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Santorini caldera has had a long history of plinian eruptions and caldera collapses, separated by 20-40 kyr interplinian periods. We have carried out a study to constrain magma storage/extraction depths beneath the caldera. We analysed H 2 O in 138 olivine-, pyroxene-and plagioclase-hosted melt inclusions from plinian and interplinian products from the last 200 kyr, and CO 2 , S, Cl, F and dD in various subsets of these. The dataset includes 64 inclusions in products of the Minoan plinian eruption of the late 17th century BCE. All the melt inclusions were ellipsoidal and isolated, with no textural evidence for volatile leakage. Mafic melt inclusions contain 1-4 wt % H 2 O and up to 1200 ppm CO 2 , 1200 ppm S, 2000 ppm Cl and 400 ppm F; silicic inclusions contain 2-7 wt % H 2 O, up to 150 ppm CO 2 , up to 400 ppm S, 2000-6000 ppm Cl and 600-1000 ppm F. The dD values of 27 representative inclusions (-37 to-104%) are intermediate between mantle and slab values and rule out significant H 2 O loss by hydrogen diffusion from olivine-hosted inclusions. H 2 O, S and Cl behave compatibly in melt inclusion suites varying from mafic to silicic in composition, showing that entrapment of many melt inclusions took place under volatile-saturated conditions. Most Santorini melts are saturated in a free COHSCl vapour phase at depths of less than $10 km; the only exceptions are basaltic melts from a single interplinian eruption, which were volatile-undersaturated up to K 2 O contents of $1 wt %. The rhyolitic melt of the Minoan eruption probably contained a free hypersaline liquid phase. H 2 O þ CO 2 saturation pressures were calculated using suitably calibrated solubility models to estimate pre-eruptive magma storage depths. Magmas feeding plinian eruptions were stored at >4 km (>100 MPa) and extracted over depth intervals of several kilometres. Plagioclase phenocrysts in rhyodacitic pumice from the Minoan eruption have cores containing melt inclusions trapped at depths up to 10-12 km (320 MPa), and rims (also orthopyroxene and clinopyroxene) containing inclusions trapped at 4-6 km (100-160 MPa). This records late-stage silicic replenishment of a <2 km thick shallow magma chamber, rather than extraction of melts syneruptively over the entire depth range. The plagioclase cores were carried from depth in the ascending melt, then overgrown by the rims in the shallow chamber. Exsolution of volatiles during ascent may have caused the replenishment melt to inject as a bubbly plume, causing mixing prior to eruption. This would explain (1) the homogeneity of the Minoan rhyodacitic magma, and (2) extraction of melt inclusions from the entire pressure spectrum during the first eruptive phase. Most silicic magmas feeding eruptions of the interplinian periods were stored in reservoirs at shallow depths (2-3 km) compared with those feeding the plinian eruptions (>4 km). Melt inclusions from the AD 726 eruption of Kameni Volcano yield a pre-eruptive storage depth of $4 km, which is similar to that estimated from geodetic data for the inflation...

International audienceRaw geological materials excavated then piled on large surface areas are submitted to pedogenetic factors. Knowledge of the evolution of this freshly exposed material is required to predict the newly developed Technosol and the corresponding ecosystem. The pedogenetic evolution of a Technosol developed on excavated Callovo-Oxfordian clay minerals (COx) is assessed from the analysis of natural soils developed on analogous materials. Work was based on the hypothesis that the evolution of raw geological materials could be deduced from that of natural soils on similar outcrops in similar climatic conditions. A comparison was made on the basis of mineralogical and geochemical criteria between the unweathered clays and soil material collected from the horizons of two reference pedons on a COx outcrop in North-Eastern France, used by forest or agriculture, and a 10-year-old Technosol derived from freshly excavated COx material piled under outdoor climatic conditions. Soil profiles were described and each sampled horizon was characterized for mineralogy, and physical and chemical properties. Soil profiles were classified as Vertic Stagnic Hypereutric Cambisol (Forest) and Vertic Stagnic Calcaric Cambisol (Meadow), and compared to the Calcaric Technosol (no vegetation yet). They clearly showed brunification and decarbonatization as the major processes having governed their evolution. Signs of clay leaching were also visible on the forest soil. A fairly good adequacy was observed between soil material sampled in the soil deep horizons (2.5 m), the Technosol deep horizon (1.7 m), and the freshly excavated material. Slight differences were recorded, however, i.e., salt loss (NaCl), sulfide oxidation, and precipitation of gypsum from sulfate and calcium released by decarbonatization, as earlier observed in leaching experiments. Salt loss is a rapid process almost completed to the same extent in the Technosol after 10 years than in the Calcaric Cambisol after centuries. The soil under forest showed signs of stronger pedogenetic evolution than the soil submitted to agriculture (meadow), probably because the latter has been refreshed by man-induced erosion. COx evolution can be predicted from the analysis of soils developed on similar outcrops. The Technosol developed on these carbonated materials would evolve as a result of extremely rapid leaching of the soluble phases, then surface enrichment of organic matter, surface decarbonatization, and progressive brunification of the whole profile as the major processes, and give rise to a Cambisol. Technosol study is an interesting approach for dating the age of pedogenetic processes

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