Accretion, Soft and Hard Collision: Similarities, Differences and an Application from the Newfoundland Appalachian Orogen

We argue there is no distinction between accretion and collision as a process, except when accretion is used in the sense of incorporating small bodies of sedimentary and/or volcanic rocks into an accretionary wedge by off-scraping or underplating. There is also a distinction when these terms are used in classifying mountain belts into accretionary and collisional orogens, although such classifications are commonly based on a qualitative assessment of the scale and nature of the accreted terranes and continents involved in formation of mountain belts. Soft collisions occur when contractional deformation and associated metamorphism are principally concentrated in rocks of the leading edge of the partially pulled-down buoyant plate and the upper plate forearc terrane. Several young arc-continent collisions show evidence for partial or wholesale subduction of the forearc such that the arc is structurally juxtaposed directly against lower plate rocks. This process may explain the poor preservation of forearcs in the geological record. Soft collisions generally change into hard collisions over time, except if the collision is rapidly followed by formation of a new subduction zone due to step-back or polarity reversal. Thickening and metamorphism of the arc's suprastructure and retro-arc part of upper plate due to contractional deformation and burial are the characteristics of a hard collision or an advancing Andean-type margin. Strong rheological coupling of the converging plates and lower and upper crust in the down-going continental margin promotes a hard collision. Application of the soft–hard terminology supports a structural juxtaposition of the Taconic soft collision recorded in the Humber margin of western Newfoundland with a hard collision recorded in the adjacent Dashwoods block. It is postulated that Dashwoods was translated dextrally along the Cabot-Baie Verte fault system from a position to the north of Newfoundland where the Notre Dame arc collided ca. 10 m.y. earlier with a wide promontory in a hyperextended segment of the Laurentian margin.Nous soutenons qu'il n'y a pas de distinction entre l'accrétion et la collision en tant que processus, sauf lorsque l'accrétion est utilisée dans le sens d'incorporer de petits corps de roches sédimentaires et / ou volcaniques dans un prisme d'accrétion par raclage ou sous-placage. Il y a également une distinction lorsque ces termes sont utilisés pour classer les chaînes de montagne en orogènes d'accrétion et de collision, bien que ces classifications soient généralement basées sur une évaluation qualitative de l'échelle et de la nature des terranes accrétés et des continents impliqués dans la formation des chaînes de montagnes.Des collisions molles se produisent lorsque la déformation par contraction et le métamorphisme associé sont principalement concentrés dans les roches du front de la plaque chevauchante partiellement abaissée et du terrane d’avant-arc de la plaque supérieure. Plusieurs jeunes collisions arc-continent montrent des preuves d'une subduction partielle ou totale de l'avant-arc de telle sorte que l'arc est directement structurellement juxtaposé contre les roches de la plaque inférieure. Ce processus peut expliquer la mauvaise préservation des avant-arcs dans les archives géologiques. Les collisions molles se transforment généralement en collisions dures au fil du temps, sauf si la collision est rapidement suivie de la formation d'une nouvelle zone de subduction en raison d'un recul ou d'une inversion de polarité. L'épaississement et le métamorphisme de la suprastructure de l'arc et de la partie rétro-arc de la plaque supérieure dus à la déformation par contraction et à l'enfouissement sont les caractéristiques d'une collision dure ou d'une marge de type andin en progression. Un fort couplage rhéologique des plaques convergentes et de la croûte inférieure et supérieure dans la marge continentale descendante favorise une collision dure.L'application de la terminologie molle-dure corrobore une juxtaposition structurelle de la collision molle taconique enregistrée dans la marge de Humber de l'ouest de Terre-Neuve avec une collision dure enregistrée dans le bloc de Dashwoods adjacent. Il est postulé que le bloc de Dashwoods a été déplacé de manière dextre le long du système de failles Cabot-Baie Verte à partir d'une position au nord de Terre-Neuve où l'arc Notre Dame est entré en collision environ 10 m.a. plus tôt avec un large promontoire dans un segment en hyper-extension de la marge laurentienne.

