Magmatism and Extension in the Foreland and Near-Trench Region of Collisional and Convergent Tectonic Systems

Foreland magmatism occurs in the lower plate during arc–continent or continent–continent collision, although it is uncommon. Ancient examples are recognized by a stratigraphic section into which mafic lavas and/or shallow sills are emplaced at a level at the top of a passive margin cover sequence, or within the overlying deeper water deposits that include mudrocks and flysch-type turbidites. Extensional structures associated with the emplacement of the volcanic rocks may develop slightly prior to or contemporaneous with the arrival of the approaching thrust front. We have selected twelve examples of magmatism in collisional forelands, modern and ancient, and have compared the tectonic associations of the magmatism with the magmatic geochemistry.   Foreland magmatic settings fall into two strikingly distinct geochemical groups: a more enriched alkaline group (Rhine-type) and a more heterogeneous tholeiitic group (Maine-type) that may show traces of prior subduction processes. In the examples where the contemporaneous extensional structures are known, faults and basins develop parallel to the thrust front for the tholeiitic group and have oblique orientations, in several cases at a high angle to the thrust front, for the alkaline group. The geochemical results are quite sufficiently distinct to permit discrimination of these two foreland magmatic rock suites from each other in ancient examples where the foreland setting is clear from geological evidence. However, magmatic products of the same range of compositions can be generated in other tectonic environments (rifts, back-arc basins), so the geochemical characteristics alone are insufficient to identify a foreland basin setting.    The alkaline Rhine-type group formed primarily in response to localized upwelling convective activity from the sub-asthenospheric mantle beneath the lower plate during collision while the tholeiitic Maine-type group formed primarily in response to melting of subcontinental asthenospheric mantle during extension of the lower plate by slab pull, and resulting lithospheric detachment. It is possible that there has been a long-term secular decrease in the occurrence of the Maine-type foreland magmatism since the early Proterozoic.RÉSUMÉBien que peu fréquent, il arrive qu’un magmatisme d’avantpays se produise dans la plaque inférieure durant une collision arc-continent ou continent-continent. Des exemples anciens ont été décrits dans une coupe stratigraphique renfermant des laves mafiques et/ou des filons-couches au haut d’une séquence de couverture de marge passive, ou au sein de dépôts de plus grandes profondeurs comme des boues ou des turbidites de type flysch. Des structures d’étirement associées à la mise en place des roches volcaniques peuvent se développer un peu avant ou en même temps que l’arrivée du front de chevauchement. Nous avons choisi douze exemples de magmatisme au sein d’avant-pays de collision, modernes et anciens, et nous avons comparé les associations tectoniques du magmatisme avec la géochimie magmatique.    Les configurations magmatiques d’avant-pays se divisent en deux groupes géochimiques très différents : un groupe alcalin plus enrichi (type-Rhin), et un groupe tholéiitique plus hétérogène (type-Maine) et qui peut montrer des traces de précédentes activités de subduction. Dans les exemples où les structures d’étirement contemporaines sont connues, les failles et les bassins se développent parallèlement au front de chevauchement pour le groupe tholéiitique, alors que leurs orientations sont obliques, voire à angles aigus au front de chevauchement pour le groupe alcalin. Les résultats géochimiques sont suffisamment distincts pour permettre de distinguer ces deux suites de roches magmatiques dans les exemples anciens où la configuration d’avant-pays est évidente de par sa géologie. Cependant, des produits magmatiques de même type compositionnel peuvent advenir dans d’autres environnements tectoniques (fosses, bassins d’arrière-arc), et donc, la caractérisation géochimique seule ne permet pas de distinguer une configuration de bassin d’avant-pays.    Le groupe alcalin de type-Rhin s’est principalement formé en réponse à une activité d’éruption de convection issue du manteau sous-asthénosphérique sous la plaque inférieure durant la collision, alors que le groupe tholéiitique de type-Maine s’est formé principalement en réaction à la fusion du manteau sous-continental asthénosphérique durant l’extension de la plaque inférieure par étirement de la plaque, et le détachement lithosphérique qui en découle. Depuis le Protérozoïque, est possible qu’il y ait eu une décroissance progressive à long terme des événements magmatiques de type-Maine

