Constraints on Miocene oceanography and climate in the Western and Central Paratethys: O-, Sr-, and Nd-isotope compositions of marine fish and mammal remains

The Paratethys evolved as a marginal sea during the Alpine-Himalayan orogeny in the Oligo-Miocene. Sediments from the northern Alpine Molasse Basin, the Vienna, and the Pannonian Basins located in the western and central part of the Paratethys thus provide unique information on regional changes in climate and oceanography during a period of active Alpine uplift Oxygen isotope compositions of well-preserved phosphatic fossils recovered from the sediments support deposition under sub-tropical to warm-temperate climate with water temperatures of 14 to 28 degrees C for the Miocene. delta(18)O values of fossil shark teeth are similar to those reported for other Miocene marine sections and, using the best available estimates of their biostratigraphic age, show a variation until the end of the Badenian similar to that reported for composite global record. The (87)Sr/(86)Sr isotope ratios of the fossils follow the global Miocene seawater trend, albeit with a much larger scatter. The deviations of (87)Sr/(86)Sr in the samples from the well-constrained seawater curve are interpreted as due to local input of terrestrially-derived Sr. Contribution of local sources is also reflected in the epsilon(Nd) values, consistent with input from ancient crystalline rocks (e.g., Bohemian Massif and/or Mesozoic sediments with epsilon(Nd) < -9. On the other hand, there is evidence for input from areas with Neogene volcanism as suggested by samples with elevated epsilon(Nd) values >-7. Excluding samples showing local influence on the water column, an average epsilon(Nd) value of -7.9 +/- 0.5 may be inferred for the Miocene Paratethys. This value is indistinguishable from the epsilon(Nd) value of the contemporaneous Indian Ocean, supporting a dominant role of this ocean in the Western and Central Paratethys. (C) 2008 Elsevier B.V. All rights reserved.

The thermal circuits of the Argentera Massif (western Alps, Italy): An example of low-enthalpy geothermal resources controlled by Neogene alpine tectonics

This work presents geochemistry and structural geology data concerning the low enthalpy geothermal circuits of the Argentera crystalline Massif in northwestern Italian Alps. I n this area some thermal springs (50-60 degreesC), located in the small Bagni di Vinadio village, discharge mixtures made up of a Na-Cl end-member and a Na-SO4 component. The latter is also discharged by the thermal springs of Terme di Valdieri located some kilometres apart within the same tectonic complex. Both end-members share the same meteoric origin and the same reservoir temperature, which is close to 150 degreesC. Explanations are thus required to understand how they reach the surface and how waters of the same origin and circulating in similar rocks can attain such different compositions. Sodium-sulphate waters discharged at both sites, likely represent the common interaction product of meteoric waters with the widespread granitic-migmatitic rocks of the Argentera Massif, whereas Na-CI waters originate through leaching of mineralised cataclastic rocks, which are rich in phyllosilicatic minerals and fluid inclusions, both acting as Cl- sources. Due to the relatively low inferred geothermal gradient of the region, -25C/km, meteoric waters have to descend to depths of 5.5-6 km to attain temperatures of similar to 150 degreesC. These relevant depths can be reached by descending meteoric waters, due to the recent extensional stress field, which allows the development of geothermal circulations at greater depths than in other sectors of the Alps by favouring a greater fractures aperture. The ascent of the thermal waters rakes place along brittle shear zones. In both sites, the thermal waters emerge at the bottoms of the valleys, close to either the lateral termination of a brittle shear zone at Terme di Valdieri, or a step-over between two en-echelon brittle shear zones at Bagni di Vinadio. These observations attest to a strong control operated on the location of outlet regions by both brittle tectonics and the minima in hydraulic potential inside the fractured massif.

Phytobenthic assemblages of Addaia Bay (Menorca, Western Mediterranean): composition and distribution

Study on the composition and distribution of Phytobenthic Assemblages of Addaia Bay (Menorca, Western Mediterranean)

Species-specific population structure in rock-specialized sympatric cichlid species in Lake Tanganyika, East Africa.

