Stratospheric Ozone destruction by the Bronze-Age Minoan eruption (Santorini Volcano, Greece).

The role of volcanogenic halogen-bearing (i.e. chlorine and bromine) compounds in stratospheric ozone chemistry and climate forcing is poorly constrained. While the 1991 eruption of Pinatubo resulted in stratospheric ozone loss, it was due to heterogeneous chemistry on volcanic sulfate aerosols involving chlorine of anthropogenic rather than volcanogenic origin, since co-erupted chlorine was scavenged within the plume. Therefore, it is not known what effect volcanism had on ozone in pre-industrial times, nor what will be its role on future atmospheres with reduced anthropogenic halogens present. By combining petrologic constraints on eruption volatile yields with a global atmospheric chemistry-transport model, we show here that the Bronze-Age 'Minoan' eruption of Santorini Volcano released far more halogens than sulfur and that, even if only 2% of these halogens reached the stratosphere, it would have resulted in strong global ozone depletion. The model predicts reductions in ozone columns of 20 to >90% at Northern high latitudes and an ozone recovery taking up to a decade. Our findings emphasise the significance of volcanic halogens for stratosphere chemistry and suggest that modelling of past and future volcanic impacts on Earth's ozone, climate and ecosystems should systematically consider volcanic halogen emissions in addition to sulfur emissions

Multiple timescale constraints for high-flux magma chamber assembly prior to the Late Bronze Age eruption of Santorini (Greece)

The rhyodacitic magma discharged during the 30–80 km3 DRE (dense rock equivalent) Late Bronze Age (LBA; also called ‘Minoan’) eruption of Santorini caldera is known from previous studies to have had a complex history of polybaric ascent and storage prior to eruption. We refine the timescales of these processes by modelling Mg–Fe diffusion profiles in orthopyroxene and clinopyroxene crystals. The data are integrated with previously published information on the LBA eruption (phase equilibria studies, melt inclusion volatile barometry, Mg-in-plagioclase diffusion chronometry), as well as new plagioclase crystal size distributions and the established pre-LBA history of the volcano, to reconstruct the events that led up to the assembly and discharge of the LBA magma chamber. Orthopyroxene, clinopyroxene and plagioclase crystals in the rhyodacite have compositionally distinct rims, overgrowing relict, probably source-derived, more magnesian (or calcic) cores, and record one or more crystallization (plag ≫ opx > cpx) events during the few centuries to years prior to eruption. The crystallization event(s) can be explained by the rapid transfer of rhyodacitic melt from a dioritic/gabbroic region of the subcaldera pluton (mostly in the 8–12 km depth range), followed by injection, cooling and mixing in a large melt lens at 4–6 km depth (the pre-eruptive magma chamber). Since crystals from all eruptive phases yield similar timescales, the melt transfer event(s), the last of which took place less than 2 years before the eruption, must have involved most of the magma that subsequently erupted. The data are consistent with a model in which prolonged generation, storage and segregation of silicic melts were followed by gravitational instability in the subcaldera pluton, causing the rapid interconnection and amalgamation of melt-rich domains. The melts then drained to the top of the pluton, at fluxes of up to 0.1–1 km3 year− 1, where steep vertical gradients of density and rheology probably caused them to inject laterally, forming a short-lived holding chamber prior to eruption. This interpretation is consistent with growing evidence that some large silicic magma chambers are transient features on geological timescales. A similar process preceded at least one earlier caldera-forming eruption on Santorini, suggesting that it may be a general feature of this rift-hosted magmatic system

Le magmatisme acide Plio-Pleistocène de la Marge<br />Tyrrhénienne (Italie Centrale) : Géochronologie,<br />Pétrogénèse et Implications Géodynamiques.

