Early diagenesis of bone and tooth apatite in fluvial and marine settings: Constraints from combined oxygen isotope, nitrogen and REE analysis

Fossil bones and teeth of Late Pleistocene terrestrial mammals from Rhine River gravels (RS) and the North Sea (NS), that have been exposed to chemically and isotopically distinct diagenetic fluids (fresh water versus seawater), were investigated to study the effects of early diagenesis on biogenic apatite. Changes in phosphate oxygen isotopic composition (delta O-18(PO4)), nitrogen content (wt.% N) and rare earth element (REE) concentrations were measured along profiles within bones that have not been completely fossilized, and in skeletal tissues (bone, dentine, enamel) with different susceptibilities to diagenetic alteration. Early diagenetic changes of elemental and isotopic compositions of apatite in fossil bone are related to the loss of the stabilizing collagen matrix. The REE concentration is negatively correlated with the nitrogen content, and therefore the amount of collagen provides a sensitive proxy for early diagenetic alteration. REE patterns of RS and NS bones indicate initial fossilization in a fresh water fluid with similar REE compositions. Bones from both settings have nearly collagen-free, REE-, U-, F- and Sr-enriched altered outer rims, while the collagen-bearing bone compacta in the central part often display early diagenetic pyrite void-fillings. However, NS bones exposed to Holocene seawater have outer rim delta O-18(PO4) values that are 1.1 to 2.6 parts per thousand higher compared to the central part of the same bones (delta O-18(PO4) = 18.2 +/- 0.9 parts per thousand, n = 19). Surprisingly, even the collagen-rich bone compacta with low REE contents and apatite crystallinity seems altered, as NS tooth enamel (delta O-18(PO4) =15.0 +/- 0.3 parts per thousand, n=4) has about 3%. lower delta O-18(PO4) values, values that are also similar to those of enamel from RS teeth. Therefore, REE concentration, N content and apatite crystallinity are in this case only poor proxies for the alteration of delta O-18(PO4) values. Seawater exposure of a few years up to 8 kyr can change the delta O-18(PO4) values of the bone apatite by > 3 parts per thousand. Therefore, bones fossilized in marine settings must be treated with caution for palaeoclimatic reconstructions. However, enamel seems to preserve pristine delta O-18(PO4) values on this time scale. Using species-specific calibrations for modern mammals, a mean delta O-18(H2O) value can be reconstructed for Late Pleistocene mammalian drinking water of around -9.2 +/- 0.5 parts per thousand, which is similar to that of Late Pleistocene groundwater from central Europe. (c) 2008 Elsevier B.V. All rights reserved.

Octacalcium Phosphate (OCP) Crystals Induce Synovial Inflammation and Cartilage

Introduction: The presence of intra-articular basic calcium phosphate (BCP) crystals, including OCP, carbonated-apatite, hydroxyapatite and tricalcium phosphate crystals, is associated with severe osteoarthritis and destructive arthropathies such as Milwaukee shoulder. Although BCP crystals displayed, in vitro, mitogenic, anabolic and catabolic responses, their intra-articular effect was never assessed.Objective: To determine the effects of OCP crystals in joints in vivo.Methods: OCP crystals (200 ug in 20 ml PBS) were injected into the right knee joint (the contra-lateral knee joint injected with 20 ul of PBS serving as a control) of wild-type mice treated or not by the IL1R antagonist Anakinra or mice deficient for the inflammasome proteins ASC and NALP3. 4 days and 17 days after crystal injection, mice were sacrificed and knee joints dissected. Histological scoring for synovial inflammation and characterisation of macrophages, neutrophils and T cells were performed. Technetium (Tc) uptake was measured at 6h, 1 and 4 days after OCP injection. Cartilage degradation was evaluated by Safranin O staining and VDIPEN immunohistochemistry. Intra-articular localisation of injected OCP crystals was evidenced by Von Kossa staining.Results: The intra-articular localisation of injected OCP crystals was evidenced by Von Kossa staining performed on non-decalcified samples embedded in methyl-metacrylate. Injection of OCP crystals into knee joints led at day 4 to an inflammatory response with intense macrophage staining and also some neutrophil recruitment in the synovial membrane. This synovitis was not accompanied by increased Tc uptake into the knee joint, Tc uptake being similar in OCP crystal injected knee or control knee at all time points investigated (6h, 1 day, 4 days). The histological modifications persisted over 17 days, with an additional fibrosis evidenced at this later time-point. The OCP crystal-induced synovitis was totally IL-1a and IL-1 independent as shown by the absence of inhibitory effects of anakinra injected into wild-type mice. Accordingly, OCP crystal-induced synovitis was similar in ASC-/- and NALP3-/- mice as no alterations of inflammation were demonstrated between these mice groups. Concerning cartilage matrix degradation, OCP crystals induced a strong breakdown of proteoglycans 4 and 17 days after injection, as measured by loss of red staining from Safranin O-stained sections of cartilage surfaces. In addition, we also measured advanced cartilage matrix destruction mediated by MMPs, as evidenced by VDIPEN staining of cartilage. OCP-mediated cartilage degradation was similar in all experimental conditions tested (WT+Anakinra, or ASC or NALP3 deficient mice).Conclusion: These data indicate in vivo that the intra-articular presence of OCP crystals is associated with cartilage destruction along with synovial inflammation. This is an interesting and new model of destructive arthropathy related to BCP crystals which will allow to assess new therapies in this disease.

