CO₂ storage in the Antarctica Sub-Continental Lithospheric Mantle as revealed by intra- and inter-granular fluids

Autor(en)

Federico Casetta, Andrea L. Rizzo, Barbara Faccini, Theodoros Ntaflos, Rainer Abart, Gabriele Lanzafame, Luca Faccincani, Lucia Mancini, Pier Paolo Giacomoni, Massimo Coltorti

Abstrakt

The investigation of the role played by CO₂ circulating within the mantle during partial melting and metasomatic/refertilization processes, together with a re-consideration of its storage capability and re-cycling in the lithospheric mantle, is crucial to unravel the Earth's main geodynamic processes. In this study, the combination of petrology, CO₂ content trapped in bulk rock- and mineral-hosted fluid inclusions (FI), and 3D textural and volumetric characterization of intra- and inter-granular microstructures was used to investigate the extent and modality of CO₂ storage in depleted and fertile (or refertilized) Sub-Continental Lithospheric Mantle (SCLM) beneath northern Victoria Land (NVL, Antarctica). Prior to xenoliths entrainment by the host basalt, the Antarctic SCLM may have stored 0.2 vol% melt and 1.1 vol% fluids, mostly as FI trails inside mineral phases but also as inter-granular fluids. The amount of CO₂ stored in FI varies from 0.1 μg_(CO2)/g_(sample) in olivine from the anhydrous mantle xenoliths at Greene Point and Handler Ridge, up to 187.3 μg/g in orthopyroxene from the highly metasomatized amphibole-bearing lherzolites at Baker Rocks, while the corresponding bulk CO₂ contents range from 0.3 to 57.2 μg/g. Irrespective of the lithology, CO₂ partitioning is favoured in orthopyroxene and clinopyroxene-hosted FI (olivine: orthopyroxene = 0.10 ± 0.06 to 0.26 ± 0.09; olivine: clinopyroxene = 0.10 ± 0.05 to 0.27 ± 0.14). The H₂O/(H₂O + CO₂) molar ratios obtained by comparing the CO₂ contents of FI to the H₂O amount retained in pyroxene lattices vary between 0.72 ± 0.17 and 0.97 ± 0.03, which is well comparable with the values measured in olivine-hosted melt inclusions from Antarctic primary lavas and assumed as representative of the partition of volatiles at the local mantle conditions. From the relationships between mineral chemistry, thermo-, oxy-barometric results and CO₂ contents in mantle xenoliths, we speculate that relicts of CO₂-depleted mantle are present at Greene Point, representing memory of a CO₂-poor tholeiitic refertilization related to the development of the Jurassic Ferrar large magmatic event. On the other hand, a massive mobilization of CO₂ took place before the (melt-related) formation of amphibole veins during the alkaline metasomatic event associated with the Cenozoic rift-related magmatism, in response to the storage and recycling of CO₂-bearing materials into the Antarctica mantle likely induced by the prolonged Ross subduction.

Organisation(en)

Department für Lithosphärenforschung

Externe Organisation(en)

Istituto Nazionale di Fisica Nucleare (INFN), Roma, Universitá degli studi di Ferrara, Università degli Studi di Milano-Bicocca, Università degli Studi di Catania, Elettra Sincrotrone Trieste, Lund University

Journal

Lithos

Band

416-417

ISSN

0024-4937

DOI

https://doi.org/10.1016/j.lithos.2022.106643

Publikationsdatum

05-2022

Peer-reviewed

Ja

ÖFOS 2012

105120 Petrologie, 105105 Geochemie

Schlagwörter

ASJC Scopus Sachgebiete

Geology, Geochemistry and Petrology

Link zum Portal

https://ucrisportal.univie.ac.at/de/publications/ef21fec1-ee20-45aa-90bc-bf6167cbf93d