European Margin Research Articles

Structural and petrological characteristics of a Jurassic detachment fault from the Mont-Blanc massif (Col du Bonhomme area, France)

Necking zones, located between the proximal and distal domains of passive margins, are characterized by important crustal thinning and the occurrence of extensional detachment faults. Here we provide a petrographic, microstructural and geochemical study of an extensional detachment fault discovered in the Mont-Blanc massif, which was located in the necking zone of the European margin during Early Jurassic rifting. The footwall of the fault consists of basement gneisses, while its hanging wall presents pre-to syn-rift deposits. A careful observation of the basement/cover contact also reveals the presence of a strain gradient affecting the Variscan gneisses, which are progressively deformed to cataclasite and to black gouges at the top basement, and sealed by undeformed Jurassic syn-rift sandstones, the Grès Singuliers, which rework fault rock pebbles. Microscale observations also indicate fluid-assisted deformation, characterized by the total breakdown of feldspars and the coeval formation of white mica, leading to strain softening along the fault plane. The overall observations point toward a rift-related detachment fault responsible for the exhumation of the internal Mont-Blanc basement, an interpretation which challenges previous models of crustal exhumation in the External massifs of the Alps. Finally, the preservation of an undeformed syn-rift sedimentary cover sealing a tectonized top basement makes this area a fossil analogue for detachment faults in necking domains. It demonstrates that preservation of pre-Alpine, rift related structures is possible even in highly deformed areas, and emphasizes the role played by pre-Alpine inheritance on the building of the Alpine Mountain belt.

Seismic Volcanostratigraphy: The Key to Resolving the Jan Mayen Microcontinent and Iceland Plateau Rift Evolution

AbstractVolcanostratigraphic and igneous province mapping of the Jan Mayen microcontinent (JMMC) and Iceland Plateau Rift (IPR) region have provided new insight into the development of rift systems during breakup processes. The microcontinent's formation involved two breakup events associated with seven distinct tectono‐magmatic phases (∼63–21 Ma), resulting in a fan‐shaped JMMC‐IPR igneous domain. Primary structural trends and anomalous magmatic activity guided initial opening (∼63–56 Ma) along a SE‐NW trend from the European margin and along a WNW‐ESE trend from East Greenland. The eastern margin of the microcontinent formed during the first breakup (∼55–53 Ma), with voluminous subaerial volcanism and emplacement of multiple sets of SSW–NNE‐aligned seaward‐dipping reflector sequences. The more gradual, second breakup (∼52–23 Ma) consisted of four northwestward migrating IPR (I–IV) rift zones along the microcontinent's southern and western margins. IPR I and II (∼52–36 Ma) migrated obliquely into East Greenland, interlinked via segments of the Iceland‐Faroe Fracture Zone, in overlapping sub‐aerial and sub‐surface igneous formations. IPR III and IV (∼35–23 Ma) formed a wide igneous domain south and west of the microcontinent, accompanied by uplift, regional tilting, and erosion as the area moved closer to the Iceland hotspot. The proto‐Kolbeinsey Ridge formed at ∼22–21 Ma and connected to the Reykjanes Ridge via the Northwest Iceland Rift Zone, near the center of the hotspot. Eastward rift transfers, toward the proto‐Iceland hotspot, commenced at ∼15 Ma, marking the initiation of segmented rift zones comparable to present‐day Iceland.

Protracted Subduction of the European Hyperextended Margin Revealed by Rutile U‐Pb Geochronology Across the Dora‐Maira Massif (Western Alps)

AbstractThe Dora‐Maira massif is an archetypal nappe stack of subducted and exhumed upper crust. Slices of continental crust experienced metamorphism at upper blueschist to ultrahigh‐pressure (UHP) eclogite‐facies conditions. While the timing of peak metamorphism in the UHP unit has been extensively studied, little is known about the other units. In order to constrain the timing and conditions of high‐pressure metamorphism, U‐Pb‐trace element analyses of rutile and titanite were carried out across the nappe stack. The data reveal Alpine peak metamorphic ages younging downwards in the stack, from ∼40 to ∼33 Ma. Greenschist‐facies retrogression of the whole massif occurred at ∼32–31 Ma, after high‐pressure metamorphism of the lowermost unit (Sanfront‐Pinerolo Unit). Tectonic implications include (a) continuous and fast exhumation of subducted continental crust, (b) long‐lived subduction from ∼60 to ∼33 Ma of the distal European margin, reconstructed to be a hyperextended margin spread over ∼130 km for the Dora‐Maira massif alone, and (c) the initiation of continental collision synchronous with the end of high‐pressure metamorphism.