Liquid line of descent of a basanitic liquid at 1.5 GPa: Constraints for metasomatic vein formation

The metasomatism observed in the oceanic and continental lithosphere is generally interpreted to represent a continuous differentiation process forming anhydrous and hydrous veins plus a cryptic enrichment in the surrounding peridotite. In order to constrain the mechanisms of vein formation and potentially clarify the nature and origin of the initial metasomatic agent, we performed a series of high-pressure experiments simulating the liquid line of descent of a basanitic magma differentiating within continental or mature oceanic lithosphere. This series of experiments has been conducted in an end-loaded piston cylinder apparatus starting from an initial hydrous ne-normative basanite at 1.5 GPa and temperature varying between 1,250 and 980°C. Near-pure fractional crystallization process was achieved in a stepwise manner in 30°C temperature steps and starting compositions corresponding to the liquid composition of the previous, higher-temperature glass composition. Liquids evolve progressively from basanite to peralkaline, aluminum-rich compositions without significant SiO2 variation. The resulting cumulates are characterized by an anhydrous clinopyroxene + olivine assemblage at high temperature (1,250-1,160°C), while at lower temperature (1,130-980°C), hydrous cumulates with dominantly amphibole + minor clinopyroxene, spinel, ilmenite, titanomagnetite and apatite (1,130-980°C) are formed. This new data set supports the interpretation that anhydrous and hydrous metasomatic veins could be produced during continuous differentiation processes of primary, hydrous alkaline magmas at high pressure. However, the comparison between the cumulates generated by the fractional crystallization from an initial ne-normative liquid or from hy-normative initial compositions (hawaiite or picrobasalt) indicates that for all hydrous liquids, the different phases formed upon differentiation are mostly similar even though the proportions of hydrous versus anhydrous minerals could vary significantly. This suggests that the formation of amphibole-bearing metasomatic veins observed in the lithospheric mantle could be linked to the differentiation of initial liquids ranging from ne-normative to hy-normative in composition. The present study does not resolve the question whether the metasomatism observed in lithospheric mantle is a precursor or a consequence of alkaline magmatism; however, it confirms that the percolation and differentiation of a liquid produced by a low degree of partial melting of a source similar or slightly more enriched than depleted MORB mantle could generate hydrous metasomatic veins interpreted as a potential source for alkaline magmatism by various authors.

Kyste synovial de l'épaule traité par aspiration et infiltration sous échographie : rapport de 3 cas avec pathologies différentes

Introduction: Les kystes synoviaux localisés à l'épaule sont des conditions rares résultant de tendinopathies rompues de la coiffe des rotateurs, d'une omarthrose sévère, d'arthropathies microcristallines de l'articulation acromio-claviculaire ou gléno-humérale, ou d'une atteinte secondaire à un rhumatisme inflammatoire chronique. Ils se présentent cliniquement le plus souvent sous la forme d'une tuméfaction fluctuante indolore en regard du moignon de l'épaule ou de l'articulation acromio-claviculaire. L'imagerie par échographie permet de caractériser aisément la présence de ces kystes. La prise en charge thérapeutique est généralement non invasive par aspiration-infiltration. Les cas réfractaires sont susceptibles de subir une intervention chirurgicale en fonction de l'âge et de l'état général du patient.Patients et Méthodes: Nous rapportons les cas de 3 patients avec imagerie par échographie et IRM ou Scanner. Le premier cas est celui d'un homme de 47 ans, greffé rénal, présentant une arthrite récidivante des épaules sur arthropathie microcristalline mixte. De multiples kystes synoviaux sont mis en évidence dans la musculature du supra-épineux gauche, communiquant avec l'articulation acromio-claviculaire. Le patient a bénéficié à plusieurs ponctions-infiltrations dirigées par ultrasonographie. Le deuxième cas est celui d'un patient de 32 ans connu pour une arthrite psoriasique évoluant depuis 6 ans. Il présente une importante tuméfaction en regard du biceps à gauche sur un kyste synovial provenant de l'articulation gléno-humérale. Il bénéficie également d'une ponction-infiltration dirigée par ultrason. Le troisième cas est celui d'une femme de 91 ans chez qui au status d'entrée on objective une volumineuse masse polylobée en regard de l'acromio-claviculaire, présente depuis 2002 qui n'a jamais été symptomatique. Un US, puis un CT montrent qu'il s'agit de volumineux kystes articulaires en relation avec une arthropathie sévère dégénérative et à apatite de l'acromio-claviculaire.Résultats: Les trois patients ont bénéficié d'une imagerie diagnostique par échographie complétée par une IRM ou Scanner. Tous les trois ont également subi une aspiration dirigée sous échographie. Dans le premier cas, deux aspiration-infiltration des kystes qui apportaient une évolution favorable avec diminution important des kystes. Dans le deuxième cas nous avons retrouvé un kyste après 2 aspirations et dans ce cas une intervention chirurgicale est considérée. Dans le troisième cas, asymptomatique, une résection à visée esthétique a été refusée par la patiente.Conclusion: Les kystes synoviaux localisés à l'épaule restent des conditions rares, provenant d'entités diverses. Nous rapportons le développement de kystes synoviaux de l'épaule dans une arthropathie microcristalline chez un patient greffé rénal, dans une arthrite psoriasique chez un jeune patient en poussée inflammatoire, et finalement de gros kystes asymptomatiques chroniques sur une atteinte dégénérative et microcristalline chez une patiente âgée. Le diagnostic de ces kystes peut être rapidement obtenu par échographie, permettant l'aspiration guidée avec analyse du liquide. En raison d'un fort taux de récidive malgré un traitement par aspiration-infiltration, une intervention chirurgicale de ces kystes est considérée.