Species richness and geographical phenotypic variation in East African lacustrine cichlids are often correlated with ecological specializations and limited dispersal. This study compares mitochondrial and microsatellite genetic diversity and structure among three sympatric rock-dwelling cichlids of Lake Tanganyika, Eretmodus cyanostictus, Tropheus moorii, and Ophthalmotilapia ventralis. The species represent three endemic, phylogenetically distinct tribes (Eretmodini, Tropheini, and Ectodini), and display divergent ecomorphological and behavioral specialization. Sample locations span both continuous, rocky shoreline and a potential dispersal barrier in the form of a muddy bay. High genetic diversity and population differentiation were detected in T. moorii and E. cyanostictus, whereas much lower variation and structure were found in O. ventralis. In particular, while a 7-km-wide muddy bay curtails dispersal in all three species to a similar extent, gene flow along mostly continuous habitat appeared to be controlled by distance in E. cyanostictus, further restricted by site philopatry and/or minor habitat discontinuities in T. moorii, and unrestrained in O. ventralis. In contrast to the general pattern of high gene flow along continuous shorelines in rock-dwelling cichlids of Lake Malawi, our study identifies differences in population structure among stenotopic Lake Tanganyika species. The amount of genetic differentiation among populations was not related to the degree of geographical variation of body color, especially since more phenotypic variation is observed in O. ventralis than in the genetically highly structured E. cyanostictus.

Sea-level changes and ammonite faunal turnover during the Lias/Dogger transition in the western Tethys

The aim of this paper was to investigate the possible connections between ammonite faunal turnover and the eustatic events recorded in Tethyan sequences during the middle Toarcian/early Bajocian time interval. For this we have analysed the biostratigraphic ranges, at the subzone level, of approximately 600 ammonite species belonging to 160 genera from several selected sections of the western Tethys (Mediterranean and Submediterranean provinces). The analysis of taxon ranges enabled us to plot curves for ammonite faunal turnovers, inter-subzonal distance, and diversity. Comparing the mentioned curves with Tethyan sequences [Hardenbol et al., 19981, we find that sea-level changes correlate well with origination and extinction events and faunal diversity. Most of the faunal turnovers correlate with stratigraphic events. Extinction events with their corresponding decrease in diversity correlate with regressive intervals and with major or minor sequence boundaries. Origination events and their corresponding increase in diversity were clearly connected with transgressions in Tethyan sequences. In several cases, the major sequence boundary and the subsequent transgressive phase correlate with major ammonite faunal turnover, whereas minor or medium sequence boundaries generally gave rise to minor or medium turnovers.

Structure and kinematics of the Siviez-Mischabel nappe in the Mattertal (western Alps of Switzerland) = Structure et cinématique de la nappe de Siviez-Mischabel le long de la vallée de Zermatt (Alpes de Suisse occidentale)

