Lifetime of an ocean island volcano feeder zone: constraints from U-Pb dating on coexisting zircon and baddeleyite, and 40Ar/39Ar age determinations, Fuerteventura, Canary Islands

High-precision isotope dilution - thermal ionization mass spectrometry (ID-TIMS) U-Pb zircon and baddeleyite ages from the PX1 vertically layered mafic intrusion Fuerteventura, Canary Islands, indicate initiation of magma crystallization at 22.10 +/- 0.07 Ma. The magmatic activity lasted a minimum of 0.52 Ma. Ar-40/Ar-39 amphibole dating yielded ages from 21.9 +/- 0.6 to 21.8 +/- 0.3, identical within errors to the U-Pb ages, despite the expected 1% theoretical bias between Ar-40/Ar-39 and U-Pb dates. This overlap could result from (i) rapid cooling of the intrusion (i. e., less than the 0.3 to 0.6 Ma 40Ar/39Ar age uncertainties) from closure temperatures (T-c) of zircon (699-988 degrees C) to amphibole (500-600 degrees C); (ii) lead loss affecting the youngest zircons; or (iii) excess argon shifting the plateau ages towards older values. The combination of the Ar-40/Ar-39 and U/Pb datasets implies that the maximum amount of time PX1 intrusion took to cool below amphibole T-c is 0.8 Ma, suggesting PX1 lifetime of 520 000 to 800 000 Ma. Age disparities among coexisting baddeleyite and zircon (22.10 +/- 0.07/0.08/0.15 Ma and 21.58 +/- 0.15/0.16/0.31 Ma) in a gabbro sample from the pluton margin suggest complex genetic relationships between phases. Baddeleyite is found preserved in plagioclase cores and crystallized early from low silica activity magma. Zircon crystallized later in a higher silica activity environment and is found in secondary scapolite and is found close to calcite veins, in secondary scapolite that recrystallised from plagioclase. close to calcite veins. Oxygen isotope delta O-18 values of altered plagioclase are high (+7.7), indicating interaction with fluids derived from host-rock carbonatites. The coexistence of baddeleyite and zircon is ascribed to interaction of the PX1 gabbro with CO2-rich carbonatite-derived fluids released during contact metamorphism.

Regulation and glucocorticoid-independent induction of lipocortin I in cultured astrocytes.

Stimulation of prostaglandin (PG) release in rat astroglial cultures by various substances, including phorbol esters, melittin, or extracellular ATP, has been reported recently. It is shown here that glucocorticoids (GCs) reduced both basal and stimulated PGD2 release. Hydrocortisone, however, did not inhibit ATP-, calcium ionophore A23187-, or tetradecanoyl phorbol acetate (TPA)-stimulated arachidonic acid release, and only TPA stimulations were affected by dexamethasone. GC-mediated inhibition of PGD2 release thus appeared to exclude regulation at the phospholipase A2 (PLA2) level. Therefore, the effects of GCs on the synthesis of lipocortin I (LC I), a potent, physiological inhibitor of PLA2, were studied in more detail. Dexamethasone was not able to enhance de novo synthesis of LC I in freshly seeded cultures and failed to increase LC I synthesis in 2-3-week-old cultures. It is surprising that LC I was the major LC synthesized in those cultures, and marked amounts accumulated with culture time, reaching plateau levels at approximately day 10. In contrast, LC I was barely detectable in vivo. This tonic inhibition of PLA2 is the most likely explanation for unsuccessful attempts to evoke PG release in astrocyte cultures by various physiological stimuli. GC receptor antagonists (progesterone and RU 38486) given throughout culture time reduced LC I accumulation and simultaneously increased PGD2 release. Nonetheless, a substantial production of LC I persisted in the presence of antagonists. Therefore, LC I induction did not seem to involve GC receptor activation. This was confirmed in serum- and GC-free brain cell aggregate cultures. Here also a marked accumulation of LC I was observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Idarubicin-loaded ONCOZENE drug-eluting embolic agents for chemoembolization of hepatocellular carcinoma: in vitro loading and release and in vivo pharmacokinetics.

PURPOSE: To present in vitro loading and release characteristics of idarubicin with ONCOZENE (CeloNova BioSciences, Inc, San Antonio, Texas) drug-eluting embolic (DEE) agents and in vivo pharmacokinetics data after transarterial chemoembolization with idarubicin-loaded ONCOZENE DEE agents in patients with hepatocellular carcinoma. MATERIALS AND METHODS: Loading efficacy of idarubicin with ONCOZENE DEE agents 100 µm and DC Bead (Biocompatibles UK Ltd, Farnham, United Kingdom) DEE agents 100-300 µm was monitored at 10, 20, and 30 minutes loading time by high-pressure liquid chromatography. A T-apparatus was used to monitor the release of idarubicin from the two types of DEE agents over 12 hours. Clinical and 24-hour pharmacokinetics data were recorded after transarterial chemoembolization with idarubicin-loaded ONCOZENE DEE agents in four patients with unresectable hepatocellular carcinoma. RESULTS: Idarubicin loading in ONCOZENE DEE agents was > 99% at 10 minutes. Time to reach 75% of the release plateau level was 37 minutes ± 6 for DC Bead DEE agents and 170 minutes ± 19 for ONCOZENE DEE agents both loaded with idarubicin 10 mg/mL. After transarterial chemoembolization with idarubicin-loaded ONCOZENE DEE agents, three partial responses and one complete response were observed with only two asymptomatic grade 3 biologic adverse events. Median time to maximum concentration for idarubicin in patients was 10 minutes, and mean maximum concentration was 4.9 µg/L ± 1.7. Mean area under the concentration-time curve from 0-24 hours was equal to 29.5 µg.h/L ± 20.5. CONCLUSIONS: ONCOZENE DEE agents show promising results with very fast loading ability, a favorable in vivo pharmacokinetics profile with a sustained release of idarubicin during the first 24 hours, and encouraging safety and responses. Histopathologic and clinical studies are needed to evaluate idarubicin release around the DEE agents in tumor tissue and to confirm safety and efficacy.