The Ocean – Continent Transition Zones Along the Appalachian – Caledonian Margin of Laurentia: Examples of Large-Scale Hyperextension During the Opening of the Iapetus Ocean

A combination of deep seismic imaging and drilling has demonstrated that the ocean-continent transition (OCT) of present-day, magma-poor, rifted continental margins is a zone of hyperextension characterized by extreme thinning of the continental crust that exhumed the lowermost crust and/or serpentinized continental mantle onto the seafloor. The OCT on present-day margins is difficult to sample, and so much of our knowledge on the detailed nature of OCT sequences comes from obducted, magma-poor OCT ophiolites such as those preserved in the upper portions of the Alpine fold-and-thrust belt. Allochthonous, lens-shaped bodies of ultramafic rock are common in many other ancient orogenic belts, such as the Caledonian – Appalachian orogen, yet their origin and tectonic significance remains uncertain. We summarize the occurrences of potential ancient OCTs within this orogen, commencing with Laurentian margin sequences where an OCT has previously been inferred (the Dalradian Supergroup of Scotland and Ireland and the Birchy Complex of Newfoundland). We then speculate on the origin of isolated occurrences of Alpine-type peridotite within Laurentian margin sequences in Quebec – Vermont and Virginia – North Carolina, focusing on rift-related units of Late Neoproterozoic age (so as to eliminate a Taconic ophiolite origin). A combination of poor exposure and pervasive Taconic deformation means that origin and emplacement of many ultramafic bodies in the Appalachians will remain uncertain. Nevertheless, the common occurrence of OCT-like rocks along the whole length of the Appalachian – Caledonian margin of Laurentia suggests that the opening of the Iapetus Ocean may have been accompanied by hyperextension and the formation of magma-poor margins along many segments.SOMMAIREDes travaux d’imagerie sismique et des forages profonds ont montré que la transition océan-continent (OCT) de marges continentales de divergence pauvre en magma exposée de nos jours, correspond à une zone d’hyper-étirement tectonique caractérisée par un amincissement extrême de la croûte continentale, qui a exhumé sur le fond marin, jusqu’à la tranche la plus profonde de la croûte continentale, voire du manteau continental serpentinisé.  Parce qu’on peut difficilement échantillonner l’OCT sur les marges actuelles, une grande partie de notre compréhension des détails de la nature de l’OCT provient d’ophiolites pauvres en magma d’une OCT obduite, comme celles préservées dans les portions supérieures de la bande plissée alpine.  Des masses lenticulaires de roches ultramafiques allochtones sont communes dans de nombreuses autres bandes orogéniques anciennes, comme l’orogène Calédonienne-Appalaches, mais leur origine et signification tectonique reste incertaine.  Nous présentons un sommaire des occurrences d’OCT potentielles anciennes de cet orogène, en commençant par des séquences de la marge laurentienne, où la présence d’OCT a déjà été déduites (le Supergroupe Dalradien d’Écosse et d'Irlande, et le complexe de Birchy de Terre-Neuve).  Nous spéculons ensuite sur l'origine de cas isolés de péridotite de type alpin dans des séquences de marge des Laurentides du Québec-Vermont et de la Virginie-Caroline du Nord, en nous concentrant sur les unités de rift d'âge néoprotérozoïque tardif (pour éviter les ophiolites du Taconique).  La conjonction d’affleurements de piètre qualité et de la déformation taconique omniprésente, signifie que l'origine et la mise en place de nombreuses masses ultramafiques dans les Appalaches demeureront incertaines.  Néanmoins, la présence fréquente de roches de type OCT tout le long de la marge Calédonnienne-Appalaches de Laurentia suggère que l'ouverture de l'océan Iapetus peut avoir été accompagnée d’hyper-étirement et de la formation de marges pauvres en magma le long de nombreux segments

Influence of deformation and fluids on Ar retention in white mica: Dating the Dover Fault, Newfoundland Appalachians

