COMMENT ON "THE ROLE OF H3O+ IN THE CRYSTAL STRUCTURE OF ILLITE" BY F. NIETO, M. MELINI, AND I. ABAD

The arguments of Nieto et al. (2010) in favor of the incorporation of H3O+ rather than H2O in interlayer positions of illite are disputable. Stoichiometric arguments suggest that the excess water in the Silver Hill illite is in the form of H2O. Moreover, recent thermodynamic models assuming the incorporation of interlayer H2O in illite provide reasonable estimates of temperature and water content using the AEM/TEM analyses of Nieto et al. (2010)

Diachronous evolution of the alpine continental subduction wedge: evidence from P-T estimates in the Briançonnais Zone houillère (France - Western Alps).

International audienceThe study of continental subduction processes requires detailed Pressure Temperature (P-T) paths to understand the kinematic of burial and exhumation of continental units. In the French Western Alps, the Briançonnais zone is a remnant of the continental subduction wedge. P-T conditions have been estimated in its most internal parts, but there is a lack of data in the western part, known as the "Zone houillère". This Briançonnais Zone houillère is classically divided into two sub-units: the upper and lower Houiller units. This study focuses on both of these in the Clarée valley, north of Briançon. In this low-grade metamorphic terrain, estimation of P-T history is complicated because there are few adapted methods and these rocks have a poor metamorphic mineralogical content, including detrital metamorphic minerals inherited from their hercynian history. Therefore, to acquire accurate P-T estimates a multi-method approach is required, involving qualitative and quantitative Raman study of Carbonaceous Material (RSCM), chemical analysis from quantified X-ray maps and thermodynamic modelling of chlorites and K-white micas. Such multi-approach P-T estimates on a sandstone sample allow distinguishing hercynian peak metamorphic conditions of 371 ± 26°C and 3.5 ± 1.4 kbar and alpine peak metamorphic conditions of 275 ± 23°C and 5.9 ± 1.7 kbar. These results are consistent with our RSCM and Tmax estimates. Raman study conducted on organic-rich schist samples shows an eastward increase of the alpine Tmax in the upper Houiller unit, from 280 to 300°C across the Briançonnais Zone houillère. In contrast, carbonaceous material included in detrital grains of muscovite in the sandstone exhibits higher temperatures. This hercynian Tmax is estimated using thermodynamic modelling at 376 ± 50°C. According to these results and previous work in more internal parts of the Briançonnais zone, a geodynamic reconstruction is proposed, which is characterized by a diachronous evolution of the Briançonnais zone involved in alpine continental subduction at different times. The geothermal gradient in the Briançonnais zone changes from 8°C/km during early continental subduction, to 40°C/km during the collisional event at about 35-30 Ma. The intermediate gradient of 15°C/km estimated in the Briançonnais Zone houillère suggests that this unit was buried later, than the more internal Briançonnais units, after 40 Ma

A thermodynamic model for di-trioctahedral chlorite from experimental and natural data in the system MgO-FeO-Al2O3-SiO2-H2O: applications to P - T sections and geothermometry

We present a new thermodynamic activity-composition model for di-trioctahedral chlorite in the system FeO-MgO-Al2O3-SiO2-H2O that is based on the Holland-Powell internally consistent thermodynamic data set. The model is formulated in terms of four linearly independent end-members, which are amesite, clinochlore, daphnite and sudoite. These account for the most important crystal-chemical substitutions in chlorite, the Fe-Mg, Tschermak and di-trioctahedral substitution. The ideal part of end-member activities is modeled with a mixing-on-site formalism, and non-ideality is described by a macroscopic symmetric (regular) formalism. The symmetric interaction parameters were calibrated using a set of 271 published chlorite analyses for which robust independent temperature estimates are available. In addition, adjustment of the standard state thermodynamic properties of sudoite was required to accurately reproduce experimental brackets involving sudoite. This new model was tested by calculating representative P-T sections for metasediments at low temperatures (<400°C), in particular sudoite and chlorite bearing metapelites from Crete. Comparison between the calculated mineral assemblages and field data shows that the new model is able to predict the coexistence of chlorite and sudoite at low metamorphic temperatures. The predicted lower limit of the chloritoid stability field is also in better agreement with petrological observations. For practical applications to metamorphic and hydrothermal environments, two new semi-empirical chlorite geothermometers named Chl(1) and Chl(2) were calibrated based on the chlorite+quartz+water equilibrium (2 clinochlore+3 sudoite=4 amesite+4 H2O+7 quartz). The Chl(1) thermometer requires knowledge of the (Fe3+/ΣFe) ratio in chlorite and predicts correct temperatures for a range of redox conditions. The Chl(2) geothermometer which assumes that all iron in chlorite is ferrous has been applied to partially recrystallized detrital chlorite from the Zone houillère in the French Western Alps

