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Volcanic outgassing rates for a stagnant lid Archean Earth: results from a coupled mantle convection, melt partitioning, and volatile speciation model

Guimond, C.M. and Noack, L. and Ortenzi, G. and Sohl, F. (2021) Volcanic outgassing rates for a stagnant lid Archean Earth: results from a coupled mantle convection, melt partitioning, and volatile speciation model. Goldschmidt Conference 2021, 2021-07-04 -- 2021-07-09, Lyon, France (virtuelle Konferenz).

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Abstract

Understanding how the Archean atmosphere evolved requires constraining mantle outgassing rates, for which observational proxies are rare and not unambiguous, yet for which modelling efforts depend quite strongly on both the presumed tectonic regime and the mantle oxygen fugacity (fO2). In particular, switching from a stagnant lid to a mobile lid regime could raise outgassing rates by an order of magnitude. However, Archean climate models will still often adopt outgassing rates in line with modern plate tectonics, despite the contested timeline of plate tectonics onset. To provide a counterbalance, we have modelled early Earth’s C-O-H outgassing if global plate tectonics had not yet initiated and if all outgassing were subaerial, for a wide range of mantle fO2, extrusive-to-intrusive volcanism ratios, and initial conditions. Our numerical model couples 2D compressible mantle convection, redox partitioning in the melt, and volatile chemical speciation. Out of the input parameters studied, mantle fO2 shows the largest effect on the gas fluxes of individual species because it controls both the volatile speciation and (for carbon) the partitioning in the melt. Hence virtually no CO2 would be outgassed below the iron-wüstite mineral redox buffer: in such reducing conditions, (i) carbonate can only partition into the melt in very limited amounts, and (ii) almost all carbon takes the form of CO instead of CO2. In contrast, the partitioning of water in the melt depends on its mantle source concentration, so the initial water budget has a non-negligible effect on H2O and H2 outgassing rates. Overall, our stagnant lid model finds average CO2 outgassing rates of not more than ~1 Tmol/yr, even for oxidized scenarios near the quartz-fayalite-magnetite buffer. This could imply that any reliance on a massive CO2 greenhouse to warm the early Earth might also contain a statement about either the survival of a primary atmosphere or the contemporaneous tectonic regime.

Item URL in elib:https://elib.dlr.de/146204/
Document Type:Conference or Workshop Item (Speech)
Title:Volcanic outgassing rates for a stagnant lid Archean Earth: results from a coupled mantle convection, melt partitioning, and volatile speciation model
Authors:
AuthorsInstitution or Email of AuthorsAuthor's ORCID iD
Guimond, C.M.Department of Earth Sciences, Bullard Laboratories, University of Cambridge, Madingley Rise, Cambridge CB3 0EZ, United KingdomUNSPECIFIED
Noack, L.Department of Earth Sciences, Freie Universitat Berlin, Malteserstraβe 74-100, 12249, Berlin, GermanyUNSPECIFIED
Ortenzi, G.gianluigi.ortenzi (at) dlr.deUNSPECIFIED
Sohl, F.frank.sohl (at) dlr.dehttps://orcid.org/0000-0003-0355-1556
Date:6 July 2021
Refereed publication:No
Open Access:No
Gold Open Access:No
In SCOPUS:No
In ISI Web of Science:No
Status:Published
Keywords:Early Earth, volcanic outgassing, mantle convection, stagnant lid, melt partitioning, redox state, volatile chemical speciation, solubility
Event Title:Goldschmidt Conference 2021
Event Location:Lyon, France (virtuelle Konferenz)
Event Type:international Conference
Event Dates:2021-07-04 -- 2021-07-09
Organizer:Geochemical Society and the European Association of Geochemistry
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Space
HGF - Program Themes:Space Exploration
DLR - Research area:Raumfahrt
DLR - Program:R EW - Space Exploration
DLR - Research theme (Project):R - Exploration of the Solar System
Location: Berlin-Adlershof
Institutes and Institutions:Institute of Planetary Research > Planetary Physics
Deposited By: Sohl, Frank
Deposited On:26 Nov 2021 07:21
Last Modified:26 Nov 2021 07:21

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