Ground-state order and spin-lattice coupling in tetrahedral spin systems Cu2Te2O5X2 (X = Br or Cl)

High-resolution ac susceptibility and thermal conductivity measurement on Cu2Te2O5X2 (X=Br,Cl) single crystals are reported. For Br-sample, sample dependence prevents one from distinguishing between possibilities of magnetically ordered and spin-singlet ground states. In Cl-sample a three-dimensional transition at 18.5 K is accompanied by almost isotropic behavior of susceptibility and almost switching behavior of thermal conductivity. Thermal conductivity studies suggest the presence of a tremendous spin-lattice coupling characterizing Cl- but not Br-sample. Below the transition Cl-sample is in a complex magnetic state involving AF order but also the elements consistent with the presence of a gap in the excitation spectrum.

Recrystallisation rims in zircon (Valle d'Arbedo, Switzerland): an integrated cathodoluminescence, LA-ICP-MS, SHRIMP, and TEM study

Recrystallization rims are a common feature of zircon crystals that underwent metamorphism. We present a microstructural and microchemical study of partially recrystallized zircon grains collected in polymetamorphic migmatites (Valle d'Arbedo, Ticino, Switzerland). The rims are bright in cathodo-luminescence (CL), with sharp and convex contacts characterized by inward-penetrating embayments transgressing igneous zircon cores. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) data and transmission electron microscopy (TEM) imaging indicate that the rims are chemically and microstructurally different from the cores. The rims are strongly depleted in REE, with concentrations up to two orders of magnitude lower than in the cores, indicating a significant loss of REE during zircon recrystallization. Enrichment in non-formula elements, such as Ca, has not been observed in the rims. The microstructure of zircon cores shows a dappled intensity at and below the 100 nm scale, possibly due to radiation damage. Other defects such as pores and dislocations are absent in the core except at healed cracks. Zircon rims are mostly dapple-free, but contain nanoscale pores and strain centers, interpreted as fluid inclusions and chemical residues, respectively. Sensitive high-resolution ion microprobe (SHRIMP) U-Pb ages show that the recrystallization of the rims took place >200 Ma ago when the parent igneous zircon was not metamict. The chemical composition and the low-Ti content of the rims indicate that they form at sub-solidus temperatures (550-650 degrees C). Recrystallization rims in Valle d'Arbedo zircon are interpreted as the result of the migration of chemical reaction fronts in which fluid triggered in situ and contemporaneous interface-coupled dissolution-reprecipitation mechanisms. This study indicates that strong lattice strain resulting from the incorporation of a large amount of impurities and structural defects is not a necessary condition for zircon to recrystallize. Our observations suggest that the early formation of recrystallization rims played a major role in preserving zircon from the more recent Alpine metamorphic overprint.

Large fluctuations in the disassembly rate of microtubules revealed by atomic force microscopy.

Atomic force microscopy (AFM) in situ has been used to observe the cold disassembly dynamics of microtubules at a previously unrealised spatial resolution. Microtubules either electrostatically or covalently bound to aminosilane surfaces disassembled at room temperature under buffer solutions with no free tubulin present. This process was followed by taking sequential tapping-mode AFM images and measuring the change in the microtubule end position as a function of time, with an spatial accuracy down to +/-20nm and a temporal accuracy of +/-1s. As well as giving average disassembly rates on the order of 1-10 tubulin monomers per second, large fluctuations in the disassembly rate were revealed, indicating that the process is far from smooth and linear under these experimental conditions. The surface bound rates measured here are comparable to the rates for GMPCPP-tubulin microtubules free in solution, suggesting that inhibition of tubulin curvature through steric hindrance controls the average, relatively low disassembly rate. The large fluctuations in this rate are thought to be due to multiple pathways in the kinetics of disassembly with differing rate constants and/or stalling due to defects in the microtubule lattice. Microtubules that were covalently bound to the surface left behind the protofilaments covalently cross-linked to the aminosilane via glutaraldehyde during the disassembly process. Further work is needed to quantitatively assess the effects of surface binding on protofibril disassembly rates, reveal any differences in disassembly rates between the plus and minus ends and to enable assembly as well as disassembly to be imaged in the microscope fluid cell in real-time.

