Crustal-scale convection and diapiric upwelling of a partially molten orogenic root (Naxos dome, Greece)

The goal of this paper is to use the structural, metamorphic and geochronological record from the migmatitic core of the Naxos dome (Greece) and its associated subdomes to address the internal dynamics of a partially molten orogenic root. U-Pb ages from ca. 24 to 16 Ma and textures of zircon in the migmatites suggest successive dissolution and precipitation cycles with a period of 1 to 2 Ma, interpreted as the timescale of convective instabilities in a ca. 20 km thick partially molten layer. Dimensional analysis indicates that convection of this root requires a viscosity lower than 1018 Pa·s, consistent with viscosity values expected for partially molten felsic rocks. Structural analysis and U-Pb geochronology of deformed granitic dikes rooting in the migmatites record the subsequent development of the Naxos dome by diapirism from ca. 16 to 13 Ma. The size of the first order migmatite dome on Naxos (5 × 12 km) requires that the unstable layer at the onset of diapirism was 5 to 10 km thick and presented a moderate viscosity contrast with its envelope. From this analysis we propose that the Naxos migmatite dome documents a two stage dynamic evolution for the partially molten root of the Aegean belt characterized by (1) crustal scale convection for at least 8 Ma and (2) diapirism for about 3 Ma during progressive thinning of the collapsing orogenic crust

The CORDEX.be initiative as a foundation for climate services in Belgium

The CORDEX.be project created the foundations for Belgian climate services by producing high-resolution Belgian climate information that (a) incorporates the expertise of the different Belgian climate modeling groups and that (b) is consistent with the outcomes of the international CORDEX ("COordinated Regional Climate Downscaling Experiment") project. The key practical tasks for the project were the coordination of activities among different Belgian climate groups, fostering the links to specific international initiatives and the creation of a stakeholder dialogue. Scientifically, the CORDEX.be project contributed to the EURO-CORDEX project, created a small ensemble of High-Resolution (H-Res) future projections over Belgium at convection-permitting resolutions and coupled these to seven Local Impact Models. Several impact studies have been carried out. The project also addressed some aspects of climate change uncertainties. The interactions and feedback from the stakeholder dialogue led to different practical applications at the Belgian national level

Leveraging Natural History Data in One- and Two-Arm Hierarchical Bayesian Studies of Rare Disease Progression

peer reviewedThe small sample sizes inherent in rare and pediatric disease settings offer significant challenges for clinical trial design. In such settings, Bayesian adaptive trial methods can often pay dividends, allowing the sensible incorporation of auxiliary data and other relevant information to bolster that collected by the trial itself. Previous work has also included the use of one-arm trials augmented by the participants’ own natural history data, from which the future course of the disease in the absence of intervention can be predicted. Patient response can then be defined by the degree to which post-intervention observations are inconsistent with the predicted “natural” trajectory. While such trials offer obvious advantages in efficiency and ethical hazard (since they expose no new patients to a placebo, anathema to patients or their parents and caregivers), they can offer no protection against bias arising from the presence of any “placebo effect,” the tendency of patients to improve merely by being in the trial. In this paper, we investigate the impact of both static and transient placebo effects on one-arm responder studies of this type, as well as two-arm versions that incorporate a small concurrent placebo group but still borrow strength from the natural history data. We also propose more traditional Bayesian changepoint models that specify a parametric functional form for the patient’s post-intervention trajectory, which in turn allow quantification of the treatment benefit in terms of the model parameters, rather than semi-parametrically in terms of a response relative to some “null” model. We compare the operating characteristics of our designs in the context of an ongoing investigation of centronuclear myopathies (CNMs), a group of congenital neuromuscular diseases whose most common and severe form is X-linked, affecting approximately 1 in 50,000 newborn boys. Our results indicate our two-arm responder and changepoint methods can offer protection against placebo effects, improving power while protecting the trial’s Type I error rate. However, further research into innovative trial designs as well as ongoing dialog with regulatory authorities remain critically important in rare disease research

Pressure-temperature-time evolution of metamorphic rocks from Naxos (cyclades, Greece) : constraints from thermobarometry and Rb/Sr dating.

