Subduction metamorphism of serpentinite‐hosted carbonates beyond antigorite-serpentinite dehydration (Nevado‐Filábride Complex, Spain)

I. Martínez Segura and M. J. Román Alpiste are thanked for their kind assistance during sample preparation and SEM operation, and M. T. Gómez‐Pugnaire and A. Jabaloy for early work on Almirez ophicarbonates. We are grateful to the Sierra Nevada National Park for providing permits for fieldwork and sampling at the Almirez massif. We further acknowledge the editorial handling by D. Whitney and D. Robinson and the reviews of M. Galvez and T. Pettke, whose comments and constructive criticism helped to improve the manuscript. We acknowledge funding from the European Union FP7 Marie‐Curie Initial Training Network ABYSS under REA Grant Agreement no. 608001 in the framework of M.D.M.'s PhD project, the Spanish ‘Agencia Estatal de Investigación’ (AEI) grants no. CGL2016‐75224‐R to V.L.S.‐V and CGL2016‐81085‐R to C.J.G and C.M and grant no. PCIN‐2015‐053 to C.J.G. The ‘Junta de Andalucía’ is also thanked for funding under grants no. RNM‐131, RNM‐374 and P12‐RNM‐3141. C.M. thanks MINECO for financing a Ramón y Cajal fellowship no. RYC‐2012‐11314 and K.H. for a Juan de la Cierva Fellowship no. FPDI‐2013‐16253 and a research contract under grant no. CGL2016‐81085‐R. This work and the research infrastructure at the IACT have received (co)funding from the European Social Fund and the European Regional Development Fund.At sub‐arc depths, the release of carbon from subducting slab lithologies is mostly controlled by fluid released by devolatilization reactions such as dehydration of antigorite (Atg‐) serpentinite to prograde peridotite. Here we investigate carbonate–silicate rocks hosted in Atg‐serpentinite and prograde chlorite (Chl‐) harzburgite in the Milagrosa and Almirez ultramafic massifs of the palaeo‐subducted Nevado‐Filábride Complex (NFC, Betic Cordillera, S. Spain). These massifs provide a unique opportunity to study the stability of carbonate during subduction metamorphism at P–T conditions before and after the dehydration of Atg‐serpentinite in a warm subduction setting. In the Milagrosa massif, carbonate–silicate rocks occur as lenses of Ti‐clinohumite–diopside–calcite marbles, diopside–dolomite marbles and antigorite–diopside–dolomite rocks hosted in clinopyroxene‐bearing Atg‐serpentinite. In Almirez, carbonate–silicate rocks are hosted in Chl‐harzburgite and show a high‐grade assemblage composed of olivine, Ti‐clinohumite, diopside, chlorite, dolomite, calcite, Cr‐ bearing magnetite, pentlandite and rare aragonite inclusions. These NFC carbonate–silicate rocks have variable CaO and CO2 contents at nearly constant Mg/ Si ratio and high Ni and Cr contents, indicating that their protoliths were variable mixtures of serpentine and Ca‐carbonate (i.e., ophicarbonates). Thermodynamic modelling shows that the carbonate–silicate rocks attained peak metamorphic conditions similar to those of their host serpentinite (Milagrosa massif; 550–600°C and 1.0–1.4 GPa) and Chl‐harzburgite (Almirez massif; 1.7–1.9 GPa and 680°C). Microstructures, mineral chemistry and phase relations indicate that the hybrid carbonate–silicate bulk rock compositions formed before prograde metamorphism, likely during seawater hydrothermal alteration, and subsequently underwent subduction metamorphism. In the CaO–MgO–SiO2 ternary, these processes resulted in a compositional variability of NFC serpentinite‐hosted carbonate–silicate rocks along the serpentine‐calcite mixing trend, similar to that observed in serpentinite‐hosted carbonate‐rocks in other palaeo‐subducted metamorphic terranes. Thermodynamic modelling using classical models of binary H2O–CO2 fluids shows that the compositional variability along this binary determines the temperature of the main devolatilization reactions, the fluid composition and the mineral assemblages of reaction products during prograde subduction metamorphism. Thermodynamic modelling considering electrolytic fluids reveals that H2O and molecular CO2 are the main fluid species and charged carbon‐bearing species occur only in minor amounts in equilibrium with carbonate–silicate rocks in warm subduction settings. Consequently, accounting for electrolytic fluids at these conditions slightly increases the solubility of carbon in the fluids compared with predictions by classical binary H2O–CO2 fluids, but does not affect the topology of phase relations in serpentinite‐hosted carbonate‐ rocks. Phase relations, mineral composition and assemblages of Milagrosa and Almirez (meta)‐serpentinite‐hosted carbonate–silicate rocks are consistent with local equilibrium between an infiltrating fluid and the bulk rock composition and indicate a limited role of infiltration‐driven decarbonation. Our study shows natural evidence for the preservation of carbonates in serpentinite‐hosted carbonate–silicate rocks beyond the Atg‐serpentinite breakdown at sub‐arc depths, demonstrating that carbon can be recycled into the deep mantle.Funding from the European Union FP7 Marie‐Curie Initial Training Network ABYSS under REA Grant Agreement no. 608001Spanish ‘Agencia Estatal de Investigación’ (AEI) grants no. CGL2016‐75224‐R to V.L.S.‐V and CGL2016‐81085‐R to C.J.G and C.M and grant no. PCIN‐2015‐053 to C.J.GJunta de Andalucía Funding under grants no. RNM‐131, RNM‐374 and P12‐RNM‐3141MINECO for financing a Ramón y Cajal fellowship no. RYC‐2012‐11314 and K.H. for a Juan de la Cierva Fellowship no. FPDI‐2013‐16253 and a research contract under grant no. CGL2016‐81085‐