From central Atlantic continental rift to Neogene uplift - western Anti-Atlas (Morocco)

P>To put constraints on the Mesozoic to recent growth of the Anti-Atlas system, we investigated the temperature-time history of rocks by applying extensive low-temperature thermochronological analysis to three Precambrian inliers along the coast and 250 km into the interior. Bedrocks yield old U-Th/He ages on zircon (248-193 Ma) and apatite (150-50 Ma) and also fission-track ages of 173-121 Ma on apatite. These datasets are interpreted as recording passive margin upward movements from central Atlantic rifting until the Early Cretaceous. A phase of sedimentary burial was evidenced for the Cretaceous-Eocene. The extension of this thin (1.5 km) basin is loosely constrained but can be extended to the western regions of northern Africa. Effects of the existing thermal perturbation of lithospheric origin 100 km below the Atlas show that the 120-60 degrees C isotherms are not much deflected. Large-scale uplift has possibly occurred in the western Anti-Atlas since c. 30 Ma and is associated with a mean denudation rate of 0.08 km Ma-1.

Monte Carlo simulations of metasomatic enrichment in the lithosphere and implications for the source of alkaline basalts

One hypothesis for the origin of alkaline lavas erupted on oceanic islands and in intracontinental settings is that they represent the melts of amphibole-rich veins in the lithosphere (or melts of their dehydrated equivalents if metasomatized lithosphere is recycled into the convecting mantle). Amphibole-rich veins are interpreted as cumulates produced by crystallization of low-degree melts of the underlying asthenosphere as they ascend through the lithosphere. We present the results of trace-element modelling of the formation and melting of veins formed in this way with the goal of testing this hypothesis and for predicting how variability in the formation and subsequent melting of such cumulates (and adjacent cryptically and modally metasomatized lithospheric peridotite) would be manifested in magmas generated by such a process. Because the high-pressure phase equilibria of hydrous near-solidus melts of garnet lherzolite are poorly constrained and given the likely high variability of the hypothesized accumulation and remelting processes, we used Monte Carlo techniques to estimate how uncertainties in the model parameters (e.g. the compositions of the asthenospheric sources, their trace-element contents, and their degree of melting; the modal proportions of crystallizing phases, including accessory phases, as the asthenospheric partial melts ascend and crystallize in the lithosphere; the amount of metasomatism of the peridotitic country rock; the degree of melting of the cumulates and the amount of melt derived from the metasomatized country rock) propagate through the process and manifest themselves as variability in the trace-element contents and radiogenic isotopic ratios of model vein compositions and erupted alkaline magma compositions. We then compare the results of the models with amphibole observed in lithospheric veins and with oceanic and continental alkaline magmas. While the trace-element patterns of the near-solidus peridotite melts, the initial anhydrous cumulate assemblage (clinopyroxene +/- garnet +/- olivine +/- orthopyroxene), and the modelled coexisting liquids do not match the patterns observed in alkaline lavas, our calculations show that with further crystallization and the appearance of amphibole (and accessory minerals such as rutile, ilmenite, apatite, etc.) the calculated cumulate assemblages have trace-element patterns that closely match those observed in the veins and lavas. These calculated hydrous cumulate assemblages are highly enriched in incompatible trace elements and share many similarities with the trace-element patterns of alkaline basalts observed in oceanic or continental setting such as positive Nb/La, negative Ce/Pb, and similiar slopes of the rare earth elements. By varying the proportions of trapped liquid and thus simulating the cryptic and modal metasomatism observed in peridotite that surrounds these veins, we can model the variations in Ba/Nb, Ce/Pb, and Nb/U ratios that are observed in alkaline basalts. If the isotopic compositions of the initial low-degree peridotite melts are similar to the range observed in mid-ocean ridge basalt, our model calculations produce cumulates that would have isotopic compositions similar to those observed in most alkaline ocean island basalt (OIB) and continental magmas after similar to 0 center dot 15 Gyr. However, to produce alkaline basalts with HIMU isotopic compositions requires much longer residence times (i.e. 1-2 Gyr), consistent with subduction and recycling of metasomatized lithosphere through the mantle. such as a heterogeneous asthenosphere. These modelling results support the interpretation proposed by various researchers that amphibole-bearing veins represent cumulates formed during the differentiation of a volatile-bearing low-degree peridotite melt and that these cumulates are significant components of the sources of alkaline OIB and continental magmas. The results of the forward models provide the potential for detailed tests of this class of hypotheses for the origin of alkaline magmas worldwide and for interpreting major and minor aspects of the geochemical variability of these magmas.