Résumé Cette étude porte sur le flanc inverse de la nappe de Siviez-Mischabel et sur les unités tectoniques sous jacentes (zone de Stalden supérieur et zone Houillère) dans la vallée menant à Zermatt. L'étude structurale du granite permien de Randa (orthogneiss oeillé) permet de mieux comprendre les effets de la déformation alpine sur les roches de socle. La cartographie détaillée de l'orthogneiss et de son encaissant, ainsi que l'étude lithostratigraphique des terrains sédimentaires associés permettent de proposer un schéma structural et cinématique du flanc inverse de la nappe de Siviez-Mischabel et de mieux comprendre ses relations avec les unités tectoniques sous-jacentes. L'analyse structurale de l'orthogneiss de Randa et de son encaissant révèle la superposition de plusieurs phases de déformation ductile. Cet orthogneiss formé sous des conditions métamorphiques du faciès schiste vert possède une forte schistosité alpine avec au moins deux linéations d'extension. La première, L1, orientée NW-SE est associée à la mise en place de la nappe. La seconde, L2, orientée SW-NE, se corrèle au cisaillement ductile du Simplon. La quantification de la déformation au moyen de la méthode de Fry sur les faciès porphyriques donne des ellipses à rapports axiaux compris entre 1.9 et 5.3, en accord avec les valeurs obtenues par d'autres marqueurs {tourmalines étirées, fibres). Les valeurs mesurées parallèlement à L1 ou L2 sont très semblables. La méthode de Fry a nécessité une étude théorique préalable afin de vérifier son applicabilité aux orthogneiss oeillés. La méthode requiert une distribution spatiale homogène et isotrope des marqueurs utilisés. Les tests statistiques effectués ont révélé que les phénocristaux de feldspath alcalin satisfont à cette condition et qu'ils peuvent être utilisés comme marqueur de la déformation au moyen de la méthode de Fry. Les valeurs obtenues révèlent l'importance du cisaillement ductile du Simplon sur la géométrie de la nappe dans la région d'étude. Le levé cartographique a permis d'améliorer la lithostratigraphie de la base de la nappe de Siviez-Mischabel. Trois formations en position renversée peuvent être observées sous les gneiss formant le coeur de la nappe. Ces trois formations forment le coeur du synclinal de St-Niklaus qui connecte la nappe de Siviez-Mischabel à la zone de Stalden supérieur. La datation par U-Pb de zircons détritiques et magmatiques par LA-ICP-MS permet de contraindre l'âge des formations observées (probablement Carbonifère à Trias précoce). Ces données ont des répercussions importantes sur la structure de la nappe dans la région, prouvant l'existence de plusieurs plis avec des séries normales et renversées bien préservées. La définition et la datation de ces formations, ainsi que leur identification dans la-Zone- Houillère avoisinante permettent de mieux comprendre la géométrie initiale et les relations tectoniques des nappes du Pennique moyen dans la vallée de Zermatt. Summary This study investigates the overturned limb of the Siviez-Mischabel nappe and underlying tectonic units (Upper Stalden zone and Houillère zone) in the Mattertal area. Detailed structural analysis in the Permian Randa granite (augen orthogneiss) allows a better understanding of the Alpine deformation effects on basement rocks. Detailed mapping of this orthogneiss and surrounding rocks, and the study of the lithostratigraphy in the related sedimentary horizons allow the proposition of a structural and kinematic model for the overturned limb of the Siviez-Mischabel and to better understand the relations with the underlying tectonic units. The structural analysis of the Randa orthogneiss and surrounding rocks revealed the superposition of several phases of ductile deformation. This orthogneiss formed under greenschist facies metamorphic conditions displays a strong Alpine foliation with at least two stretching lineations. The first lineation, L1, is oriented NW-SE and is related to the nappe emplacement northward. The second one, L2, is related to the Simplon ductile shear zone. Strain estimation using the Fry method has been performed on porphyritic facies of the Randa orthogneiss. The obtained ellipses have axial ratios varying between 1.9 and 5.3, in agreement with strain estimation obtained from other markers (stretched turmalines, fringes). The strain values are very similar if measured parallel to L1 or to L2. A theoretical approach was necessary to verify the relevant application of the Fry method to augen orthogneiss. This method requires that the distribution of the used markers has to be homogeneous and isotropic. Statistical tests have been done and revealed that K-feldspar phenocrysts satisfy these conditions and can be used as strain markers with the Fry method. The obtained strain measurements revealed the importance of the Simplon ductile shear zone on the geometry of the nappe in the studied area. Mapping has improved the lithostratigraphy at the base of the Siviez-Mischabel nappe. Three overturned formations can be observed below the gneisses forming the core of the nappe. These three formations form the St-Niklaus syncline, which connects the Siviez-Mischabel nappe to the underlying Upper Stalden zone. U-Pb dating of detrital and magmatic zircons by LA-ICPMS allowed the age of the observed formations to be constrained (presumably Carboniferous to Early Triassic). This data has critical implications for nappe structure in the region, composed of few recumbent folds with well preserved normal and overturned limbs. The definition and dating of these formations, as well as their identification in the adjacent "Houillère Zone" improve the understanding of the geometry and tectonic relations of the Middle Penninic nappes in the Mattertal.