Evolutionary games on complex networks : the emergence and maintenance of cooperation

Abstract The object of game theory lies in the analysis of situations where different social actors have conflicting requirements and where their individual decisions will all influence the global outcome. In this framework, several games have been invented to capture the essence of various dilemmas encountered in many common important socio-economic situations. Even though these games often succeed in helping us understand human or animal behavior in interactive settings, some experiments have shown that people tend to cooperate with each other in situations for which classical game theory strongly recommends them to do the exact opposite. Several mechanisms have been invoked to try to explain the emergence of this unexpected cooperative attitude. Among them, repeated interaction, reputation, and belonging to a recognizable group have often been mentioned. However, the work of Nowak and May (1992) showed that the simple fact of arranging the players according to a spatial structure and only allowing them to interact with their immediate neighbors is sufficient to sustain a certain amount of cooperation even when the game is played anonymously and without repetition. Nowak and May's study and much of the following work was based on regular structures such as two-dimensional grids. Axelrod et al. (2002) showed that by randomizing the choice of neighbors, i.e. by actually giving up a strictly local geographical structure, cooperation can still emerge, provided that the interaction patterns remain stable in time. This is a first step towards a social network structure. However, following pioneering work by sociologists in the sixties such as that of Milgram (1967), in the last few years it has become apparent that many social and biological interaction networks, and even some technological networks, have particular, and partly unexpected, properties that set them apart from regular or random graphs. Among other things, they usually display broad degree distributions, and show small-world topological structure. Roughly speaking, a small-world graph is a network where any individual is relatively close, in terms of social ties, to any other individual, a property also found in random graphs but not in regular lattices. However, in contrast with random graphs, small-world networks also have a certain amount of local structure, as measured, for instance, by a quantity called the clustering coefficient. In the same vein, many real conflicting situations in economy and sociology are not well described neither by a fixed geographical position of the individuals in a regular lattice, nor by a random graph. Furthermore, it is a known fact that network structure can highly influence dynamical phenomena such as the way diseases spread across a population and ideas or information get transmitted. Therefore, in the last decade, research attention has naturally shifted from random and regular graphs towards better models of social interaction structures. The primary goal of this work is to discover whether or not the underlying graph structure of real social networks could give explanations as to why one finds higher levels of cooperation in populations of human beings or animals than what is prescribed by classical game theory. To meet this objective, I start by thoroughly studying a real scientific coauthorship network and showing how it differs from biological or technological networks using divers statistical measurements. Furthermore, I extract and describe its community structure taking into account the intensity of a collaboration. Finally, I investigate the temporal evolution of the network, from its inception to its state at the time of the study in 2006, suggesting also an effective view of it as opposed to a historical one. Thereafter, I combine evolutionary game theory with several network models along with the studied coauthorship network in order to highlight which specific network properties foster cooperation and shed some light on the various mechanisms responsible for the maintenance of this same cooperation. I point out the fact that, to resist defection, cooperators take advantage, whenever possible, of the degree-heterogeneity of social networks and their underlying community structure. Finally, I show that cooperation level and stability depend not only on the game played, but also on the evolutionary dynamic rules used and the individual payoff calculations. Synopsis Le but de la théorie des jeux réside dans l'analyse de situations dans lesquelles différents acteurs sociaux, avec des objectifs souvent conflictuels, doivent individuellement prendre des décisions qui influenceront toutes le résultat global. Dans ce cadre, plusieurs jeux ont été inventés afin de saisir l'essence de divers dilemmes rencontrés dans d'importantes situations socio-économiques. Bien que ces jeux nous permettent souvent de comprendre le comportement d'êtres humains ou d'animaux en interactions, des expériences ont montré que les individus ont parfois tendance à coopérer dans des situations pour lesquelles la théorie classique des jeux prescrit de faire le contraire. Plusieurs mécanismes ont été invoqués pour tenter d'expliquer l'émergence de ce comportement coopératif inattendu. Parmi ceux-ci, la répétition des interactions, la réputation ou encore l'appartenance à des groupes reconnaissables ont souvent été mentionnés. Toutefois, les travaux de Nowak et May (1992) ont montré que le simple fait de disposer les joueurs selon une structure spatiale en leur permettant d'interagir uniquement avec leurs voisins directs est suffisant pour maintenir un certain niveau de coopération même si le jeu est joué de manière anonyme et sans répétitions. L'étude de Nowak et May, ainsi qu'un nombre substantiel de travaux qui ont suivi, étaient basés sur des structures régulières telles que des grilles à deux dimensions. Axelrod et al. (2002) ont montré qu'en randomisant le choix des voisins, i.e. en abandonnant une localisation géographique stricte, la coopération peut malgré tout émerger, pour autant que les schémas d'interactions restent stables au cours du temps. Ceci est un premier pas en direction d'une structure de réseau social. Toutefois, suite aux travaux précurseurs de sociologues des années soixante, tels que ceux de Milgram (1967), il est devenu clair ces dernières années qu'une grande partie des réseaux d'interactions sociaux et biologiques, et même quelques réseaux technologiques, possèdent des propriétés particulières, et partiellement inattendues, qui les distinguent de graphes réguliers ou aléatoires. Entre autres, ils affichent en général une distribution du degré relativement large ainsi qu'une structure de "petit-monde". Grossièrement parlant, un graphe "petit-monde" est un réseau où tout individu se trouve relativement près de tout autre individu en termes de distance sociale, une propriété également présente dans les graphes aléatoires mais absente des grilles régulières. Par contre, les réseaux "petit-monde" ont, contrairement aux graphes aléatoires, une certaine structure de localité, mesurée par exemple par une quantité appelée le "coefficient de clustering". Dans le même esprit, plusieurs situations réelles de conflit en économie et sociologie ne sont pas bien décrites ni par des positions géographiquement fixes des individus en grilles régulières, ni par des graphes aléatoires. De plus, il est bien connu que la structure même d'un réseau peut passablement influencer des phénomènes dynamiques tels que la manière qu'a une maladie de se répandre à travers une population, ou encore la façon dont des idées ou une information s'y propagent. Ainsi, durant cette dernière décennie, l'attention de la recherche s'est tout naturellement déplacée des graphes aléatoires et réguliers vers de meilleurs modèles de structure d'interactions sociales. L'objectif principal de ce travail est de découvrir si la structure sous-jacente de graphe de vrais réseaux sociaux peut fournir des explications quant aux raisons pour lesquelles on trouve, chez certains groupes d'êtres humains ou d'animaux, des niveaux de coopération supérieurs à ce qui est prescrit par la théorie classique des jeux. Dans l'optique d'atteindre ce but, je commence par étudier un véritable réseau de collaborations scientifiques et, en utilisant diverses mesures statistiques, je mets en évidence la manière dont il diffère de réseaux biologiques ou technologiques. De plus, j'extrais et je décris sa structure de communautés en tenant compte de l'intensité d'une collaboration. Finalement, j'examine l'évolution temporelle du réseau depuis son origine jusqu'à son état en 2006, date à laquelle l'étude a été effectuée, en suggérant également une vue effective du réseau par opposition à une vue historique. Par la suite, je combine la théorie évolutionnaire des jeux avec des réseaux comprenant plusieurs modèles et le réseau de collaboration susmentionné, afin de déterminer les propriétés structurelles utiles à la promotion de la coopération et les mécanismes responsables du maintien de celle-ci. Je mets en évidence le fait que, pour ne pas succomber à la défection, les coopérateurs exploitent dans la mesure du possible l'hétérogénéité des réseaux sociaux en termes de degré ainsi que la structure de communautés sous-jacente de ces mêmes réseaux. Finalement, je montre que le niveau de coopération et sa stabilité dépendent non seulement du jeu joué, mais aussi des règles de la dynamique évolutionnaire utilisées et du calcul du bénéfice d'un individu.

