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Highly CO_2-supersaturated melts in the Pannonian lithospheric mantle – A transient carbon reservoir?

Créon, Laura and Rouchon, Virgile and Youssef, Souhail and Rosenberg, Elisabeth and Delpech, Guillaume and Szabó, Csaba and Remusat, Laurent and Mostefaoui, Smail and Asimow, Paul D. and Antoshechkina, Paula M. and Ghiorso, Mark S. and Boller, Elodie and Guyot, François (2017) Highly CO_2-supersaturated melts in the Pannonian lithospheric mantle – A transient carbon reservoir? Lithos, 286-287 . pp. 519-533. ISSN 0024-4937. https://resolver.caltech.edu/CaltechAUTHORS:20170525-161258053

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Abstract

Subduction of carbonated crust is widely believed to generate a flux of carbon into the base of the continental lithospheric mantle, which in turn is the likely source of widespread volcanic and non-volcanic CO_2 degassing in active tectonic intracontinental settings such as rifts, continental margin arcs and back-arc domains. However, the magnitude of the carbon flux through the lithosphere and the budget of stored carbon held within the lithospheric reservoir are both poorly known. We provide new constraints on the CO_2 budget of the lithospheric mantle below the Pannonian Basin (Central Europe) through the study of a suite of xenoliths from the Bakony-Balaton Highland Volcanic Field. Trails of secondary fluid inclusions, silicate melt inclusions, networks of melt veins, and melt pockets with large and abundant vesicles provide numerous lines of evidence that mantle metasomatism affected the lithosphere beneath this region. We obtain a quantitative estimate of the CO_2 budget of the mantle below the Pannonian Basin using a combination of innovative analytical and modeling approaches: (1) synchrotron X-ray microtomography, (2) NanoSIMS, Raman spectroscopy and microthermometry, and (3) thermodynamic models (Rhyolite-MELTS). The three-dimensional volumes reconstructed from synchrotron X-ray microtomography allow us to quantify the proportions of all petrographic phases in the samples and to visualize their textural relationships. The concentration of CO_2 in glass veins and pockets ranges from 0.27 to 0.96 wt.%, higher than in typical arc magmas (0–0.25 wt.% CO_2), whereas the H_2O concentration ranges from 0.54 to 4.25 wt.%, on the low end for estimated primitive arc magmas (1.9–6.3 wt.% H_2O). Trapping pressures for vesicles were determined by comparing CO2 concentrations in glass to CO_2 saturation as a function of pressure in silicate melts, suggesting pressures between 0.69 to 1.78 GPa. These values are generally higher than trapping pressures for fluid inclusions determined by Raman spectroscopy and microthermometry (0.1–1.1 GPa). The CO_2/silicate melt mass ratios in the metasomatic agent that percolated through the lithospheric mantle below the Pannonian Basin are estimated to be between 9.0 and 25.4 wt.%, values consistent with metasomatism either by (1) silicate melts already supersaturated in CO_2 before reaching lithospheric depths or (2) carbonatite melts that interacted with mantle peridotite to generate carbonated silicic melts. Taking the geodynamical context of the Pannonian Basin and our calculations of the CO_2/silicate melt mass ratios in the metasomatic agent into account, we suggest that slab-derived melts initially containing up to 25 wt.% of CO_2 migrated into the lithospheric mantle and exsolved CO_2–rich fluid that became trapped in secondary fluid inclusions upon fracturing of the peridotite mineral matrix. We propose a first-order estimate of 2000 ppm as the minimal bulk CO_2 concentration in the lithospheric mantle below the Pannonian Basin. This transient carbon reservoir is believed to be degassed through the Pannonian Basin due to volcanism and tectonic events, mostly focused along the lithospheric-scale regional Mid-Hungarian shear Zone.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1016/j.lithos.2016.12.009DOIArticle
http://www.sciencedirect.com/science/article/pii/S0024493716304340PublisherArticle
ORCID:
AuthorORCID
Asimow, Paul D.0000-0001-6025-8925
Antoshechkina, Paula M.0000-0002-3358-5186
Alternate Title:Highly CO2-supersaturated melts in the Pannonian lithospheric mantle – A transient carbon reservoir?
Additional Information:© 2017 Elsevier B.V. Received 22 August 2016, Accepted 8 December 2016, Available online 16 December 2016. This project was funded by IFP Energies nouvelles. The European Synchrotron Research Facility of Grenoble, the ID19 beamline team and more specifically Paul Tafforeau are thanked for their financial and technical support. The National NanoSIMS facility at the MNHN was established by funds from the CNRS, Région Ile de France, Ministère délégué à l'Enseignement supérieur et à la Recherche, and the MNHN. PDA and PMA acknowledge support by the US NSF geoinformatics program, award 1550934. We are grateful to Marie-Claude Lynch and Herman Ravelojaona for their precious assistance with X-ray tomography and sample preparations. The paper benefitted from thoughtful reviews by Andrea Giuliani and an anonymous reviewer.
Funders:
Funding AgencyGrant Number
IFP Energies nouvellesUNSPECIFIED
European Synchrotron Research Facility of GrenobleUNSPECIFIED
Centre National de la Recherche Scientifique (CNRS)UNSPECIFIED
Région Ile de FranceUNSPECIFIED
Ministère délégué à l'Enseignement supérieur et à la RechercheUNSPECIFIED
Muséum national d'Histoire naturelleUNSPECIFIED
NSFEAR-1550934
Subject Keywords:X-ray microtomography; Mantle xenoliths; CO2 budget; Lithospheric mantle
Record Number:CaltechAUTHORS:20170525-161258053
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20170525-161258053
Official Citation:Laura Créon, Virgile Rouchon, Souhail Youssef, Elisabeth Rosenberg, Guillaume Delpech, Csaba Szabó, Laurent Remusat, Smail Mostefaoui, Paul D. Asimow, Paula M. Antoshechkina, Mark S. Ghiorso, Elodie Boller, François Guyot, Highly CO2-supersaturated melts in the Pannonian lithospheric mantle – A transient carbon reservoir?, Lithos, Volumes 286–287, August 2017, Pages 519-533, ISSN 0024-4937, https://doi.org/10.1016/j.lithos.2016.12.009. (http://www.sciencedirect.com/science/article/pii/S0024493716304340)
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:77778
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:06 Jun 2017 22:19
Last Modified:29 Oct 2019 19:50

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