The Italian Neogene magmatism is characterized by a large petrological andgeochemical variety, covering almost all the magmatic rocks pattern known worldwide. Mostof the geodynamic models are based upon the recent widespread Quaternary volcanism,comprising mafic to intermediate lavas. In contrast, the felsic magmatism which correspondsto the first manifestations of the Tyrrhenian margin is much less voluminous, outcropswithout or with few associated mafic-intermediate rocks, and is less known.The goals of this thesis are: (1) to precise the age of these manifestations, (2) to betterunderstand the origin of this magmatism (determinating the sources) and, (3) to insert theseconstraints in the general framework of the Italian magmatism and the opening of theTyrrhenian Sea. A combined geochronological and petro-geochemical study has thus beencarried out on felsic Tuscan edifices (San Vincenzo, Roccastrada and Amiata) and the Ponzaand Palmarola islands (Pontine Archipelago, Campanian area, Gaeta gulf).Twenty-five K-Ar datings (Cassignol-Gillot technique) have been performed on thePonza and Palmarola islands rocks. The beginning of the volcanic activity of Palmarola hasbeen dated for the first time at 1.64 ± 0.02 Ma; the obtained Quaternary (Pleistocene) age is incontradiction with the Pliocene age which was proposed on stratigraphical criteria.Concerning Ponza, a new rhyolites episode had been recovered at 3.1-2.9 Ma. BetweenPliocene and Pleistocene, the volcanism changed from orogenic calc-alkaline in Ponza to atransitional magmatism in Palmarola whose chemical signature approaches those of intraplatealkaline magmatism. This occurred in only 1.3 Ma. A petrogenetic model is proposed for themagma of Ponza and Palmarola from new mineralogical and isotopic data. It impliesfractional crystallization coupled with more or less strong crustal contamination, fromdifferent mantle liquids.Accurate and reproducible ages have been obtained for the Tuscan Province edifices(San Vincenzo, Roccastrada and Amiata). New Sr, Nd and Pb isotopic data confirmed thehybrid character of Monte Amiata volcano in terms of sources, between the Tuscan and theRoman provinces. Based on our new ages, we propose a new possible scenario for itsvolcanological evolution.The principal component analysis of the lead isotopic data set of all the studied felsicmanifestations has permitted to identify the two main source components at the origin of theserocks. The dominant component is mantellic and corresponds to a mixing between DM andHIMU end-members, while the second is an enriched crustal-derived end-member. Thesouthernmost felsic rocks (Pontine) show the strongest influence of the DM+HIMUcomponent. Thus, even with so differentiated rocks and at so small scale (central Italy), wefind the general trend of the whole Italian peninsula and Sicily derived from the isotopic studyof mafic rocks, which shows a general DM+HIMU mixing plus a crustal-derived endmember.The influence of the DM+HIMU end-member increases from North to South ofItaly.When extended at the scale of the whole Tyrrhenian margin, the PCA allows identifying twosource domains delimitated by a major lithospheric discontinuity, the 41 Parallel Line, and inwhich the evolution of the components is different. The northern domain characteristics couldbe controlled by a lower lithosphere delamination, whereas in the southern domain they mightbe due to the fast slab roll-back. In both domains, the invoked processes would trigger theupwelling of asthenospheric material.Le magmatisme Néogène italien est caractérisé par une grande variété pétrologique et géochimique, couvrant presque entièrement le spectre des roches magmatiques connues dans le monde entier. Le volcanisme récent, Quaternaire, comprenant des laves de compositionbasiques et intermédiaires, est à la base de la majorité des modèles géodynamiques. Comparativement, le magmatisme acide, correspondant aux premières manifestations sur la marge Tyrrhénienne est beaucoup pour les édifices de la Province Toscane (San Vincenzo, Roccastrada et Amiata). Pour le volcan de Monte Amiata, de nouvelles données isotopiques Sr-Nd et Pb confirment qu'il est en terme de sources un hybride entre les Province Toscane et Romaine. Nous proposons grâce aux âges obtenus un nouveau scénario pour sa mise en place. L'analyse en composantes principales (ACP) des données isotopiques du Pb de toutes les manifestations acides étudiées dans cette thèse a permis d'identifier les deux composants source à l'origine de ces roches. Le composant le plus important est un pôle mantelliquecorrespondant à un mélange entre DM et HIMU, tandis que le second, dont le rôle est mineur comparé au premier, est un pôle enrichi de type crustal. Les roches acides les plus au Sud (Pontines) montrent une influence plus forte du composant DM+HIMU. Ainsi, même sur desroches aussi différenciées et à plus petite échelle (l'Italie centrale), on retrouve la tendance générale propre à l'ensemble de la péninsule Italienne et de la Sicile, dérivée de l'étude isotopique des roches basiques, qui montre un mélange général entre DM et HIMU auquel s'ajoute un composant dérivé de la croûte. L'influence du pôle DM-HIMU est croissante duNord au Sud de l'Italie. Etendue à l'échelle de la marge Tyrrhénienne italienne, l'ACP permet d'identifier deuxdomaines sources, délimités par une discontinuité lithosphérique majeure de l'Italie centrale, le 41ème Parallèle, dans lesquels les composants évoluent différemment. Les caractéristiques du domaine Nord pourraient être contrôlées par un processus de délamination de la lithosphère inférieure, celles du domaine Sud par un retrait rapide du slab, les deuxphénomènes provoquant une remontée asthénosphérique

Le magmatisme acide Plio-Pleistocène de la Marge<br />Tyrrhénienne (Italie Centrale) : Géochronologie,<br />Pétrogénèse et Implications Géodynamiques.

