Characteristic reflection patterns in the southeast Canadian cordillera, northern Appalachians and Swiss Alps

There are some striking similarities and some differences between the seismic reflection sections recorded across the fold and thrust belts of the southeast Canadian Cordillera, Quebec-Maine Appalachians and Swiss Alps. In the fold and thrust belts of all three mountain ranges, seismic reflection surveys have yielded high-quality images of. (1) nappes (thin thrust sheets) stacked on top of ancient continental margins; (2) ramp anticlines in the hanging walls of faults that have ramp-flat or listric geometries; (3) back thrusts and back folds that developed during the terminal phases of orogeny; and (4) tectonic wedges and regional decollements. A principal result of the Cordilleran and Appalachian deep crustal studies has been the recognition of master decollements along which continental margin strata have been transported long distances, whereas a principal result of the Swiss Alpine deep crustal program has been the identification of the Adriatic indenter, a crustal-scale wedge that caused delamination of the European lithosphere. Significant crustal roots are observed beneath the fold and thrust belts of the Alps, southeast Canadian Cordillera and parts of the southern Appalachians, but such structures beneath the northern Appalachians have probably been removed by post-orogenic collapse and/or crustal attenuation associated with the Mesozoic opening of the Atlantic Ocean.

Bimodal magmatism as a consequence of the post-collisional readjustment of the thickened Variscan continental lithosphere (Aiguilles Rouges - Mont Blanc Massifs, Western Alps)

High Precision U-Pb zircon and monazite dating in the Aiguilles Rouges-Mont Blanc area allowed discrimination of three short-lived bimodal magmatic pulses: the early 332 Ma Mg-K Pormenaz monzonite and associated 331 Ma peraluminous Montees Pelissier monzogranite; the 307 Ma cordierite-bearing peraluminous Vallorcine and Fully intrusions; and the 303 Fe-K Mont Blanc syenogranite. All intruded syntectonically along major-scale transcurrent faults at a time when the substratum was experiencing tectonic exhumation, active erosion recorded in detrital basins and isothermal decompression melting dated at 327-320 Ma. Mantle activity and magma mixing are evidenced in all plutons by coeval mafic enclaves, stocks and synplutonic dykes. Both crustal and mantle sources evolve through time, pointing to an increasingly warm continental crust and juvenile asthenospheric mantle sources. This overall tectono-magmatic evolution is interpreted in a scenario of post-collisional restoration to normal size of a thickened continental lithosphere. The latter re-equilibrates through delamination and/or erosion of its mantle root and tectonic exhumation/erosion in an overall extensional regime. Extension is related to either gravitational collapse or back-are extension of a distant subduction zone.

Surgical glues: are they really adhesive?

OBJECTIVE: The aim of this study is to create a standard test to approve the efficacy of a surgical sealant. An industrial test, the bulge-and-blister test, which is very convenient for measuring adhesion energy, is applied to the surgical field to quantify adhesion of bioadhesives. METHODS: Samples were composed of two circular layers of equine pericardium glued by the surgical sealant studied. The sample was fixed to a support with an industrial glue. The support and the bottom layer were perforated in the centre to allow injection of pressurised water. Water was progressively introduced through the hole in the support and the bottom layer to create a blister with constant radius, increasing height and internal pressure during this first step. At a critical pressure, delamination started, the radius and height of the blister increased and the pressure decreased. At this point, the adhesion energy could be determined. The experimental parameters were measured with a pressure sensor and an optical profilometry device for deflection. RESULTS: Adhesion testing was carried out in eight paired equine pericardium samples bonded with a Dermabond cyanoacrylate glue. The average value of the practical adhesion energy is 2.3 Jm(-2) with a standard deviation of 1.5 Jm(-2). CONCLUSION: Application of the bulge-and-blister test to the surgical field was achieved and allowed a quantification of adhesion of a surgical glue. Such information is essential to compare the different surgical glues presently available. The study of the impact of bonding conditions such as pressure, hygrometry or setting conditions will provide a better understanding of the characteristics of adhesion in the surgical field.

