Structure and evolution of the Baikal rift: A synthesis

Active continental rifts are spectacular manifestations of the deformation of continents but are not very numerous at the surface of the Earth. Among them, the Baikal rift has been extensively studied during the last decades. Yet no simple scenario explains its origin and development because the style of rifting has changed throughout its ∼30 Myr history. In this paper, we use forward and inverse models of gravity data to map the Moho and lithosphere-asthenosphere boundary in three dimensions. We then integrate these new results with existing geophysical and geological data on the Baikal rift structure and dynamics, and propose a scenario of its evolution. Earthquake depths, mantle xenoliths, heat flow, and seismic and gravity models advocate for a normal to moderately thinned continental lithosphere and crust, except beneath the Siberian craton, which exhibits a >100-km-thick lithosphere. Relatively thin lithosphere (70–80 km) is found east and south of the rift system and is in spatial connection with the Hangai-Hövsgöl region of anomalous mantle in Mongolia. From top to bottom, the rift structure is asymmetric and appears strongly controlled by the geometry of the suture zone bounding the Siberian craton. Moreover, the mode of topography support changes significantly along the length of the rift: mountain ranges south and north of the rift are underlain by negative Bouguer anomalies, suggesting deep crustal roots and/or anomalous mantle; rift shoulders in the center of the rift seem to result from flexural uplift. The commonly assumed “two-stage” rift evolution is not corroborated by all stratigraphic and seismic data; however, it seems clear that during the Oligocene, an “early stage,” which might be dominated by strike-slip tectonics instead of pure extension, created primitive basins much different from the present ones. Most of the “true” rift basins seem to have initiated later, during the Late Miocene or Pliocene. This kinematic change from strike-slip to extensional tectonics in the Baikal rift is part of a more general kinematic reorganization of Asia and can be associated with the rapid growth of the Tibetan plateau and the end of marginal basins opening along the Pacific boundary

Oblique rifting at oceanic ridges: Relationship between spreading and stretching directions from earthquake focal mechanisms

International audienceThe relationship between spreading and stretching directions is investigated at oblique-spreading oceanic ridges using earthquake focal mechanisms. The stretching direction at ridge axes corresponds to the direction of the greatest principal strain epsilon1 taken as the mean trend of the seismic T-axes of extensional earthquake focal mechanisms. It is compared with the spreading direction provided by global plate-motion models. We find that the stretching direction trends approximately halfway between the spreading direction and the normal to the ridge trend, a result in line with analogue experiments of oblique rifting. This result is satisfactorily accounted for with an analytical model of oblique rifting, for which the direction of epsilon1 is calculated with respect to rifting obliquity for different amounts of stretching using continuum mechanics. For low stretching factors, typical of incremental seismic deformations, epsilon1 obliquity is two times lower than rifting obliquity. For higher stretching factors, the stretching and spreading directions become parallel

Micro-tectonic constraints on the evolution of the Barles half-window (Digne Nappe, southern Alps). Implications for the timing of folding in the Valensole foreland basin

International audienceThe "Vélodrome" overturned syncline, at the northern margin of the Cenozoic foreland basin of Valensole in SE France, was formed during the Late Cenozoic at the front of the Digne nappe. Microstructural analyses reveal that mesoscale faulting in the molassic series, from the Oligocene "Molasse Rouge" at the base to the middle to late Miocene "Valensole Conglomerates" at the top, partly occurred before the folding, as layer-parallel shortening: the NNE-SSW-directed compression is recorded by two systems of reverse and strike-slip faults, which formed when the strata were still horizontal and were passively tilted as folding occurred. These data suggest that the Vélodrome folding postdates the deposition of the Valensole Conglomerates and occurred in late Miocene-Pliocene times during the emplacement of the Digne nappe. These results are difficult to reconcile with the interpretation of the Vélodrome as a growth fold progressively formed in 10-15 m.y. during the deposition of the Miocene molasses. Structural data collected in the Barles tectonic half-window enable to reconstruct the evolution of the deformation since the Jurassic. The two main phases of shortening, the pre-Oligocene Pyrenean-Provençal and the Mio-Pliocene Alpine phases, are almost homoaxial with a direction of compression trending N-S for the former and NNE-SSW for the later. A late Eocene-basal Oligocene N-S extensional episode is documented between these two phases, probably in relation with the formation of the western European rift system. The direction of extension of the Liassic rifting of the Alpine Tethys is roughly constrained in the NW-SE quadrant. Paleo-stress field reconstruction brings consistent results at the regional scale and proves to be a powerful tool to decipher the evolution of the deformation in a remarkably complicated tectonic setting