Tectonomagmatic evolution of Western Amazonia: Geochemical characterization and zircon U-Pb geochronologic constraints from the Peruvian Eastern Cordilleran granitoids

The results of a coupled, in situ laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U-Pb study on zircon and geochemical characterization of the Eastern Cordilleran intrusives of Peru reveal 1.15 Ga of intermittent magmatism along central Western Amazonia, the Earth's oldest active open continental margin. The eastern Peruvian batholiths are volumetrically dominated by plutonism related to the assembly and breakup of Pangea during the Paleozoic-Mesozoic transition. A Carboniferous-Permian (340-285 Ma) continental arc is identified along the regional orogenic strike from the Ecuadorian border (6 degrees S) to the inferred inboard extension of the Arequipa-Antofalla terrane in southern Peru (14 degrees S). Widespread crustal extension and thinning, which affected western Gondwana throughout the Permian and Triassic resulted in the intrusion of the late- to post-tectonic La Merced-San Ramon-type anatectites dated between 275 and 220 Ma, while the emplacement of the southern Cordillera de Carabaya peraluminous granitoids in the Late Triassic to Early Jurassic (220-190 Ma) represents, temporally and regionally, a separate tectonomagmatic event likely related to resuturing of the Arequipa-Antofalla block. Volcano-plutonic complexes and stocks associated with the onset of the present Andean cycle define a compositionally bimodal alkaline suite and cluster between 180 and 170 Ma. A volumetrically minor intrusive pulse of Oligocene age (ca. 30 Ma) is detected near the southwestern Cordilleran border with the Altiplano. Both post-Gondwanide (30-170 Ma), and Precambrian plutonism (691-1123 Ma) are restricted to isolated occurrences spatially comprising less than 15% of the Eastern Cordillera intrusives. Only one remnant of a Late Ordovician intrusive belt is recognized in the Cuzco batholith (446.5 +/- 9.7 Ma) indicating that the Famatinian arc system previously identified in Peru along the north-central Eastern Cordillera and the coastal Arequipa-Antofalla terrane also existed inboard of this parautochthonous crustal fragment. Hitherto unknown occurrences of late Mesoproterozoic and middle Neoproterozoic granitoids from the south-central cordilleran segment define magmatic events at 691 +/- 13 Ma, 751 +/- 8 Ma, 985 +/- 14 Ma, and 1071-1123 +/- 23 Ma that are broadly coeval with the Braziliano and Grenville-Sunsas orogenies, respectively. Our data suggest the existence of a continuous orogenic belt in excess of 3500 km along Western Amazonia during the formation of Rodinia, its ``early'' fragmentation prior to 690 Ma, and support a model of reaccretion of the Paracas-Arequipa-Antofalla terrane to western Gondwana in the Early Ordovician with subsequent detachment of the Paracas segment in form of the Mexican Oaxaquia microcontinent in Middle Ordovician. A tectonomagmatic model involving slab detachment, followed by underplating of cratonic margin by asthenospheric mantle is proposed for the genesis of the volumetrically dominant Late Paleozoic to early Mesozoic Peruvian Cordilleran batholiths.

An international registry on autoinflammatory diseases: the Eurofever experience.

OBJECTIVE: To report on the demographic data from the first 18 months of enrollment to an international registry on autoinflammatory diseases in the context of the Eurofever project. METHODS: A web-based registry collecting baseline and clinical information on autoinflammatory diseases and related conditions is available in the member area of the PRINTO web-site. Anonymised data were collected with standardised forms. RESULTS: 1880 (M:F=916:964) individuals from 67 centers in 31 countries have been entered in the Eurofever registry. Most of the patients (1388; 74%), reside in western Europe, 294 (16%) in the eastern and southern Mediterranean region (Turkey, Israel, North Africa), 106 (6%) in eastern Europe, 54 in Asia, 27 in South America and 11 in Australia. In total 1049 patients with a clinical diagnosis of a monogenic autoinflammatory diseases have been enrolled; genetic analysis was performed in 993 patients (95%): 703 patients have genetically confirmed disease and 197 patients are heterozygous carriers of mutations in genes that are mutated in patients with recessively inherited autoinflammatory diseases. The median diagnosis delay was 7.3 years (range 0.3-76), with a clear reduction in patients born after the identification of the first gene associated with autoinflammatory diseases in 1997. CONCLUSIONS: A shared online registry for patients with autoinflammatory diseases is available and enrollment is ongoing. Currently, there are data available for analysis on clinical presentation, disease course, and response to treatment, and to perform large scale comparative studies between different conditions.