Upper Triassic to Cretaceous radiolaria from Nicaragua and northern Costa Rica - The Mesquito composite oceanic terrane

We propose a new terrane subdivision of Nicaragua and Northern Costa Rica, based on Upper Triassic to Upper Cretaceous radiolarian biochronology of ribbon radiolarites, the newly studied Siuna Serpentinite Mélange, and published 40Ar/39Ar dating and geochemistry of mafic and ultramafic igneous rock units of the area. The new Mesquito Composite Oceanic Terrane (MCOT) comprises the southern half of the Chortis Block, that was assumed to be a continental fragment of N-America. The MCOT is defined by 4 corner localities characterized by ultramafic and mafic oceanic rocks and radiolarites of Late Triassic, Jurassic and Early Cretaceous age: 1. The Siuna Serpentinite Mélange (NE-Nicaragua), 2. The El Castillo Mélange (Nicaragua/Costa Rica border), 3.The Santa Elena Ultramafics (N-Costa Rica) and, 4. DSDP Legs 67/84. 1. The Siuna Serpentinite Mélange contains, high pressure metamorphic mafics and Middle Jurassic (Bajocian-Bathonian) radiolarites in original, sedimentary contact with arc-metandesites. The Siuna Mélange also contains Upper Jurassic black detrital chert formed in a marginal (fore-arc?) basin shortly before subduction. A phengite 40Ar/39Ar -cooling age dates the exhumation of the high pressure rocks as 139 Ma (earliest Cretaceous). 2. The El Castillo Mélange comprises a radiolarite block tectonically embedded in serpentinite that yielded a diverse Rhaetian (latest Triassic) radiolarian assemblage, the oldest fossils recovered so far from S-Central America. 3. The Santa Elena Ultramafics of N-Costa Rica together with the serpentinite outcrops near El Castillo (2) in Southern Nicaragua, are the southernmost outcrops of the MCOT. The Santa Elena Unit (3) itself is still undated, but it is thrust onto the middle Cretaceous Santa Rosa Accretionary Complex (SRAC), that contains Lower to Upper Jurassic, highly deformed radiolarite blocks, probably reworked from the MCOT, which was the upper plate with respect to the SRAC. 4. Serpentinites, metagabbros and basalts have long been known from DSDP Leg 67/84 (3), drilled off Guatemala in the Nicaragua-Guatemala forearc basement. They have been restudied and reveal 40Ar/39Ar dated Upper Triassic to middle Cretaceous enriched Ocean Island Basalts and Jurassic to Lower Cretaceous depleted Island arc rocks of probable Pacific origin. The area between localities 1-4 is largely covered by Tertiary to Recent arcs, but we suspect that its basement is made of oceanic/accreted terranes. Earthquake seismic studies indicate an ill-defined, shallow Moho in this area. The MCOT covers most of Nicaragua and could extend to Guatemala to the W and form the Lower (southern) Nicaragua Rise to the NE. Some basement complexes of Jamaica, Hispaniola and Puerto Rico may also belong to the MCOT. The Nicoya Complex s. str. has been regarded as an example of Caribbean crust and the Caribbean Large Igneous Province (CLIP). However, 40Ar/39Ar - dates on basalts and intrusives indicate ages as old as Early Cretaceous. Highly deformed Jurassic and Lower Cretaceous radiolarites occur as blocks within younger intrusives and basalts. Our interpretation is that radiolarites became first accreted to the MCOT, then became reworked into the Nicoya Plateau in Late Cretaceous times. This implies that the Nicoya Plateau formed along the Pacific edge of the MCOT, independent form the CLIP and most probably unrelated with he Galapagos hotspot. No Jurassic radiolarite, no older sediment age than Coniacian-Santonian, and no older 40Ar/39Ar age than 95 Ma is known from S-Central America between SE of Nicoya and Colombia. For us this area represents the trailing edge of the CLIP s. str.

Triassic pelagic deposits of Timor: palaeogeographic and sea-level implications

In West Timer, Triassic deposits are found in the Parautochthonous Complex, as well as in the Allochthonous series of Sonnebait. A detailed biostratigraphic investigation integrating field observations and facies analysis, allowed the reconstruction of a synthetic lithostratigraphic succession for the Upper Triassic, a stratigraphic transition from Carnian shales to Upper Norian-Rhaetian limestones is also shown by this study. The fossil content predominantly originates from an open marine environment; lithostratigraphic Units A-E are dated on the basis of radiolaria and palynomorphs, and Unit H, on ammonites and conodonts. The presence of pelagic bioclasts, together with normal grading, horizontal laminations, and current ripples, is indicative of a distal slope to basin environment. The ammonite rich condensed limestone of Unit H was deposited on a `pelagic carbonate plateau' exposed to storms and currents. The organic facies have been used as criteria for biostratigraphy, palaeoenvironmental interpretation, and sequence stratigraphy. The palaeontological analysis of the Triassic succession of West Timer is based on the investigation of radiolaria and palynomorphs, in the marls and limestones of Units A-E, and also on ammonites and conodonts in the condensed limestone of Unit H. Units A and B are Carnian (Cordevolian) in age, based on the occurrence of the palynomorph Camerosporites secatus, associated with `Lueckisporites' cf. singhii, Vallasporites ignacii, Patinosporites densus and Partitisporites novimundanus. Unit C is considered as Norian, on the basis of a relatively high percentage of Gliscopollis meyeriana and Granuloperculatipollis rudis. Unit D contains significant palynomorphs and radiolaria; the organic facies, characterized by marine elements, is dominated by the Norian dinocysts Heibergella salebrosacea and Heibergella aculeata; the radiolaria confirm the Norian age. They range from the lowermost Norian to the lower Upper Norian. Unit E also contains radiolaria, associated in the upper part with the well-known marker of the Upper Norian, Monotis salinaria. For Unit E, the radiolaria attest to a Lower to Upper Norian age based on the occurrence of Capnodoce and abundant Capnuchosphaera; the upper part is Upper Norian to Rhaetian based on the presence of Livarella valida. Finally, the blocks of condensed limestone with ammonites and conodonts of Unit H allowed the reconstruction of a synthetic stratigraphic succession of Upper Carnian to Upper Norian age. Our stratigraphic data lead to the suggestion that the Allochthonous complex, classically interpreted as a tectonic melange of the accretionary prism of the island Arc of Banda. is a tectonically dismembered part of a Triassic lithostratigraphic succession. (C) 2000 Elsevier Science B.V. All rights reserved.