THE ADULA NAPPE: STRATIGRAPHY, STRUCTURE AND KINEMATICS OF AN EXHUMED HIGH-PRESSURE NAPPE

This study analyses the stratigraphy, structure and kinematics of the northern part of the Adula nappe of the Central Alps. The Adula nappe is one of the highest basement nappes in the Lower Penninic nappe stack of the Lepontine Dome. This structural position makes possible the investigation of the transition between the Helvetic and North Penninic paleogeographic domains. The Adula nappe is principally composed of crystalline basement rocks. The investigation of the pre-Triassic basement shows that it contains several Palaeozoic detrital metasedimentary formations dated from the Cambrian to the Ordovician. These formations contain also some volcanic or intrusive magmatic rocks. Ordovician metagranites dated at ~450 Ma are also a common rock-type of the Adula basement. These formations underwent Alpine and Variscan deformation and metamorphism. Permian granites (Zervreila orthogneiss, dated at ~290 Ma) have intruded this pre-structured basement in a post-orogenic geodynamic context. Due to their age, the Zervreila orthogneiss are good markers for alpine deformation. The stratigraphy of the Mesozoic and Paleogene sedimentary cover of the Adula nappe is essential to unraveling its pre- orogenic history. The autochthonous cover is assigned to a North Penninic Triassic series that testifies for a transition between the Helvetic and Briançonnais Triassic domains. The Adula domain goes through an emersion during the Middle Jurassic, and is part of a topographic high during the first phase of the Alpine rift. The sediments of the late Middle Jurassic show a drowning phase associated with a tectonic activity and a breccia formation. In the neighbouring domains, coeval with the drowning phase in the Adula domain, a strong extensional crustal delamination and a scattered magmatic activity is associated with the main opening of the North Penninic domain. The Upper Jurassic of the Adula nappe is characterized by a carbonate formation comparable with those in the Helvetic or Subbriaçonnais domains. Flysch s.l. deposition starts probably at the end of the Cretaceous. These sediments are deposited on a large unconformity testifying for a Cretaceous sedimentary gap. The Adula nappe exhibits a very complex structure. This structure is formed by several deformation phases. Two ductile deformations are responsible for the nappe emplacement. The first deformation phase is associated with a folding compatible with a top-to-south movement at the top of the nappe. The second phase is dominant and pervasive throughout the whole nappe. It goes with a strong north vergent folding and the main nappe emplacement. These two phases cause the exhumation and emplacement of a coherent, although pre-structured, piece of continental crust. Two further deformation phases postdate the nappe emplacement. - Ce travail concerne l'étude géologique de la partie nord de la nappe de l'Adula dans les Alpes centrales. La nappe de l'Adula est l'une des nappes cristallines la plus élevée dans la pile des nappes du Pennique inférieur des Alpes lepontines. Cette position particulière permet d'étudier la transition entre les nappes des domaines helvétique et pennique inférieur. La nappe de l'Adula est principalement composée de socle cristallin : l'étude de l'histoire géologique du socle est donc l'un des thèmes de cette recherche. Ce socle contient plusieurs formations métasédimentaires paléozoïques du Cambrien à I'Ordovicien. Ces métasédiments sont issus de formations clastiques comprenant souvent des roches magmatiques volcaniques et intrusives. Ces métasédiments ont subi les cycles orogéniques varisque et alpin. La nappe de l'Adula contient plusieurs corps magmatiques granitiques métamorphisés. Les premiers métagranites sont Ordovicien et témoignent d'un environnement de marge active. Ces granites sont aussi polymétamorphiques. Les deuxièmes métagranites sont représentés par les orthogneiss de type Zervreila. Ce métagranite est d'âge permien (-290 Ma). Il est mis en place dans un contexte tectonique post-orogénique. Ce granite est un maqueur de la déformation alpine car il n'est pas affecté par les orogenèses précédentes, flippy Le contenu stratigraphique des roches mésozoïques et cénozoiques de la couverture sédimentaire de la nappe de l'Adula est'important pour en étudier son histoire pré-alpine. La couverture autochtone est composée d'une série d'âge triasique d'affinité nord-pennique, un faciès qui marque la transition entre les domaines helvétiques et briançonnais au Trias. Le domaine paléogéographique représenté dans la nappe de l'Adula connaît une émersion pendant le Jurassique moyen. Cette émersion marque le commencement du rift dans le domaine alpin. La sédimentation de la fin du Jurassique moyen est marquée par une transgression marine accompagnée par des mouvements tectoniques et la formation d'une brèche. Cette transgression est contemporaine des importants mouvements tectoniques et des manifestations magmatiques dans les unités voisines qui marquent la phase principale d'ouverture du bassin nord-pennique. Le Jurassique supérieur est caractérisé par l'instauration d'une sédimentation carbonatée comparable à celle du domaine helvétique ou subbriançonnais. Une sédimentation flyschoïde, probablement du Crétacé à Tertiaire, est déposée sur une importante discordance qui témoigne d'une lacune au Crétacé. La structure complexe de la nappe de l'Adula témoigne de nombreuses phases de déformation. Ces phases de déformation sont en partie issues de la mise en place de la nappe et de déformations plus tardives. La mise en place de la nappe produit deux phases de déformation ductile : la première produit un plissement compatible avec un cisaillement top-vers-le sud dans la partie supérieure de la nappe; la deuxième produit un intense plissement qui accompagne la mise en place de la nappe vers le nord. Ces deux phases de déformation témoignent d'un mécanisme d'exhumation par déformation ductile d'un bloc cohérent.