Sarcomeric M-band alterations as a marker for human dilated cardiomyopathy

Purpose: The M-band is an important cytoskeletal structure in the centre of the sarcomere, believed to cross-link the thick filament lattice. Its main components are three closely related modular proteins from the myomesin gene family: Myomesin, M-protein and myomesin-3. Each muscle is characterized by its unique M-band protein composition, depending on the contractile parameters of a particular fiber. To investigate the role of the M-band in one of the most relevant and clinically increasing cardiac diseases, we analyzed the expression of myomesin proteins in dilated cardiomyopathy (DCM).Methods: In a previous study we analyzed mouse models suffering from DCM, demonstrating that the embryonic heart specific EH-myomesin splicing isoform was up-regulated directly corresponding to the degree of cardiac dysfunction and ventricular dilation. Based on this study, human ventricular and atrial samples (n=32) were obtained during heart surgery after informed consent and approval by an institutional review board. Patients were aged 30-70 years and suffered from dilated cardiomyopathy (DCM;n=13), Hypertrophic Cardiomyopathy (HCM;n=10) or served as controls (n=9). Patients suffering from DCM or HCM were in endstage heart-failure (NYHA III-IV) and either underwent heart transplantation or Left Ventricular Assist Device (LVAD) implantation. Heart samples from patients who underwent valve surgery or congenital heart surgery served as controls. Heart Samples were analyzed using RT-PCR, Western blot, and immunofluorescence.Results: By investigating the expression pattern of myomesins, we found that DCM is accompanied by specific M-band alterations, which were more pronounced in ventricular samples compared to the atrium. Changes in the amounts of different myomesins during DCM occurred in a cell-specific manner, leading to a higher heterogeneity of the cytoskeleton in cardiomyocytes through the myocardial wall with some cells switching completely to an embryonic phenotype.Conclusions: Here we present that the embryonic heart specific EH-myomesin isoform is up-regulated in human DCM. The alterations of the M-band protein composition might be part of a general adaptation of the sarcomeric cytoskeleton to unfavorable working conditions in the failing heart and may modify the mechanical properties of the cardiomyocytes. We suggest that the upregulation of EH-myomesin might play a pivotal role in DCM and might support classical imagingas a novel sarcomeric marker for this disease.