Precision of tibial tunnel placement under arthroscopic control alone in posterior cruciate ligament reconstruction: A radiological study

Introduction: Accurate and reproducible tibial tunnel placement minimizing the risk of neurovascular damage is a crucial condition for successful arthroscopic reconstruction of the posterior cruciate ligament (PCL). This step is commonly performed under fluoroscopic control. Hypothesis: Performing the tibial tunnel under exclusive arthroscopic control allows accurate and reliable tunnel placement according to recommendations in the literature. Materials and Methods: Between February 2007 and December 2009, 108 arthroscopic single bundle PCL reconstructions in tibial tunnel technique were performed. The routine postoperative radiographs were screened according to previously defined quality criterions. After critical analysis, the radiographs of 48 patients (48 knees) were enrolled in the study. 10 patients had simultaneous ACL reconstruction and 7 had PCL revision surgery. The tibial tunnel was placed under direct arthroscopic control through a posteromedial portal using a standard tibial aming device. Key anatomical landmarks were the exposed tibial insertion of the PCL and the posterior horn of the medial meniscus. First, the centre of the posterior tibial tunnel outlet on the a-p view was determined by digital analysis of the postoperative radiographes. Its distance to the medial tibial spine was measured parallel to the tibia plateau. The mediolateral position was expressed by the ratio between the distance of the tunnel outlet to the medial border and the total width of the tibial plateau. On the lateral view the vertical tunnel position was measured perpendicularly to a tangent of the medial tibial plateau. All measurement were repeated at least twice and carried out by two examiners. Results: The mean mediolateral tunnel position was 49.3 ± 4.6% (ratio), 6.7 ± 3.6 mm lateral to the medial tibial spine. On the lateral view the tunnel centre was 10.1 ± 4.5 mm distal to the bony surface of the medial tibial plateau. Neurovascular damage was observed in none of our patients. Conclusion: The results of this radiological study confirm that exclusive arthroscopic control for tibial tunnel placement in PCL reconstruction yields reproducible and accurate results according to the literature. Our technique avoids radiation, facilitates the operation room setting and enables the surgeon to visualize the anatomic key landmarks for tibial tunnel placement.

Clinal variation in a brown lemur (Eulemur spp.) hybrid zone: Combining morphological, genetic and climatic data to examine stability.

Studies of hybrid zones can inform our understanding of reproductive isolation and speciation. Two species of brown lemur (Eulemur rufifrons and E. cinereiceps) form an apparently stable hybrid zone in the Andringitra region of south-eastern Madagascar. The aim of this study was to identify factors that contribute to this stability. We sampled animals at 11 sites along a 90-km transect through the hybrid zone and examined variation in 26 microsatellites, the D-loop region of mitochondrial DNA, six pelage and nine morphological traits; we also included samples collected in more distant allopatric sites. Clines in these traits were noncoincident, and there was no increase in either inbreeding coefficients or linkage disequilibrium at the centre of the zone. These results could suggest that the hybrid zone is maintained by weak selection against hybrids, conforming to either the tension zone or geographical selection-gradient model. However, a closer examination of clines in pelage and microsatellites indicates that these clines are not sigmoid or stepped in shape but instead plateau at their centre. Sites within the hybrid zone also occur in a distinct habitat, characterized by greater seasonality in precipitation and lower seasonality in temperature. Together, these findings suggest that the hybrid zone may follow the bounded superiority model, with exogenous selection favouring hybrids within the transitional zone. These findings are noteworthy, as examples supporting the bounded superiority model are rare and may indicate a process of ecologically driven speciation without geographical isolation.

Prothèses totales de genoux. Analyse clinique et numérique des micromouvements de l'implant tibial [Total knee prosthesis. Clinical and numerical study of micromovements of the tibial implant].

INTRODUCTION: The importance of the micromovements in the mechanism of aseptic loosening is clinically difficult to evaluate. To complete the analysis of a series of total knee arthroplasties (TKA), we used a tridimensional numerical model to study the micromovements of the tibial implant. MATERIAL AND METHODS: Fifty one patients (with 57 cemented Porous Coated Anatomic TKAs) were reviewed (mean follow-up 4.5 year). Radiolucency at the tibial bone-cement interface was sought on the AP radiographs and divided in 7 areas. The distribution of the radiolucency was then correlated with the axis of the lower limb as measured on the orthoradiograms. The tridimensional numerical model is based on the finite element method. It allowed the measurement of the cemented prosthetic tibial implant's displacements and the micromovements generated at bone-ciment interface. A total load (2000 Newton) was applied at first vertically and asymetrically on the tibial plateau, thereby simulating an axial deviation of the lower limbs. The vector's posterior inclination then permitted the addition of a tangential component to the axial load. This type of effort is generated by complex biomechanical phenomena such as knee flexion. RESULTS: 81 per cent of the 57 knees had a radiolucent line of at least 1 mm, at one or more of the tibial cement-epiphysis jonctional areas. The distribution of these lucent lines showed that they came out more frequently at the periphery of the implant. The lucent lines appeared most often under the unloaded margin of the tibial plateau, when axial deviation of lower limbs was present. Numerical simulations showed that asymetrical loading on the tibial plateau induced a subsidence of the loaded margin (0-100 microns) and lifting off at the opposite border (0-70 microns). The postero-anterior tangential component induced an anterior displacement of the tibial implant (160-220 microns), and horizontal micromovements with non homogenous distribution at the bone-ciment interface (28-54 microns). DISCUSSION: Comparison of clinical and numerical results showed a relation between the development of radiolucent lines and the unloading of the tibial implant's margin. The deleterious effect of lower limbs' axial deviation is thereby proven. The irregular distribution of lucent lines under the tibial plateau was similar of the micromovements' repartition at the bone-cement interface when tangential forces were present. A causative relation between the two phenomenaes could not however be established. Numerical simulation is a truly useful method of study; it permits to calculate micromovements which are relative, non homogenous and of very low amplitude. However, comparative clinical studies remain as essential to ensure the credibility of results.