Micro-cartographie P-T- dans les roches métamorphiques. Applications aux Alpes et à l'Himalaya

L'étude de la dynamique de la lithosphère, en particulier les processus de transports verticaux et horizontaux de matière, requiert de pouvoir reconstruire avec la plus grande précision l'évolution géodynamique des chaînes de montagne. C'est le rôle des trajets pression-température-temps-déformation (P-T-t-e) qui permettent, pour un fragment de roche, de reconstruire son histoire à partir de l'étude texturale et chimique des minéraux métamorphiques à l'équilibre. En effet, les roches métamorphiques présentent des mosaïques de paléo-équilibres thermodynamiques locaux entre des minéraux de paragénèses qui cristallisent à différentes conditions de pressions et de températures. Le problème abordé dans ce mémoire est celui de la reconstruction des trajets pression-température, en combinant l'utilisation d'approches thermobarométriques directes, comme les pseudosections calculées par minimisation d'énergie, et indirectes, comme la technique du multi-équilibre avec une vision en deux dimensions grâce à une approche micro-cartographique. Cependant, l'utilisation conjointe de techniques d'imagerie chimiques et d'estimations thermobarométriques requiert un grand nombre de calculs, et donc des logiciels conviviaux à la disposition de la communauté. Dans cette thèse, nous proposons des programmes pour la cartographie et les calculs thermodynamiques, puis un nouveau modèle de solution solide pour les chlorites et, enfin, des exemples d'applications dans les Alpes et en Himalaya. Nous avons développé un jeu de programmes écrits en Matlab, qui permettent (1) de traiter des images chimiques et de calculer des cartes pression-température : XMapTools, et (2) de chercher des équilibres thermodynamiques et de tracer des réactions chimiques : PT-lines, MultiPlot et Meamp. Un modèle de solution solide pour les chlorites a été proposé en ajoutant un pôle pur di-trioctahédriques. Ce modèle permet de calculer, par minimisation d'énergie, des pseudosections à basse température, ou encore de modéliser des interactions fluide-roche. Dans un deuxième temps, nous proposons d'appliquer les techniques de micro-cartographie et de thermobarométrie à des exemples naturels variés afin d'essayer d'apporter des contraintes supplémentaires pour reconstruire des modèles d'évolutions géodynamiques des chaînes de subduction-collision. Pour les Alpes, des trajets P-T-e et P-T-t ont été proposés pour des unités où jusqu'ici, faute de techniques disponibles, les estimations étaient basées uniquement sur la présence de minéraux index du métamorphisme. Ces nouvelles données ont permis de mettre en évidence un fort couplage entre l'exhumation du prisme océanique et l'écaillage crustal de la plaque continentale subduite. Pour l'Himalaya, nous avons montré qu'il est possible de reconstruire un trajet pression-température continu à partir d'images chimiques en utilisant notre nouvel outil : XMapTools.The study of the lithosphere dynamics such as vertical and horizontal material transport processes requires the detailed reconstruction of the geodynamic evolution of the mountain belts. These geodynamic models are classically constrained using pressure-temperature-time-deformation (P-T-t-e) paths unravelled from textural and chemical study of metamorphic rocks fragments. Metamorphic rocks are made by mosaic of local thermodynamic equilibria involving minerals that grew at different temporal, pressure, and temperature conditions. The topic of this thesis is the reconstruction of pressure-temperature paths by combining direct techniques such as pseudosection computed by energy minimization and inverse techniques such as multi-equilibrium, in space, i.e. two-dimensions, using a micro-mapping approach. The use of chemical images and thermodynamic modelling requires user-friendly programs freely available for the community. In this thesis, we first propose a set of programs and a new solid solution model for chlorite and also two application examples are proposed in the Alps and the Himalaya. We propose a set of programs written in Matlab (1) for microprobe image processing and the computation of pressure temperature maps: XMapTools, (2) for multi-equilibrium calculations using different thermodynamic data and solid solution models: PT-lines, MultiPlot and Meamp. A new solid solution model for chlorite is presented including a di-trioctahedral chlorite end-member. This model can be used to calculate pseudosection phase diagrams and for fluid-rock interaction modelling. Thermodynamic modelling and micro-mapping techniques are used together to add new constraints to the geodynamic models of subduction-collision mountain belts. In the French Western Alps, P-T-e and P-T-t paths are recovered for some metamorphic units in which the available estimates were only based on the occurrence of index minerals. These new thermobarometric and radiometric data indicate a strong coupling between the exhumation of the oceanic accretionary wedge and the continental subducting plate. In The Himalaya, we studied a new eclogite occurrence and we propose a detailed and continuous P-T path calculated using our newly created program XMapTools.SAVOIE-SCD - Bib.électronique (730659901) / SudocGRENOBLE1/INP-Bib.électronique (384210012) / SudocGRENOBLE2/3-Bib.électronique (384219901) / SudocSudocFranceF