White mica 40Ar/39Ar analyses may provide useful constraints on the timing of tectonic processes, but complex geological and thermal histories can perturb Ar systematics in a variety of ways. Ductile shear zones represent excellent case studies for exploring the link(s) between dynamic re-/neo-crystallization of white mica and coeval enhanced fluid flow, and their effect on 40Ar/39Ar dates. White mica 40Ar/39Ar dates were collected from compositionally similar granites that record different episodes of deformation with proximity to the Dover Fault, a terrane-bounding strike-slip shear zone in the Appalachian orogen, Newfoundland, Canada. 40Ar/39Ar data were collected in situ by laser ablation and by step heating single crystals. Results were compared to each other and against complementary U-Pb zircon and monazite, and K-Ar fault gouge analysis. Although step-heat 40Ar/39Ar is a widely applied method in orogenic settings, this dataset shows that relatively flat step-heat 40Ar/39Ar spectra are in contradiction with wide spreads in in-situ 40Ar/39Ar dates from the same samples, and that plateau dates in some cases yielded mixed dates of equivocal geological significance. This result indicates that the step-wise release of Ar from white mica likely homogenizes and obscures spatially-controlled Ar isotope reservoirs in white mica from sheared rocks. In contrast, in situ laser ablation 40Ar/39Ar analysis preserves the spatial resolution of 40Ar reservoirs that have been variably reset by deformation and fluid interaction. This study therefore suggests that laser ablation is the best method for dating the timing of deformation recorded by white mica. Final interpretation of results should be guided by microstructural analysis, estimation of deformation temperature, chemical characterization of white mica, and complementary chronometers. Overall the dataset shows that granitic protoliths were emplaced between 430-422 Ma (U-Pb zircon). High strain deformation along the Wing Pond Shear Zone occurred between ca. 422-405 Ma (U-Pb monazite and 40Ar/39Ar). Subsequent patchy Ar loss in white mica occurred locally during low T shear (40Ar/39Ar). K-Ar dating of authigenic illite in fault gouge from the broadly co-linear brittle Hermitage Bay Fault indicates that slip along the terrane boundary persisted until at least the Mississippian

Early detection of risk for maltreatment within Dutch preventive child health care: A proxy-based evaluation of the long-term predictive validity of the SPARK method

Background: For effective prevention of child maltreatment, it is crucial that risk factors for child maltreatment are identified as early as possible. In the Dutch preventive child healthcare, the SPARK-method is used for this purpose.Objective: The current study investigated the predictive validity of the SPARK-method for predicting child protection activities, as a proxy for child maltreatment, and whether the estimation can be improved with an actuarial module.Participants and setting: Participants included a community sample of 1582 children of approximately 18-months-old for whom the SPARK was administered during well-child visits at home (51 %) or at the well-baby clinic (49 %).Methods: SPARK measurements were linked to data on child protection orders and residential youth care over a 10-year follow-up period. The predictive validity was evaluated using Area Under the receiver operating characteristic Curve (AUC) values.Results: Results showed good predictive validity for the SPARK clinical risk assessment (AUC = 0.723; large effect). The actuarial module led to a significant improvement in predictive validity (AUC = 0.802; large effect), z = 2.05, p = .04.Conclusion: These results show that the SPARK is suitable for estimating the risk of child protection activities and that the actuarial module is a valuable addition. The SPARK can be used to support professionals in preventive child healthcare with their decision on appropriate follow-up actions

On-line extraction of polymers, oligomers, additives and monomers by multiple solvents on packed HPLC columns

Extn. of monomers, additives, oligomers, and polymers from a blend is very time-consuming and labor intensive. Using a special guard column and multi-solvent gradient liq. chromatog. (HPLC), the extn. and anal. can be performed in one ste

Conical epidermal cells cause velvety colouration and enhanced patterning in <i>Mandevilla</i> flowers