High-precision dating and origin of synsedimentary volcanism in the Late Carboniferous Salvan-Dorenaz basin (Aiguilles-Rouges Massif, Western Alps)

Late Variscan volcanic activity is documented in the Late Carboniferous Salvan-Dorenaz sedimentary basin and in the neighboring basement units of the Aiguilles-Rouges and Mont-Blanc crystalline massifs (Western Alps). Precise U/Pb isotopic dating, zircon morphology and geochemical analyses indicate that volcanism occurred during short-lived pulses and that coexisting crustal and mantle sources were involved in the production of melts. Volcanic and subvolcanic products were emplaced along major N-S to NNE-SSW transtensional fracture zones, similar to the ones that governed intense basement exhumation and that favored the formation and filling of the Late Carboniferous Salvan-Dorenaz continental basin. In the Aiguilles-Rouges massif, dacitic flows outcropping at the base of the Salvan-Dorenaz basin erupted at 308 +/- 3 Ma; they represent the surface equivalent of the nearby Vallorcine peraluminous granite and associated rhyolitic dykes (311 +/- 17 Ma). In the Mont Blanc massif, calc-alkaline rhyolitic dykes were emplaced simultaneously (307 +/- 2 Ma) at shallow crustal levels, but they derive from deeper magma sources denoting enhanced mantellic activity. Recently identified tuffs and volcaniclastic layers embedded at different levels of the Salvan-Dorenaz stratigraphic record testify a 295 +3/-4 Ma old episode of highly explosive volcanism from distant volcanic centers, possibly located in the Aar-Gotthard massifs (Central Alps). Their zircon typology is highly heterogeneous. documenting wall-rock contamination of the melts and/or admixture of crustal sediments, whereas consistent subpopulations point to high-temperature magmas of deep-seated origin and alkaline affinity. The dated volcanic layers from the Salvan-Dorenaz basin set the beginning of the detrital sedimentation at 308 +/- 3 Ma and constrain the deposition of 1.5-1.7 km thick of elastic sediments within a time span of 10-15 Ma. These results infer minimum, long-term subsidence rates during basin evolution in the order of >0.1 mm/a, while in the surrounding basement units estimated exhumation rates are in the range of 1 mm/a. All dated rocks contain inherited zircon populations about 350, 450 or 600 Ma old.

Longer term clinical and virological outcome of sub-Saharan African participants on antiretroviral treatment in the Swiss HIV Cohort Study.

OBJECTIVES: Persons from sub-Saharan Africa (SSA) are increasingly enrolled in the Swiss HIV Cohort Study (SHCS). Cohorts from other European countries showed higher rates of viral failure among their SSA participants. We analyzed long-term outcomes of SSA versus North Western European participants. DESIGN: We analyzed data of the SHCS, a nation-wide prospective cohort study of HIV-infected adults at 7 sites in Switzerland. METHODS: SSA and North Western European participants were included if their first treatment combination consisted of at least 3 antiretroviral drugs (cART), if they had at least 1 follow-up visit, did not report active injecting drug use, and did not start cART with CD4 counts >200 cells per microliter during pregnancy. Early viral response, CD4 cell recovery, viral failure, adherence, discontinuation from SHCS, new AIDS-defining events, and survival were analyzed using linear regression and Cox proportional hazard models. RESULTS: The proportion of participants from SSA within the SHCS increased from 2.6% (<1995) to 20.8% (2005-2009). Of 4656 included participants, 808 (17.4%) were from SSA. Early viral response (6 months) and rate of viral failure in an intent-to-stay-on-cART approach were similar. However, SSA participants had a higher risk of viral failure on cART (adjusted hazard ratio: 2.03, 95% confidence interval: 1.50 to 2.75). Self-reported adherence was inferior for SSA. There was no increase of AIDS-defining events or mortality in SSA participants. CONCLUSIONS: Increased attention must be given to factors negatively influencing adherence to cART in participants from SSA to guarantee equal longer-term results on cART.

