Gondwana breakup: Messages from the North Natal Valley

The Natal Valley, offshore Mozambique, is a key area for understanding the evolution of East Gondwana. Within the scope of the integrated multidisciplinary PAMELA project, we present new wide‐angle seismic data and interpretations, which considerably alter Geoscience paradigms. These data reveal the presence of a 30‐km‐thick crust that we argue to be of continental nature. This falsifies all the most recent palaeo‐reconstructions of the Gondwana. This 30‐km‐thick continental crust 1,000 m below sea level implies a complex history with probable intrusions of mantle‐derived melts in the lower crust, connected to several occurrences of magmatism, which seems to evidence the crucial role of the lower continental crust in passive margin genesis.     

Apodized Lyot coronagraph for SPHERE/VLT

SPHERE (which stands for Spectro-Polarimetric High-contrast Exoplanet REsearch) is a second-generation Very Large Telescope (VLT) instrument dedicated to high-contrast direct imaging of exoplanets which first-light is scheduled for 2011. Within this complex instrument one of the central components is the apodized Lyot coronagraph (ALC). The present paper reports on the most interesting aspects and results of the whole numerical study made during the design of the ALC for SPHERE/VLT. The method followed for this study is purely numerical, but with an end-to-end approach which is largely fed by a number of instrumental feedbacks. The results obtained and presented in this paper firstly permit to finalize the optical design before laboratory performance testing of the ALC being built for SPHERE/VLT (see paper II ??Laboratory tests and performances??), but will also hopefully help conceiving future other instruments alike, for example within the very promising extremely large telescope perspective.     

High resolution TEM of chondritic carbonaceous matter: Metamorphic evolution and heterogeneity

Abstract– The insoluble carbonaceous matter from 12 chondrites (CI, CM, CO, CV, EH, and UOC), was characterized by high resolution transmission electron microscopy (HRTEM). Besides ubiquitous nanoglobules, the insoluble organic matter from petrologic type 1 and 2 chondrites and Semarkona (LL 3.0) is composed of a highly disordered polyaromatic component. No structural differences were observed between these IOMs, in agreement with the limited thermal metamorphism they all experienced. In chondrites of petrologic type >3.0, the evolution of the IOM is controlled by the extent of thermal metamorphism. The polyaromatic layers, shorter than 1 nm in petrologic type ≤3.0 chondrites, grow up to sizes between 5 and 10 nm in petrologic type >3.6 chondrites, contributing to the increase of the degree of structural order. In addition, we find rare, but ubiquitous onion‐like carbons, which may be the product of nanodiamond graphitization. The insoluble carbonaceous matter of the enstatite chondrite Sahara 97096 (EH 3) is different from the other meteorites studied here. It is more heterogeneous and displays a high abundance of graphitized particles. This may be the result of a mixture between (1) the disordered carbon located in the matrix, and (2) catalytic graphitized phases associated with metal, potentially originating from partial melting events. The structural and nanostructural evolution are similar in all IOMs. This suggests that the structure of the accreted precursors and the parent body conditions of their secondary thermal modifications (temperature, duration, and pressure) were similar. The limited degree of organization of the most metamorphosed IOMs compared with terrestrial rocks submitted to similar temperature suggests that the conditions are not favorable to graphitization processes, due to the chemical nature of the precursor or the lack of confinement pressure.     

East-west diachronism of the collisional stage In the french Massif Central Implications for the European Variscan Orogen

Abstract

This paper presents a review of radiometric data relevant to the collisional history of the french Massif Central, located in the southern branch of the European Variscan Belt. Previous U-Pb, Rb-Sr and К-Ar data are discussed together with ⁴⁰Ar-³⁹Ar mineral ages newly acquired on the high-grade metamorphic nappes of the eastern part of the massif. The petrological and tectonic setting of the dated rocks and minerals is discussed in order to provide a successful understanding of the ages. The radiometric data now available in the frenili Massif Central show that the main teclono-nietamorphic evolution took place at least 360340 Ma ago in the eastern part and at least 390-370 Ma ago in the western part. This diachronism is closely correlated with (i) a difference in the nature and number of units involved in the collisional process and (ii) the establishment of contrasted thermal regimes in the eastern and western parts during collision. Similar chronological, lithological and thermal evolutions are observed along the southern branch of the European Variscan Belt. These fundamental contrasts are debated in order to point out their possible consequences on the evolution through lime and space of the Variscan orogen.     

Distribution and chronology of Pleistocene permafrost features in France: Database and first results

Numerous periglacial features (polygons, nets, soil stripes, ice‐wedge pseudomorphs and sand‐wedge casts, involutions) have been recorded in France by examining bibliographical sources and aerial photographs. These data show that a large part of France was affected by permafrost during the Pleistocene and only the southern Aquitaine Basin and Languedoc seem to have been beyond its maximum extent. The first OSL ages obtained from the aeolian infill of wedge structures indicate that at least two phases of thermal contraction cracking occurred in southwestern France between ～25 and 36 ka. Chronostratigraphical data from loess in northern France indicate that these episodes correspond to the formation of ice‐wedge networks associated with tundra gleys. In the latter region, two additional permafrost episodes probably occurred during the Last Glacial, the older one corresponding to the end of Marine Isotope Stage (MIS) 4 around 60 ka and the more recent one to MIS 2 around 19–16 ka. Although stratigraphical data indicate that these episodes were relatively short (about one millennium), relict permafrost may have existed for longer periods in northern France.     

