Circum-Alpine marine circulation and paleoenvironmental conditions during the Miocene

Trace element and isotopic compositions of marine fossils and sediment were analyzed from several Miocene deposits in the circum-Alpine region in order to reconstruct the paleoceanographic and paleoclimatic changes related to sea level changes, basin evolution and Alpine orogeny. To the north and the east the Alps were border by an epicontinental sea, the Paratethys, while to the south the Mediterranean surrounded the uplifting mountains during the Miocene. The thesis mainly focused on sediments and fossils sampled from Miocene beds of these two oceanic provinces. The north Alpine Molasse, the Vienna and Pannonian Basins were located in the Western and Central Paratethys. O-isotope compositions of well-preserved phosphatic fossils in these sediments support deposition under sub-tropical to warm-temperate climate with water temperatures between 14 to 28 °C for the Miocene. δ18O values of fossil shark teeth from different horizons vary similarly to those of the global trend until the end of the Badenian, however the δ18O values show wider range, which indicates local effects iii the sub-basins. The trend of 87Sr/86Sr in the samples roughly agrees with an open ocean environment for the Miocene. Yet a number of samples deviate from typical open ocean compositions with higher ratios suggesting modification of seawater by local and old terrestrial sources. In contrast, two exceptional teeth from the locality of La Moliere have extremely low δ18O values and low 87Sr/86Sr. However, the REE patterns of their enameloid are similar to those of teeth having O and Sr isotopic compositions typical of a marine setting at this site. Collectively, this suggests that the two teeth formed while the sharks frequented a freshwater environment with very low 18O-content and 87Sr/86Sr controlled by Mesozoic calcareous rocks. This is consistent with a paleogeography of high-elevation (~2300m) Miocene Alps adjacent to a marginal sea. The local effects are also reflected in the εNd values of the Paratethyan fossils, which is compatible with input from ancient crystalline rocks and Mesozoic sediments, while other samples with elevated εNd values indicate an influence of Neogene volcanism on the water budget. Excluding samples whose isotopic compositions reflect a local influence on the water column, an average εNd value of -7.9 ± 0.5 may be inferred for the Paratethys seawater. This value is indistinguishable from the Miocene value of the Indian Ocean, supporting a dominant role of ludo-Pacific water masses in the Paratethys. Regarding the Mediterranean, stable C-and O-isotope compositions of benthic and planktonic foraminifera from the Umbria-Marche region (UMC) have an offset typical for their habitats and the changes in composition mimic global changes, suggesting that the regional conditions of climate and the carbon cycle were controlled by global changes. The radiogenic isotope compositions of the fossil assemblages allow for distinction of periods. From 25 to 19 Ma, high εNd values and low 87Sr/86Sr of sediments and fossils support intense tectonism and volcanism, related to the opening of the western Mediterranean. Between 19 and 13 Ma the Mediterranean has εNd values that are largely controlled by incursion of Indian Ocean water. Brief periods of local hinterland control on seawater compositions are indicated by spikes in the εNd record, coinciding with volcanic events and a short sea-level decrease at about 15.2 Ma. Lower 87Sr/86Sr compared to the open ocean is compatible with rapid uplift of the hinterland and intense influx of Sr from Mesozoic carbonates of the western Apennines, while higher 87Sr/86Sr for other sites indicates erosion of old crustal silicate rocks. Finally, from 13 to 7 Ma the fossils have 87Sr/86Sr similar to those of Miocene seawater and their εNd values indicates fluctuating influence of Atlantic, and Indian Ocean or Paratethys sources of seawater entering the Mediterranean, driven by global sealevel changes and local tectonism. RÉSUMÉ DE LA THÈSE Les compositions en éléments traces et isotopiques de fossiles marins et de sédiments on été analysées à partir de nombreux dépôts marins dans la région circum Alpine dans le but de reconstruire les changements paléocéanographiques et paléoclimatiques liés aux changements du niveau marin, à l'évolution en bassins et à l'orogénie alpine. Au nord et à l'est des Alpes, une mer épicontinentale appelée Paratéthys s'est ouverte, alors que plus au sud la mer Méditerranée bordait au Miocène les Alpes naissantes. Le but de cette recherche est de se concentrer sur les sédiments et les fossiles provenant des couches du Miocènes de ces deux provinces marines. Les bassins de la Molasse Alpine du nord, de Vienne et Pannonien étaient situés au niveau de la Paratéthys Occidentale et Centrale. Les compositions isotopiques de l'oxygène de fossiles phosphatés bien préservés dans ces sédiments étayent la théorie d'un dépôt sous un climat subtropical à tempéré chaud avec des températures entre 14 et 28°C pendant le Miocène. Les valeurs δ18O des fossiles sont similaires à la tendance globale jusqu'à la fin du Badénien. Cependant les larges fluctuations en δ18O indiquent des effets locaux au niveau des sous bassins. En outre, deux dents de requin exceptionnelles présentent des valeurs extrêmement basses de δ18O. Ces données suggèrent que ces deux dents se sont formées alors que les requins fréquentaient un environnement d'eau douce avec de faibles valeurs de 18O. Le calcul de la composition isotopique de l'oxygène de cette eau douce permet d'obtenir une estimation de la paléoélévatian moyenne des Alpes du Miocène (~2300m). La tendance 87Sr/86Sr pour ces échantillons concorde approximativement avec un environnement d'océan ouvert au cours du Miocène. Toutefois un nombre d'échantillons dévie des compositions d'océan ouvert typiques, avec des rapports élevés suggérant des modifications de l'eau de mer par des sources locales et terrestres. Les effets locaux sont aussi reflétés au