New stratigraphic data from the Lower Penninic between the Adula nappe and the Gotthard massif and consequences for the tectonics and the paleogeography of the Central Alps

New stratigraphic data along a profile from the Helvetic Gotthard Massif to the remnants of the North Penninic Basin in eastern Ticino and Graubunden are presented. The stratigraphic record together with existing geochemical and structural data, motivate a new interpretation of the fossil European distal margin. We introduce a new group of Triassic facies, the North-Penninic-Triassic (NPT), which is characterised by the Ladinian "dolomie bicolori". The NPT was located in-between the Briançonnais carbonate platform and the Helvetic lands. The observed horizontal transition, coupled with the stratigraphic superposition of an Helvetic Liassic on a Briaçonnais Triassic in the Luzzone-Terri nappe, links, prior to Jurassic rifting, the Briançonnais paleogeographic domain at the Helvetic Margin, south of the Gotthard. Our observations suggest that the Jurassic rifting separated the Briançonnais domain from the Helvetic margin by complex and protracted extension. The syn-rift stratigraphic record in the Adula nappe and surroundings suggests the presence of a diffuse rising area with only moderately subsiding basins above a thinned continental and proto-oceanic crust. Strong subsidence occurred in a second phase following protracted extension and the resulting delamination of the rising area. The stratigraphic coherency in the Adula's Mesozoic questions the idea of a lithospheric mélange in the eclogitic Adula nappe, which is more likely to be a coherent alpine tectonic unit. The structural and stratigraphic observations in the Piz Terri-Lunschania zone suggest the activity of syn-rift detachments. During the alpine collision these faults are reactivated (and inverted) and played a major role in allowing the Adula subduction, the "Penninic Thrust" above it and in creating the structural complexity of the Central Alps.

Alkali-calcic and alkaline post-orogenic (PO) granite magmatism: petrologic constraints and geodynamic settings

The end of an orogenic Wilson cycle corresponds to amalgamation of terranes into a Pangaea and is marked by widespread magmatism dominated by granitoids. The post-collision event starts with magmatic processes still influenced by subducted crustal materials. The dominantly calc-alkaline suites show a shift from normal to high-K to very high-K associations. Source regions are composed of depleted and later enriched orogenic subcontinental lithospheric mantle, affected by dehydration melting and generating more and more K- and LILE-rich magmas. In the vicinity of intra-crustal magma chambers, anatexis by incongruent melting of hydrous minerals may generate peraluminous granitoids bearing mafic enclaves. The post-collision event ends with emplacement of bimodal post-orogenic (PO) suites along transcurrent fault zones. Two suites are defined, (i) the alkali-calcic monzonite-monzogranite-syenogranite-alkali feldspar granite association characterised by [biotite + plagioclase] fractionation and moderate [LILE + HFSE] enrichments and (ii) the alkaline monzonite-syenite-alkali feldspar granite association characterised by [amphibole + alkali feldspar] fractionation and displaying two evolutionary trends, one peralkaline with sodic mafic mineralogy and higher enrichments in HFSE than in LILE, and the other aluminous biotite-bearing marked by HFSE depletion relative to LILE due to accessory mineral precipitation. Alkali-calcic and alkaline suites differ essentially in the amounts of water present within intra-crustal magma chambers, promoting crystallisation of various mineral assemblages. The ultimate enriched and not depleted mantle source is identical for the two PO suites. The more primitive LILE and HFSE-rich source rapidly replaces the older orogenic mantle source during lithosphere delamination and becomes progressively the thermal boundary layer of the new lithosphere. Present rock compositions are a mixture of major mantle contribution and various crustal components carried by F-rich aqueous fluids circulating within convective cells created around magma chambers. In favourable areas, PO suites pre-date a new orogenic Wilson cycle. (C) 1998 Elsevier Science B.V. All rights reserved.

