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

• Published in: Lithos
• Main Authors: Casetta, Federico, Rizzo, Andrea L., Faccini, Barbara, Ntaflos, Theodoros, Abart, Rainer, Lanzafame, Gabriele, Faccincani, Luca, Mancini, Lucia, Giacomoni, Pier Paolo, Coltorti, Massimo
• Other Authors: Casetta, F, Rizzo, A, Faccini, B, Ntaflos, T, Abart, R, Lanzafame, G, Faccincani, L, Mancini, L, Giacomoni, P, Coltorti, M
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier BV 2022
• Subjects: Alkaline metasomatism; CO2 storage; Fluid inclusion; Inter-granular fluid; Sub-Continental Lithospheric Mantle; Synchrotron X-ray microtomography; Antarc*; Antarctic; Antarctica; Victoria Land
• Online Access: https://hdl.handle.net/10281/428289; https://doi.org/10.1016/j.lithos.2022.106643

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 ...