Magmatism, serpentinization and life: Insights through drilling the Atlantis Massif (IODP Expedition 357)

IODP Expedition 357 used two seabed drills to core 17 shallow holes at 9 sites across Atlantis Massif ocean core complex (Mid-Atlantic Ridge 30°N). The goals of this expedition were to investigate serpentinization processes and microbial activity in the shallow subsurface of highly altered ultramafic and mafic sequences that have been uplifted to the seafloor along a major detachment fault zone. More than 57 m of core were recovered, with borehole penetration ranging from 1.3 to 16.4 meters below seafloor, and core recovery as high as 75% of total penetration in one borehole. The cores show highly heterogeneous rock types and alteration associated with changes in bulk rock chemistry that reflect multiple phases of magmatism, fluid-rock interaction and mass transfer within the detachment fault zone. Recovered ultramafic rocks are dominated by pervasively serpentinized harzburgite with intervals of serpentinized dunite and minor pyroxenite veins; gabbroic rocks occur as melt impregnations and veins. Dolerite intrusions and basaltic rocks represent the latest magmatic activity. The proportion of mafic rocks is volumetrically less than the amount of mafic rocks recovered previously by drilling the central dome of Atlantis Massif at IODP Site U1309. This suggests a different mode of melt accumulation in the mantle peridotites at the ridge-transform intersection and/or a tectonic transposition of rock types within a complex detachment fault zone. The cores revealed a high degree of serpentinization and metasomatic alteration dominated by talc-amphibole-chlorite overprinting. Metasomatism is most prevalent at contacts between ultramafic and mafic domains (gabbroic and/or doleritic intrusions) and points to channeled fluid flow and silica mobility during exhumation along the detachment fault. The presence of the mafic lenses within the serpentinites and their alteration to mechanically weak talc, serpentine and chlorite may also be critical in the development of the detachment fault zone and may aid in continued unroofing of the upper mantle peridotite/gabbro sequences. New technologies were also developed for the seabed drills to enable biogeochemical and microbiological characterization of the environment. An in situ sensor package and water sampling system recorded real-time variations in dissolved methane, oxygen, pH, oxidation reduction potential (Eh), and temperature and during drilling and sampled bottom water after drilling. Systematic excursions in these parameters together with elevated hydrogen and methane concentrations in post-drilling fluids provide evidence for active serpentinization at all sites. In addition, chemical tracers were delivered into the drilling fluids for contamination testing, and a borehole plug system was successfully deployed at some sites for future fluid sampling. A major achievement of IODP Expedition 357 was to obtain microbiological samples along a west–east profile, which will provide a better understanding of how microbial communities evolve as ultramafic and mafic rocks are altered and emplaced on the seafloor. Strict sampling handling protocols allowed for very low limits of microbial cell detection, and our results show that the Atlantis Massif subsurface contains a relatively low density of microbial life

Point sur les appareils domestiques de traitement d'eau

L'installation d'appareils domestiques de traitement d'eau est de plus en plus courante en France, et pour le moment non contrôlée par les autorités sanitaires. Ce travail a eu pour objet d'établir un état des lieux de la situation en France afín d'aider a le prise de decision en la matière. Un court recensement des différents appareils de traitement met en avant leurs avantages et inconvénients et fournit des indications sur leur efficacité. Les quelques études menees à ce jour ne permettent pas de conclure à l'absence de risques pour la santé des consommateurs. Le risque lié á une contamination microbienne semble cependant le plus important, et principalement lié à la qualité de la maintenance. Des études devraient être poursuivies pour établir de façon plus precise les risques sanitaires encourus par les utilisateurs de tels dispositifs. Le marché des appareils de traitement d'eau est un marché éclaté, difficile a appréhender et a contrôler. Les outils disponibles (réglementation, normalisation et certification) ne garantissent pas, dans leurs modalités d'application actuelles, leur efficacité et leur innocuité. Différents types de controles peuvent être imagines à divers stades de la chame de fabrication et de distribution de ces produits. Pour ce qui concerne les produits neufs, le développement et la mise en ceuvre d'un essai de controle de l'innocuité sanitaire des appareils est important. Un protocole existe, mais il pourrait largement simplifié sans impacter de maniere significative sur sa dimension sanitaire. Les protocoles établis par NSF, DWI et la circulaire du 25 novembre 2002 constituent d'autres bonnes sources d'inspiration. Quant au contrôle de leur efficacité il ne semble pas constituer un enjeu sanitaire majeur en France dans la mesure où l'eau est supposée potable au compteur. Cet aspect ne nécessite done sans doute pas un cadre réglementaire. Avant tout, les efforts devraient étre concentres sur l'installation et la maintenance des systémes domestiques de traitement et sur le professionnalisme des techniciens intervenant sur ces produits

Hepatic microsomal metabolism of 1,3-butadiene.

1. In rat liver microsomes, 1,3-butadiene was metabolized to butadiene monoxide, which was subsequently transformed into 3-butene-1,2-diol by microsomal epoxide hydrolase. 2. In the metabolism of butadiene oxide in microsomes, four metabolites were detected, namely two stereoisomers of DL-diepoxybutane, and two stereoisomers of 3,4-epoxy-1,2-butanediol. No meso-diepoxybutane was detected