The hypogene iron oxide copper-gold mineralization in the Mantoverde District, Northern Chile

The Mantoverde iron oxide copper-gold (IOCC) district, northern Chile, is known for its Cu production from supergene ores. Recently, exploration outlined an additional hypogene ore resource of 440 Mt with 0.56 percent Cu, and 0.12 g/t An. The hypogene sulfide mineralization occurs mainly as chalcopyrite and pyrite, typically in specularite or magnetite-cemented breccias and associated stockworks. The host rocks underwent variably intense K feldspar alteration, chloritization, sericitization, silicification, and/or carbonatization. A district scale Na(-Ca) alteration is absent. The IOCC mineralization in the district shows a strong tectonic control by northwest- to north-northwest-trending brittle structures. Large Cu sulfide-rich veins or Cu sulfide-cemented breccias are absent. Therefore, head grades of 4 percent Cu are an exception. There is a positive correlation between Cu and An grades. Gold is probably contained mostly in chalcopyrite and pyrite. Elevated concentrations of light rare-earth elements (LREE) occur locally but are attributed to redistribution of LREE within the deposits rather than to derivation from external sources. The Cu-Au ores in the Mantoverde district are low in and have relatively low contents in heavy metals that are potentially hazardous to the environment, such as As (avg 14 ppm), Hg (<5 ppm), or Cd (<0.2 ppm). The sulfur isotope ratios of chalcopyrite from the IOCC deposits lie between -5.6 and 8.9 per mil delta(34)S(VCDT). They show systematic variations within the district, which are interpreted to reflect relative distance to inferred fluid conduits and the level of deposition within the hydrothermal system. Most initial (87)Sr/(86)Sr values of altered volcanic rocks and hydrothermal calcite from the Mantoverde district are between 0.7031 and 0.7060 and are similar to those of the igneous rocks of the region. Lead isotope ratios of chalcopyrite are consistent with Pb (and by inference Cu) derived from Early Cretaceous magmatism. The sulfur, strontium, and lead isotope data of chalcopyrite, calcite gangue, or altered host rocks, respectively, are compatible with a genetic model that involves cooling of metal and sulfur-bearing magmatic-hydrothermal fluids that mix with meteoric waters or seawater at relatively shallow crustal levels. An additional exotic sulfur input is likely, though not required, for the copper mineralization. Apart from the IOCC. deposits, there are a number of smaller magnetite(-apatite) bodies in the district. These are geologically similar to the Cu-Au-bearing magnetite bodies, but are related to splays of the north-south-trending Atacama fault zone and differ in alteration and texture.

Weathering and the mobility of phosphorus in the catchments and forefields of the Rhone and Oberaar glaciers, central Switzerland: Implications for the global phosphorus cycle on glacial-interglacial timescales