niveau des valeurs en εNd des fossiles paratéthysiens. Ceci est cohérent avec un apport d'anciennes roches cristallines et de sédiments mésozoïques, tandis que d'autres échantillons avec des valeurs hautes de εNd indiquent une influence d'un volcanisme néogène dans le budget marin. En excluant les échantillons dont les compositions isotopiques confirment une influence locale, une valeur moyenne de εNd de 7.9 t 0.5 peut être déduite pour l'eau de la Parathétys. Cette valeur est semblable à la valeur correspondant à l'Océan Indien durant le Miocène, confirmant un rôle dominant de cet océan dans la Paratéthys. Au niveau de la Méditerranée, les compositions en isotopes stables du Carbone et de l'Oxygène de foraminifères planctoniques et benthique de la région Umbria-Marche présentent un offset typique à leurs habitats. De plus les changements dans leurs compositions suivent les changements globaux, suggérant ainsi que les conditions climatiques régionales et le cycle du carbone étaient contrôlés par des phénomènes globaux. La composition en isotopes radiogéniques d'assemblages fossiles permet une reconnaissance sur trois périodes distinctes. De 25 à 19 millions d'années (Ma), des valeurs élevées de εNd et un faible rapport 87Sr/86Sr dans les sédiments soutiennent l'idée d'une activité tectonique et volcanique intense, liée à l'ouverture de la Méditerranée occidentale. Entre 19 et 13 Ma, la Méditerranée montre des valeurs de εNd qui sont largement contrôlées par une incursion d'eau provenant de l'Océan Indien. En effet, aux alentours de 15,2 Ma, des pics dans l'enregistrement des valeurs de εNd, coïncidant avec des événements volcaniques et de brèves diminutions du niveau marin. Enfin, de 13 à 7 Ma, les fossiles ont des rapports ß7Sr/8fiSr similaires à ceux de l'eau de mer au Miocène. Leurs valeurs de εNd indiquent une influence changeante de l'océan Atlantique, et de l'océan Indien ou des sources d'eau de merde la Parathétys qui entrent dans les bassins méditerranéens. Ce changement est guidé par des modifications globales du niveau marin et par la tectonique locale. RÉSUMÉ DE LA THÈSE (POUR LE GRAND PUBLIC) Les analyses des compositions en éléments traces et isotopiques des fossiles marins sont un outil très utile pour reconstruire les conditions océaniques et climatiques anciennes. Ce travail de thèse se concentre sur les sédiments déposés dans un environnement marin proches des Alpes au cours du Miocène, entre 23 et 7 millions d'années (Ma). Cette période est caractérisée par une tectonique alpine active, ainsi que par des changements climatiques et océanographiques globaux importants. Dans le but de tracer ces changements, les compositions isotopiques du Strontium, du Néodyme, de l'Oxygène et du Carbone ont été analysées dans des fossiles bien préservés ainsi que les sédiments contemporains. Les échantillons proviennent de deux provinces océaniques distinctes, la première est la Mer Méditerranée, et l'autre est une mer épicontinentale appelée Parathétys, qui existait au nord et à l'est des Alpes durant le Miocène. Au niveau de la Parathétys Occidentale et Orientale, les compositions isotopiques d'oxygène de dents de requins confirment un dépôt sous un climat subtropical à tempéré chaud avec des températures d'eau entre 14 et 28°C au Miocène. En outre, deux dents de requins exceptionnelles ont enregistré des compositions isotopiques d'oxygène extrêmement basses. Cela suggère que ces deux dents se sont formées alors que les requins entraient dans un système d'eau douce. Le calcul de la composition isotopique de l'oxygène de cette eau douce permet d'obtenir une estimation de la paléoélévation des Alpes au Miocène qui est aussi élevée que celle d'aujourd'hui. La tendance isotopique du Strontium pour ces échantillons concorde approximativement avec un environnement d'océan ouvert. Cependant un certain nombre d'échantillons indique des modifications de l'eau de mer par des sources terrestres locales. Les effets locaux sont aussi visibles au niveau des compositions isotopiques du Néodyme, qui sont en accord avec un apport provenant de roches cristallines anciennes et de sédiments du Mésozoïque, alors que d'autres échantillons indiquent une influence volcanique néogène dans le budget marin. A l'exclusion des échantillons dont les compositions correspondent à une influence locale, les compositions isotopiques du Néodyme de la Parathétys sont très similaires aux valeurs de l'Océan Indien, montrant ainsi un rôle important des masses d'eau IndoPacifiques dans cette région. Au niveau de la Méditerranée, les compositions en isotopes stables du Carbone et de l'Oxygène de foraminifères planctoniques et benthique de la région Umbria-Marche présentent un offset typique à leurs habitats. De plus, les changements dans leurs compositions suivent les changements globaux, suggérant ainsi que les conditions climatiques régionales et le cycle du carbone étaient contrôlés par des phénomènes globaux. La composition en isotopes radiogéniques d'assemblages fossiles permet une reconnaissance sur trois périodes distinctes. De 25 à 19 Ma, des rapport isotopiques élevés pour le Néodyme et faibles pour le Strontium dans les sédiments et les fossiles soutiennent l'idée d'une activité tectonique et volcanique intense, liée à l'ouverture de la Méditerranée occidentale. Entre 19 et 13 Ma, la Méditerranée présente des rapports isotopiques du Néodyme qui sont largement contrôlés par une incursion d'eau provenant de l'Océan Indien. En effet, aux alentours de 15,2 Ma, des pics dans l'enregistrement des valeurs des isotopes du Néodyme coïncident avec des événements volcaniques et de brèves diminutions du niveau marin. Finalement, de 13 à 7 Ma, les fossiles ont des rapports isotope Strontium similaires à ceux de l'eau de mer au Miocène. Les rapports isotopiques du Néodyme indiquent une influence changeante de l'océan Atlantique, et de l'océan Indien ou des sources d'eau de mer de la Parathétys qui entrent dans les bassins méditerranéens. Ce changement est guidé par des modifications globales du niveau marin et par la tectonique locale.