El comercio con Africa y el Mediterraneo en las costas orientales de Hispania entre los siglos V y VII: las producciones cerámicas

Il risultato delle indagini condotte negli anni scorsi nei depositi archeologici della Catalogna, sia urbani, sia rurali, consente di determinare le tendenze delle importazioni e dell’economia in quest’area occidentale della penisola iberica fra il V secolo e la fine del VI-inizi del VII. In questa sede viene proposta una sintesi interpretativa dei dati disponibili, specialmente in rapporto al commercio delle ceramiche africane che costituivano le principali importazioni. Allo stato delle ricerche si possono avanzare alcune riflessioni. Se è vero che l’occupazione di Cartagine da parte dei Vandali nel 439 potrebbe aver determinato alcuni cambiamenti nella commercializzazione dei materiali africani, non va escluso che, tra la metà e la seconda metà del V secolo, il rafforzamento politico del regno vandalo abbia causato alcuni importanti cambiamenti tipologici nelle ceramiche africane (sigillata D, anfore) e un nuovo impulso alla relativa commercializzazione. Tra la seconda metà del VI secolo e la prima metà del VII (e forse anche la seconda metà) è proseguito l’arrivo di ceramica africana, proveniente soprattutto dall’area tunisina e, in minore quantità, dal Mediterraneo orientale. L’importazione di sigillata africana ha subito un significativo calo in questo periodo, ma non sparisce del tutto almeno fino agli inizi del VII secolo. Nel contempo è documentato un aumento considerevole della presenza di anfore africane, tanto che non può essere accolta l’ipotesi della cessazione delle importazioni tra la metà e il pieno VI secolo. Di conseguenza la rivalità politica fra i Visigoti e i Bizantini non si è tradotta nella scomparsa del commercio fra la penisola iberica e il Nord Africa, anche se è ben documentata una notevole diminuzione dei prodotti africani nel nord della provincia bizantina di Spania. La causa (o le cause) della fine dell’arrivo delle importazioni mediterranee lungo i litorali ispanici non può essere accertata con sicurezza. D’altra parte le ragioni di questo fenomeno vanno ricercate non solo nei centri di consumo, ma anche nelle aree di produzione, sicché sembra probabile che, come viene tradizionalmente ritenuto, la fine delle esportazioni fu determinata dall’invasione islamica dell’Africa settentrionale.

Mechanisms of garnet growth in eclogites of the Zermatt-Saas Fee unit, Western Alps

