fralick, Philip
Source :
Chemical Geology. May2020, Vol. 541, pN.PAG-N.PAG. 1p.
Publication Year :
2020

Abstract

δ2H were measured in water present in tiny primary fluid inclusions trapped in Mesoproterozoic (≈1.4 Ga) and Neoproterozoic (≈0.8 Ga) halite crystals. While the hydrogen concentrations range from 300 to 1500 ppm for the whole sample collection, δ2H values range from −74‰ to −54‰ (VSMOW) for the Mesoproterozoic halite sampled from the Sibley Group, Ontario, Canada, and from −89 to −38‰ for the Neoproterozoic halite from the Browne Formation, Officer Basin, Australia. The amount of evaporation required to precipitate halite is accompanied by a deuterium-enrichment of 30‰ to 90‰. It means that the original aqueous solutions had δ2H values comprised between −140‰ and −90‰. Considering the estimated tropical paleolatitudes for both depositional environments, surface waters were most likely significantly deuterium-depleted relative to modern ones. If such interpretation is partly at variance with the geological record, it could be reconciliated with some modelling outputs of the long-term water cycle. Indeed, several mechanisms produce a progressive deuterium-enrichment of the oceans. Those identified so far are the addition of deuterium-rich extraterrestrial water (cometary dust), the loss of H during water photodissociation by ultraviolet radiation in the upper atmosphere, and the isotopic fractionation that takes place during the hydroxylation of nominally-anhydrous mantle rock-forming minerals. We also propose that the major process able to shift through time the δ2Η of the hydrosphere is the reduction of H 2 O into H 2 during the serpentinization of mantle rocks at mid-ocean ridges. [ABSTRACT FROM AUTHOR]

Details

Language :
English
ISSN :
00092541
Volume :
541
Database :
Academic Search Index
Journal :
Chemical Geology
Publication Type :
Academic Journal
Accession number :
142699821
Full Text :
https://doi.org/10.1016/j.chemgeo.2020.119583