In this study we evaluate the dynamics of the biophile element phosphorus (P) in the catchment and proglacial areas of the Rhone and Oberaar glaciers (central Switzerland). We analysed erosion and dissolution rates of P-containing minerals in the subglacial environment by sampling water and suspended sediment in glacier outlets during three ablation and two accumulation seasons. We also quantified biogeochemical weathering rates of detrital P in proglacial sedimentary deposits using two chronosequences of samples of fresh, suspended, material obtained from the Oberaar and Rhone water outlets, Little-Ice-Age (LIA) moraines and Younger Dryas (YD) tills in each catchment. Subglacial P weathering is mainly a physical process and detrital P represents more than 99%, of the precipitation-corrected total P denudation flux (234 and 540 kg km(-2) yr(-1) for the Rhone and Oberaar catchments, respectively). The calculated detrital P flux rates are three to almost five times higher than the world average flux. The precipitation-corrected soluble reactive P (SRP) flux corresponds to 1.88-1.99 kg km(-2) yr(-1) (Rhone) and 2.12-2.44 kg km(-2) yr(-1) (Oberaar), respectively. These fluxes are comparable to those of tropical rivers draining transport-limited, tectonically inactive weathering areas. In order to evaluate the efficiency of detrital P weathering in the Rhone and Oberaar proglacial areas, we systematically graded apatite grains extracted from the chronosequence in each catchment relative to weathering-induced changes in their surface morphologies (grades 1-4). Fresh apatite grains are heavily indented and dissolution rounded (grade 1). LIA grains from two 0-10 cm deep moraine samples show extensive dissolution etching, similar to surface grains from the YD profile (mean grades 2.7, 3.5 and 3.5, respectively). In these proglacial deposits, the weathering front deepens progressively as a function of time due to biocorrosion in the evolving acidic pedosphere, with mechanical indentations on grains acting as sites of preferential dissolution. We also measured iron-bound, organic and detrital P concentrations in the chronosequence and show that organic and iron-bound P has almost completely replaced detrital P in the top layers of the YD profiles. Detrital P weathering rates are calculated as 3 10 and 280 kg km(-2) yr(-1) for LIA moraines and 10 kg km(-2) yr(-1) for YD tills. During the first 300 years of glacial sediment exposure P dissolution rates are shown to be approximately 70 times higher than the mean global dissolved P flux from ice-free continents. After 11.6 kyr the flux is 2.5 times the global mean. These data strengthen the argument for substantial changes in the global dissolved P flux on glacial-interglacial timescales. A crude extrapolation from the data described here suggests that the global dissolved P flux may increase by 40-45% during the first few hundred years of a deglaciation phase

Application of low temperature thermochronology to understanding cooling and exhumation in the Central Swiss Alps