Deciphering temperature, pressure and oxygen-activity conditions of chlorite formation

International audienceThe advantages and limits of empirical, semi-empirical and thermodynamic methods devoted to the estimation of chlorite-formation temperature are discussed briefly. The results of semiempirical and thermodynamic approaches with different assumptions regarding the redox state of iron in chlorite are compared for a large set of natural data covering a range of pressure conditions from a few hundred bars to 18 kbar and temperature from 100 to 500°C. The T-XFe3+ evolution estimated using the thermodynamic approach of Vidal et al. (2005) shows a systematic increase in XFe3+ with decreasing temperature, which is compatible with the decrease in aO2 buffered by magnetite- or hematite-chlorite equilibrium. This trend as well as the observed increase in vacancies in chlorite with decreasing temperature is interpreted as the incorporation of Fe3+-sudoite. The standard-state properties of this endmember have been derived to reproduce the observed T-aO2-XFe3+ evolutions. It can be used to estimate T-aO2-XFe3 values with a Chl-Qtz-H2O multi-equilibrium approach. When combining our results with those of other studies published recently, it appears that thermodynamic approaches and mapping techniques developed for metamorphic rocks can be used to discuss the conditions of formation of very low-grade rocks where kinetics is much more sluggish than in metamorphic rocks. This requires use of appropriate analytical tools and techniques with a spatial resolution of a few hundred nanometres

Concentration of osmoregulated periplasmic glucans (OPGs) modulates the activation level of the RcsCD RcsB phosphorelay in the phytopathogen bacteria Dickeya dadantii

International audienceOsmoregulated periplasmic glucans (OPGs) are general constituents of many Proteobacteria. Synthesis of these oligosaccharides is repressed by increased osmolarity of the medium. OPGs are important factors required for full virulence in many zoo-or phytopathogens including Dickeya dadantii. The phytopathogen enterobacterium D. dadantii causes soft-rot disease on a wide range of plant species. The total loss of virulence of opg-negative strains of D. dadantii is linked to the constitutive activation of the RcsCD RcsB phosphorelay highlighting relationship between this phosphorelay and OPGs. Here we show that OPGs control the RcsCD RcsB activation in a concentration-dependent manner, are required for proper activation of this phosphorelay by medium osmolarity, and a high concentration of OPGs in planta is maintained to achieve the low level of activation of the RcsCD RcsB phosphorelay required for full virulence in D. dadantii

Nanoscale precipitation coating: the deposition of inorganic films through step-by-step spray-assembly.

Thin films and surface coatings play an important role in basic and applied research. Here we report on a new, versatile, and simple method ("precipitation coating") for the preparation of inorganic films, based on the alternate spraying of complementary inorganic salt solutions against a receiving surface on which the inorganic deposit forms. The method applies whenever the solubility of the deposited material is smaller than that of the salts in the solutions of the reactants. The film thickness is controlled from nanometers to hundreds of micrometers simply by varying the number of spraying steps; 200 spray cycles, corresponding to less than 15 min deposition time, yield films with thicknesses exceeding one micrometer and reaching tens of micrometers in some cases. The new solution-based process is also compatible with conventional layer-by-layer assembly and permits the fabrication of multimaterial sandwich-like coatings.journal articleresearch support, non-u.s. gov't2010 Aug 24importe

Spray-on organic/inorganic films: a general method for the formation of functional nano- to microscale coatings.

journal article2010 Dec 27importe