THESIS ABSTRACT Garnets are one of the key metamorphic minerals used to study peak metamorphic conditions or crystallization ages. Equilibrium is typically assumed between the garnet and the matrix. This thesis attempts to understand garnet growth in the Zermatt-Saas Fee (ZSF) eclogites, and discusses consequences for Sm/Nd and Lu/Hf dating and the equilibrium assumption. All studied garnets from the ZSF eclogites are strongly zoned in Mn, Fe, Mg, and Ca. Methods based on chemical zoning patterns and on 3D spatial statistics indicate different growth mechanisms depending on the sample studied. Garnets from the Pfulwe area are grown in a system where surface kinetics likely dominated over intergranular diffusion kinetics. Garnets fram two other localities, Nuarsax and Lago di Cignana, seem to have grown in a system where intergranular diffusion kinetics were dominating over surface kinetics, at least during initial growth. Garnets reveal strong prograde REE+Y zoning. They contain narrow central peaks for Lu + Yb + Tm ± Er and at least one additional small peak towards the rim. The REE Sm + Eu + Gd + Tb ± Dy are depleted in the cores but show one prominent peak close to the rim. It is shown that these patterns cam be explained using a transient matrix diffusion model where REE uptake is limited by diffusion in the matrix surrounding the porphyroblast. The secondary peaks in the garnet profiles are interpreted to reflect thermally activated diffusion due to a temperature increase during prograde metamorphism. The model predicts anomalously low 176Lu/177Hf and 147Sm/144Nd ratios in garnets where growth rates are fast compared to diffusion of the REE, which decreases garnet isochron precisions. The sharp Lu zoning was further used to constrain maximum Lu volume diffusion rates in garnet. The modeled minimum pre-exponential diffusion coefficient which fits the measured central peak is in the order of Do = 5.7* 106 m2/s, taking an activation energy of 270 kJ/mol. The latter was chosen in agreement with experimentally determined values. This can be used to estimate a minimum closure temperature of around 630°C for the ZSF zone. Zoning of REE was combined with published Lu/Hf and Sm/Nd age information to redefine the prograde crystallization interval for Lago di Cignana UHP eclogites. Modeling revealed that a prograde growth interval in the order of 25 m.y. is needed to produce the measured spread in ages. RÉSUMÉ Le grenat est un minéral métamorphique clé pour déterminer les conditions du pic de métamorphisme ainsi que l'âge de cristallisation. L'équilibre entre le grenat et la matrice est requis. Cette étude a pour but de comprendre la croissance du grenat dans les éclogites de la zone de Zermatt-Saas Fee (ZSF) et d'examiner quelques conséquences sur les datations Sm/Nd et Lu/Hf. Tous les grenats des éclogites de ZSF étudiés sont fortement zonés en Mn, Fe, Mg et partiellement en Ca. Les différentes méthodes basées sur le modèle de zonation chimique ainsi que sur les statistiques de répartition spatiale en 3D indiquent un mécanisme de croissance différent en fonction de la localité d'échantillonnage. Les grenats provenant de la zone de Pfulwe ont probablement crû dans un système principalement dominé par la cinétique de surface au détriment de 1a cinétique de diffusion intergranulaire. Les grenats provenant de deux autres localités, Nuarsax et Lago di Cignana, semblent avoir cristallisé dans un système dominé par la diffusion intergranulaire, au moins durant les premiers stades de croissance. Les grenats montrent une forte zonation prograde en Terres Rares (REE) ainsi qu'en Y. Les profils présentent au coeur un pic étroit en Lu + Yb+ Tm ± Er et au moins un petit pic supplémentaire vers le bord. Les coeurs des grenats sont appauvris en Sm + Eu + Gd + Tb ± Dy, mais les bords sont marqués par un pic important de ces REE. Ces profils s'expliquent par un modèle de diffusion matricielle dans lequel l'apport en REE est limité par la diffusion dans la matrice environnant les porphyroblastes. Les pics secondaires en bordure de grain reflètent la diffusion activée par l'augmentation de la température lors du métamorphisme prograde. Ce modèle prédit des rapports 176Lu/177Hf et 147Sm/144Nd anormalement bas lorsque les taux de croissance sont plus rapides que la diffusion des REE, ce qui diminue la précision des isochrones impliquant le grenat. La zonation nette en Lu a permis de contraindre le maximum de diffusion volumique par une approche numérique. Le coefficient de diffusion minimum modélisé en adéquation avec les pics mesurés est de l'ordre de