International audienc

Petrology of Fe-Ti-rich rodingites from Western Carpathians

International audienc

Generation and emplacement of Triassic granitoids within the Songpan Ganze accretionary-orogenic wedge in a context of slab retreat accommodated by tear faulting, Eastern Tibetan plateau, China

International audienceThe eastern Songpan Ganze accretionary-orogenic wedge (northern Tibetan plateau) is characterized by extensive magmatism coeval with Middle to Upper Triassic closure of the Paleotethys Ocean along a double subduction system, traced by the Kunlun-Anyemaqen suture to the north and the Jinsha-Litang suture to the south. New field, petrographic and geochemical data on Mesozoic plutons intrusive into Triassic metasediments of the eastern Songpan Ganze wedge are presented and integrated in a review of available data for the region. Three types of granitoids are distinguished: (i) high-K calc-alkaline granite to granodiorite (Yanggon, Maoergai, Markam, Sheng Meng, Xue Sheng, Taiyanghe, Menggu, Manai, Dusong Xian, Tagong and Jiulong plutons), (ii) high-K alkaline granite (Nyanbaoyeche and Rilong plutons and the Niuxingou shoshonitic syenite), and (iii) peraluminous S-type granite (Markam and Manai leucogranites). Elemental and isotopic signatures of these granitoids are consistent with the implication of both crustal (Yangtze craton, and Songpan Ganze metasediments) and mantle (asthenospheric mantle and metasomatised lithospheric mantle) sources. Based on (i) the ages of the plutons that are concomitant with the end of the northern and southern subductions of the Paleo-Tethys, (ii) the position of the plutons intrusive in the crustal tectonically accreted units decoupled from the downgoing plate of this double subduction system, (iii) the diversity of their petrological and geochemical signatures, we propose that magma emplaced in the Songpan Ganze accretionary-orogenic wedge were generated at the end of the Paleotethys closure in a context of slab retreat, accommodated by a tear fault along the passive margin of the South China block. Indeed, we argue that this context is the most favourable to trigger synchronous partial melting of (i) the suprasubduction enriched mantle wedge owing to lowering of the mantle solidus by metasomatism, (ii) the upwelled undepleted asthenospheric mantle into the tear fault owing to decompression, (iii) the metasomatized lithospheric continental mantle of the Yangtze craton owing to the temperature increase associated to the asthenospheric upwelling and (iv) the rocks of the Songpan Ganze accretionary wedge composed of metasediments and Yangtze continental margin basement owing to the combined effects of increased radioactive heat production and mantle heat flux. We propose that the concentration of plutons along the eastern margin of the Songpan Ganze results from focussed migration and emplacement of the granitic magmas guided by the development of a tear fault along the former passive eastern margin of the Yangtze craton as a consequence of the Paleotethys slab retreat

First in situ U-Pb dating of supergene copper mineralization: case study from Atacama desert, Chile

