The Saint-Georges-sur-Loire olistostrome, a key zone to understand the Gondwana-Armorica boundary in the Variscan belt (Southern Brittany, France).

In the southern part of the French Armorican massif, the Ligerian domain is located along the boundary between Gondwana and Armorica. Lithological, geochemical and structural data on the Saint-Georges-sur-Loire Unit, which is the northern part of the Ligerian domain, allow us to distinguish two sub-units. A southern sub-unit, formed by various blocks (chert, limestone, sandstone, rhyolite, mafic rocks) of Silurian to Middle Devonian age included as olistoliths in a Middle-Late Devonian terrigeneous matrix, overthrusts a sandstone-pelite northern sub-unit. Both units experienced two deformation events. The first one is a top-to-the-NW thrusting and the second one is a left-lateral wrenching. The Saint-Georges-sur-Loire Unit is an accretionary prism formed during the Late Devonian closure of the Layon rift, coeval with the main phase of the Variscan orogeny. The Layon rift, which according to the mafic olistoliths was partly floored by oceanic crust, appears as a buffer structural zone that accounts for the lack in Central Brittany of any tectonic or sedimentary echo of the closure of the Medio-European Ocean. The tectonic evolution of the Saint-Georges-sur-Loire Unit supports a polyorogenic model for this part of the Variscan Belt

Discussion on a new model for the Hercynian Orogen of Gondwana France and Iberia by D. Shelley & G. Bossière.

In spite of numerous studies, the geodynamic evolution of the Hercynian Orogeny of Western Europe is still controversial. In a recent paper, Shelley and Bossière (2000) propose that the Hercynian Orogeny in Iberia and France was a ‘collage' of distinct fault-bounded ‘terranes' developed during a major dextral wrenching of more than 2000 km. This interpretation is in line with that already proposed by Badham (1982) but is at variance with most other published models that emphazise tangential tectonics, that is to say thrusting and collision tectonics driven by oceanic and continental subduction (e.g. Matte; Ledru; Dias and Faure and references therein). The Shelley and Bossière model has been criticized for parts dealing with the Iberian branch of the orogen by Pereira and Silva (2001). In the following, we shall comment on the strike-slip model for the S. Armorican branch of the belt, on the basis of first-hand geological data aquired from the SE part of the Armorican Massif ( Cartier and Cartier) and general considerations on the Hercynian Belt

Structure de l'unité de Saint-Georges-sur-Loire et du domaine ligérien (Massif Armoricain). Implications géodynamiques pour la chaîne hercynienne.

