Ichneumonid wasps from Madagascar. VI. The genus Pristomerus (Hymenoptera: Ichneumonidae: Cremastinae)

Pristomerus species of Madagascar are revised. We report 15 species, of which 12 are newly described: P. guinness sp. nov., P. hansoni sp. nov., P. kelikely sp. nov., P. keyka sp. nov., P. moramora sp. nov., P. melissa sp. nov., P. patator sp. nov., P. ranomafana sp. nov., P. roberti sp. nov., P. vahaza sp. nov., P. veloma sp. nov. and P. yago sp. nov. Pristomerus albescens (Morley) and P. cunctator Tosquinet are newly recorded from Madagascar and new host and/or distribution records are provided for this species. A dichotomous key to all species is provided. The zoogeographical relation of the Malagasy fauna of Pristomerus with respect to mainland Africa is discussed: only three of the 15 species are reported to occur outside of Madagascar, suggesting a high level of endemism in Madagascar which was not unexpected

Contrasting geophysical and geochemical signatures of a volcano at the axis of the Wharton Fossil Ridge (N-E Indian Ocean)

International audienceThe Styx volcano is a prominent seamount (20-30 km diameter, 2500 m high) located at the axis of the Wharton fossil spreading center (N-E Indian Ocean), where seafloor spreading stopped 40 Ma ago. Gravity modeling shows that it was emplaced on a weak lithosphere, in agreement with an on axis origin when seafloor spreading was active. The rocks dredged at the summit of the volcano are extreme typical alkaline basalts, indicating a deep enriched mantle source. We show here that most of this seamount was emplaced during the final stage of the seafloor spreading in the Wharton Basin. We then discuss how alkaline magmatism can be emplaced at the summit of the Styx

Behavior of halogens during the degassing of felsic magmas

International audienceResidual concentrations of halogens (F, Cl, Br, I) and H2O in glass (matrix glass and melt inclusions) have been determined in a series of volcanic clasts (pumice and lava‐dome fragments) of plinian, vulcanian and lava dome‐forming eruptions. Felsic magmas from calc‐alkaline, trachytic and phonolitic systems have been investigated: Montagne Pelée and Soufrière Hills of Montserrat (Lesser Antilles), Santa Maria‐Santiaguito (Guatemala), Fogo (Azores) and Vesuvius (Italy). The behavior of halogens during shallow H2O degassing primarily depends on their incompatible character and their partitioning between melt and exsolved H2O vapor. However, variations in pre‐eruptive conditions, degassing kinetics, and syn‐eruptive melt crystallization induce large variations in the efficiency of halogen extraction. In all systems studied, Cl, Br and I are not fractionated from each other by differentiation or by degassing processes. Cl/Br/I ratios in melt remain almost constant from the magma reservoir to the surface. The ratios measured in erupted clasts are thus characteristic of pre‐eruptive magma compositions and may be used to trace deep magmatic processes. F behaves as an incompatible element and, unlike the other halogens, is never significantly extracted by degassing. Cl, Br and I are efficiently extracted from melts at high pressure by H2O‐rich fluids exsolved from magmas or during slow effusive magma degassing, but not during rapid explosive degassing. Because H2O and halogen mobility depends on their speciation, which strongly varies with pressure in both silicate melts and exsolved fluids, we suggest that the rapid pressure decrease during highly explosive eruptions prevents complete equilibrium between the diverse species of the volatiles and consequently limits their degassing. Conversely, degassing in effusive eruptions is an equilibrium process and leads to significant halogen output in volcanic plumes

Dégradation de l’absorptance solaire de matériaux thermo-optiques contaminés par la propulsion électrique

International audienceOne of the objectives of this work was to contaminate samples by the erosion of different targets in order to study the effect of this contamination on their thermo-optical properties. The second objective was to validate the Spacecraft Plasma Interaction System (SPIS) module dedicated to simulation of erosion and contamination.First, experiments were conducted in IDEFIXe chamber at ONERA to expose OSR and SSM to contamination created by the erosion of targets representing elements of a spacecraft using electric propulsion, subject to ions bombardment. The targets were submitted to Xe+ ions beam. Samples were placed facing the target and were then submitted to the contamination by erosion products. The quantity of contaminants was estimated through a quartz micro-balance. Reflectance of the contaminated samples was then measured to evaluate the effect on their solar absorptance and their surface was characterized by XPS.Different targets and different samples were used allowing us to extract general tendencies and phenomenology.In a second time, simulations of the test were performed with SPIS. These simulations have allowed us reproducing experimental results, validating the code and proposing erosion mechanisms for polymeric materials

Quantification of water content and speciation in natural silicic glasses (phonolite, dacite, rhyolite) by confocal microRaman spectrometry

International audienceThe determination of total water content (H2OT: 0.1-10 wt%) and water speciation (H2Omolecular/OH) in volcanic products by confocal microRaman spectrometry are discussed for alkaline (phonolite) and calcalkaline (dacite and rhyolite) silicic glasses. Shape and spectral distribution of the total water band (H2OT) at not, vert, similar3550 cm−1 show systematic evolution with glass H2OT, water speciation and NBO/T. In the studied set of silicic samples, calibrations based on internal normalization of the H2OT band to a band related to vibration of aluminosilicate network (TOT) at not, vert, similar490 cm−1 vary with glass peraluminosity. An external calibration procedure using well-characterized glass standards is less composition-dependent and provides excellent linear correlation between total dissolved water content and height or area of the H2OT Raman band. Accuracy of deconvolution procedure of the H2OT band to quantify water speciation in water-rich and depolymerized glasses depends on the strength of OH hydrogen bonding. System confocal performance, scattering from embedding medium and glass microcrystallinity have a crucial influence on accuracy of Raman analyses of water content in glass-bearing rocks and melt inclusions in crystals

