Redox estimates through trace elements partitioning: application on two Italian volcanoes, model comparison and overview on different geodynamic environments

Oxygen fugacity of Earth’s mantle is one of the most debated issues of petrology. While is evident that the arc-related magmas are more oxidized than MORB and intraplate magmas, however, is not yet possible to produce a model that can uniquely determine this thermodynamic parameter for the depth of the Earth. Furthermore, there is not a clear cause that create this difference of redox conditions between volcanic products. Recently, several experimental models based on the V partitioning between olivine and mafic melt were published and proposed as tools for investigating the redox state of mantle melts for different geodynamic environments. During this PhD we have applied different oxybarometers on natural products, including many V-fO2 models, in order to compute the redox state of some volcanic products and compare the results obtained from different oxybarometers. Here, we selected Mt. Etna and Ischia island in order to investigate the redox conditions of an intraplate and a subduction-related magmatism. Samples were selected from the most primitive eruptions from both volcanoes (FS eruption, for Mt. Etna and Vateliero Thepra for Ischia). Melt inclusions and relative host olivines major elements were analyzed using EMPA, while trace elements were measured using LA ICP-MS. Finally, we studied Hyblean xenoliths from literature data. The chosen volcanic systems have been studied in the past, and our results are in good agreement with literature data. This evidence allows us to propose V-oxybarometers as strong tools for the redox computing. Moreover, the relationship between some trace element ratios and the computed redox state leads to support the hypothesis that address the cause of the different redox state of intraplate and arc primary magmas to contamination of the magmatic source. This hypothesis is in contrast with studies which address the different redox state due to magma evolution processes.