The majority of angiosperms have flowers with conical epidermal cells, which are assumed to have various functions, such as enhancing the visual signal to pollinators, but detailed optical studies on how conical epidermal cells determine the flower's visual appearance are scarce. Here we report that conical epidermal cells of Mandevilla sanderi flowers effectively reduce surface gloss and create a velvety appearance. Owing to the reduction in surface gloss, the flower further makes more efficient use of floral pigments and light scattering structures inside the flower. The interior backscattering yields a cosine angular dependence of reflected light, meaning that the flowers approximate near-perfect (Lambertian) diffusers, creating a visual signal that is visible across a wide angular space. Together with the large flowers and the tilted corolla tips, this generates a distinct visual pattern, which may enhance the visibility to pollinators

Application of four dyes in gene expression analyses by microarrays

BACKGROUND: DNA microarrays are widely used in gene expression analyses. To increase throughput and minimize costs without reducing gene expression data obtained, we investigated whether four mRNA samples can be analyzed simultaneously by applying four different fluorescent dyes. RESULTS: Following tests for cross-talk of fluorescence signals, Alexa 488, Alexa 594, Cyanine 3 and Cyanine 5 were selected for hybridizations. For self-hybridizations, a single RNA sample was labelled with all dyes and hybridized on commercial cDNA arrays or on in-house spotted oligonucleotide arrays. Correlation coefficients for all combinations of dyes were above 0.9 on the cDNA array. On the oligonucleotide array they were above 0.8, except combinations with Alexa 488, which were approximately 0.5. Standard deviation of expression differences for replicate spots were similar on the cDNA array for all dye combinations, but on the oligonucleotide array combinations with Alexa 488 showed a higher variation. CONCLUSION: In conclusion, the four dyes can be used simultaneously for gene expression experiments on the tested cDNA array, but only three dyes can be used on the tested oligonucleotide array. This was confirmed by hybridizations of control with test samples, as all combinations returned similar numbers of differentially expressed genes with comparable effects on gene expression

Ordovician volcanic and hypabyssal rocks in the central and southern Miramichi Highlands: their tectonic setting and relationship to contemporary volcanic rocks in northern New Brunswick

New analyses of mafic igneous rocks from the central Miramichi Highlands have led us to modify the interpretation of its tectonic setting. New samples have been obtained from the Bam ford Brook and Trousers Lake areas of New Brunswick, and the Danforth area in Maine. All subalkalic mafic rocks, including the Trousers Lake striped amphibolites, are associated with a thick sequence of metasedimentary rocks and all are continental tholeiites, analogous to tholeiitic suites in the Tetagouche Group of the northern Miramichi Highlands. The presence of alkalic basalt and comendite in this area supports this correlation. In the southern Miramichi Highlands of Maine, silicic and intermediate volcanic rocks form part of the Woodstock-Meductic arc-related volcanic suite. R&#xC9;SUM&#xC9; De nouvelles analyses de roches ign&#xE9;es mafiques provenant du centre des hautes-terres de la Miramichi nous ont conduit &#xE0; modifier l’interpr&#xE9;tation de leur environnement tectonique. De nouveaux &#xE9;chantillons ont &#xE9;t&#xE9; recueillis dans les r&#xE9;gions du ruisseau Bamford et du lac Trousers au Nouveau-Brunswick, et dans la r&#xE9;gion de Danforth au Maine. Toutes les roches mafiques subalcalines, incluant les amphibolites rubann&#xE9;es du lac Trousers, sont associ&#xE9;es avec une s&#xE9;quence &#xE9;paisse de roches m&#xE9;tas&#xE9;dimentaires et sont toutes des thol&#xE9;iites continentales, similaires aux suites thol&#xE9;iitiques appartenant au Groupe de T&#xE9;tagouche du nord des hautes-terres de la Miramichi. La pr&#xE9;sence de basaltes alcalins et de comendites dans cette r&#xE9;gion appuie cette corr&#xE9;lation. Dans le sud des hautes-terres de la Miramichi au Maine, les volcanites siliceuses et inlermddiaires constituent une partie de la suite volcanique d'arc de Woodstock-Meductic. [Traduit par le journal