THESIS ABSTRACT : Low-temperature thermochronology relies on application of radioisotopic systems whose closure temperatures are below temperatures at which the dated phases are formed. In that sense, the results are interpreted as "cooling ages" in contrast to "formation ages". Owing to the low closure-temperatures, it is possible to reconstruct exhumation and cooling paths of rocks during their residence at shallow levels of the crust, i.e. within first ~10 km of depth. Processes occurring at these shallow depths such as final exhumation, faulting and relief formation are fundamental for evolution of the mountain belts. This thesis aims at reconstructing the tectono-thermal history of the Aar massif in the Central Swiss Alps by means of zircon (U-Th)/He, apatite (U-Th)/He and apatite fission track thermochronology. The strategy involved acquisition of a large number of samples from a wide range of elevations in the deeply incised Lötschen valley and a nearby NEAT tunnel. This unique location allowed to precisely constrain timing, amount and mechanisms of exhumation of the main orographic feature of the Central Alps, evaluate the role of topography on the thermochronological record and test the impact of hydrothermal activity. Samples were collected from altitudes ranging between 650 and 3930 m and were grouped into five vertical profiles on the surface and one horizontal in the tunnel. Where possible, all three radiometric systems were applied to each sample. Zircon (U-Th)/He ages range from 5.1 to 9.4 Ma and are generally positively correlated with altitude. Age-elevation plots reveal a distinct break in slope, which translates into exhumation rate increasing from ~0.4 to ~3 km/Ma at 6 Ma. This acceleration is independently confirmed by increased cooling rates on the order of 100°C/Ma constrained on the basis of age differences between the zircon (U-Th)/He and the remaining systems. Apatite fission track data also plot on a steep age-elevation curve indicating rapid exhumation until the end of the Miocene. The 6 Ma event is interpreted as reflecting tectonically driven uplift of the Aar massif. The late Miocene timing implies that the increase of precipitation in the Pliocene did not trigger rapid exhumation in the Aar massif. The Messinian salinity crisis in the Mediterranean could not directly intensify erosion of the Aar but associated erosional output from the entire Alps may have tapered the orogenic wedge and caused reactivation of thrusting in the Aar massif. The high exhumation rates in the Messinian were followed by a decrease to ~1.3 km/Ma as evidenced by ~8 km of exhumation during last 6 Ma. The slowing of exhumation is also apparent from apatite (U-Th)1He age-elevation data in the northern part of the Lötschen valley where they plot on a ~0.5km/Ma line and range from 2.4 to 6.4 Ma However, from the apatite (U-Th)/He and fission track data from the NEAT tunnel, there is an indication of a perturbation of the record. The apatite ages are youngest under the axis of the valley, in contrast to an expected pattern where they would be youngest in the deepest sections of the tunnel due to heat advection into ridges. The valley however, developed in relatively soft schists while the ridges are built of solid granitoids. In line with hydrological observations from the tunnel, we suggest that the relatively permeable rocks under the valley floor, served as conduits of geothermal fluids that caused reheating leading to partial Helium loss and fission track annealing in apatites. In consequence, apatite ages from the lowermost samples are too young and the calculated exhumation rates may underestimate true values. This study demonstrated that high-density sampling is indispensable to provide meaningful thermochronological data in the Alpine setting. The multi-system approach allows verifying plausibility of the data and highlighting sources of perturbation. RÉSUMÉ DE THÈSE : La thermochronologie de basse température dépend de l'utilisation de systèmes radiométriques dont la température de fermeture est nettement inférieure à la température de cristallisation du minéral. Les résultats obtenus sont par conséquent interprétés comme des âges de refroidissement qui diffèrent des âges de formation obtenus par le biais d'autres systèmes de datation. Grâce aux températures de refroidissement basses, il est aisé de reconstruire les chemins de refroidissement et d'exhumation des roches lors de leur résidence dans la croute superficielle (jusqu'à 10 km). Les processus qui entrent en jeu à ces faibles profondeurs tels que l'exhumation finale, la fracturation et le faillage ainsi que la formation du relief sont fondamentaux dans l'évolution des chaînes de montagne. Ces dernières années, il est devenu clair que l'enregistrement thermochronologique dans les orogènes peut être influencé par le relief et réinitialisé par l'advection de la chaleur liée à la circulation de fluides géothermaux après le refroidissement initial. L'objectif de cette thèse est de reconstruire l'histoire tectono-thermique du massif de l'Aar dans les Alpes suisses Centrales à l'aide de trois thermochronomètres; (U-Th)/He sur zircon, (U-Th)/He sur apatite et les traces de fission sur apatite. Afin d'atteindre cet objectif, nous avons récolté un grand nombre d'échantillons provenant de différentes altitudes dans la vallée fortement incisée de Lötschental ainsi que du tunnel de NEAT. Cette stratégie d'échantillonnage nous a permis de contraindre de manière précise la chronologie, les quantités et les mécanismes d'exhumation de cette zone des Alpes Centrales, d'évaluer le rôle de la topographie sur l'enregistrement thermochronologique et de tester l'impact de l'hydrothermalisme sur les géochronomètres. Les échantillons ont été prélevés à des altitudes comprises entre 650 et 3930m selon 5 profils verticaux en surface et un dans le tunnel. Quand cela à été possible, les trois systèmes radiométriques ont été appliqués aux échantillons. Les âges (U-Th)\He obtenus sur zircons sont compris entre 5.l et 9.4 Ma et sont corrélés de manière positive avec l'altitude. Les graphiques représentant l'âge et l'élévation montrent une nette rupture de la pente qui traduisent un accroissement de la vitesse d'exhumation de 0.4 à 3 km\Ma il y a 6 Ma. Cette accélération de l'exhumation est confirmée par les vitesses de refroidissement de l'ordre de 100°C\Ma obtenus à partir des différents âges sur zircons et à partir des autres systèmes géochronologiques. Les données obtenues par traces de fission sur apatite nous indiquent également une exhumation rapide