The Italian Neogene magmatism is characterized by a large petrological andgeochemical variety, covering almost all the magmatic rocks pattern known worldwide. Mostof the geodynamic models are based upon the recent widespread Quaternary volcanism,comprising mafic to intermediate lavas. In contrast, the felsic magmatism which correspondsto the first manifestations of the Tyrrhenian margin is much less voluminous, outcropswithout or with few associated mafic-intermediate rocks, and is less known.The goals of this thesis are: (1) to precise the age of these manifestations, (2) to betterunderstand the origin of this magmatism (determinating the sources) and, (3) to insert theseconstraints in the general framework of the Italian magmatism and the opening of theTyrrhenian Sea. A combined geochronological and petro-geochemical study has thus beencarried out on felsic Tuscan edifices (San Vincenzo, Roccastrada and Amiata) and the Ponzaand Palmarola islands (Pontine Archipelago, Campanian area, Gaeta gulf).Twenty-five K-Ar datings (Cassignol-Gillot technique) have been performed on thePonza and Palmarola islands rocks. The beginning of the volcanic activity of Palmarola hasbeen dated for the first time at 1.64 ± 0.02 Ma; the obtained Quaternary (Pleistocene) age is incontradiction with the Pliocene age which was proposed on stratigraphical criteria.Concerning Ponza, a new rhyolites episode had been recovered at 3.1-2.9 Ma. BetweenPliocene and Pleistocene, the volcanism changed from orogenic calc-alkaline in Ponza to atransitional magmatism in Palmarola whose chemical signature approaches those of intraplatealkaline magmatism. This occurred in only 1.3 Ma. A petrogenetic model is proposed for themagma of Ponza and Palmarola from new mineralogical and isotopic data. It impliesfractional crystallization coupled with more or less strong crustal contamination, fromdifferent mantle liquids.Accurate and reproducible ages have been obtained for the Tuscan Province edifices(San Vincenzo, Roccastrada and Amiata). New Sr, Nd and Pb isotopic data confirmed thehybrid character of Monte Amiata volcano in terms of sources, between the Tuscan and theRoman provinces. Based on our new ages, we propose a new possible scenario for itsvolcanological evolution.The principal component analysis of the lead isotopic data set of all the studied felsicmanifestations has permitted to identify the two main source components at the origin of theserocks. The dominant component is mantellic and corresponds to a mixing between DM andHIMU end-members, while the second is an enriched crustal-derived end-member. Thesouthernmost felsic rocks (Pontine) show the strongest influence of the DM+HIMUcomponent. Thus, even with so differentiated rocks and at so small scale (central Italy), wefind the general trend of the whole Italian peninsula and Sicily derived from the isotopic studyof mafic rocks, which shows a general DM+HIMU mixing plus a crustal-derived endmember.The influence of the DM+HIMU end-member increases from North to South ofItaly.When extended at the scale of the whole Tyrrhenian margin, the PCA allows identifying twosource domains delimitated by a major lithospheric discontinuity, the 41 Parallel Line, and inwhich the evolution of the components is different. The northern domain characteristics couldbe controlled by a lower lithosphere delamination, whereas in the southern domain they mightbe due to the fast slab roll-back. In both domains, the invoked processes would trigger theupwelling of asthenospheric material.Le magmatisme Néogène italien est caractérisé par une grande variété pétrologique et géochimique, couvrant presque entièrement le spectre des roches magmatiques connues dans le monde entier. Le volcanisme récent, Quaternaire, comprenant des laves de compositionbasiques et intermédiaires, est à la base de la majorité des modèles géodynamiques. Comparativement, le magmatisme acide, correspondant aux premières manifestations sur la marge Tyrrhénienne est beaucoup pour les édifices de la Province Toscane (San Vincenzo, Roccastrada et Amiata). Pour le volcan de Monte Amiata, de nouvelles données isotopiques Sr-Nd et Pb confirment qu'il est en terme de sources un hybride entre les Province Toscane et Romaine. Nous proposons grâce aux âges obtenus un nouveau scénario pour sa mise en place. L'analyse en composantes principales (ACP) des données isotopiques du Pb de toutes les manifestations acides étudiées dans cette thèse a permis d'identifier les deux composants source à l'origine de ces roches. Le composant le plus important est un pôle mantelliquecorrespondant à un mélange entre DM et HIMU, tandis que le second, dont le rôle est mineur comparé au premier, est un pôle enrichi de type crustal. Les roches acides les plus au Sud (Pontines) montrent une influence plus forte du composant DM+HIMU. Ainsi, même sur desroches aussi différenciées et à plus petite échelle (l'Italie centrale), on retrouve la tendance générale propre à l'ensemble de la péninsule Italienne et de la Sicile, dérivée de l'étude isotopique des roches basiques, qui montre un mélange général entre DM et HIMU auquel s'ajoute un composant dérivé de la croûte. L'influence du pôle DM-HIMU est croissante duNord au Sud de l'Italie. Etendue à l'échelle de la marge Tyrrhénienne italienne, l'ACP permet d'identifier deuxdomaines sources, délimités par une discontinuité lithosphérique majeure de l'Italie centrale, le 41ème Parallèle, dans lesquels les composants évoluent différemment. Les caractéristiques du domaine Nord pourraient être contrôlées par un processus de délamination de la lithosphère inférieure, celles du domaine Sud par un retrait rapide du slab, les deuxphénomènes provoquant une remontée asthénosphérique