Do = 5.7*10-6 m2/s, en prenant une énergie d'activation ~270 kJ/mol déterminée expérimentalement. Ainsi, la température de clôture minimale est estimée aux alentours de 630°C pour la zone ZSF. Des nouvelles données de zonation de REE sont combinées aux âges obtenus avec les rapports Lu/Hf et Sm/Nd qui redéfissent l'intervalle de cristallisation prograde pour les éclogites UHP de Lago di Cignana. La modélisation permet d'attribuer au minimum un intervalle de croissance prograde de 25 Ma afin d'obtenir les âges préalablement mesurés. RESUME GRAND PUBLIC L'un des principaux buts du pétrologue .métamorphique est d'extraire des roches les informations sur l'évolution temporelle, thermique et barométrique qu'elles ont subi au cours de la formation d'une chaîne de montagne. Le grenat est l'un des minéraux clés dans une grande variété de roches métamorphiques. Il a fait l'objet de nombreuses études dans des terrains d'origines variées ou lors d'études expérimentales afin de comprendre ses domaines de stabilité, ses réactions et sa coexistence avec d'autres minéraux. Cela fait du grenat l'un des minéraux les plus attractifs pour la datation des roches. Cependant, lorsqu'on l'utilise pour la datation et/ou pour la géothermobarométrie, on suppose toujours que le grenat croît en équilibre avec les phases coexistantes de la matrice. Pourtant, la croissance d'un minéral est en général liée au processus de déséquilibre. Cette étude a pour but de comprendre comment croît le grenat dans les éclogites de Zermatt - Saas Fee et donc d'évaluer le degré de déséquilibre. Il s'agit aussi d'expliquer les différences d'âges obtenues grâce aux grenats dans les différentes localités de l'unité de Zermatt-Saas Fee. La principale question posée lors de l'étude des mécanismes de croissance du grenat est: Parmi les processus en jeu lors de la croissance du grenat (dissolution des anciens minéraux, transport des éléments vers le nouveau grenat, précipitation d'une nouvelle couche en surface du minéral), lequel est le plus lent et ainsi détermine le degré de déséquilibre? En effet, les grenats d'une des localités (Pfulwe) indiquent que le phénomène d'adhérence en surface est le plus lent, contrairement aux grenats des autres localités (Lago di Cignana, Nuarsax) dans lesquels ce sont les processus de transport qui sont les plus lents. Cela montre que les processus dominants sont variables, même dans des roches similaires de la même unité tectonique. Ceci implique que les processus doivent être déterminés individuellement pour chaque roche afin d'évaluer le degré de déséquilibre du grenat dans la roche. Tous les grenats analysés présentent au coeur une forte concentration de Terres Rares: Lu + Yb + Tm ± Er qui décroît vers le bord du grain. Inversement, les Terres Rares Sm + Eu + Gd + Tb ± Dy sont appauvries au coeur et se concentrent en bordure du grain. La modélisation révèle que ces profils sont-dus à des cinétiques lentes de transport des Terres Rares. De plus, les modèles prédisent des concentrations basses en éléments radiogéniques pères dans certaines roches, ce qui influence fortement sur la précision des âges obtenus par la méthode d'isochrone. Ceci signifie que les roches les plus adaptées pour les datations ne doivent contenir ni beaucoup de grenat ni de très gros cristaux, car dans ce cas, la compétition des éléments entre les cristaux limite à de faibles concentrations la quantité d'éléments pères dans chaque cristal.

P-wave velocities of samples from the Penninic of the western Alps along NFP20-west seismic-reflection profiles

Using the transit pulse method, we have determined compressional wave velocities of rocks from various geological units belonging to the Penninic zone along the NFP20-West profiles of the Swiss western Alps. The velocities have been measured at confining pressures up to 400 MPa, along three orthogonal axes defined by the macrostructure of the rocks. The samples analysed show a degree of metamorphism ranging from greenschist to eclogite facies. This collection includes schists, dolomites, gneisses and ophiolitic rocks. The mean velocities range from 5.9 km/s for a quartzitic calcschist to 7.9 km/s for an eclogitic metagabbro. The velocity anisotropy is as high as 20 %. The range of acoustic impedance is wide, from 15 to 27 10(6) kg/m2s. From these measurements, normal incident reflection coefficients for likely rock assemblages within and between geological units were estimated in order to interpret zone of the strong reflections recorded along the seismic profiles. Reflection coefficients as high as 0.17 could be determined.