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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 confi

Waterlogged archaeological wood can provide information on past human activities and technology but its structure may be modified due to microbial deterioration. Knowing its conservation state is fundamental for its restoration. Aim of this work was to test the use of non-destructive portable NMR for the microstructural characterization and preservation state of three archaeological wood samples (Roman age, 5th century AD). 1D T₁ and T₂ relaxation time distributions, as well as 2D T₁-T₂ and D-T₂ distributions were measured by single-sided NMR and interpreted with the help of high resolution magnetic resonance imaging (MRI) and optical microscopy. Due to the complexity of the ancient wood samples, in this first study a multi-analytical approach was required. It allowed the characterization of both waterlogged softwood (spruce) and hardwood (chestnut and maple) by quantifying relaxation times and diffusion water components affected by the presence of degradation products such as fungi, paramagnetic agents, and microstructural changes. Optical microscopy was needed to investigate the sub-microscopic wood elements not resolved by MRI and validate indirect single-sided NMR investigations. Observations and results of this study will allow the improvement of single-sided NMR protocols for the analyses of archaeological wood in situ with portable NMR.

Dissolution of clinopyroxene (cpx) in a K-basaltic melt from the Campi Flegrei Volcanic District (Italy) has been investigated through dissolution and dissolution-crystallization experiments at pressure of 0.8 GPa, superliquidus temperature of 1350 °C, and dwell times between 0.5 and 1 h. The obtained dissolution rates range from 7.9·10−6 cm s−1 to 6.1·10−6 cm s−1 as a function of dwell time. In the dissolution-crystallization experiment (1300 °C; 0.8 GPa; 2 h), the formation of overgrowth rims accompanied by new cpx crystals suggests that the injection of recharge magmas in basaltic reservoir may lead to inverse or oscillatory zonation. The interaction between cpx and K-basaltic melt at ~1570 °C was studied by in situ radiography using synchrotron radiation combined with the Paris-Edinburgh press. This resulted in cpx resorption to occur depending on the temperature conditions with respect to the liquidus temperature of the cpx (TcpxL). The calculated cpx dissolution rates are ~5·10−3 cm s−1 at T ≤ TcpxL and ~ 3·10−2 cm s−1 at T ≥ TcpxL. The role of crystal dissolution in the estimation of magma residence times has been also tested for a natural magmatic system by interpolating the dissolution rates (~10−5–10−6 cm s−1) with the textural data of cpx phenocrysts from the Agnano-Monte Spina pyroclastic deposit at Campi Flegrei caldera (Campanian region, Italy). Results from calculations indicate that the time required for partial or complete resorption of phenocrysts varies from ~0.5 to ~40 h, and that the effect of crystal dissolution may be relevant to estimate magma residence times whether significant dissolution occurs during magma mixing processes.

This chapter reviews the distribution of carbon-bearing phases in the crust, mantle, and the core. It presents conditions of stability of various carbon-bearing phases - such as carbonate minerals, carbon-bearing fluids, graphite, diamond, and carbides - and how these stabilities put limits on the carbon budget of the mantle. The chapter also discusses expectations about how stability may have varied throughout geologic time, given the thermal and redox evolution of the Earth. Finally, this chapter also presents recent discoveries about carbon mineral evolution.