Can Moroccan Atlas lithospheric thinning and volcanism be induced by Edge-Driven Convection?

International audienceThe Moroccan lithosphere is characterized by an anomalously thinned area, located beneath the Atlas domains, which forms a singular narrow NE-SW directed strip overlain by Cenozoic alkaline volcanism. The origin of this thinning and volcanism is still a matter of debate. The proposed models invoke processes either related to the Mediterranean slab or mantle plumes. Herein, we propose an alternative Edge-Driven Convection (EDC) model involving small-scale convection at the boundary between the West-African craton and the Atlas lithosphere. Our comparison of the Atlas lithosphere velocity and volcanism episodes during the last 80 Ma points out that volcanism occurs when plate moves at velocities c.<1 cm a)1, a velocity sufficiently low to trigger EDC. This is the first process that could explain the c. 20 Ma volcanism shutdown separating the two volcanic episodes of the Atlas. In addition, it may successfully account for the lithosphere thinning location and geometry and volcanism geochemistry

Hybrid character and pre-eruptive events of Mt Amiata volcano (Italy) inferred from geochronological, petro-geochemical and isotopic data

International audienceA new geochronological and geochemical study was carried out to better constrain the petrogenesis and eruptive history of Monte Amiata, a large Pleistocene trachydacitic volcano of Southern Tuscany. Previous studies suggested a magma mixing origin between calc-alkaline silicic melts from the Tuscan Magmatic Province (TMP) and potassic mafic melts like those found in the Roman Magmatic Province (RMP). Two eruptive episodes-the first at ca. 300 kyr, the second at ca. 200 kyr-were distinguished from the few available ages. However, both the involvement of a RMP-like melt as mafic end-member and the timing of volcanic activity remained to be ascertained. The K-Ar ages obtained on plagioclase, sanidine and glass separated from Mt Amiata volcanic rocks demonstrate the sanidine is the most suitable phase for K-Ar dating. Sanidine yields ages of 304-293 kyr for the basal trachydacitic unit (BTC), 298-280 kyr in the domes unit (DLC) and unexpected older ages of 312-308 kyr for the more mafic summit lava unit (OLL). A careful re-examination of the literature ages together with those obtained in this study shows that they tend to a common age of ca. 300 kyr whatever the volcanic unit. We interpret this as a reset of the K-Ar chronometer in response to a consequent recharge of the silicic magma reservoir by hot mafic melts. This recharge most probably triggered the first volcanic eruption of Mt Amiata magmas. In our model, we suppose an initially chemically-stratified magma chamber; the input of deep hot mafic melts reset the crystals clock and probably allowed the eruption of the huge amount of trachydacitic crystal mush. We propose that the controversial BTC unit could have emplaced during a non-explosive eruption if we consider either pre-eruption passive degassing or extrusion of the trachydacites as magmatic foam. First Pb isotopic data of mafic enclaves from the trachydacitic units, together with major and trace elements and new Sr and Nd data support the magma mixing as the dominant process at the origin of the Mt Amiata volcanic rocks. The similar LILE/HFSE ratios evidenced in this contribution between the magmatic enclaves of Mt Amiata and RMP volcanic rocks, together with their comparable Sr, Nd and Pb isotopic compositions, definitively argue for the involvement of a RMP-like melt in the mixing. The Mt Amiata is thus indisputably a hybrid volcano between TMP and RMP in terms of petrogenesis and ages

