首页|CO2 storage in the Antarctica Sub-Continental Lithospheric Mantle as revealed by intra- and inter-granular fluids
CO2 storage in the Antarctica Sub-Continental Lithospheric Mantle as revealed by intra- and inter-granular fluids
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The investigation of the role played by CO2 circulating within the mantle during partial melting and meta-somatic/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 ±.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 mantie 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.
CO2 storageSub-Continental Lithospheric MantleAlkaline metasomatismFluid inclusionsSynchrotron X-ray microtomographyInter-granular fluids
Federico Casetta、Andrea L. Rizzo、Barbara Faccini
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Department of Lithospheric Research, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria
Istituto Nazionaie di Geofisica e Vulcanologia, Sezione di Palermo, Via Ugo La Molfa 153, 90146 Palermo, Italy
Department of Physics and Earth Sciences, University of Ferrara, Via Saragat 1, 44121 Ferrara, Italy
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