jusqu'à la fin du Miocène. Nous interprétons cet évènement à 6 Ma comme étant lié à l'uplift tectonique du massif de l'Aar. Le fait que cet évènement soit tardi-miocène implique qu'une augmentation des précipitations au Pliocène n'a pas engendré cette exhumation rapide du massif de l'Aar. La crise Messinienne de la mer méditerranée n'a pas pu avoir une incidence directe sur l'érosion du massif de l'Aar mais l'érosion associée à ce phénomène à pu réduire le coin orogénique alpin et causer la réactivation des chevauchements du massif de l'Aar. L'exhumation rapide Miocène a été suivie pas une diminution des taux d'exhumation lors des derniers 6 Ma (jusqu'à 1.3 km\Ma). Cependant, les âges (U-Th)\He sur apatite ainsi que les traces de fission sur apatite des échantillons du tunnel enregistrent une perturbation de l'enregistrement décrit ci-dessus. Les âges obtenus sur les apatites sont sensiblement plus jeunes sous l'axe de la vallée en comparaison du profil d'âges attendus. En effet, on attendrait des âges plus jeunes sous les parties les plus profondes du tunnel à cause de l'advection de la chaleur dans les flancs de la vallée. La vallée est creusée dans des schistes alors que les flancs de celle-ci sont constitués de granitoïdes plus durs. En accord avec les observations hydrologiques du tunnel, nous suggérons que la perméabilité élevée des roches sous l'axe de la vallée à permi l'infiltration de fluides géothermaux qui a généré un réchauffement des roches. Ce réchauffement aurait donc induit une perte d'Hélium et un recuit des traces de fission dans les apatites. Ceci résulterait en un rajeunissement des âges apatite et en une sous-estimation des vitesses d'exhumation sous l'axe de la vallée. Cette étude à servi à démontrer la nécessité d'un échantillonnage fin et précis afin d'apporter des données thermochronologiques de qualité dans le contexte alpin. Cette approche multi-système nous a permi de contrôler la pertinence des données acquises ainsi que d'identifier les sources possibles d'erreurs lors d'études thermochronologiques. RÉSUMÉ LARGE PUBLIC Lors d'une orogenèse, les roches subissent un cycle comprenant une subduction, de la déformation, du métamorphisme et, finalement, un retour à la surface (ou exhumation). L'exhumation résulte de la déformation au sein de la zone de collision, menant à un raccourcissement et un apaissessement de l'édifice rocheux, qui se traduit par une remontée des roches, création d'une topographie et érosion. Puisque l'érosion agit comme un racloir sur la partie supérieure de l'édifice, des tentatives de corrélation entre les épisodes d'exhumation rapide et les périodes d'érosion intensive, dues aux changements climatiques, ont été effectuées. La connaissance de la chronologie et du lieu précis est d'une importance capitale pour une quelconque reconstruction de l'évolution d'une chaîne de montagne. Ces critères sont donnés par un retraçage des changements de la température de la roche en fonction du temps, nous donnant le taux de refroidissement. L'instant auquel les roches ont refroidit, passant une certaine température, est contraint par l'application de techniques de datation par radiométrie. Ces méthodes reposent sur la désintégration des isotopes radiogéniques, tels que l'uranium et le potassium, tous deux abondants dans les roches de la croûte terrestre. Les produits de cette désintégration ne sont pas retenus dans les minéraux hôtes jusqu'au moment du refroidissement de la roche sous une température appelée 'de fermeture' , spécifique à chaque système de datation. Par exemple, la désintégration radioactive des atomes d'uranium et de thorium produit des atomes d'hélium qui s'échappent d'un cristal de zircon à des températures supérieures à 200°C. En mesurant la teneur en uranium-parent, l'hélium accumulé et en connaissant le taux de désintégration, il est possible de calculer à quel moment la roche échantillonnée est passée sous la température de 200°C. Si le gradient géothermal est connu, les températures de fermeture peuvent être converties en profondeurs actuelles (p. ex. 200°C ≈ 7km), et le taux de refroidissement en taux d'exhumation. De plus, en datant par système radiométrique des échantillons espacés verticalement, il est possible de contraindre directement le taux d'exhumation de la section échantillonnée en observant les différences d'âges entre des échantillons voisins. Dans les Alpes suisses, le massif de l'Aar forme une structure orographique majeure. Avec des altitudes supérieures à 4000m et un relief spectaculaire de plus de 2000m, le massif domine la partie centrale de la chaîne de montagne. Les roches aujourd'hui exposées à la surface ont été enfouies à plus de 10 km de profond il y a 20 Ma, mais la topographie actuelle du massif de l'Aar semble surtout s'être développée par un soulèvement actif depuis quelques millions d'années, c'est-à-dire depuis le Néogène supérieur. Cette période comprend un changement climatique soudain ayant touché l'Europe il y a environ 5 Ma et qui a occasionné de fortes précipitations, entraînant certainement une augmentation de l'érosion et accélérant l'exhumation des Alpes. Dans cette étude, nous avons employé le système de datation (U-TH)/He sur zircon, dont la température de fermeture de 200°C est suffisamment basse pour caractériser l'exhumation du Néogène sup. /Pliocène. Les échantillons proviennent du Lötschental et du tunnel ferroviaire le plus profond du monde (NEAT) situé dans la partie ouest du massif de l'Aar. Considérés dans l'ensemble, ces échantillons se répartissent sur un dénivelé de 3000m et des âges de 5.1 à 9.4 Ma. Les échantillons d'altitude supérieure (et donc plus vieux) documentent un taux d'exhumation de 0.4 km/Ma jusqu'à il y a 6 Ma, alors que les échantillons situés les plus bas ont des âges similaires allant de 6 à 5.4 Ma, donnant un taux jusqu'à 3km /Ma. Ces données montrent une accélération dramatique de l'exhumation du massif de l'Aar il y a 6 Ma. L'exhumation miocène sup. du massif prédate donc le changement climatique Pliocène. Cependant, lors de la crise de salinité d'il y a 6-5.3 Ma (Messinien), le niveau de la mer Méditerranée est descendu de 3km. Un tel abaissement de la surface d'érosion peut avoir accéléré l'exhumation des Alpes, mais le bassin sud alpin était trop loin du massif de l'Aar pour influencer son érosion. Nous arrivons à la conclusion que la datation (U-Th)/He permet de contraindre précisément la chronologie et l'exhumation du massif de l'Aar. Concernant la dualité tectonique-érosion, nous suggérons que, dans le cas du massif de l'Aar, la tectonique prédomine.

