Publication Date:
2024-01-12
Description:
The study of the oxidation state of lithospheric mantle-derived rocks allows modelling the deep cycle of volatiles
(e.g., C, H, O, N and S) in the Earth’s interior, which in turn plays a role in magma genesis, metasomatism and
volcanic degassing. At the oxygen fugacity (i.e., fO2) recorded by residual abyssal peridotites, volatile elements
like carbon are predicted to be in the immobile form of graphite. However, the compilation of the redox state of
worldwide-distributed continental xenoliths shows evidence of their oxidation and refertilization through time
by deeply formed subduction-related metasomatic fluids. The analyses of fluid inclusions in mantle-derived
minerals like olivine (or pyroxenes) represent a snapshot of the volatile circulation in depth, whose noble
gases signature (He, Ar, Ne) is used to identify their possible source. This study aims to reconstruct the origin of
mantle metasomatism underneath the Hyblean Plateau (Sicily, Italy) and its redox history through the investigation of spinel-peridotite nodules, combining fO2 estimates with noble gases and fluid inclusions chemistry from hand-picked olivine grains. We analyzed eight mantle xenoliths classified as spinel lherzolites and spinel harzburgites from the Valle Guffari (Hyblean Plateau, Sicily). The calculated logfO2 is higher than that of most cratonic xenoliths worldwide ranging between 0.28 and 1.27 log units above to the fayalite-magnetite-quartz (FMQ) reference buffer. Micro-Raman measurements on olivine grains with dendritic trails of (metasomatic) fluid inclusions reveal an assemblage made of Mg-Ca carbonates ± sulfide ± elemental sulfur ± CO2 in the most reduced sample, and Mg-Ca carbonates ± sulfates ± CO2 in the most oxidized sample, the latter associated with a silicate glass and (secondary) hydrous phases. Both assemblages are taken as evidence of the product of crystallization of deeply originated volatile-bearing silicate melts. Analyses of He, Ar, and Ne in olivine grains confirm the evidence of a mantle source reworked by metasomatic processes. Our data suggest that an initially residual Hyblean lithospheric mantle was affected by extensive oxidizing events at several depths caused by the interaction with slab-derived CO2-rich silicate metasomatic liquids.
Description:
Published
Description:
107337
Description:
OSV2: Complessità dei processi vulcanici: approcci multidisciplinari e multiparametrici
Description:
JCR Journal
Keywords:
Redox state
;
Raman
;
M¨ossbauer spectroscopy
;
Noble gases
;
Abyssal peridotites
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
Permalink