Western Préalpes Médianes Romandes: Timing and structure. A review.

Between the original position and their present day location as klippen, the Prealpes Medianes underwent a complex history of paleotectonics and alpine tectonics. Due to the opening of the Piemont ocean the Brianconnais sedimentation realm of the Prealpes Medianes evolved as a rim basin of the northern passive margin during Jurassic to Eocene times. Different paleotectonic features (normal faults, synsedimentary growth structures, inversion structures) developed and were active above a basal detachment in evaporitic layers. The tectonic movements were a consequence of thermal events in the crust. Isolated from the Iberic continent at the end of the Late Cretaceous, the Brianconnais exotic terrain was incorporated into the accretionary prism of the closing Piemont ocean and the incipient alpine orogeny during the Lutetian-Bartonian. The Prealpes Medianes were detached from their homeland during the Bartonian-Priabonian and were transported onto the foreland. The tectonic style is one of a thin-skinned foreland fold and thrust belt. Fault associated fold development above a main decollement, together with internal deformation, represent the Prealpes Medianes main structural features. The very low-grade metamorphic conditions have their origin in the heat flux induced by tectonic burial by overriding nappes in the accretionary prism. After having been transported on top of the developing Helvetic nappes the Prealpes were emplaced in their present day position in front of the Alpine mountain belt during Oligocene times. Post-emplacement and out of sequence thrusting, possibly younger than Oligocene, is observed and can be related to thrusting in the sedimentary substratum and the basement.