Genetic recombination is targeted towards gene promoter regions in dogs

The identification of the H3K4 trimethylase, PRDM9, as the gene responsible for recombination hotspot localization has provided considerable insight into the mechanisms by which recombination is initiated in mammals. However, uniquely amongst mammals, canids appear to lack a functional version of PRDM9 and may therefore provide a model for understanding recombination that occurs in the absence of PRDM9, and thus how PRDM9 functions to shape the recombination landscape. We have constructed a fine-scale genetic map from patterns of linkage disequilibrium assessed using high-throughput sequence data from 51 free-ranging dogs, Canis lupus familiaris. While broad-scale properties of recombination appear similar to other mammalian species, our fine-scale estimates indicate that canine highly elevated recombination rates are observed in the vicinity of CpG rich regions including gene promoter regions, but show little association with H3K4 trimethylation marks identified in spermatocytes. By comparison to genomic data from the Andean fox, Lycalopex culpaeus, we show that biased gene conversion is a plausible mechanism by which the high CpG content of the dog genome could have occurred.Comment: Updated version, with significant revision

Lawrence Head Volcanics and Dunnage Mélange, Newfoundland Appalachians: Origin by Ordovician Ridge Subduction or in Back-Arc Rift?

This paper reviews the geological setting and reports new geochemical trace element data from the Ordovician Lawrence Head Volcanics (LHV) and the underlying gabbro sills in the Exploits Group. In combination with existing published analyses and ages of these rocks, the volcanic rocks and sills are indistinguishable in composition and age, and the data are consistent with the hypothesis that they represent the same (mostly E-MORB composition) magmatic event in the early–mid Darriwilian (~465 ± 2 Ma). The LHV and their enclosing strata show regional evidence for: 1) upward decline of volume and grain size of arc-derived volcaniclastic materials over the uppermost interval of turbidite sedimentary strata below the LHV; 2) change to shallow marine conditions locally by the end of the LHV event, followed immediately by significant subsidence, and 3) no evidence of coarse-grained clastic input, nor of normal faulting, during or immediately after LHV magmatism. Ridge–trench interaction (ridge subduction) at a subduction system is consistent with all of these features and spatial distribution of related elements, but a rift (back-arc) origin over a subduction zone can only accommodate the compositions, and is inconsistent with the geological evidence. The Dunnage Mélange (DM) has been interpreted either as olistostromal in a developing back-arc rift basin, or as a subduction accretionary prism. Peraluminous intrusions in the mélange (Coaker Porphyry ― CP) are more readily explained by ridge subduction, and a previously reported zircon age (469 ± 4 Ma) is consistent with the age of the LHV and gabbro sills, also interpreted as products of ridge subduction. Localization of the CP in the eastern area of DM, and of most of the large LHV-derived volcanic blocks in the western DM, suggests a slightly younger age, and perhaps a different mechanism, for the origin of the western DM.SOMMAIRECet article passe en revue le contexte géologique et présente de nouvelles données géochimiques d’éléments traces des roches volcaniques ordoviciennes de Lawrence Head (LHV) et des filons-couches de gabbro sous-jacents du Groupe Exploits.  Considérant la combinaison des données d’analyse publiées et des datations de ces roches, les roches volcaniques et les filons-couches sont indiscernables tant en composition qu’en âge, et les données sont compatibles avec l’hypothèse selon laquelle ils représentent le même événement magmatique (principalement E-MORB) du Darriwilien précoce à moyen (~465 ± 2 Ma).  Les LHV ainsi que les strates de l’encaissant renferment des indices régionaux qui montrent : 1) que le volume et la granulométrie des matériaux volcanoclastiques d’arc diminuent vers le haut dans l’intervalle supérieur des strates de turbidites sédimentaires sous les LHV; 2) que le changement vers des milieux marins peu profonds localement vers la fin de l’événement des LHV a été suivi immédiatement par une subsidence importante, et 3) qu’il n’existe pas d’indices d’apports clastiques à gros grains, non plus que de formation de failles normales, durant ou immédiatement après le magmatisme des LHV.  L’interaction crête-fosse (subduction de la crête) au lieu d’un système de subduction concorde avec toutes ces caractéristiques et la répartition spatiale des éléments reliés, alors qu’une origine de crête (arrière-arc) au-dessus d’une zone de subduction ne peut expliquer que les compositions et qu’elle est incompatible avec l’évidence géologique.  Le Dunnage Mélange (DM) a été interprété soit comme un olistostome dans un bassin d’arrière-arc en développement, ou comme un prisme d’accrétion de subduction.  Les intrusions hyperalumineuses dans le mélange (Porphyre Coaker — CP), s’explique plus facilement par une subduction de crête, et un âge de datation sur zircon de (469 ± 4 Ma) correspond à l’âge des LHV et des filons-couche de gabbro, aussi interprétés comme produits d’une subduction de crête.  La localisation du CP dans la portion orientale du DM, et de la majeure partie des grands blocs volcaniques dérivés des LHV de la portion ouest du DM, suggère un âge légèrement plus jeune, et peut-être un mécanisme différent, pour l’origine de la portion ouest du DM