International audienceDirect dating of copper mineralization remains challenging, yet an important objective for both metallogenic studies and prospecting purposes. Here, we present a first attempt of U-Pb dating of copper-rich minerals from the Mina Sur exotic deposit from the Chuquicamata copper mine (Chile).The Mina Sur exotic copper deposit is located in northern Chile, within the Chuquicamata mining district, about 6 km south of the world class Chuquicamata porphyry copper deposit. It was discovered in 1957 from drilling in sub-alluvial channels and copper extraction began in 1969. The copper mineralization consists mainly of chrysocolla, Mn-rich chrysocolla (also known as copper-pitch or black chrysocolla), pseudomalachite bedding and atacamite emplaced mainly as cement in gravels but also filling fractures in the bedrock. Geomorphological, mineralogical and structural studies (Mortimer et al., 1977; Munchmeyer, 1996) have shown that the Mina Sur deposit is derived from the lateral migration of copper-rich solutions from the Chuquicamata porphyry deposit. The latter was formed by the 33-31 Ma old hydrothermal alteration (Ar/Ar dating of K-feldspar and sericite; Reynolds et al., 1998) of the 35-33 Ma old porphyry (U/Pb dating on zircon; Ballard et al., 2001). However, the age of the Mina Sur exotic deposit is unknown.A suite of Mn-rich chrysocolla clasts surrounded by pseudomalachite layers have been characterized and dated by in-situ U-Th-Pb LA-ICP-MS analyses. The data obtained on pseudomalachite define a concordant date of 19.45 0.21 Ma. In the Mn-rich chrysocolla clasts, the data yield concordant to sub-concordant dates between 12 and 7-6 Ma. These dates are therefore not consistent with the date obtained on the pseudomalachite layers that coat them. This could reflect either Pb loss linked to late fluids that affected specifically these clasts or an analytical bias due to the fact that there is no chrysocolla standard available for in-situ U-Pb dating. Assuming a recent lead loss, the chrysocolla data yield an intercept date of 23 ± 15 Ma, which is compatible with the younger U-Pb date obtained on the pseudomalachite.This preliminary study demonstrates, for the first time, that supergene copper mineralization can be dated by the U-Th-Pb method. Furthermore, the age obtained on pseudomalachite indicate that Mina Sur deposition took place at ca. 20 Ma, about 10 Ma after the unroofing and hydrothermal alteration at Chuquicamata, a result that is consistent with the supergene ages already known supergene in the Atacama Desert

Etat thermique de la croûte varisque dans lemassif nord-pyrénéen du Saint Barthélémy

National audienceLa chaîne Varisque est classiquement interprétée comme le résultatd’une subduction océanique suivie d’une collision continentaleet d’un épisode tardif de haute température. La singularitédu segment pyrénéen est la prédominance de cet épisode tardivarisquequi est caractérisé au premier ordre par une déformationmajeure synchrone d’un métamorphisme de haute température etd’un magmatisme varié. Cependant, la source de chaleur responsabledu métamorphisme et du magmatisme reste débattue.L’objectif de cette étude est de déterminer les trajets P-Tt-déformation à l’échelle d’un massif nord-pyrénéen, le SaintBarthélémy, et de discuter des causes de l’évolution des gradientsgéothermiques.Le massif du Saint Barthélémy est composé de deux unités séparéespar une zone de cisaillement à faible pendage. L’unitésupérieure du Saint Barthélémy représente la croûte varisquesupérieure constituée de migmatites et de micaschistes alors quel’unité basale, formée de gneiss granulitiques, correspond au débutde la coûte inférieure. Les granulites des massifs nord-pyrénéenssont les reliques les plus profondes de la croûte varisque mises àl’affleurement lors du cycle alpin. L’ensemble du massif est caractérisépar une déformation majeure rétrograde par rapport au picthermique suivie d’une localisation de la déformation le long debandes de cisaillement chaudes. Les données P-T-t-déformationindiquent une température homogène de 800 C sur l’ensemblede la croûte médiane de 10 à 20 km pendant le pic thermique à300 Ma (datation U-Pb sur zircons et monazites de granulites etmigmatites). Dans la partie supérieure de la croûte, on observe ungradient maximum supérieur à 80 C/km à 10 km de profondeur.Nous suggérons que ce géotherme est induit par la migration deliquides depuis la base de la croûte jusqu’à la profondeur de miseen place des corps magmatiques dans la partie supérieure du massif.Un second épisode thermique est enregistré à 280 Ma. Nousproposons que cet épisode permien soit lié à la relaxation thermiquede la croûte. En effet, le chemin rétrograde montre unrefroidissement de la croûte granulitique du Saint Barthélémy aucours de l’exhumation. L’évolution du géotherme, caractéristiquedes massifs nord-pyrénéens, suit un épisode magmatique diversifiéà ca. 305 Ma à l’échelle de la chaîne. Cette coïncidence, ainsique l’absence d’enregistrement d’épaississement crustal, suggèreune origine mantellique de l’anomalie thermique tardi-varisque