The cover basement contact beneath the Rawil axial depression (Western Alps) - True amplitude seismic processing, petrophysical properties, and modeling

Since 1986, several near-vertical seismic reflection profiles have been recorded in Switzerland in order to map the deep geologic structure of the Alps. One objective of this endeavour has been to determine the geometries of the autochthonous basement and of the external crystalline massifs, important elements for understanding the geodynamics of the Alpine orogeny. The PNR-20 seismic line W1, located in the Rawil depression of the western Swiss Alps, provides important information on this subject. It extends northward from the `'Penninic front'' across the Helvetic nappes to the Prealps. The crystalline massifs do not outcrop along this profile. Thus, the interpretation of `'near-basement'' reflections has to be constrained by down-dip projections of surface geology, `'true amplitude'' processing, rock physical property studies and modelling. 3-D seismic modelling has been used to evaluate the seismic response of two alternative down-dip projection models. To constrain the interpretation in the southern part of the profile, `'true amplitude'' processing has provided information on the strength of the reflections. Density and velocity measurements on core samples collected up-dip from the region of the seismic line have been used to evaluate reflection coefficients of typical lithologic boundaries in the region. The cover-basement contact itself is not a source of strong reflections, but strong reflections arise from within the overlaying metasedimentary cover sequence, allowing the geometry of the top of the basement to be determined on the basis of `'near-basement'' reflections. The front of the external crystalline massifs is shown to extend beneath the Prealps, about 6 km north of the expected position. A 2-D model whose seismic response shows reflection patterns very similar to the observed is proposed.

Origin of siderite mineralisation in Petrova and Trgovska Gora Mts., NW Dinarides

The Petrova and Trgovska Gora Mts. (Gora=Mountain) are Variscan basement units incorporated into the northwestern Dinarides during the Alpine orogeny. They host numerous siderite-quartz-polysulphide, siderite-chalcopyrite, siderite-galena and barite veins, as well as stratabound hydrothermal-replacement ankerite bodies within carbonates in non-metamorphosed, flysch-like Permo-Carboniferous sequences. The deposits have been mined for Cu, Pb, Ag and Fe ores since Medieval times. Fluid inclusion studies of quartz from siderite-polysulphide-quartz and barite veins of both regions have shown the presence of primary aqueous NaCl-CaCl(2)+/- MgCl(2)-H(2)O +/- CO(2) inclusions. The quartz-sulphide stage of both regions show variable salinities; 2.7-26.2 wt% NaCl eq. for the Trgovska Gora region and 3.4-23.4 wt% NaCl eq. for the Petrova gora region, and similar homogenisation temperatures (100-230A degrees C). Finally, barite is precipitated from low salinity-low temperature solutions (3.7-15.8 wt % NaCl equ. and 115-145A degrees C). P-t conditions estimated via isochore construction yield formation temperatures between 180-250A degrees C for the quartz-sulphide stage and 160-180A degrees C for the barite stage, using a maximum lithostatic pressure of 1 kbar (cc. 3 km of overburden). The sulphur isotope composition of barite from both deposits indicates the involvement of Permian seawater in ore fluids. This is supported by the elevated bromium content of the fluid inclusion leachates (120-660 ppm in quartz, 420-960 ppm in barite) with respect to the seawater, indicating evaporated seawater as the major portion of the ore-forming fluids. Variable sulphur isotope compositions of galena, pyrite and chalcopyrite, between -3.2 and +2.7aEuro degrees, are interpreted as a product of incomplete thermal reduction of the Permian marine sulphate mixed with organically- and pyrite-bound sulphur from the host sedimentary rocks. Ore-forming fluids are interpreted as deep-circulating fluids derived primarily from evaporated Permian seawater and later modified by interaction with the Variscan basement rocks. (40)Ar/(39)Ar data of the detrital mica from the host rocks yielded the Variscan age overprinted by an Early Permian tectonothermal event dated at 266-274 Ma. These ages are interpreted as those reflecting hydrothermal activity correlated with an incipient intracontinental rifting in the Tethyan domain. Nevertheless, 75 Ma recorded at a fine-grained sericite sample from the alteration zone is interpreted as a result of later resetting of white mica during Campanian opening/closure of the Sava back arc in the neighbouring Sava suture zone (Ustaszewski et al. 2008).