M. Michel FAURE, Professeur, Université d'Orléans - Directeur de ThèseM. Florentin PARIS, Directeur de Recherche, Rennes I - RapporteurM. Philippe MATTE, Directeur de Recherche, Montpellier - RapporteurM. Philippe ROSSI, Ingénieur BRGM, Orléans - ExaminateurM. Patrick LEDRU, Ingénieur BRGM, Orléans - ExaminateurM. Hubert LARDEUX, Professeur, Université Catholique de L'Ouest, Angers - InvitéThe Saint-Georges-sur-Loire unit crops out in the Armorican Massif, more precisely in the Ligerian Domain between the Lanvaux-les-Ponts-de-Cé anticline and the Nort-sur-Erdre fault. This peculiar unit is divided into two subunits : the sandstone-pelite subunit to the North (Early Ordovician-Early Silurian) and the blocky volcanic-clastic subunit to the South. The southern subunit is considered as an olistostrome and includes blocks of various lithologies and ages, namely : Early Silurian black chert, Late Silurian to Middle Devonian limestone, Late Silurian mafic lava, acidic lava of probably Cambrian age and sandstone blocks. These blocks are mixed in a pebbly-mudstone matrix with locally turbidite-type sandstone-mudstone alternations reaching a probable Middle to Late Devonian age. This chaotic subunit presents a S0-1 surface deformed by folds overturned to the North and a NW-SE trending southward dipping cleavage bears a N-S to N60E stretching lineation. This southern subunit overthrusts the northern sandstone-pelite subunit. When moving northward to the sandstone-pelite subunit, upright folds or recumbent folds overturned to the North are found and a NW-SE stretching and mineral lineation develops. This lineation and mylonites become more and more conspicuous when moving to the Lanvaux anticline. The blocky southern subunit constitutes an intermediate zone between the low grade Paleozoic terranes to the North and the South-verging high metamorphic grade Champtoceaux and Mauges nappes to the South. A new geodynamic interpretation is proposed to account for the Saint-Georges-sur-Loire unit in a model implying North Gondwana and Armorica plate interactions in Paleozoic times. This interpretation suggests the activity of diachronic subduction zones with opposite dips in Armorica, emphasizes the role of the Nort-sur-Erdre polyphase fault and explains the geotectonic nature of the Saint-Georges-sur-Loire unit as a chaotic unit formed in an accretionary prism linked with the « Layon rift » closure.L'unité de Saint-Georges-sur-Loire située dans le domaine ligérien entre la ride de Lanvaux-Les-Ponts-de-Cé au Nord et la faille de Nort-sur-Erdre au Sud constitue une zone clef pour la compréhension de la géodynamique hercynienne. Cette unité est constituée de deux sous-unités distinctes, l'unité sans blocs schisto-gréseuse au Nord (Ordovicien inférieur à Silurien inférieur) et l'unité à blocs, schisto-gréseuse et volcanique au Sud. L'unité à blocs méridionale est considérée comme un olistostrome dévonien à blocs mono- ou poly-lithologiques de nature et d'âges variés : radiolarites (Silurien), calcaires (Silurien sup. à Dévonien moy.), laves et tufs basiques (Silurien), rhyolites et grès. Ces blocs sont remaniés au sein d'une matrice schisto-gréseuse d'âge probable Dévonien moyen à supérieur. Cette unité à blocs est déformée par des plis synchisteux déversés vers le Nord et présente une linéation d'allongement N-S à N60E ; elle chevauche l'unité sans blocs. Des plis droits ou légèrement déversés vers le Nord sont rencontrés dans l'unité sans blocs, ainsi qu'une linéation minérale et d'allongement NW-SE de plus en plus marquée à mesure que l'on se rapproche de la bande ductile de Lanvaux, où elle s'exprime pleinement. L'unité à blocs constitue également une zone intermédiaire entre des terrains paléozoïques peu métamorphiques à vergences nord dans le sous-domaine ligérien septentrional et des terrains impliqués dans la structure de nappes de Champtoceaux et le métamorphisme de haute pression, à structures vers le Sud dans le sous-domaine méridional. Une nouvelle interprétation géodynamique intégrant toutes les données disponibles est donc proposée afin de replacer l'unité de Saint-Georges-sur-Loire dans un schéma interprétatif à plus grande échelle. Cette interprétation précise l'évolution du domaine nord gondwanien et de la marge sud de la microplaque Armorica au Paléozoïque. Elle souligne l'existence de zones de subductions diachrones et de vergences opposées au sein de la microplaque Armorica, met en valeur le rôle de la faille de Nort-sur-Erdre, considérée comme une zone de suture polyphasée majeure en Armorique et précise la nature géotectonique de l'unité de Saint-Georges-sur-Loire, formation chaotique déposée dans un prisme d'accrétion lié à la fermeture du « rift du Layon »

Structure de l'unité de Saint-Georges-sur-Loire et du domaine ligérien (Massif armoricain) (implications géodynamiques pour la chaîne hercynienne)

ORLEANS-BU Sciences (452342104) / SudocORLEANS-ISTO (452342307) / SudocSudocFranceF

The Hercynian orogeny in the South Armorican Massif (Saint-Georges-sur-Loire Unit, Ligerian Domain, France): rifting and welding of continental stripes

A new approach to explain the Western Hercynian Belt is given by a lithological and structural study of the St-Georges-sur-Loire Unit (southern part of the French Armorican Massif). This unit is interpreted as a Devonian olistostrome sheared to the North. It is formed in an accretionary prism linked with a south-dipping subduction zone, called the Layon subduction zone. It results from a chaotic sedimentation including exotic blocks of various lithologies and ages in a Middle Devonian pebbly mudstone matrix. An inovative geodynamic model involving microblock rifting and collision is discussed to explain the presence of the St-Georges-sur-Loire Unit in the Armorican Massif. This model involves two Palaeozoic subductions and emphasizes the role of the Nort-sur-Erdre fault, considered as a major polyphase suture zone separating South and Central Armorica

Vulnerability to earthquake of Beirut residents (Lebanon) : perception, knowledge, and protection strategies

International audienc

Paleozoic geodynamic evolution of mid-europa from the example of the French Massifs.