Basic calcium phosphate crystals induce monocyte/macrophage IL-1(beta) secretion through the NLRP3 inflammasome in vitro.

Basic calcium phosphate (BCP) crystals are associated with severe osteoarthritis and acute periarticular inflammation. Three main forms of BCP crystals have been identified from pathological tissues: octacalcium phosphate, carbonate-substituted apatite, and hydroxyapatite. We investigated the proinflammatory effects of these BCP crystals in vitro with special regard to the involvement of the NLRP3-inflammasome in THP-1 cells, primary human monocytes and macrophages, and mouse bone marrow-derived macrophages (BMDM). THP-1 cells stimulated with BCP crystals produced IL-1β in a dose-dependent manner. Similarly, primary human cells and BMDM from wild-type mice also produced high concentrations of IL-1β after crystal stimulation. THP-1 cells transfected with short hairpin RNA against the components of the NLRP3 inflammasome and mouse BMDM from mice deficient for NLRP3, apoptosis-associated speck-like protein, or caspase-1 did not produce IL-1β after BCP crystal stimulation. BCP crystals induced macrophage apoptosis/necrosis as demonstrated by MTT and flow cytometric analysis. Collectively, these results demonstrate that BCP crystals induce IL-1β secretion through activating the NLRP3 inflammasome. Furthermore, we speculate that IL-1 blockade could be a novel strategy to inhibit BCP-induced inflammation in human disease.

Early Variscan I-type pluton in the pre-Alpine basement of the Western Alps: The ca. 360 Ma Cogne diorite (NW-Italy)

Located at the internal border of the Grand-Saint-Bernard Zone, the diorite and its aureole lie on top of intensively studied Alpine eclogitic units but this pluton, poorly studied yet, has kept locally almost undeformed. The pluton intruded, at similar to 360 Ma, country-rocks mostly composed of dark shales with Na2O > K2O and minor mafic intercalations of tholeiitic basalt affinity. This association is characteristic of the Vanoise (France) basement series, where available age determinations suggest an Early Paleozoic age. Parts of the pluton, and of its hornfels aureole that is evidenced here for the first time, in the Punta Bioula section of Valsavaranche valley (NW-Italy), have been well-preserved from the Alpine deformation. Syn-emplacement hardening, dehydration-induced, probably prevented strain-enhanced Alpine recrystallization. Magmatic rock-types range continuously from subordinate mafic types at SiO2 similar to 48%, of hornblendite with cumulative or appinite affinities, to the main body of quartz diorite to quartz monzonite (SiO2 up to 62%). P-T estimates for the pluton emplacement, based on the abundance of garnet in the hornfelses, using also zircon and apatite saturation thermometry and Al-in-hornblende barometry, suggest T similar to 800-950 degrees C and minimum P in the 0.2-0.5 GPa range, with records of higher pressure conditions (up to 1-2 GPa?) in hornblendite phlogopite-cored amphibole. The high-K, Na > K, calcalkaline geochemistry is in line with a destructive plate-margin setting. Based on major element data and radiogenic isotope signature (epsilon Nd-360 Ma from -1.2 to + 0.9, Sr-87/Sr-86(360 MA) from 0.7054 to 0.7063), the parental magmas are interpreted in terms of deep-seated metabasaltic partial melts with limited contamination from shallower sources, the low radiogenic Nd-content excluding a major contribution from Vanoise tholeiites. There is no other preserved evidence for Variscan magmatism of similar age and composition in the Western Alps, but probable analogs are known in the western and northern parts of French Massif Central. Regarding the Alpine tectonics, not only the age of the pluton and its host-rocks (instead of the Permo-Carboniferous age previously believed), but also its upper mylonitic contact, suggest revisions of the Alpine nappe model. The Cogne diorite allegedly constituted the axial part of the E-verging ``pli en retour [backfold] du Valsavaranche'', a cornerstone of popular Alpine structural models: in fact, the alleged fold limbs, as attested here by field and geochemical data, do not belong to the same unit, and the backfold hypothesis is unfounded. (C) 2012 Elsevier B.V. All rights reserved.

Constraints on the late thermotectonic evolution of the Western Alps - Evidence for episodic rapid uplift

Forty-two new apatite and zircon fission track ages are presented for samples from the Western Alps in southern Switzerland, northern Italy, and southeastern France. Measured ages plotted against assumed closure temperatures yield cooling patterns for the final cooling, uplift, and exhumation of the Western Alps. Similar fission track zircon ages in the Penninic Gran Paradiso massif, Dent Blanche nappe, Sesia-Lanzo Zone, and Ivrea Zone indicate cooling of all four units to approximately 225-degrees-C by 33 Ma. Differences in apatite ages reveal differential cooling of the four blocks between 33 Ma and the present. In the Sesia-Lanzo Zone, similarity of apatite ages regardless of elevation, together with near-volcanic confined fission track length patterns suggest rapid cooling and uplift at approximately 25 Ma compared with slow cooling of other Western Alps units around 12 Ma. Uplift is thus not continuous but episodic, often over a short time interval beyond the resolution of other methods. Such episodes of uplift, as revealed here in the Sesia-Lanzo Zone, may be the rule rather than the exception.