Characteristic Textures of Recrystallized, Peritectic, and Primary Magmatic Olivine in Experimental Samples and Natural Volcanic Rocks

International audienceOlivine textures are potentially important recorders of olivine origin and crystallization conditions. Primary magmatic and xenocrystic origins are commonly considered for olivine from ultramafic to intermediate magmas, while secondary olivine origins (i.e. crystals formed by recrystallization or peritectic reaction) are rarely considered in the interpretation of magmatic phenocrysts. The main aim of our study was to determine textures that are characteristic for secondary magmatic olivine and non-characteristic, or at least rare, for primary magmatic olivine. To characterize the textures of the different olivine types, we review previous experimental work and present new textural data for olivine from four melanorite melting and eight basalt crystallization experiments. We (i) qualitatively characterize olivine textures using transmitted light and back-scattered electron microscopy; and (iii) semi-quantitatively characterize the 2D surface area of olivine branches and individual crystals, their 2D and calculated 3D shapes, and 2D grain boundary segmen

P, T, X magma storage conditions of the dominantly silicic explosive eruptions from Santorini volcano (Aegean Arc, Greece)

International audienceIt has been increasingly recognized that dramatic changes in magma storage conditions can occur over very short periods of time at a single volcano and might be in close relationships with stress variations imposed on the crustal plumbing by the overlying volcano as it changes shape and volume over time. The Santorini volcano (South Aegean Arc) is an ideal target to unravel these potential relationships as its history is marked by alternating episodes of edifice construction and caldera collapses and the chronostratigraphy is well constrained. We focused our study on the products of the four major, dominantly silicic, explosive eruptions of Santorini: the Lower Pumice 1 and 2 (200 to 180 ka; 1st explosive cycle) and, the Cape Riva and the Minoan (~ 21 to 3 ka, 2nd explosive cycle). In order to precisely define the P, T, fO2, X (X for volatiles) storage conditions of the silicic magmas prior to these eruptions, we carried out a detailed micro-petrological and geochemical study on natural samples combined with an experimental work. The selected silicic components of the four eruptions are dacite to rhyodacite (SiO2 = 67-70 wt.%) with similar mineral paragenesis (plagioclase, orthopyroxene, clinopyroxene, ilmenite, magnetite, apatite ± pyrrhotite) and crystallinity < 20%. High resolution BSE images of plagioclase and pyroxene phenocrysts and EMPA profiles reveal a complex crystallization history. Plagioclases display fine-scale oscillatory normal zoning, resorbtion zones where melt inclusions (MI) of rhyolitic compositions were trapped, and An-rich sieved cores. Clinopyroxenes also show zoning patterns and include rhyolitic MI. Both interstitial glass and MI are Cl-rich (~3000 ppm) while F and S are less abundant (F ≤ 700 ppm, S ≤ 100 ppm). Determination of H2O contents by SIMS is in progress at the CRPG-Nancy (previous measurements from the literature gave ~ 5 wt.% H2O in the Minoan rhyodacite and ~4 wt.% in the Lower Pumice 2). Ilmenite-magnetite geothermometry indicates temperatures ranging from ~850 to 900°C and deltaNNO ~ -1. For experimental work, the natural rocks were melted twice at 1400°C and 1 atm; the resulting dry glasses were used as starting materials. Each composition was loaded in Au capsules as powdered glass together with known amounts of water and CO2 (added as silver oxalate) keeping the XH2Oloaded [=moles of H2O/(H2O+CO2) ] in the range 1 - 0.6. We run crystallization experiments by using an Internally Heated Pressure Vessel (ISTO-CNRS) pressurised by an Ar-H2 mixture. The investigated conditions were: T = 850°C and 900°C with P = 2 and 4 kbar and fO2 ~ FMQ, for a total of 20 charges per experiment. The experimental products are analysed by SEM and then by EMPA for major elements compositions of the glass and minerals. Dissolved water content will be determined using the "by difference" method and the SIMS. The experimental work is still in progress; the results of this set of experiments will be presented in our communication