Subduction of continental crust in the Western Alps

As a result of recent deep reflection and refraction seismology the crustal structure of the Western Alps is now quite well-defined. However, this raises the question of what is present below the Moho, such as a crustal eclogitic root. This study attempts to estimate the volume of this eclogitic root on the basis of palinspastic reconstructions. Even with a minimum estimate of the crustal material involved in the subduction processes which took place during the Alpine orogeny, a significant eclogitized crustal root must be present down to depths of around 100 km below the Po plain. A maximum estimate suggests that a large part of this root could now be recycled in the asthenosphere.

Oxygen-isotope thermometry of quartz-calcite veins - Unraveling the thermal-tectonic history of the subgreenschist facies Morcles nappe (Swiss Alps)

Combined structural analysis and oxygen isotope thermometry of syntectonic quartz-calcite fibrous veins can be used to correlate the thermal history of deformed rocks,vith specific structural and tectonic events. Results are presented for the Mercies nappe in the western Helvetic Alps, Switzerland, where mineral parageneses, illite `'crystallinity,'' and fluid inclusion chemistry record an apparent peak metamorphic temperature gradient that increased across the Morcles nappe from anchizonal conditions in the foreland to epizonal conditions in its hinterland root zone. Twenty-seven quartz-calcite veins were analyzed in this study in order to determine the temperatures of veining during formation and deformation of the nappe, Peak metamorphic temperatures ranged from approximate to 260 to 290 degrees C in the shallower, foreland localities and to approximate to 330 to 350 degrees C in the deeper, more hinterland localities at the end of S1-foliation formation, related to large-scale folding. Temperatures gradually decreased throughout the nappe during subsequent development of the S2 foliation and S3 crenulation cleavage, Uplift and erosion of the overlying nappe pile resulted in slow cooling of the Morcles nappe during the waning stages of the Alpine Orogeny. The dominant foliation-forming deformation of the Morcles nappe occurred at elevated temperatures over the course of 10 to 15 Ma. Combined structure-oxygen isotope analyses of quartz-calcite veins yield better temperature and temporal constraints on the thermal histories of subgreenschist vein-bearing tectonites than do other geothermometers.

Ore genesis of Pb-Zn deposits in the Nappe zone of Northern Tunisia: Constraints from Pb-S-C-O isotopic systems

The Jalta and Jebel Ghozlane ore deposits are located in the extreme North of Tunisia, within the Nappe zone. The mineralization of Jalta, hosted in Triassic dolostones and the overlying Mio-Pliocene conglomerates, consists of abundant galena, barite, and cerussite with accessory sphalerite, pyrite, and jordanite. At Jebel Ghozlane, large Pb-Zn concentrations occur in the Triassic dolostones and Eocene limestones. The mineral association consists of galena, sphalerite, barite, and celestite and their oxidation products (cerussite, smithsonite, and anglesite). Lead isotope ratios in galena from both districts are relatively homogeneous ((206)Pb/(204)Pb = 18.702-18.823, (207)Pb/(204)Pb = 15.665-15.677, (208)Pb/(204)Pb = 38.725-38.875). The delta(34)S values for sulfates from both areas (+12.2 to +16.2 parts per thousand at Jalta and + 14.3 to + 19.4 parts per thousand at Jebel Ghozlane) are compatible with a derivation of sulfur from marine sulfates, possibly sourced from the Triassic evaporites. The delta(34)S values of the sulfides have a range between -10 and +12.5 parts per thousand at Jalta, and between -9.1 and +22.1 parts per thousand at Jebel Ghozlane. The large range of values suggests reduction of the sulfate by bacterial and/or thermochemical reduction of sulfate to sulfur. The high delta(34)S values of sulfides require closed-system reduction processes. The isotopically light carbon in late calcites (-6.3 to -2.5 parts per thousand) and authigenic dolomite (-17.6 parts per thousand) suggests an organic source of at least some of the carbon in these samples, whereas the similarity of the delta(18)O values between calcite (+24.8 parts per thousand) and the authigenic dolomite (+24.7 parts per thousand) of Jalta and their respective host rocks reflects oxygen isotope buffering of the mineralizing fluids by the host rock carbonates. The secondary calcite isotope compositions of Jalta are compatible with a hydrothermal fluid circulation at approximately 100 to 200 degrees C, but temperatures as low as 50 degrees C may be indicated by the late calcite of Jebel Ghozlane (delta(18)O of +35.9 parts per thousand). Given the geological events related to the Alpine orogeny in the Nappe zone (nappe emplacement, bimodal volcanism, and reactivation of major faults, such as Ghardimaou-Cap Serrat) and the Neogene age of the host rocks in several localities, a Late-Miocene age is proposed for the Pb-Zn ore deposits considered in this study. Remobilization of deep-seated primary deposits in the Paleozoic sequence is the most probable source for metals in both localities considered in this study and probably in the Nappe zone as a whole. (C) 2011 Elsevier B.V. All rights reserved.