Plate tectonics of the Altaids

Abstract: The Altaids consist in a huge accretionary-type belt extending from Siberia through Mon-golia, northern China, Kyrgyzstan and Kazakhstan. They were formed from the Vendian through the Jurassic by the accretion of numerous displaced and exotic terranes (e.g. island arc, ribbon microcontinent, seamount, basaltic plateau, back-arc basin). The number, nature and origin of the terranes differ according to the palaeotectonic models of the different authors. Thanks to a geo- dynamic study (i.e. definition of tectonic settings and elaboration of geodynamic scenarios) and plate tectonics modelling, this work aims to present an alternative model explaining the Palaeozoic palaeotectonic evolution of the Altaids. Based on a large set of compiled geological data related to palaeogeography and geodyna¬mic (e.g. sedimentology, stratigraphy, palaeobiogeography, palaeomagnetism, magmatism, me- tamorphism, tectonic...), a partly new classification of the terranes and sutures implicated in the formation of the Altaids is proposed. In the aim to elaborate plate tectonics reconstructions, it is necessary to fragment the present arrangement of continents into consistent geological units. To avoid confusion with existing terminology (e.g. tectonic units, tectono-stratigraphic units, micro- continents, terranes, blocks...), the new concept of "Geodynamic Units (GDU)" was introduced. A terrane may be formed by a set of GDUs. It consists of a continental and/or oceanic fragment which has its own kinematic and geodynamic evolution for a given period. With the same ap-proach, the life span and type of the disappeared oceans is inferred thanks to the study of the mate-rial contained in suture zones. The interpretation of the tectonic settings within the GDUs comple-ted by the restoration of oceans leads to the elaboration of geodynamic scenarios. Since the Wilson cycle was presented in 1967, numerous works demonstrated that the continental growth is more complex and results from diverse geodynamic scenarios. The identification of these scenarios and their exploitation enable to elaborate plate tectonics models. The models are self-constraining (i.e. space and time constraints) and contest or confirm in turn the geodynamic scenarios which were initially proposed. The Altaids can be divided into three domains: (1) the Peri-Siberian, (2) the Kazakhstan, and (3) the Tarim-North China domains. The Peri-Siberian Domain consists of displaced (i.e. Sayan Terrane Tuva-Mongolian, Lake-Khamsara Terrane) and exotic terranes (i.e. Altai-Mongolian and Khangai-Argunsky Terrane) accreted to Siberia from the Vendian through the Ordovician. Fol-lowing the accretion of these terranes, the newly formed Siberia active margin remained active un-til its part collision with the Kazakhstan Superterrane in the Carboniferous. The eastern part of the active margin (i.e. East Mongolia) continued to act until the Permian when the North-China Tarim Superterrane collided with it. The geodynamic evolution of the eastern part of the Peri-Siberian Domain (i.e. Eastern Mongolia and Siberia) is complicated by the opening of the Mongol-Okhotsk Ocean in the Silurian. The Kazakhstan Domain is composed of several continental terranes of East Gondwana origin amalgamated together during the Ordovician-Silurian time. After these different orogenic events, the Kazakhstan Superterrane evolved as a single superterrane until its collision with a Tarim-North China related-terrane (i.e. Tianshan-Hanshan Terrane) and Siberian Continent during the Devonian. This new organisation of the continents imply a continued active margin from Siberia, to North China through the Kazakhstan Superterrane and the closure of the Junggar- Balkash Ocean which implied the oroclinal bending of the Kazakhstan Superterrane during the entire Carboniferous. The formation history of the Tarim-North China Domain is less complex. The Cambrian northern passive margin became active in the Ordovician. In the Silurian, the South Tianshan back-arc Ocean was open and led to the formation of the Tianshan-Hanshan Terrane which collided with the Kazakhstan Superterrane during the Devonian. The collision between Siberia and the eastern part of the Tarim-North China continents (i.e. Inner Mongolia), implied by the closure of the Solonker Ocean, took place in the Permian. Since this time, the major part of the Altaids was formed, the Mongol-Okhotsk Ocean only was still open and closed during the Jurassic. Résumé: La chaîne des Altaïdes est une importante chaîne d'accrétion qui s'étend en Sibérie, Mon-golie, Chine du Nord, Kirghizstan