Point defects and texture of Pd1-xInx sputtered intermetallic thin films

Pd1-xInx thin films (0.4 < x < 0.56) were prepared by radio frequency sputtering from a multi-zone target. The properties of these Hume-Rothery alloys were studied by X-ray diffractometry, electron probe microanalysis and scanning tunneling microscopy. The diffraction spectra were analyzed to obtain the intensity ratio of the (100) superlattice line to the (200) normal line, together with the variations of the lattice constant. The results ape explained quantitatively by a model based on point defects, i.e. Pd vacancies in In-rich films and Pd antisite atoms in Pd-rich films. In-rich films grow preferentially in the [100] direction while Pd-rich films grow preferentially in the [110] direction. The grains in indium-rich sputtered films appear to be enclosed in an atomically thick, indium-rich layer. The role of texture and the influence of point defects on electrical resistivity is also reported. (C) 1996 Elsevier Science Limited.

Mutation hot spots in 5q31-linked corneal dystrophies.

Mutations in the BIGH3 gene on chromosome 5q31 cause four distinct autosomal dominant diseases of the human cornea: granular (Groenouw type I), Reis-Bücklers, lattice type I, and Avellino corneal dystrophies. All four diseases are characterized by both progressive accumulation of corneal deposits and eventual loss of vision. We have identified a specific recurrent missense mutation for each type of dystrophy, in 10 independently ascertained families. Genotype analysis with microsatellite markers surrounding the BIGH3 locus was performed in these 10 families and in 5 families reported previously. The affected haplotype could be determined in 10 of the 15 families and was different in each family. These data indicate that R555W, R124C, and R124H mutations occurred independently in several ethnic groups and that these mutations do not reflect a putative founder effect. Furthermore, this study confirms the specific importance of the R124 and R555 amino acids in the pathogenesis of autosomal dominant corneal dystrophies linked to 5q.

Climate oscillations and species interactions: large-scale congruence but regional differences in the phylogeographic structures of an alpine plant and its monophagous insect

Aim. To predict the fate of alpine interactions involving specialized species, using a monophagous beetle and its host-plant as a case study. Location. The Alps. Methods. We investigated genetic structuring of the herbivorous beetle Oreina gloriosa and its specific host-plant Peucedanum ostruthium. We used genome fingerprinting (in the insect and the plant) and sequence data (in the insect) to compare the distribution of the main gene pools in the two associated species and to estimate divergence time in the insect, a proxy for the temporal origin of the interaction. We quantified the similarity in spatial genetic structures by performing a Procrustes analysis, a tool from the shape theory. Finally, we simulated recolonization of an empty space analogous to the deglaciated Alps just after ice retreat by two lineages from two species showing unbalanced dependence, to examine how timing of the recolonization process, as well as dispersal capacities of associated species, could explain the observed pattern. Results. Contrasting with expectations based on their asymmetrical dependence, patterns in the beetle and plant were congruent at a large scale. Exceptions occurred at a regional scale in areas of admixture, matching known suture zones in Alpine plants. Simulations using a lattice-based model suggested these empirical patterns arose during or soon after recolonization, long after the estimated origin of the interaction c. 0.5 million years ago. Main conclusions. Species-specific interactions are scarce in alpine habitats because glacial cycles have limited opportunities for coevolution. Their fate, however, remains uncertain under climate change. Here we show that whereas most dispersal routes are paralleled at large scale, regional incongruence implies that the destinies of the species might differ under changing climate. This may be a consequence of the host-dependence of the beetle that locally limits the establishment of dispersing insects.

Novel nuclear ribonucleoprotein structural components in the dormouse adrenal cortex during hibernation.