Evolution of the Helvetic shelf (Switzerland) during the Barremian-early Aptian : paleoenvironmental, paleogeographic and paleoceanographic controlling factors

The Early Cretaceous has experienced the development of large shallow-water carbonate platform in tropical and subtropical regions, favoured by exceptionally warm climatic conditions, optimal trophic conditions and a suitable tectonic and paleogeographic context. This period was also characterized by shorter intervals, in which the widespread deposition of marine sediments enriched in organic matter occurred ("oceanic anoxic episodes": OAE). This study focuses on the Barremian- Aptian interval, during which the Urgonian platform developed throughout the northern Tethyan passive margin. Due to the Alpine orogeny, sediments belonging to this platform - named locally Schrattenkalk Formation, are presently outcropping in the Helvetic Alps. This study aims to reconstruct the paleogeographic evolution of the Helvetic platform, and to define the environmental and oceanographic factors, which influenced its development. Several key episodes in the life of this platform have been identified: - The installation of the platform, covering hemipelagic sediments of the Drusberg Member, near the limit between the early and late Barremian. - The temporary change of carbonate production type during the basal Aptian, with the deposition of the Rawil Member. - And finally the definitive interruption of photozoan carbonate platform sedimentation in the study area, during the early Aptian. The sedimentological, biostratigraphical and chemostratigraphic (8I3C) data lead to the sequential subdivision of eleven sections and one core, located throughout the different Helvetic nappes of Switzerland. The sequence stratigraphie framework, initially defined for the Urgonian carbonate platform of the Vercors area (SE France), is confirmed in the Helvetic nappes, where the same number of sequences was observed. Many similarities between these two areas are put forward in this work. The sequence stratigraphie framework helped to highlight the installation of a bioclastic body, included in the Schrattenkalk Formation, since the middle Early Barremian (sequence B2). The age of the installation of the rudist-rich limestone, which corresponds to the Urgonian facies sensu stricto, is attributed to the late Barremian (maximum flooding surface of the sequence B3). This age coincides with the one determined in other northern Tethyan areas for the installation of the Urgonian platform. The results of this study show a strong tectonic control of the platform architecture, with the presence of syn-sedimentary faults in a perpendicular position to the progradation direction of the platform. The presence of these faults was highlighted by the study of the evolution of the microfacies distribution and by thickness variations in different areas. Sea level fluctuations also played an important role in the various life phases of the platform. Three major falls in sea level have been identified. A significant emersion of the proximal domain has been observed, involving an important drop of the relative sea level, leading to the exposure of the Drusberg Member hemipelagic series. A second major drop in sea level is identified near the Barremian-Aptian boundary, and a third is registered on the top of the Upper Schrattenkalk Member on the whole platform; it is associated with a karst affecting the underlying limestones to a depth of over 20 meters. This observation sheds new light on the conditions linked to the demise of Urgonian platform, which was strongly influenced by this phase of emersion.