The Paleozoic orogen that forms the backbone of Mid-Europa results from the collision between Gondwana, Laurussia and several microcontinents. The French Massif Central and Massif Armoricain belong to three tectonic and paleogeographic domains. Namely, the entire Massif Central and the south part of the Massif Armoricain belong to the North Gondwana margin, the Central Armorican Domain is a part of Armorica microcontinent and the Léon Domain is a piece of another microcontinent. The N. Gondwana margin and Léon Domain are made of a stack of syn-metamorphic nappes, conversely, the Central Armorican Domain consists of a Proterozoic basement built up by the Neoproterozoic Cadomian orogeny and a Paleozoic basement weakly deformed by upright folds related to wrench faults. The bulk architecture of the North Gondwana margin id the result of three main tectonic and metamorphic events that followed a Late Silurian high-pressure metamorphism whose associated structures are poorly documented. The Early Devonian D1 event (ca 385 Ma) is responsible for top-to-the-SW nappe stacking coeval with migmatization and exhumation of high-pressure rocks. The Late Devonian-Early Carboniferous D2 event (360-350 Ma) is associated to a medium pressure/temperature metamorphism during which top-to-the-NW shearing develops. The Visean D3 event (335-330 Ma) is characterized by contrasted tectonic regimes. A synmetamorphic top-to-the-south ductile shearing is widespread in south Massif Central whereas in north Massif Central, D3 is coeval with the onset of synorogenic extension. Orogen-parallel (E-W) extension develops coevally with Namurian-Westphalian plutonism, and orogen-transverse (N-S) extension took place in Late Carboniferous (ca 300 Ma). The Variscan Belt is also characterized by several magmatic events. The Early Cambrian and Early Ordovician pre-orogenic alkaline magmatisms correspond to the rifting events that separated Avalonia, Armorica and Léon microcontinents from Gondwana. The Early-Middle Devonian calc-alkaline magmatism is related to the Gondwana-directed subduction of the Rheic Ocean. Other magmatic events are due to the crustal melting that took place in Carboniferous times in response to D2 and D3 events. Late Visean and younger magmatic stages are coeval with extensional tectonics. These structural, metamorphic and magmatic events are replaced in a geodynamic evolution model at the scale of Western Europe

Paleozoic tectonic evolution of medio-europa from the example of the french massif central and massif armoricain

International audienceThe French Massif Central and Massif Armoricain belong to three tectonic and paleogeographic domains of the Medio-Europa Variscan Orogen. The entire Massif Central and southern part of the Massif Armoricain belong to the North Gondwana margin, the Central Armorican Domain is a part of Armorica microcontinent and the Léon Domain is a piece of another microcontinent. The N. Gondwana margin and Léon Domain are made of a stack of metamorphic nappes, conversely, the Central Armorican Domain consists of a Proterozoic basement built up by the Neoproterozoic Cadomian orogeny and a Paleozoic sedimentary cover weakly deformed by upright folds related to wrenching. The architecture of the North Gondwana margin results of three main tectonic-metamorphic events that follow an early Late Silurian (ca 415 Ma) high-pressure metamorphism whose associated structures are poorly documented. The Early Devonian D1 event is responsible for top-to-the-SW nappes coeval with migmatization and exhumation of high-pressure rocks around 385-380 Ma. The Late Devonian-Early Carboniferous D2 event is a top-to-the-NW shearing coeval with an intermediate pressure-temperature metamorphism dated around 360-350 Ma. The Visean D3 event is a top-to-the-south shearing widespread in the south Massif Central whereas in north Massif Central, D3 corresponds to the onset of synorogenic extension. The Variscan Belt is also characterized by a widespread magmatism. The Early-Middle Devonian calc-alkaline magmatism is related to the southward subduction of the Rheic Ocean. The Carboniferous magmatic events are the crustal melting response of D2 and D3 tectonic events. Late Visean, Namurian and Westphalian magmatic stages are coeval with extensional tectonics controlled by NW-SE stretching. These structural, metamorphic and magmatic events are replaced in a geodynamic evolution model involving two cycles of microcontinent drifting, rewelding and continental collision

General practitioners remuneration methods: what consequences?