The roles of flux- and decompression melting and their respective fractionation lines for continental crust formation: Evidence from the Kohistan arc

Delamination and foundering of the lower continental crust (LCC) into the mantle is part of the crust-forming mechanism. However, knowledge of the composition and mineralogy of the preserved or delaminated LCC over geological timescales remains scarce. We provide a synopsis of recent research within the Kohistan arc (Pakistan) and demonstrate that hydrous and less hydrous liquid lines of descent related to flux assisted and decompression mantle melting, respectively, produce compositionally different lower crustal rocks. The argument refers to two lower crustal sections exposed in Kohistan, the older Southern Plutonic Complex (SPC) and the younger Chilas Complex. The SPC typifies a hydrous, high-pressure fractionation sequence of olivine-pyroxenes-garnet-Fe/Ti-oxide-amphibole-plagioclase. The Chilas Complex illustrates a less hydrous fractionation sequence of olivine-clinopyroxene-orthopyroxene-plagioclase-amphibole. Despite the similarity of the Chilas Complex rocks to proposed lower crust compositions, the less hydrous fractionation results in unrealistically small volumes of silica-rich rocks, precluding the Chilas Complex gabbros to represent the magmatic complement to the upper crust. The composition of the SPC lower crust differs markedly from bulk lower crust estimates, but is complementary to silica-rich rocks exposed along this section and in the Kohistan batholith. These observations inspire a composite model for the formation of continental crust (CC) where the negatively buoyant delaminated and the buoyant preserved lower continental crusts (LCC) differ in genesis, mineralogy, and composition. We propose that the upper, non-sedimentary subsequent removal of the complementary, negatively buoyant garnet-pyroxene-amphibole-plagioclase-rich cumulates. In contrast, the LCC, which is buoyant and preserved over geological timescales, is formed by less hydrous parental mantle melts. We suggest that the bulk continental crust composition is related to mixing of these petrologically not directly related end members. Published by Elsevier B.V.

New stratigraphic data from the Lower Penninic between the Adula nappe and the Gotthard massif and consequences for the tectonics and the paleogeography of the Central Alps

New stratigraphic data along a profile from the Helvetic Gotthard massif to the remnants of the North Penninic basin in eastern Ticino and Graubunden are presented. The stratigraphic record together with existing geochemical and structural data, motivate a new interpretation of the fossil European distal margin. We introduce a new group of Triassic facies, the North-Penninic-Triassic (NPT), which is characterised by the Ladinian ``dolomie bicolori''. The NPT was located in-between the Brianconnais carbonate platform and the Helvetic lands. The observed horizontal transition, coupled with the stratigraphic superposition of a Helvetic Liassic on a Briaconnais Triassic in the Luzzone-Terri nappe, links, prior to Jurassic rifting, the Brianconnais paleogeographic domain at the Helvetic margin, south of the Gotthard. Our observations suggest that the Jurassic rifting separated the Brianconnais domain from the Helvetic margin by complex and protracted extension. The syn-rift stratigraphic record in the Adula nappe and surroundings suggests the presence of a diffuse rising area with only moderately subsiding basins above a thinned continental and proto-oceanic crust. Strong subsidence occurred in a second phase following protracted extension and the resulting delamination of the rising area. The stratigraphic coherency in the Adula's Mesozoic questions the idea of a lithospheric m lange in the eclogitic Adula nappe, which is more likely to be a coherent alpine tectonic unit. The structural and stratigraphic observations in the Piz Terri-Lunschania zone suggest the activity of syn-rift detachments. During the alpine collision these faults are reactivated (and inverted) and played a major role in allowing the Adula subduction, the ``Penninic Thrust'' above it and in creating the structural complexity of the Central Alps. (C) 2012 Elsevier B.V. All rights reserved.