The intermediate step in fractionation trends of mildly alkaline volcanic suites: An experimental insight from the Pavin trachyandesite (Massif Central, France)

International audienceWe examined magma storage conditions and eruptive dynamics for the trachyandesite (~58 wt% SiO2, 9–10 wt% alkalis) of the Pavin monogenetic volcano, a maar-like explosive crater belonging to a small group of youngest volcanoes in the Massif Central. By confronting the natural samples to experimental products, we constrained pre-eruptive conditions around 950–975 °C, 150–200 MPa (~5.5–7.0 km in depth), NNO+1.5, and 4.5–5.5 wt% melt H2O. There is petrological evidence of magma crystallization in the conduit up to shallow levels (~50 MPa; 2 km in depth) before fragmentation into pumice clasts in the last kilometre of ascent. The experiments highlight the role of biotite and of crystallization pressure in defining separate compositional trends of residual liquids, i.e. alkaline (trachytes) versus sub-alkaline (dacite-rhyolite)

Physical-informed machine learning prediction of properties of oxide glasses

International audienceGlass is a material for the future with an infinity of compositions. To speed up the finding of new compositions with specific values of properties, the deep learning is an efficient method. Here, this method is used to predict physical properties as density, Young's modulus or dynamical viscosity. To do that, physical inspired models are developed. The general method is first presented with the databases used in this contribution. To predict density, the fitting is operated on the molar volume. For the Young's modulus, the fitting is achieved on the packing factor. The Poisson coefficient is determined according to the Makishima-Mackenzie's model. For each prediction, a comparison with experimental data is provided. Finally, predictions are used to see which oxide is the more relevant to enhance the Young's modulus, for instance

Chlorine and fluorine behavior in apatite-fluid-silicate melt systems

International audienceThe fluctuation of halogen contents (Cl, F) of volcanic gases is potentially a good precursor signal of volcanic crises, yet the Cl and F behavior in magmas is complex due to the interplay between melt, fluid and halogens-bearing crystals. In magmatic rocks, Cl and F are the main constituents of apatite, an ubiquitous accessory magmatic mineral. As a result, apatite is increasingly being used as a geochemical tool for unravelling halogen behavior as it allows to record the fugacities of key volatile species. In this context, the behavior of Cl and F in coexisting apatite, fluids and a variety of silicate melts (rhyodacite, basalt, phonolite) has been investigated experimentally as a function of pressure, temperature, oxygen fugacity, and fluid composition. Experiments have been done using internally heated pressure vessels at 50-200 MPa, 800-1100 • C, fO 2 from NNO-1 to NNO+2 and starting fluid : Cl content between 0 and 15 wt%. Run products were analysed by SEM, EPMA and Raman spectroscopy. F and Cl contents of fluids were estimated by mass-balance. The results show that chlorine and fluorine partitioning in the apatite-melt-fluid system is dependent on all investigated parameters. In detail, for the rhyodacite composition, when the Cl content in starting fluid increases, the chlorine content of apatite increases (from 0.2 to 2.5 wt%) with the Cl content of melt (between 0.1 and 1 wt%) and fluid (between 0.2 and 22 wt%). When the pressure decreases (200 to 50 MPa with temperature and Cl content of the starting fluid being constant) the Cl content in apatite increases (2.2 to 2.7 wt%) with Cl content in melt (0.7-1wt%) while the bulk Cl content in fluid decreases (from 22 to 5 wt%). Cl and F always favor apatite relative to fluid and silicate melt, though in several run products, the behavior of F is difficult to evaluate owing to analytical errors for its measurement in glasses at low contents (<1000 ppm). For the two other compositions, experiments have been performed and their analytical characterisation is underway. With the gathered data, a solubility model of Cl (and F) is being currently developed for the magma compositions investigated, using the method of Piccoli & Candela (1994) to obtain Cl and F fugacities. Finally, in situ experiments using a transparent IHPV equipped with sapphire windows connected to a Raman spectrometer will be carried out in the near future in order to determine the fluid composition in equilibrium with the melt and the conditions of salt (Na-K)Cl saturation in silicate melts

Halogens partitioning between apatite, fluid and silicate melts

International audienceThe fluctuation of halogen contents (chlorine and fluorine) of volcanic gases is a good precursor signal of volcanic crises, yet the Cl and F behavior in magmas is complex due to the interplay between melt, fluid and halogens bearing crystals. In magmatic rocks, Cl and F arethe main constituents of apatite, an ubiquitous accessory magmatic mineral.As a result, apatite is increasingly being used as a geochemical tool for unravelling halogen behavior as it allows to record the fugacities of key volatile species. In this context, the behavior of Cl and F in coexisting apatite, fluids and a variety of silicate melts (rhyodacite, basalt, phonolite)has been investigated experimentally as a function of pressure, temperature, oxygen fugacity, and fluid composition. Experiments have been done using internally heated pressure vessels at 50-200 MPa, 800-1100°C, fO2 from NNO-1 to NNO+2 and with either a Cl-bearing aqueousfluid. Run products were analysed by SEM, EPMA and Raman spectroscopy. F and Cl contents of fluids were estimated by mass-balance.The results show that halogens partitioning in the apatitemelt-fluid system is dependent on all investigated parameters.Indeed, Cl concentrations in the rhyodacite melts increase with increasing Cl content in the fluid phase. With constantCl concentration in the fluid phase, the amount of Cl in melts (between 0.1 and 1 wt%) and apatites (2.2 to 2.7 wt%)increases as the pressure decreases. We observed the same variations in phonolitic and basaltic melts. Though in severalrun products, the behavior of F is difficult to evaluate owing to analytical errors for its measurement in melts at lowcontents (<1000 ppm). With the gathered data, a solubility model of Cl (and F) is developed for the magmacompositions investigated, using the method of Piccoli & Candela [1] to obtain Cl and F fugacities.Finally, in situ experiments using a transparent IHPV connected to a Raman spectrometer are carried out in order todetermine the fluid composition in equilibrium with the melt and the conditions of salt (Na-K)Cl saturation in silicatemelts.[1] Piccoli and Candela (1994) Am J Sci 294 92-135

New insights into the rapid germination process of lentil and cowpea seeds: High thiamine and folate, and low α-galactoside content

International audienceDuring germination sensu-stricto in pulses, an increase in the content of thiamine (B1) and folate (B9) vitamins is expected, along with a reduction in alpha-galactoside levels. The aim of our study was to optimize germination to increase the nutritional quality of lentils and cowpeas. An experimental design was carried out at 12 h and 24 h of imbibition to analyze the effects of temperature, light, and water content on thiamine, folate, and alpha-galac-toside content. Germination increased thiamine content by 152% in lentils, while in cowpeas, the increase was only 10%. Folate content in cowpea increased by 33%, while alpha-galactoside content decreased by 99% in cowpeas and by 48% in lentils. Germination sensu-stricto can be safely implemented by any food company worldwide as it is simple and involves less sanitary risk than sprouting. This opens up opportunities for enhancing food nutrient content and new ways of processing pulses