Adrenocortical cell nuclei of the dormouse Muscardinus avellanarius were investigated by electron microscopic immunocytochemistry in hibernating, arousing and euthermic individuals. While the basic structural constituents of the cell nucleus did not significantly modify in the three groups, novel structural components were found in nuclei of hibernating dormice. Lattice-like bodies (LBs), clustered granules (CGs), fibrogranular material (FGM) and granules associated with bundles of nucleoplasmic fibrils (NF) all contained ribonucleoproteins (RNPs), as shown by labeling with anti-snRNP (small nuclear RNP), anti-m3G-capped RNA and anti-hnRNP (heterogeneous nuclear RNP) antibodies. Moreover, the FGM also showed immunoreactivity for the proliferation associated nuclear antigen (PANA) and the non-snRNP splicing factor SC-35. All these nuclear structural components disappeared early during arousal and were not found in euthermic animals. These novel RNP-containing structures, which have not been observed in other tissues investigated so far in the same animal model, could represent storage and/or processing sites for pre-mRNA during the extreme metabolic condition of hibernation, to be quickly released upon arousal. NFs, which had been sometimes found devoid of associated granules in nuclei of brown adipose tissue from hi-bernating dormice, were present in much higher amounts in adrenocortical cell nuclei; they do not contain RNPs and their role remains to be elucidated. The possible roles of these structures are discussed in the frame of current knowledge of morpho-functional relationships in the cell nucleus.

Are the light-harvesting I complexes from Rhodospirillum rubrum arranged around the reaction centre in a square geometry?

The basic photosynthetic unit containing the reaction centre and the light-harvesting I complex (RC-LHI) of the purple non-sulphur bacterium Rhodospirillum rubrum was purified and reconstituted into two-dimensional (2D) membrane crystals. Transmission electron microscopy using conventional techniques and cryoelectron microscopy of the purified single particles and of 2D crystals yielded a projection of the RC-LHI complex at a resolution of at least 1.6 nm. In this projection the LHI ring appears to have a square symmetry and packs in a square crystal lattice. The square geometry of the LHI ring was observed also in images of single isolated particles of the RC-LHI complex. However, although the LHI units are packed identically within the crystal lattice, a new rotational analysis developed here showed that the reaction centres take up one of four possible orientations within the ring. This fourfold disorder supports our interpretation of a square ring symmetry and suggests that a hitherto undetected component may be present within the photosynthetic unit.

Numerical simulation of gel electrophoresis of DNA knots in weak and strong electric fields.

Gel electrophoresis allows one to separate knotted DNA (nicked circular) of equal length according to the knot type. At low electric fields, complex knots, being more compact, drift faster than simpler knots. Recent experiments have shown that the drift velocity dependence on the knot type is inverted when changing from low to high electric fields. We present a computer simulation on a lattice of a closed, knotted, charged DNA chain drifting in an external electric field in a topologically restricted medium. Using a Monte Carlo algorithm, the dependence of the electrophoretic migration of the DNA molecules on the knot type and on the electric field intensity is investigated. The results are in qualitative and quantitative agreement with electrophoretic experiments done under conditions of low and high electric fields.

On the role of kerato-epithelin in the pathogenesis of 5q31-linked corneal dystrophies.

PURPOSE: Recently, the authors identified a gene, BIGH3, in which different mutations cause a group of hereditary corneal dystrophies: lattice type I and IIIA (CDLI and CDLIIIA), granular Groenouw type I (CDGGI), Avellino (CDA), and Reis-Bücklers' (CDRB). All these disorders are characterized by the progressive accumulation of corneal deposits with different structural organization. Experiments were conducted to determine the role of kerato-epithelin (KE), the product of BIGH3, in the pathogenesis of the diseases. METHODS: KE-15 and KE-2, two rabbit antisera raised against peptides from the 69-364 and 426 - 682 amino acid regions of KE respectively, were used for immunohistology of the corneas obtained after keratoplasty in six CDLI patients, three CDGGI patients, and one CDA patient. RESULTS: The nonamyloid deposits observed in CDGGI stained intensively with KE-15 and KE-2, whereas the amyloid deposits in all analyzed CDLI corneas reacted to KE-2 but not to KE-15. In the CDA cornea, where amyloid and nonamyloid inclusions were present, positive staining with both antisera was observed. CONCLUSIONS: Pathologic amyloid and nonamyloid deposits observed in CDLI, CDGGI-, and CDA-affected corneas are caused by KE accumulation. Different staining patterns of amyloid and nonamyloid deposits observed with antibodies against the amino and carboxyl termini of KE suggest that two mechanisms of KE misfolding are implicated in the pathogenesis of 5q31-linked corneal dystrophies.

Neutron structure of type-III antifreeze protein allows the reconstruction of AFP-ice interface.