et Kazakhstan. Elle s'est formée durant la période du Vendian au Jurassique par l'accrétion de nombreux terranes déplacés ou exotiques (par exemple arc océa-nique, microcontinent, guyot, plateau basaltique, basin d'arrière-arc...). Le nombre, la nature ou encore l'origine diffèrent selon les modèles paléo-tectoniques proposés par les différents auteurs. Grâce à une étude géodynamique (c'est-à-dire définition des environnements tectoniques et éla-boration de scénarios géodynamiques) et à la modélisation de la tectonique des plaques, ce travail propose un modèle alternatif expliquant l'évolution paléo-tectonique des Altaïdes. Basé sur une large compilation de données géologiques pertinentes en termes de paléo-géographie et de géodynamique (par exemple sédimentologie, stratigraphie, paléo-biogéographie, paléomagnétisme, magmatisme, métamorphisme, tectonique...), une nouvelle classification des terranes et des sutures impliqués dans la formation des Altaïdes est proposée. Dans le but d'élabo¬rer des reconstructions de plaques tectoniques, il est nécessaire de fragmenter l'arrangement actuel des continents en unités tectoniques cohérentes. Afin d'éviter les confusions avec la terminolo¬gie existante (par exemple unité tectonique, unité tectono-stratigraphique, microcontinent, block, terrane...), le nouveau concept d' "Unité Géodynamique (UGD)" a été introduit. Un terrane est formé d'une ou plusieurs UGD et représente un fragment océanique ou continental défini pas sa propre cinétique et évolution géodynamique pour une période donnée. Parallèlement, la durée de vie et le type des océans disparus (c'est-à-dire principal ou secondaire) est déduite grâce à l'étude du matériel contenu dans les zones de sutures. L'interprétation des environnements tectoniques des UGD associés à la restauration des océans mène à l'élaboration de scénarios géodynamiques. Depuis que le Cycle de Wilson a été présenté en 1967, de nombreux travaux ont démontré que la croissance continentale peut résulter de divers scénarios géodynamiques. L'identification et l'ex-ploitation de ces scénarios permet finalement l'élaboration de modèles de tectonique des plaques. Les modèles sont auto-contraignants (c'est-à-dire contraintes spatiales et temporelles) et peuvent soit contester ou confirmer les scénarios géodynamiques initialement proposés. Les Altaïdes peuvent être divisées en trois domaines : (1) le Domaine Péri-Sibérien, (2) le Domaine Kazakh, et (3) le Domaine Tarim-Nord Chinois. Le Domaine Péri-Sibérien est composé de terranes déplacés (c'est-à-dire Terrane du Sayan, Tuva-Mongol et Lake-Khamsara) et exotiques (c'est-à-dire Terrane Altai-Mongol et Khangai-Argunsky) qui ont été accrétés au craton Sibérien durant la période du Vendien à l'Ordovicien. Suite à l'accrétion de ces terranes, la marge sud-est de la Sibérie nouvellement formée reste active jusqu'à sa collision partielle avec le Superterrane Ka-zakh au Carbonifère. La partie est de la marge active (c'est-à-dire Mongolie de l'est) continue son activité jusqu'au Permien lors de sa collision avec le Superterrane Tarim-Nord Chinois. L'évolu¬tion géodynamique de la partie est du Domaine Sibérien est compliquée par l'ouverture Silurienne de l'Océan Mongol-Okhotsk qui disparaîtra seulement au Jurassique. Le Domaine Kazakh est composé de plusieurs terranes d'origine est-Gondwanienne accrétés les uns avec les autres avant ou pendant le Silurien inférieur et leurs evolution successive sous la forme d'un seul superterrane. Le Superterrane Kazakh collisione avec un terrane Tarim-Nord Chinois (c'est-à-dire Terrane du Tianshan-Hanshan) durant le Dévonien et le continent Sibérien au Dévonien supérieur. Ce nouvel agencement des plaques induit une marge active continue le long des continents Sibérien, Kazakh et Nord Chinois et la fermeture de l'Océan Junggar-Balkash qui provoque le plissement oroclinal du Superterrane Kazakh durant le Carbonifère. L'histoire de la formation du Domaine Tarim-Nord Chinois est moins complexe. La marge passive nord Cambrienne devient active à l'Ordovicien et l'ouverture Silurienne du bassin d'arrière-arc du Tianshan sud mène à la formation du terrane du Tianshan-Hanshan. La collision Dévonienne entre ce dernier et le Superterrane Kazakh provoque la fermerture de l'Océan Tianshan sud. Finalement, la collision entre la Sibérie et la partie est du continent Tarim-Nord Chinois (c'est-à-dire Mongolie Intérieure) prend place durant le Permien suite à la fermeture de l'Océan Solonker. La majeure partie des Altaïdes est alors formée, seul l'Océan Mongol-Okhotsk est encore ouvert. Ce dernier se fermera seulement au Jurassique.

