EGU2020-16794, updated on 12 Jun 2020
https://doi.org/10.5194/egusphere-egu2020-16794
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Geochemistry of basic magmatism of Western Antarctic Rift: implications for volatiles storage and recycling in the mantle

Pier Paolo Giacomoni1, Carmelo Ferlito2, Costanza Bonadiman1, Federico Casetta1, Luisa Ottolini3, Alberto Zanetti3, and Massimo Coltorti1
Pier Paolo Giacomoni et al.
  • 1Department of Physics and Earth Science, University of Ferrara, Ferrara, Italy (gcmppl@unife.it)
  • 2Department of Biological, Environmental and Geological Sciences, University of Catania, Catania, Italy
  • 3Institute of Geoscience and Georesources-CNR, Pavia (Italy)

The petrologic study of olivine-hosted melt inclusions (MIs) from alkaline primary Cenozoic basalts of Northern Victoria Land (Antarctica) provide new insights on the role of volatiles in the onset of rift-related magmatism. The concentration of volatile species (H2O, CO2, F, Cl) have been determined by Secondary Ion Mass Spectrometry (SIMS) on a selection of MIs which have been previously re-homogenized at high pressure and temperature conditions in order to avoid any heterogeneity and reducing the H diffusion. The least differentiated MIs vary in composition from basanitic to alkaline basalts, analogously to what is found in McMurdo volcanics, while their volatile concentrations reach up to 2.64 wt% H2O, 3900 ppm CO2, 1377 ppm F and 1336 Cl. Taking into account the most undegassed MIs a H2O/(H2O+CO2) ratio equal to 0.88 was determined, which in turn brings the CO2 content in the basanitic melt with the highest water content up to 8800 ppm.

Major and trace element melting modelling indicate that basanite and alkali basalt composition can be reproduced by 3 and 7% of partial melting of an amphibole-bearing spinel lherzolite respectively. Assuming a perfect incompatible behavior for H2O and CO2 these melting proportions allow to constrain the water and CO2 contents in the mantle source in the range 780-840 and 264-273 ppm respectively. The resulting CO2/Nb, CO2/Ba and H2O/Ce ratio are lower than those estimated for Depleted MORB Mantle (DMM), suggesting that the NVL Cenozoic alkaline magmatism could be originated by an enriched mantle source composed by a range from 70% to 60% of Enriched Mantle (EM) and from 30% to 40% of Depleted Morb Mantle (DMM).

A global comparison of fluid-related, highly incompatible and immobile/low incompatible elements such as Li, K, Cl, Ba, Nb, Dy and Yb allow to put forward that the prolonged (~500 to 100 Ma) Ross subduction event played a fundamental role in  providing the volatile budget into the lithospheric mantle before the onset of the Cenozoic continental rifting.

How to cite: Giacomoni, P. P., Ferlito, C., Bonadiman, C., Casetta, F., Ottolini, L., Zanetti, A., and Coltorti, M.: Geochemistry of basic magmatism of Western Antarctic Rift: implications for volatiles storage and recycling in the mantle, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16794, https://doi.org/10.5194/egusphere-egu2020-16794, 2020