Antifreeze proteins (AFPs) inhibit ice growth at sub-zero temperatures. The prototypical type-III AFPs have been extensively studied, notably by X-ray crystallography, solid-state and solution NMR, and mutagenesis, leading to the identification of a compound ice-binding surface (IBS) composed of two adjacent ice-binding sections, each which binds to particular lattice planes of ice crystals, poisoning their growth. This surface, including many hydrophobic and some hydrophilic residues, has been extensively used to model the interaction of AFP with ice. Experimentally observed water molecules facing the IBS have been used in an attempt to validate these models. However, these trials have been hindered by the limited capability of X-ray crystallography to reliably identify all water molecules of the hydration layer. Due to the strong diffraction signal from both the oxygen and deuterium atoms, neutron diffraction provides a more effective way to determine the water molecule positions (as D(2) O). Here we report the successful structure determination at 293 K of fully perdeuterated type-III AFP by joint X-ray and neutron diffraction providing a very detailed description of the protein and its solvent structure. X-ray data were collected to a resolution of 1.05 Å, and neutron Laue data to a resolution of 1.85 Å with a "radically small" crystal volume of 0.13 mm(3). The identification of a tetrahedral water cluster in nuclear scattering density maps has allowed the reconstruction of the IBS-bound ice crystal primary prismatic face. Analysis of the interactions between the IBS and the bound ice crystal primary prismatic face indicates the role of the hydrophobic residues, which are found to bind inside the holes of the ice surface, thus explaining the specificity of AFPs for ice versus water.