The effect of muscle fatigue on stimulus intensity requirements for central and peripheral fatigue quantification.

PURPOSE: The present study was designed to determine the stimulation intensity necessary for an adequate assessment of central and peripheral components of neuromuscular fatigue of the knee extensors. METHODS: Three different stimulation intensities (100, 120 and 150 % of the lowest intensity evoking a plateau in M-waves and twitch amplitudes, optimal stimulation intensity, OSI) were used to assess voluntary activation level (VAL) as well as M-wave, twitch and doublet amplitudes before, during and after an incremental isometric exercise performed by 14 (8 men) healthy and physically active volunteers. A visual analog scale was used to evaluate the associated discomfort. RESULTS: There was no difference (p > 0.05) in VAL between the three intensities before and after exercise. However, we found that stimulating at 100 % OSI may overestimate the extent of peripheral fatigue during exercise, whereas 150 % OSI stimulations led to greater discomfort associated with doublet stimulations as well as to an increased antagonist co-activation compared to 100 % OSI. CONCLUSION: We recommend using 120 % OSI, as it constitutes a good trade-off between discomfort and reliable measurements.

Phosphorus and carbon burial during cretaceous oceanic anoxic events, links with climatic changes

According to Jenkyns (2010), oceanic anoxic events (OAE) record profound changes in the climatic and paleoceanographic state of the planet and represent major disturbances in the global carbon cycle. One of the most studied OAEs on a worldwide scale is the Cenomanian-Turonian OAE 2, which is characterized by a pronounced positive excursion in carbon-isotope records and the important accumulation of organic-rich sediments. The section at Gongzha (Tibet) and the sections at Barranca and Axaxacualco (Mexico) are located in remote parts of the Tethys, and show δ13C records, which are well correlated with those of classical Tethyan sections. Both sections, however, do not exhibit the presence of organic-rich sediments. Phosphorus Mass Accumulation Rates (PMAR) in Tibet show a pattern similar to that observed in the Tethys by Mort et al. (2007), which suggests enhanced Ρ regeneration during the OAE 2 time interval, though there is no evidence for anoxic conditions in Tibet. Ρ appears here to have been mainly driven by detrital influx and sea-level fluctuations. The sections at Barranca and Axaxacualco show that the Mexican carbonate platform persisted during this anoxic event, which allowed the evolution of platform fauna otherwise not present in Tethyan sections. The persistence of this carbonate platform close to the Caribbean Igneous Plateau, which is thought to have released bio-limiting metals, is explained by local uplift which delayed the drowning of the platform and a specific oceanic circulation that permitted the preservation of oligotrophic conditions in the area. The Coniacian-Santonian OAE (OAE3) appears to have been more dependent on local conditions than OAE2. The presence of black shales associated with OAE3 appear to have been restricted to shallow-water settings and epicontinental seas in areas located around the Atlantic Ocean. The sections at Olazagutia (Spain), and Ten Mile - Arbor Park (USA), two potential Global Boundary Stratotype Sections and Points (GSSP) sites, are devoid of organic-rich sediments and lack a δ13C positive excursion around the C-S boundary. The Gabal Ekma section (Sinai, Egypt) exhibits accumulations of organic-rich sediments, in addition to phosphorite bone beds layers, which may have been linked to an epicontinental upwelling zone and/or storm inputs. Our data suggest that OAE 3 is rarely expressed by truly anoxic conditions and seems to have been linked to local conditions rather than global paleoenvironmental change. The evidence for detrital-P being the likely cause of Ρ fluctuations during the OAEs studied here does not negate the idea that anoxia was the principal driver of these fluctuations in the western Tethys. However, an explanation is required as to why the Ρ accumulation signatures are mirrored in both oxic and anoxic sedimentary successions. 'Eustatic/climatic' and 'productivity/anoxic' models may have both operated simultaneously in different parts of the world depending on local conditions, both producing similar trends in Ρ accumulation. - Selon Jenkyns (2010), les événements anoxiques océaniques enregistrent de profonds changements dans le climat et la paléoceanographie de la planète et représente des perturbations majeures du cycle du carbone. L'un des plus étudiés à l'échelle mondiale est l'ΟΑΕ2 du Cénomanien-Turonien, qui est caractérisé par une très forte excursion positive des isotopes du carbone et une importante accumulation de sédiments riche en matière organique. La section de Gongzha (Tibet) et les sections de Barranca et Axaxcualco (Mexique) sont situées aux confins de la Téthys, et enregistrent une courbe isotopique en δ13C parfaitement corrélable avec les sections téthysiennes, mais ne montre pas d'accumulation de black shales. Le taux de phosphore en accumulation de masses (PMAR) au Tibet montre un pattern similaire observé également par Mort et al. (2007) dans la Téthys, suggérant un model de régénération du Ρ durant l'anoxie, cependant aucune conditions anoxiques régnent dans la région du Tibet. Ρ apparaît donc principalement guidé par le détritisme et les fluctuations du niveau marin. Les sections de Barranca et d'Axaxacualco montrent que la plateforme carbonatée mexicaine persiste durant cet événement anoxique, et permet le développement d'une faune de plateforme qui n'est pas présente dans les sections téthysiennes. La persistance de cette plateforme carbonatée si proche du plateau Caribéen, qui est connu pour le relâchement de métaux bio-limitant, peut être expliqué par un soulèvement tectonique local qui inhibe l'ennoiement de la plateforme et une circulation océanique spécifique qui permet la préservation de conditions oligotrophiques dans cette région. L'événement anoxique océanique du Coniacien-Santonien apparaît plus dépendant des conditions locales que pour l'ΟΑΕ2. Les black shales associés à POAE3 sont restreints aux zones situées autour de l'océan Atlantique et plus particulièrement aux eaux peu profondes et épicontinentales. Les sections d'Olazagutia (Espagne), Ten Mile Creek et Arbor Park (USA), qui sont deux potentielles sections GSSP (Sections de stratotype de limite globaux et de points), ne montre pas d'accumulation de black shales et pas de forte excursion positive en δ13C autour de la limite C-S. La section de Gabal Ekma (Sinai, Egypte) montre des accumulations de black shales, en plus des couches de phosphorites et d'accumulation d'os (« bone beds »), vraisemblablement lié à des zones active d'upwelling épicontinentale et/ou d'apport de tempêtes. Nos données suggèrent que l'OAE 3 est rarement exprimé par de vraies conditions anoxiques et semble être plus lié à des conditions plus locales que des changements paléo-environnementaux globaux, comme observés pour le Cénomanien- Turonien. Les arguments pour un modèle lié au phosphore détritique qui serait la cause des fluctuations du phosphore total durant les OAEs, n'écartent pas l'idée que l'anoxie est la principale cause de ces fluctuations dans les sections riches en matière organique de l'Ouest téthysien. Cependant une explication est nécessaire pour comprendre pourquoi la signature de l'accumulation du phosphore est semblable dans les successions sédimentaires déposées dans des conditions oxygénées et anoxiques. Les modèles « Eustatisme/Climat » et « Productivité/anoxie » ont simultanément opéré dans les différentes parties du monde dépendant de conditions locales, et ont produit des tendances similaires en accumulation de phosphore.

Étude des sédiments quaternaires, de la molasse et sa tectonique, dans le Grand Lac (Léman) à partir de données sismiques 2D et 3D