Alpine tectonic evolution of a Jurassic subduction-accretionary complex: Deformation, kinematics and 40Ar/39Ar age constraints on the Mesozoic low-grade schists of the Circum-Rhodope Belt in the eastern Rhodope-Thrace region, Bulgaria-Greece

Deformation of the Circum-Rhodope Belt Mesozoic (Middle Triassic to earliest Lower Cretaceous) low-grade schists underneath an arc-related ophiolitic magmatic suite and associated sedimentary successions in the eastern Rhodope-Thrace region occurred as a two-episode tectonic process: (i) Late Jurassic deformation of arc to margin units resulting from the eastern Rhodope-Evros arc-Rhodope terrane continental margin collision and accretion to that margin, and (ii) Middle Eocene deformation related to the Tertiary crustal extension and final collision resulting in the closure of the Vardar ocean south of the Rhodope terrane. The first deformational event D-1 is expressed by Late Jurassic NW-N vergent fold generations and the main and subsidiary planar-linear structures. Although overprinting, these structural elements depict uniform bulk north-directed thrust kinematics and are geometrically compatible with the increments of progressive deformation that develops in same greenschist-facies metamorphic grade. It followed the Early-Middle Jurassic magmatic evolution of the eastern Rhodope-Evros arc established on the upper plate of the southward subducting Maliac-Meliata oceanic lithosphere that established the Vardar Ocean in a supra-subduction back-arc setting. This first event resulted in the thrust-related tectonic emplacement of the Mesozoic schists in a supra-crustal level onto the Rhodope continental margin. This Late Jurassic-Early Cretaceous tectonic event related to N-vergent Balkan orogeny is well-constrained by geochronological data and traced at a regional-scale within distinct units of the Carpatho-Balkan Belt. Following subduction reversal towards the north whereby the Vardar Ocean was subducted beneath the Rhodope margin by latest Cretaceous times, the low-grade schists aquired a new position in the upper plate, and hence, the Mesozoic schists are lacking the Cretaceous S-directed tectono-metamorphic episode whose effects are widespread in the underlying high-grade basement. The subduction of the remnant Vardar Ocean located behind the colliding arc since the middle Cretaceous was responsible for its ultimate closure, Early Tertiary collision with the Pelagonian block and extension in the region caused the extensional collapse related to the second deformational event D-2. This extensional episode was experienced passively by the Mesozoic schists located in the hanging wall of the extensional detachments in Eocene times. It resulted in NE-SW oriented open folds representing corrugation antiforms of the extensional detachment surfaces, brittle faulting and burial history beneath thick Eocene sediments as indicated by 42.1-39.7 Ma Ar-40/Ar-39 mica plateau ages obtained in the study. The results provide structural constraints for the involvement components of Jurassic paleo-subduction zone in a Late Jurassic arc-continental margin collisional history that contributed to accretion-related crustal growth of the Rhodope terrane. (C) 2011 Elsevier Ltd. All rights reserved.

Discordances between phylogenetic and morphological patterns in alpine leaf beetles attest to an intricate biogeographic history of lineages in postglacial Europe.

Pleistocene glacial and interglacial periods have moulded the evolutionary history of European cold-adapted organisms. The role of the different mountain massifs has, however, not been accurately investigated in the case of high-altitude insect species. Here, we focus on three closely related species of non-flying leaf beetles of the genus Oreina (Coleoptera, Chrysomelidae), which are often found in sympatry within the mountain ranges of Europe. After showing that the species concept as currently applied does not match barcoding results, we show, based on more than 700 sequences from one nuclear and three mitochondrial genes, the role of biogeography in shaping the phylogenetic hypothesis. Dating the phylogeny using an insect molecular clock, we show that the earliest lineages diverged more than 1 Mya and that the main shift in diversification rate occurred between 0.36 and 0.18 Mya. By using a probabilistic approach on the parsimony-based dispersal/vicariance framework (MP-DIVA) as well as a direct likelihood method of state change optimization, we show that the Alps acted as a cross-roads with multiple events of dispersal to and reinvasion from neighbouring mountains. However, the relative importance of vicariance vs. dispersal events on the process of rapid diversification remains difficult to evaluate because of a bias towards overestimation of vicariance in the DIVA algorithm. Parallels are drawn with recent studies of cold-adapted species, although our study reveals novel patterns in diversity and genetic links between European mountains, and highlights the importance of neglected regions, such as the Jura and the Balkanic range.

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.