Consensus is Easier Than Reliable Broadcast

RapportWe consider asynchronous distributed systems with message losses and process crashes. We study the impact of finite process memory on the solution to consensus, repeated consensus and reliable broadcast. With finite process memory, we show that in some sense consensus is easier to solve than reliable broadcast, and that reliable broadcast is as difficult to solve as repeated consensus: More precisely, with finite memory, consensus can be solved with failure detector S , and P − (a variant of the perfect failure detector which is stronger than S ) is necessary and sufficient to solve reliable broadcast and repeated consensus

Normal Aging Modulates the Neurotoxicity of Mutant Huntingtin

Aging likely plays a role in neurodegenerative disorders. In Huntington's disease (HD), a disorder caused by an abnormal expansion of a polyglutamine tract in the protein huntingtin (Htt), the role of aging is unclear. For a given tract length, the probability of disease onset increases with age. There are mainly two hypotheses that could explain adult onset in HD: Either mutant Htt progressively produces cumulative defects over time or “normal” aging renders neurons more vulnerable to mutant Htt toxicity. In the present study, we directly explored whether aging affected the toxicity of mutant Htt in vivo. We studied the impact of aging on the effects produced by overexpression of an N-terminal fragment of mutant Htt, of wild-type Htt or of a β-Galactosidase (β-Gal) reporter gene in the rat striatum. Stereotaxic injections of lentiviral vectors were performed simultaneously in young (3 week) and old (15 month) rats. Histological evaluation at different time points after infection demonstrated that the expression of mutant Htt led to pathological changes that were more severe in old rats, including an increase in the number of small Htt-containing aggregates in the neuropil, a greater loss of DARPP-32 immunoreactivity and striatal neurons as assessed by unbiased stereological counts

Quand le consensus est plus simple que la diffusion fiable

International audienceNous nous intéressons à l'impact de la limitation de la mémoire sur des problèmes algorithmiques distribués classiques dans le contexte de systèmes asynchrones sujets aux pannes franches

Le Marais des Paluns

Les zones humides méditerranéennes sont au cœur de multiples enjeux environnementaux. Les zones humides de la Palun connectées à l’étang de Berre sont une zone spéciale de conservation située à l’aval d’un bassin versant anthropisé. Une contamination diffuse et cumulative dans le temps des sédiments y a été identifiée. C’est dans ce contexte qu’un travail a été mené sur un procédé de traitement des eaux du bassin versant de la Palun pour favoriser la résilience du marais récepteur face à la pollution chronique. Les possibilités de réalisation d’une zone humide artificielle en amont du marais, dédiée à l’épuration des eaux, ont été réfléchies en lien avec les usages et les attentes parfois divergentes des acteurs du territoire. La réparation des atteintes environnementales dans le contexte socio-économique contraint de l’étang de Berre a été interrogée à partir des savoirs issus de l’écologie de la restauration et de la sociologie.Mediterranean wetlands are subject to many environmental issues. The Palun wetlands in connection with the industrialized Berre lagoon are a special area of conservation located downstream of an anthropised watershed and where diffuse and cumulative contaminations of the sediments were detected. A work was then carried out on a water treatment process in the Palun watershed to promote the resilience of the receiving marsh. The possibilities of creating a constructed wetland upstream to treat all waters have been reflected in connection with the potential divergent uses and expectations of the territory actors. Repairing environmental damages in the particular socio-economic context of the Berre lagoon was considered from the knowledge of restoration ecology and sociology

Lactobacillus rhamnosus GG encapsulation by spray-drying: milk proteins clotting control to produce innovative matrices

A well-known probiotic strain, L.\ua0rhamnosus GG, was encapsulated by spray-drying in milk water-insoluble matrices upon reconstitution in hot water by exploiting and controlling the clotting reaction of milk proteins during the process. The feed solution, composed of probiotic bacteria and milk proteins, was or not subjected to the action of chymosin, a proteolytic enzyme. To optimize microencapsulation efficiency, different outlet air temperatures were tested (55, 70 and 85\ua0°C). After spray-drying, small microparticles were recovered for further characterization. All drying conditions led to excellent bacterial survival rates