Improving the Representation of the Nocturnal Near-Neutral Surface Layer in the Urban Environment with a Mesoscale Atmospheric Model

A new approach to improve the representation of surface processes in the Global Environmental Multiscale (GEM) atmospheric model associated with the exchanges between the urban canopy and the atmosphere is presented. Effects of the urban canopy on the evolution of surface-layer wind, temperature, moisture, and turbulence are directly parametrized in order to allow realistic interactions between the canopy elements (i.e., roofs, roads, and walls) and the atmosphere at GEM’s multiple vertical levels that are positioned inside the canopy. Surface energy budgets as implemented in the Town Energy Balance (TEB) scheme have been used to determine temperatures of the urban canopy elements for the proposed multilayer scheme. Performance of the multilayer scheme is compared against standard implementations of the TEB scheme for one nighttime intensive observation period of the Joint Urban 2003 experiment held in Oklahoma City, USA. Although the new approach is found to have a negligible impact on urban surface-layer wind profiles, it improves the prediction of near-neutral nocturnal profiles of potential temperature close to the surface. The urban heat island effect is simulated with a better accuracy by the multilayer approach. The horizontal temperature gradient across the central business district of the city along the direction of flow is also reasonably well captured by the proposed scheme.     

Towards a dedicated impact portal to bridge the gap between the impact and climate communities : Lessons from use cases

Future climate evolution is of primary importance for the societal, economical, political orientations and decision-making. It explains the increasing use of climate projections as input for quantitative impact studies, assessing vulnerability and defining adaptation strategies in different sectors. Here we analyse 17 national and representative use cases so as to identify the diversity of the demand for climate information depending on user profiles as well as the best practices, methods and tools that are needed to answer the different requests. A particular emphasis is put on the workflow that allows to translate climate data into suitable impact data, the way to deal with the different sources of uncertainty and to provide a suited product to users. We identified three complementary tools to close the gap between climate scientists and user needs: an efficient interface between users and providers; an optimized methodology to handle user requests and a portal to facilitate access to data and elaborated products. We detail in the paper how these three tools can limit the intervention of experts, educate users, and lead to the production of useful information. This work provides the basis on which the ENES (European Network for Earth System Modelling) Portal Interface for the Climate Impact Communities is built.     

Diffusion and Mixing in Main-Sequence Stars

The element settling which occurs inside stars, also called `microscopic diffusion', due to the combined effect of gravity, thermal gradient, radiative acceleration and concentration gradient, leads to abundance variations which cannot be neglected in the computations of stellar structure. These processes where first introduced to account for abundance anomalies in `peculiar stars', but their importance in the so-called `normal' stars is now fully acknowledged, specially after the evidence of helium settling in the Sun from helioseismology. The reason why abundance variations as large as predicted by microscopic diffusion are not always observed is due to the influence of macroscopic motions, like rotation-induced mixing, or mass loss, which increase the settling time scales. In the present review, I discuss the theories of element settling and rotation-induced mixing and the importance of their coupling. I also give some comments about the links between diffusion processes and asteroseismology.     

Mechanical Heating in Disk-Driven Winds – Thermal Structure & Observational Predictions

Following the work of Garcia et al. (2001a) (GFCB), we compute the thermal properties and ionization structure of magnetically-driven disk winds. The original model's dominant heating function along the jet, ambipolar diffusion, is augmented by a mechanical heating term supposed to arise from weak shocks, as used by (Shang et al., 2002). We add this mechanical heating function to a cold disk wind model and calculate its effect on the jet as a whole. The temperature and ionization of the flow are calculated in the case of cold jet solutions consistent with the underlying accretion disk (Ferreira, 1997). These solutions are compared to those of (GFCB) in order to quantitatively determine the effect of the mechanical heating on the flow. We then use the computed thermal and ionization structures to calculate jet synthetic observations. We find that the addition of mechanical heating leads to higher electron fractions, in turn leading to increased line fluxes and line ratios approaching observed values.     

The Role of the Inclination in the Captures in External Resonances in the Three Body Problem

Interested in the role of the inclination in our results (Jancart and Lemaitre, 2001), we analyze the process of resonance trapping due to general dissipation forces in the frame of the spatial restricted three body problem and in the case of external mean motion resonances. We compute our simulations by using the three-dimensional Extended Schubart Averaging integrator developed by Moons (1994) for all mean motion resonances. We complete it by adding the averaged contributions of general dissipative forces like Murray has proposed in the article (1994). The behavior of the inclination is especially pointed out.