Elemental and isotopic zoning in natural alpine quartz

THESIS ABSTRACT : Stable isotope geochemistry is used to help resolve a large number of geological questions. In order to do this, it is essential to understand the different mechanisms that govern isotopic fractionation processes between different phases and to identify the conditions required to reach equilibrium fractionation. However, at low temperatures, these processes are poorly constrained and many factors can induce differential partitioning of the isotopes between sectors of a mineral species and the fluid during mineral growth. This can result in so-called 'sector zoning' of a mineral species. The aim of this thesis is to evaluate the occurrence of sector zoning of the oxygen isotopes and trace elements in natural α-quartz crystals and to identify the reasons for such zoning. The implications for the fluid-mineral interactions are studied in the context of the Alpine metamorphism. The approach chosen has focused on examining the crystal structure, cathodoluminescence appearance (CL), and on relating elemental (e.g. Li, Na, Al, P, K, Ca, Ge, Ti, Fe) to stable oxygen isotope compositions between and along different growth sectors. Low temperature quartz samples were selected from Alpine veins in different localities, where growth conditions have already been well constrained. The mineralogy as well as the isotopic compositions of the host rocks were also investigated, in order to interpret the variations obtained between the different growth stages in the framework of fluid-rock interaction during Alpine metamorphism. Depending on the growth conditions, most of the studied quartz is strongly zoned in CL, and it reveals corresponding zonations in the trace element content (e.g. growth zoning). Aluminium, substituting for Si in the lattice, was found in concentrations up to 1000's ppma, and its distribution is strongly related to Li and H and to a lesser extent, to Ge. Elemental sector zoning is evident from the distribution of these three elements since they exhibit differences in their respective concentrations between faces for distinct growth zones, with prismatic faces having the lowest Al contents. Quartz from veins in magmatic rocks, for example, tend to have lower Al concentrations and similar concentrations of Li and Ti suggesting also a contribution of these elements from the host rock. The relationship between Al and Li is still correlated. Only Alpine crystals grown at higher temperatures (~400°C) without any CL zoning feature are free of these impurities and do not show such zoning characteristics. Differences in the δ18O values were measured between different faces principally in the AIenriched growth zones or stages. These results were confirmed by the means of two different methods (in situ/non in situ). However, it was determined that the Al concentrations do not affect significantly oxygen isotope fractionations at 300°C. The results altogether suggest that the presence of sector zoning in quartz crystals is real, but not universal, and henceforth should be taken into consideration for any use of these systems. The occurrence of disequilibrium partitioning has been enhanced and is possibly related to kinetic processes as well as structural effects that do not affect similarly trace element incorporation and isotopic fractionation. In situ measurements also revealed fine scale δ18O zonations along growth paths that are useful to constrain fluid-rock interactions during Alpine metamorphism. Variations in the δ18O values present along growth vectors indicate changes in the fluid composition and origin. Association with oxygen isotope composition of the host rock allows for the deduction of interactions between rocks, veins and consequently fluids, as well as fluid regimes. RESUME DE LA THESE : A basses températures, (i.e. <400°C) les différents mécanismes qui régissent le fractionnement isotopique ainsi que les conditions nécessaires pour établir un état d'équilibre sont peu connus et nombre de paramètres peuvent entraîner un partitionnement chimique différentiel entre différents secteurs d'un minéral et le fluide en contact. Ainsi, ce travail de thèse a pour but d'évaluer la possible présence de zonages sectoriels en isotopes de l'oxygène mais aussi en éléments traces dans des cristaux naturels de quartz-α de basses températures, ainsi que les raisons d'un tel phénomène et enfin ses implications sur les interactions fluide-roche, principalement dans le cadre du métamorphisme Alpin. La structure et l'apparence en cathodoluminescence (CL) des échantillons ont été caractérisées avant de retracer en détail les compositions en élément traces (Li, Na, Al, P, K, Ca, Ge, Ti, Fe) et en isotopes de l'oxygène, le long et entre différents secteurs. Les échantillons de quartz sélectionnés proviennent majoritairement de veines Alpine de différentes localités, où les conditions de croissance ont été déjà bien caractérisées. Les compositions minéralogiques et isotopiques de la roche encaissante ont aussi été examinées, pour contraindre les variations obtenues dans un contexte Alpin. Selon leurs conditions de croissance, la plupart des cristaux étudiés sont fortement zonés, ce qui est souligné par un zonage des concentrations en éléments traces (e.g. zonage de croissance). L'Aluminium, qui peut se substituer à la Silice dans le réseau cristallin, a été retrouvé jusqu'en très grandes concentrations dans certaines zones (plusieurs milliers de ppma). De plus, la distribution en Al est fortement liée à celles de Li et H, ainsi que dans une moindre mesure à Ge. La présence de zonage sectoriel est évidente au niveau de ces éléments qui montrent de larges différences de concentrations entre différentes faces pour une même zone de croissance, avec les concentrations les plus basses retrouvées dans les faces prismatiques. Les quartz de veines situées dans des roches magmatiques par exemple possèdent des concentrations en Li et Ti de même ordre de grandeur, confirmant le rôle de la composition de la roche encaissante. La relation Li/Al est toujours fortement présente, mais ce rapport est fonction de la face mesurée. Seuls les cristaux Alpins de plus hautes températures (400°C) ne possédant pas de zones en CL ne présentent aucune de ces caractéristiques. Des différences dans les valeurs de δ18O de zones identiques enrichies en Al ont clairement été mesurées entre les différentes faces r, z, et m, mais aussi au sein d'une même seule zone, indiquant que le fractionnement a probablement eu lieu en déséquilibre. Il a été déterminé que la présence d'Al dans ces teneurs n'avait qu'un faible effet sur le fractionnement isotopique de l'oxygène. L'utilisation de deux méthodes différentes a permis d'obtenir des résultats in situ et non in situ concordants. La comparaison des résultats obtenus permet de démontrer que le zonage sectoriel est bien présent dans certains cristaux de quartz, et dépend des conditions de formation. La présence d'un partitionnement différentiel des éléments traces peut être due à des effets cinétiques aussi bien que structuraux, alors que le zonage sectoriel des isotopes de l'oxygène aurait d'autres origines. Il est alors évident que la possibilité de zonage sectoriel doit être désormais pris en considération avant toute interprétations de données isotopiques de cristaux zonés. Les mesures in situ ont de plus permis de distinguer de fines variations des valeurs δ18O au cours de la croissance, qui peuvent aider à retracer la circulations des fluides dans les Alpes durant cette période. En association avec les compositions des roches encaissantes, ii est possible de déduire les interactions entre roches, veines, et par conséquent fluides, au cours de différentes étapes. RESUME GRAND PUBLIC : La géochimie des isotopes stables a pris beaucoup d'importance depuis ces dernières années pour aider à résoudre nombre de questions géologiques, en se basant sur les caractéristiques du fractionnement isotopiques pour différents systèmes. Il est donc nécessaire d'avoir une connaissance approfondie des mécanismes qui s'appliquent au fractionnement isotopique entre les minéraux et les fluides à partir desquels ils se forment. Ces mécanismes ont été bien approchés par différents types de calibrations pour des systèmes à hautes températures, cependant cela n'est pas aussi évident pour les systèmes à des températures inférieures à 400-500°C. Ce travail de thèse a pour but d'aider à la description et la compréhension des phénomènes qui peuvent affecter le fractionnement isotopique à basses températures, ainsi que leurs implications, à partir de l'étude de cristaux de quartz. Le choix des échantillons s'est porté sur des cristaux naturels formés à des températures inférieures ou égales à 400°C, provenant majoritairement de fissures hydrothermales Alpines dont les conditions de formation ont déjà été déterminées. L'étude des cristaux Alpin permet de plus de replacer les résultats obtenus dans le contexte du métamorphisme Alpin au cours du Miocène (21-13 Ma). Après examen de la structure et de la morphologie des cristaux, et leur caractérisation par cathodoluminescence (CL), des analyses chimiques détaillées sur les éléments en traces pouvant entrer dans le réseau cristallin du quartz comme impuretés (i.e. Li, Na, Al, P, K, Ca, Ge, Ti), et des isotopes stables de l'oxygène, ont été menées. En fonction des conditions de croissance, la plupart des cristaux présentent des zonations, qui peuvent être facilement reliées à la distribution des éléments traces analysés par microsonde électronique, sonde ionique (SIMS) et LA-ICPMS. De fortes concentrations d'Aluminium (plusieurs milliers de parties par million atomique) ont pu être observées dans les zones les plus externes des cristaux. De plus, les concentrations en Al et en Li sont toujours corrélées; la présence d'Hydrogène déduite à partir d'analyses par FTIR suit cette même tendance. Les différentes faces des cristaux présentent des concentrations distinctes d'Al, Li et H pour des mêmes zones de croissance, avec par exemple les concentrations les plus faibles dans les zones des faces prismatiques. Cela implique la présence d'un zonage sectoriel, qui a déjà été observé principalement dans des carbonates mais jamais décrit auparavant pour des quartz. Seuls les cristaux alpins homogènes en CL dont la croissance s'est faite à plus haute température (400°C) ne présentent aucune de ces caractéristiques. Par analogie avec le zonage sectoriel en Al, élément qui se substitue au Si dans le réseau cristallin du quartz, il est possible de penser qu'un zonage sectoriel pourrait aussi s'appliquer aux isotopes de l'oxygène. Des précédentes études avaient en effet émis cette hypothèse. Nos résultats ont été obtenus à partir d'analyses à la fois in- situ par SIMS, et par extraction assistée par laser-CO2 sur des parties de quartz soigneusement séparées, et sont en accord entre les deux méthodes. Un zonage sectoriel est en effet bien présent pour les cristaux alpins, mais principalement au niveau des zones très riches en Aluminium. Cependant, il a été déterminé que la présence d'Al dans ces teneurs avait un effet plus que minimal sur le fractionnement isotopique de l'oxygène. Des différences importantes ont été observées entre les faces r & z mais aussi au sein d'une même et seule zone, indiquant que le fractionnement a pu avoir lieu en déséquilibre, ce qui est aussi visible au niveau des valeurs totalement opposées entre faces pour la dernière phase de croissance de certains cristaux. Ainsi l'association de ces résultats laisse suggérer que la présence d'un zonage sectoriel peut être liée à différents paramètres tels que le taux de croissance ou la structure de surface du cristal, mais qui n'affectent pas de la même façon l'incorporation des éléments traces et le fractionnement isotopique. La possibilité d'un zonage sectoriel est importante à prendre en compte lors de toute interprétation de données isotopiques. Les analyses des isotopes de l'oxygène effectuées par SIMS ont aussi permis de distinguer des variations importantes à petite échelle au cours de la croissance. Des mesures faites par laser CO2 sur certaines roches encaissantes, ont permis distinguer plusieurs étapes dans la croissance des minéraux et de déduire le rôle de l'encaissant et le type de fluide. En association avec de précédentes études, il a été ainsi possible de mieux contraindre la formation de ces cristaux dans le contexte alpin et la circulation de fluide au cours du métamorphisme alpin durant le Miocène.