RESUME L'Institut de Géophysique de l'Université de Lausanne a développé au cours de ces dernières années un système d'acquisition de sismique réflexion multitrace à haute résolution 2D et 3D. L'objectif de cette thèse était de poursuivre ce développement tout améliorant les connaissances de la géologie sous le lac Léman, en étudiant en particulier la configuration des grands accidents sous-lacustres dans la Molasse (Tertiaire) qui forme l'essentiel du substratum des formations quaternaires. En configuration 2D, notre système permet d'acquérir des profils sismiques avec une distance inter-CDP de 1,25 m. La couverture varie entre 6 et 18 selon le nombre de traces et la distance inter-tir. Le canon à air (15/15 eu. in.), offre une résolution verticale de 1,25 ni et une pénétration maximale de 300 m sous le fond de l'eau. Nous avons acquis au total plus de 400 km de sections 2D dans le Grand Lac et le Haut Lac entre octobre 2000 et juillet 2004. Une campagne de sismique 3D a fourni des données au large d'Evian sur une surface de 442,5 m sur 1450 m, soit 0,64 km2. La navigation ainsi que le positionnement des hydrophones et de la source ont été réalisés avec des GPS différentiels. Nous avons utilisé un traitement sismique conventionnel, sans appliquer d'AGC et en utilisant une migration post-stack. L'interprétation du substratum antéquaternaire est basée sur l'identification des sismofaciès, sur leurs relations avec les unités géologiques adjacentes au lac, ainsi que sur quelques données de forages. Nous obtenons ainsi une carte des unités géologiques dans le Grand Lac. Nous précisons la position du chevauchement subalpin entre la ville de Lausanne, sur la rive nord, et le bassin de Sciez, sur la rive sud. Dans la Molasse de Plateau, nous avons identifié les décrochements de Pontarlier et de St. Cergue ainsi que plusieurs failles non reconnues jusqu'ici. Nous avons cartographié les accidents qui affectent la Molasse subalpine ainsi que le plan de chevauchement du flysch sur la Molasse près de la rive sud du lac. Une nouvelle carte tectonique de la région lémanique a ainsi pu être dressée. L'analyse du substratum ne montre pas de failles suggérant une origine tectonique de la cuvette lémanique. Par contre, nous suggérons que la forme du creusement glaciaire, donc de la forme du lac Léman, a été influencée par la présence de failles dans le substratum antéquaternaire. L'analyse des sédiments quaternaires nous a permis de tracer des cartes des différentes interfaces ou unités qui les composent. La carte du toit du substratum antéquaternaire montre la présence de chenaux d'origine glaciaire dont la profondeur maximale atteint la cote -200 ni. Leur pente est dirigée vers le nord-est, à l'inverse du sens d'écoulement actuel des eaux. Nous expliquons cette observation par l'existence de circulations sous-glaciaires d'eau artésienne. Les sédiments glaciaires dont l'épaisseur maximale atteint 150 ni au centre du lac ont enregistré les différentes récurrences glaciaires. Dans la zone d'Evian, nous mettons en évidence la présence de lentilles de sédiments glaciolacustres perchées sur le flanc de la cuvette lémanique. Nous avons corrélé ces unités avec des données de forage et concluons qu'il s'agit du complexe inférieur de la pile sédimentaire d'Evian. Celui-ci, âgé de plus de 30 000 ans, serait un dépôt de Kame associé à un lac périglaciaire. La sismique réflexion 3D permet de préciser l'orientation de l'alimentation en matériel détritique de l'unité. La finesse des images obtenues nous permet également d'établir quels types d'érosion ont affecté certaines unités. Les sédiments lacustres, dont l'épaisseur maximale imagée atteint plus de 225 m et sans doute 400 ni sous le delta du Rhône, indiquent plusieurs mécanismes de dépôts. A la base, une mégaturbidite, épaisse d'une trentaine de mètres en moyenne, s'étend entre l'embouchure de la Dranse et le delta du Rhône. Au-dessus, la décantation des particules en suspension d'origine biologique et détritique fournit l'essentiel des sédiments. Dans la partie orientale du lac, les apports détritiques du Rhône forment un delta qui prograde vers l'ouest en s'imbriquant avec les sédiments déposés par décantation. La structure superficielle du delta a brutalement évolué, probablement à la suite de l'évènement catastrophique du Tauredunum (563 A.D.). Sa trace probable se marque par la présence d'une surface érosive que nous avons cartographiée. Le delta a ensuite changé de géométrie, avec notamment un déplacement des chenaux sous-lacustres. Sur l'ensemble de nos sections sismiques, nous n'observons aucune faille dans les sédiments quaternaires qui attesterait d'une tectonique postglaciaire du substratum. ABSTRACT During the last few years the institute of Geophysics of the University of Lausanne cleveloped a 2D and 3D high-resolution multichannel seismic reflection acquisition system. The objective of the present work was to carry on this development white improving our knowledge of the geology under Lake Geneva, in particular by studying the configuration of the large accidents affecting the Tertiary Molasse that makes up the basement of most Quaternary deposits. In its 2D configuration, our system makes it possible to acquire seismic profiles with a CDP interval of 1.25 m. The fold varies from 6 to 18 depending on the number of traces and the shooting interval. Our air gun (15/15 cu. in.) provides a vertical resolution of 1.25 m and a maximum penetration depth of approximately 300 m under water bottom. We acquired more than 400 km of 2D sections in the Grand Lac and the Haut Lac between October 2000 and July 2004. A 3D seismic survey off the city of Evian provided data on a surface of 442.5 m x 1450 m (0.64 km2). Ship's navigation as well as hydrophone- and source positioning were carried out with differential GPS. The seismic data were processed following a conventional sequence without .applying AGC and using post-stack migration. The interpretation of the pre-Quaternary substratum is based on sismofacies, on their relationships with terrestrial geological units and on some borehole data. We thus obtained a map of the geological units in the Grand Lac. We defined the location of the subalpine thrust from Lausanne, on the north shore, to the Sciez Basin, on the south shore. Within the Molasse de Plateau, we identified the already know Pontarlier and St Cergue transforms Fault as well as faults. We mapped faults that affect subalpine Molasse as well as the thrust fault plane between alpine flysch and Molasse near the lake's south shore. A new tectonic map of the Lake Geneva region could thus be drawn up. The substratum does not show faults indicating a tectonic origin for the Lake Geneva Basin. However, we suggest that the orientation of glacial erosion, and thus the shape of Lake Geneva, vas influenced by the presence of faults in the pre-Quaternary basement. The analysis of Quaternary sediments enabled us to draw up maps of various discontinuities or internal units. The top pre-Quaternary basement map shows channels of glacial origin, the deepest of them reaching an altitude of 200 m a.s.l. The channel's slopes are directed to the North-East, in opposite direction of the present water flow. We explain this observation by the presence of artesian subglacial water circulation. Glacial sediments, the maximum thickness of which reaches 150 m in the central part of the lake, record several glacial recurrences. In the Evian area, we found lenses of glacio-lacustrine sediments set high up on the flank of the Lake Geneva Bassin. We correlated these units with on-land borehole data and concluded that they represent the lower complex of the Evian sedimentary pile. The lower complex is aider than 30 000 years, and it could be a Kame deposit associated with a periglacial lake. Our 3D seismic reflexion survey enables us to specify the supply direction of detrital material in this unit. With detailed seismic images we established how some units were affected by different erosion types. The lacustrine sediments we imaged in Lake Geneva are thicker than 225 m and 400 m or more Linder the Rhone Delta. They indicate several depositional mechanisms. Their base is a major turbidite, thirty meters thick on average, that spreads between the Dranse mouth and the Rhone delta. Above this unit, settling of suspended biological and detrital particles provides most of the sediments. In the eastern part of the lake, detrital contribution from the Rhone builds a delta that progrades to the west and imbricates with the settling sediments. The shallow structure of the Rhone delta abruptly evolved, probably after the catastrophic Tauredunum event (563 A.D.). It probably coincides with an erosive surface that we mapped. As a result, the delta geometry changed, in particular associated with a displacement of water bottom channels. In all our seismic sections, we do not observe fault in the Quaternary sediments that would attest postglacial tectonic activity in the basement.