peer reviewedIntroduction. The health reform law crystallizes the tensions between the different health system players. Besides the specific issue of third-party payment, which will be addressed in an upcoming article, some professional organizations wish to strengthen fee for servicies while others call for more mixed forms of remuneration. Many economic analyses were conducted to study the benefits and limits of each mode of physician compensation. This article offers a synthesis of the literature about these modes: fee for service, capitation, payment performance and wage labor. Method. Collaborative literature analysis between doctors and health economist. The databases searched were MEDLINE, the Cochrane Library and CAIRN. Results. Each mode has specific benefits and limits for the financer, the physicians and the patients. Fee for services increases physician productivity but may increases health spending. Capitation and salary decrease care supply but might help to control health spending and to develop preventive activities. The effectiveness of pay for performance is now being questioned. The current trend is to promote mixed forms of remuneration, hoping to combine the advantages and limit the share of defects of each modality. The complexity of such systems makes it difficult to compare from one country to another. Discussion. The choice of a mode by the financer must take into account both the possible combinations of different payment methods and the developments or societal aspirations to meet population health needs.Introduction. La réforme de la loi de santé cristallise des tensions entre les différents acteurs du système de santé. Outre la question du tiers payant, qui sera abordée dans un prochain article, certaines organisations professionnelles souhaitent renforcer la place du paiement à l’acte quand d’autres plaident pour plus de mixité des modes de rémunération. De nombreux travaux d’analyse économique ont été menés dans le but d’étudier les avantages et inconvénients propres à chacun des modes de rémunération des médecins. Cet article propose une synthèse des données concernant différentes modalités de rémunération des médecins : le paiement à l’acte, la capitation, la rémunération à la performance et le salariat. Méthode. Travail collaboratif d’analyse de la littérature entre médecins et économistes de la santé. Les bases de données consultées ont été MEDLINE, la bibliothèque Cochrane et CAIRN. Résultats. Chaque mode de rémunération comporte des avantages et des inconvénients, aussi bien pour le financeur que pour les médecins et les patients. Le paiement à l’acte augmente la productivité des médecins mais peut majorer les dépenses de santé. La capitation et le salariat diminuent l’offre de soins mais permettent de contrôler les dépenses de santé et de développer des activités préventives. L’efficacité de la rémunération à la performance est aujourd’hui remise en question. La tendance actuelle vise à favoriser la mixité des modes de rémunération en espérant y associer les avantages de chaque modalité et limiter la part des défauts de chacune. La complexité des systèmes rend difficile la comparaison d’un pays à l’autre. Conclusion. Le choix des modes de rémunération par le financeur est un choix qui doit prendre en compte les possibilités de combinaisons des différents modes de rémunération et les évolutions ou les aspirations sociétales pour répondre aux besoins de santé de la population

Intimin gene (eae) subtypes-based real-time PCR strategy for the specific detection of Shiga toxin-producing Escherichia coli serotypes O157:H7, O26:H11, O103:H2, O111:H8 and O145:H28 in cattle feces

International audienceShiga toxin-producing Escherichia coli (STEC) belonging to serotypes O157:H7, O26:H11, O103:H2, O111:H8 and O145:H28 are known to be associated with particular subtypes of the intimin gene (eae), namely γ1, β1, ɛ, θ and γ1, respectively. This study aimed at evaluating the usefulness of their detection for the specific detection of these five main pathogenic STEC serotypes in cattle feces. Using real-time PCR assays, 58.7% of 150 fecal samples were found positive for at least one of the four targeted eae subtypes. The simultaneous presence of stx, eae and one of the five O group markers was found in 58.0% of the samples, and the five targeted stx/eae/O genetic combinations were detected 143 times. However, when taking into consideration the association between eae subtypes and O group markers, the resulting stx/eae-subtype/O combinations were detected only 46 times. The 46 isolation assays performed allowed to recover 22 E. coli strains belonging to one of the five targeted STEC serogroups. By contrast, only 2 out of 39 isolation assays performed on samples that were positive for stx, eae and an O group marker, but were negative for the corresponding eae subtype, were successful. Characterization of the 24 E. coli isolates showed that 6 were STEC, including 1 O157:H7, 3 O26:H11 and 2 O145:H28. The remaining 18 strains corresponded to atypical enteropathogenic E. coli (aEPEC). Finally, the more discriminating eae subtypes-based PCR strategy described here may be helpful for the specific screening of the five major STEC in cattle feces