Magma Storage Conditions of Large Plinian Eruptions of Santorini Volcano (Greece)

International audienceThe intensive variables of dacitic-rhyodacitic magmas prior to four large Plinian eruptions of Santorini Volcano over the last 200 kyr (Minoan, Cape Riva, Lower Pumice 2 and Lower Pumice 1) were determined by combining crystallization experiments with study of the natural products, including the volatile contents of melt inclusions trapped in phenocrysts. Phase equilibria of the silicic magmas were determined at pressures of 1, 2 and 4 kbar, temperatures of 850-900°C, fluid (H2O + CO2)-saturation, XH2O [= molar H2O/(H2O + CO2)] between 0*6 and 1 (melt H2O contents of 2-10 wt %), and redox conditions of FMQ (fayalite-magnetite-quartz buffer) or NNO + 1 (where NNO is Ni-NiO buffer). Experiments were generally successful in reproducing the phenocryst assemblage of the natural products. The phase relationships vary significantly among the investigated compositions, revealing a sensitivity to small variations in whole-rock compositions. Our results show that the pre-eruptive storage conditions of the four silicic magmas were all very similar. The magmas were stored at T = 850-900°C and P ≥ 2 kbar, under moderately reduced conditions (ΔNNO = −0*9 to −0*1), and were poor in fluorine (∼500-800 ppm) and sulphur (≤100 ppm), but rich in water and chlorine (5-6 wt % and 2500-3500 ppm, respectively). In all cases, the melts were slightly undersaturated with respect to H2O, but most probably saturated with respect to H2O + Cl ± CO2 and a brine. The Santorini magma plumbing system appears to be dominated by a large, long-lived (≥200 kyr) predominantly silicic magma storage region situated at ≥8 km depth, from which crystal-poor melt batches were extracted during the largest caldera-forming eruptions of the volcanic system

Santorini volcano magma plumbing system: constraints from a combined experimental and natural products study

International audienceSantorini Volcano constitutes a serious hazard in the Aegean region of Greece. The recent 2011-2012 episode of caldera unrest has focussed attention on the magma plumbing system of the volcano, and notably on the depths of storage of different magma batches. We investigated the differentiation conditions of mafic-intermediate magmas, as well as the pre-eruptive storage conditions of dacitic-rhyodacitic magmas prior to the four largest Plinian eruptions of the volcano over the last 200 ka (Minoan, Cape Riva, Lower Pumice 2, Lower Pumice 1). The intensive variables (P, T, fO2, volatiles content) were determined by combining laboratory crystallization experiments with study of the natural products (including volatiles in melt inclusions). Our results show that the magma plumbing system is dominated by a large, long-lived ( 200 ka) storage region at about 8 km depth (2 kb), from which the silicic magmas are derived. This region is fed by injections from a deeper, mafic reservoir located at the boundary between the upper and lower crust ( 15 km; 4 kb). Mantle-derived basalts stall in the 15 km storage region, where they fractionate to basaltic andesite (55 to 58 wt.% SiO2) with 2-3 wt.% H2O through crystallization of about 60 wt.% of oliv, cpx, plag, mt/ilm and opx, at 1040-1000°C, 4 kbar, fO2 = FMQ-0.5. The basaltic-andesitic magmas then ascent to about 8 km where they either (1) experience a last episode of equilibration prior to eruption, or (2) fractionate to produce dacitic to rhyodacitic liquids. Prior to the major Plinian eruptions, the silicic magmas were stored at T = 850-900°C, under relatively reduced conditions ( FMQ or, NNO = -0.9 to -0.1), with melts depleted in fluorine ( 500-700 ppm) and particularly in sulphur (<100 ppm) but rich in water and chlorine (5-6 wt.%, ca. 2500-3500 ppm, respectively) probably co-existing with a hydrosaline liquid, at pressure 2 kbar. The fact that Santorini dacites-rhyodacites have high enough dissolved Cl for the melts to be saturated with hydrosaline liquid (and maybe vapor) before Plinian eruptions has significant consequences on the Cl degassing budget, which was previously estimated as insignificant