Measurements of electron emission under electron impact on BN sample for incident electron energy between 10 eV and 1000 eV

International audienceElectron emission measurements have been performed on a BN sample by using a new specific protocol and experimental setup , which allows characterizing electron emission under electron impact on resistive material in a short time and with a wide variety of extracted data: total electron emission yield, emitted electron energy distribution, elastically backscattered electron emission yield and energy efficiency of electron-surface interaction. Methodology, calibration, biases corrections and results are presented in this letter. Results are compared to that measured on another material SiO2. As there are few published data on electron emission at low incident electron energy on BN sample, it is expected that these measurements could be useful for numerous studies implying electron emission on BN surface

Influence of composition and thermal history of volcanic glasses on water content as determined by micro-Raman spectrometry

International audienceDevelopment of Raman spectrometry for quantification of water content in natural glasses requires the assessment of the dependence of the technique on glass composition and thermal history. In the low frequency domain, Raman spectra topology varies due to glass depolymerization and substitution in the framework of (Si4+)IV by alkali-balanced (Al3+)IV and (Fe3+)IV in calcalkaline (rhyolite to basaltic andesite) and alkaline (trachyte, phonolite to alkali basalt) glasses. These processes result in strong dependence of previous analytical procedure (internal calibration) on glass composition. Here, we show that an analytical procedure based on calibration to an external standard is only faintly composition-dependent for Si-rich alkaline glasses (trachytes-phonolites). For a given glass composition, thermal history also plays a fundamental role in the choice of Raman procedure for water analysis. Repeated cycles of thermal annealing induce microcrystallization of hydrous trachyte glasses and modify cation distribution in the glass structure. Application of these concepts to analysis of banded obsidians suggests that small-scale heterogeneities in glasses are not simply related to magma degassing, but could depend on thermal history and consequent relaxation paths in the melt

First records of Charipinae (Hymenoptera Cynipoidea Figitidae) from the Corsica island

Charipinae fauna from the Corsica Island has been studied. Five Alloxysta and one Apocharips species are cited for the first time in this island: Alloxysta arcuata (Kieffer, 1902), A. brevis (Thomson, 1862), A. castanea (Hartig, 1841), A. citripes (Thomson, 1862), A. victrix (Westwood, 1833) and Apocharips trapezoidea (Hartig, 1841). These identifications are the first record of these two genera and the Charipinae subfamily from the Corsica Island. Short descriptions and diagnoses are given for all Charipinae species present in this island. A key to distinguish them is also given

Evidence for a new shallow magma intrusion at La Soufrière of Guadeloupe (Lesser Antilles). Insights from long-term geochemical monitoring of halogen- rich hydrothermal fluids

International audienceMore than three decades of geochemical monitoring of hot springs and fumaroles of La Soufrière of Guadeloupe allows the construction of a working model of the shallow hydrothermal system. This system is delimited by the nested caldera structures inherited from the repeated flank collapse events and the present dome built during the last magmatic eruption (1530 AD) and which has been highly fractured by the subsequent phreatic or phreatomagmatic eruptions. Because it is confined into the low volume, highly compartmented and partially sealed upper edifice structure, the hydrothermal system is highly reactive to perturbations in the volcanic activity (input of deep magmatic fluids), the edifice structure (sealing and fracturing) and meteorology (wet tropical regime). The current unrest, which began with a mild reactivation of fumarolic activity in 1990, increased markedly in 1992 with seismic swarms and an increase of degassing from the summit of the dome. In 1997 seismic activity increased further and was accompanied by a sudden high-flux HCl-rich gas from summit fumaroles. We focus on the interpretation of the time-series of the chemistry and temperature of fumarolic gases and hot springs as well as the relative behaviours of halogens (F, Cl, Br and I). This extensive geochemical time-series shows that the deep magmatic fluids have undergone large changes in composition due to condensation and chemical interaction with shallow groundwater (scrubbing). It is possible to trace back these processes and the potential contribution of a deep magmatic source using a limited set of geochemical time series: T, CO2 and total S content in fumaroles, T and Cl- in hot springs and the relative fractionations between F, Cl, Br and I in both fluids. Coupling 35 years of geochemical data with meteorological rainfall data and models of ion transport in the hydrothermal aquifers has allowed us to identify a series of magmatic gas pulses into the hydrothermal system since the 1976-1977 crisis. The contrasting behaviours of S- and Cl- bearing species in fumarolic gas and in thermal springs suggests that the current activity is the result of a new magma intrusion which was progressively emplaced at shallow depth since ~1992. Although it might still be evolving, the characteristics of this new intrusion indicate that it hasalready reached a magnitude similar to the intrusion that was emplaced during the 1976-1977 eruptive crisis. The assessment of potential hazards associated with evolution of the current unrest must consider the implications of recurrent intrusion and further pressurization of the hydrothermal system on the likelihood of renewed phreatic explosive activity. Moreover, the role of hydrothermal pressurization on the basal friction along low-strength layers within the upper part of the edifice must be evaluated with regards to partial flank collapse. At this stage enhanced monitoring, research, and data analysis is required to quantify the uncertainties related to future scenarios of renewed eruptive activity and magmatic evolution