The influence of bacterial activity on phosphorite formation in the Miocene Monterey Formation, California

Authigenic phosphorites from the Miocene Monterey Formation (California) including an autochthonous phosphatic laminite were analyzed for molecular biomarkers, element content, and sulfur isotopic composition of associated pyrite and sulfate to evaluate the role of bacterial activity in the precipitation of phosphate minerals. The phosphorites formed in a depositional environment typified by upwelling with dynamic bottom currents and hardground formation. Pyrite enclosed in the phosphorites shows delta S-34 values as low as -36.5 parts per thousand VCDT, which is consistent with bacterial sulfate reduction. In a three-step extraction phosphorite dissolution extraction procedure, molecular fossils of sulfate-reducing bacteria (di-O-alkyl glycerol ethers and short-chain branched fatty acids i- and ai-C-15:0, i- and ai-C-17:0, and 10MeC(16:0)) were preferentially released from the mineral lattice. This suggests that the molecular fossils were tightly bound to carbonate fluorapatite, indicating that sulfate-reducing bacteria were involved in mineral formation. A close association of sulfate-reducing bacteria with large sulfide-oxidizing bacteria, which was previously suggested to favor carbonate fluorapatite precipitation, could neither be confirmed nor excluded for the Miocene Monterey Formation phosphorites. (C) 2012 Elsevier B.V. All rights reserved.