Le holter implantable: Reveal®

Mise au point sur le hotter implantable (Reveal®). Connaissances actuelles et implications thérapeutiques. La syncope est un problème fréquent touchant environ un tiers des adultes durant leur vie. C'est un motif de consultation habituel aux urgences et ses causes sont souvent multiples et rendent son diagnostic difficile. Malgré des investigations extensives et coûteuses la cause syncopale reste dans environ 30% des cas d'étiologie indéterminée. Les progrès récents dans le monitoring cardiaque à long terme ont permis d'inclure dans le choix des tests diagnostiques un outil très intéressant dans l'investigation de la syncope d'étiologie indéterminée (SOI). Il s'agit du moniteur ECG implantable (MEI) ou Reveal®. Il y a un peu plus de 10 ans un prototype de MEI a été implanté dans un petit collectif de patients souffrants de SOI récidivantes et a permis d'établir un diagnostic chez la plupart d'entre eux. Dès lors le système s'est modernisé avec une diminution importante de la taille et du poids permettant actuellement d'enregistrer le rythme cardiaque sur une durée de 18 à 24 mois. Le système peut stocker dans sa mémoire un tracé ECG soit à l'aide d'un activateur externe déclenché par le patient, soit de façon spontanée en présence d'un rythme cardiaque lent ou rapide. Son implantation se fait en anesthésie locale, en position sous-cutanée pectorale gauche. Les complications et les problèmes infectieux sont rares. Plusieurs études récentes se sont intéressées à l'apport diagnostique du MEI dans la prise en charge de la SOI. La plus grande porte sur un collectif de 206 patients. L'apport diagnostique des différentes études varie de 40% à 64%. Cependant la plupart de ces études ne comportaient pas de prise en charge standardisée ou avaient des critères d'inclusion précis. Nous nous sommes intéressés aux résultats de notre prise en charge de la syncope au cours de ces 6 dernières années. Une consultation spécialisée de la syncope a été mise en place en 1999. La consultation offre l'accès à tout le plateau technique propre à l'investigation de syncopes à savoir un tilt-test avec mesure continue non invasive de la pression artérielle, examens échocardiographiques et test d'effort. Si nécessaire, le bilan peut être complété par une étude électrophysiologique (EEP) et/ou une coronarographie: Tous les patients bénéficient d'une anamnèse ciblée suivi d'un examen clinique et d'un électrocardiogramme. Une échocardiographie n'est effectuée qu'en cas de suspicion de cardiopathie sous-jacente. Un holter ou R-test ne sont réalisés qu'en présence de syncopes ou palpitations fréquentes. Les investigations se poursuivent par un tilt test suivi d'un massage du sinus carotidien en position debout et couchée. Un test d'hyperventilation n'est pratiqué que chez les patients avec traits phobiques, dépressifs ou troubles de type panique. L'EEP n'est pratiquée que chez les patients dont la syncope reste d'étiologie indéterminée après investigations initiales et chez ceux souffrant d'une cardiopathie sous jacente documentée ; elle est aussi indiquée chez ceux dont le coeur est normal mais chez qui la syncope est associée à des traumatismes ou à l'origine d'un accident de voiture. Le MEI est proposé lorsque toutes les investigations initiales restent négatives, généralement chez les sujets ayant souffert de plus d'une syncope ou de complications sérieuses. Notre expérience pratique d'une consultation de la syncope ouverte au tout venant nous montre qu'une prise en charge standardisée non invasive permet d'identifier une cause syncopale chez plus de 60% des patients. Chez les patients souffrant de syncopes récidivantes ou traumatiques d'étiologie indéterminée après investigations conventionnelles, l'apport diagnostique du MEI est élevé (64%) durant un suivi moyen de 9 mois, ce qui permet d'identifier certaines causes syncopales écartées précédemment par des tests ciblés. Parmi ces dernières, retenons plus particulièrement les tachycardies nodales et crises d'épilepsie.

Transcranial Doppler Pulsatility Index: What it is and What it Isn't.

BACKGROUND: Transcranial Doppler (TCD) pulsatility index (PI) has traditionally been interpreted as a descriptor of distal cerebrovascular resistance (CVR). We sought to evaluate the relationship between PI and CVR in situations, where CVR increases (mild hypocapnia) and decreases (plateau waves of intracranial pressure-ICP). METHODS: Recordings from patients with head-injury undergoing monitoring of arterial blood pressure (ABP), ICP, cerebral perfusion pressure (CPP), and TCD assessed cerebral blood flow velocities (FV) were analyzed. The Gosling pulsatility index (PI) was compared between baseline and ICP plateau waves (n = 20 patients) or short term (30-60 min) hypocapnia (n = 31). In addition, a modeling study was conducted with the "spectral" PI (calculated using fundamental harmonic of FV) resulting in a theoretical formula expressing the dependence of PI on balance of cerebrovascular impedances. RESULTS: PI increased significantly (p < 0.001) while CVR decreased (p < 0.001) during plateau waves. During hypocapnia PI and CVR increased (p < 0.001). The modeling formula explained more than 65% of the variability of Gosling PI and 90% of the variability of the "spectral" PI (R = 0.81 and R = 0.95, respectively). CONCLUSION: TCD pulsatility index can be easily and quickly assessed but is usually misinterpreted as a descriptor of CVR. The mathematical model presents a complex relationship between PI and multiple haemodynamic variables.

The lower Triassic anachronistic carbonate facies in space and time

The end-Permian mass extinction greatly affected the sedimentary record, but the sedimentary response was not limited to the Permian-Triassic boundary interval. This transformation extended to sedimentation that spanned the entire Early Triassic. Calcimicrobialites play an important role throughout this time interval, and at least four main events of anomalous carbonate deposition can be shown. A post-extinction calcimicrobial unit occurs above the extensive Permian skeletal carbonate platform exposed in the Taurus Mountains (southern Turkey), in south Armenia, north-west north and Central Iran along the Zagros Mountains. The calcimicrobial unit formed during the flooding of the platform that took place during the earliest Triassic. A similar calcimicrobialite formed during late Griesbachian to Dienerian time atop the shallow Permian skeletal carbonate platform largely exposed in south China. A third event occurred during the Early Olenekian on the first Mesozoic isolated pelagic plateau (Baid seamount, Oman Mountains). Here the change in carbonate sedimentation is reflected in the occurrence of thrombolites and carbonate seafloor fans. Near the end of Early Triassic time, unusual carbonate deposition is recorded both on an isolated pelagic plateau of the Western Tethys (Halstatt limestone of Dobrogea, Romania) and on the eastern Panthalassa margin of the western United States. In the western United States, the event is represented by stromatolites and thrombolites in the Virgin Limestone of the Moenkopi Formation and by seafloor fans in the middle and upper members of the Union Wash Formation. These unusual episodes of anomalous carbonate deposition illustrate a fundamental change in sedimentation that occurred in the aftermath of the end-Permian mass extinction.