PERIOD DETERMINATION FOR NEA (162421) 2000 ET70

Lightcurve analysis for (162421) 2000 ET70 was performed in collaboration with observers in Uruguay, Australia, and the United States from observations obtained during the asteroid’s favorable opposition in 2012. The synodic rotation period was found to be 8.947 ± 0.001 h and the lightcurve amplitude was 0.60 ± 0.07 mag

8077 HOYLE: A SHORT PERIOD ASTEROID

The main-belt asteroid 8077 Hoyle was observed on 13 nights over a span of 47 days in 2012 April-May. A bimodal synodic period of 2.7454 ± 0.0002 h and an amplitude of 0.20 ± 0.02 mag. were obtained

LIGHTCURVE ANALYSIS OF FOUR ASTEROIDS

From June 2011 through May 2012 May, photometric data for four asteroids were obtained using the Southeastern Association for Research in Astronomy (SARA) telescope located at the Kitt Peak National Observatory. The following synodic periods were found: 4808 Ballaero, P = 8.8976 ± 0.0007 h; 7750 McEwen, P = 27.82 ± 0.01 h; 11941 Archinal, P = 2.717 ±0.006 h; and (47035) 1998WS, P = 7.996 ± 0.001 h

A requirement for filopodia extension toward Slit during Robo-mediated axon repulsion

Axons navigate long distances through complex 3D environments to interconnect the nervous system during development. Although the precise spatiotemporal effects of most axon guidance cues remain poorly characterized, a prevailing model posits that attractive guidance cues stimulate actin polymerization in neuronal growth cones whereas repulsive cues induce actin disassembly. Contrary to this model, we find that the repulsive guidance cue Slit stimulates the formation and elongation of actin-based filopodia from mouse dorsal root ganglion growth cones. Surprisingly, filopodia form and elongate toward sources of Slit, a response that we find is required for subsequent axonal repulsion away from Slit. Mechanistically, Slit evokes changes in filopodium dynamics by increasing direct binding of its receptor, Robo, to members of the actin-regulatory Ena/VASP family. Perturbing filopodium dynamics pharmacologically or genetically disrupts Slit-mediated repulsion and produces severe axon guidance defects in vivo. Thus, Slit locally stimulates directional filopodial extension, a process that is required for subsequent axonal repulsion downstream of the Robo receptor.National Institutes of Health (U.S.) (Grant F32-CA165700)National Institutes of Health (U.S.) (Grant R01-GM068678)National Institutes of Health (U.S.) (Grant P30-CA014051

Understanding how stroke telerehabilitation works and for whom to inform recommendations for practice: The TELSTAR study protocol

Telerehabilitation (TR) shows promise as a method of remote service delivery, yet there is little guidance to inform implementation in the context of the National Health Service (NHS) in England. This paper presents the protocol for a realist synthesis study aiming to investigate how TR can be implemented to support the provision of high quality, equitable community-based stroke rehabilitation and under what conditions. Using a realist approach, we will synthesise information from: 1) a comprehensive evidence review; 2) qualitative interviews with clinicians (n≤30), and patient-family carer dyads (n≤60), from three purposively selected community stroke rehabilitation services in England. Working groups including rehabilitation professionals, service users and policy makers will co-develop actionable recommendations. Insights from the review and the interviews will be synthesised to test and refine programme theories that explain how TR works and for whom in clinical practice and draw key messages for service implementation. This protocol highlights the need to improve our understanding of TR implementation in the context of multidisciplinary, community-based stroke service provision. We suggest the use of realist methodology and co-production to inform evidence-based recommendations which consider the needs and priorities of clinicians and people affected by stroke