Anatomy of a deformed upper crust fragment from western Alpine Corsica (France): insights into continental subduction processes

ABSTRACT In Corsica Island (France), a belt of metamorphic continental units derived from the European margin is exposed at the western rim of the Alpine Corsica. This study provides a complete anatomy of one of these units (Tour de Valletto Unit) consisting of a Palaeozoic basement covered by an Early Jurassic – late Eocene sedimentary succession. This unit records a polyphase tectono-metamorphic history acquired during the late Eocene – lower early Miocene convergence processes involving the Adria and Europe continental plates. Using a multidisciplinary approach, we reconstructed in detail the P-T path of the Tour de Valletto Unit. The path shows a metamorphic climax at blueschist facies conditions suggesting that the unit was accreted at c. 40 km of depth. After its accretion, the Tour de Valletto Unit was exhumed up to the Earth surface following a path characterized by an increase of temperature and a decrease of pressure. The reconstructed tectono-metamorphic history of the Tour de Valletto Unit is compared with those of the other continental units located in western Alpine Corsica to discuss the exhumation processes active during continental subduction.

The Literary Politics of Mitteleuropa: Reconfiguring Spatial Memory in Austrian and Yugoslav Literature after 1945 by Yvonne Zivkovic

Reviewed by: The Literary Politics of Mitteleuropa: Reconfiguring Spatial Memory in Austrian and Yugoslav Literature after 1945 by Yvonne Zivkovic Sabine Egger The Literary Politics of Mitteleuropa: Reconfiguring Spatial Memory in Austrian and Yugoslav Literature after 1945. By Yvonne Zivkovic. Rochester, NY: Camden House. 2021. 319 pp. £95. ISBN 978–1-64014–088–2. Yvonne Zivkovic's study discusses how post-war writers in Austria and Yugoslavia have re-imagined the concept of Mitteleuropa as a cultural space between nostalgia and totalitarianism from 1945 to the present. In four chapters the book compares Central European memory spaces in the writing of Ingeborg Bachmann and Peter Handke between 1945 and the 1960s, Danilo Kiš and Aleksandar Tišma from 1960 to 1989, and Christoph Ransmayr and Dubravka Ugrešić after 1990, placing them within the framework of twentieth-century discourses on Mitteleuropa and twenty-first-century images of Europe and its potential dissolution. Chapter 1 links ideas of a transnational Mitteleuropa, put forward by politicians like Friedrich Naumann or Tomáš Garrigue Masaryk, and Jewish Austrian writers Stefan Zweig, Joseph Roth or Ödön von Horváth, to Milan Kundera's and György Konrád's critical debate [End Page 210] of the 1980s. What emerges is a conflicted idea of Mitteleuropa, situated between hope and melancholia, utopian and dystopian visions of a multi-ethnic and pluralist territory left behind by the Habsburg Empire, and a 'mental space', following Lefebvre, shaped by the cultural heritage of the European enlightenment. Zivkovic argues that Claudio Magris's The Habsburg Myth does not capture the critical and dystopian dimension of these writings. The latter is already highlighted in Ruth Klüger's painful memory of 'Mitteleuropäer in Birkenau', which Zivkovic references in her opening (p. 1). The importance of Jewish authors in the literary politics of Mitteleuropa and the significance of the destruction of Jewish culture is brought to the fore throughout the book. Chapter 3 focuses on Kiš and Tišma, two Jewish Yugoslav writers from the Serbian border province of Vojvodina, who approach this difficult past through their distinct aesthetics. A further focus lies on the extent to which the ideas of Mitteleuropa discussed are political, even when they are represented as explicitly apolitical or 'antipolitical'. By using the latter as a term Konrád chose to distance his writing from the Soviet bloc in 1982, Ugrešić places herself within this tradition of Central European literature (p. 263). Zivkovic's comparative approach reveals surprising parallels in the ways Austrian and former Yugoslavian writers approach Mitteleuropa as a trope and mental space. Both Bachmann and Kiš reflect on the late turn towards Holocaust memory in their respective countries and historical settings. Drawing on a spectrum of literary traditions, post-communist memories and their recent experience of the fragmentation of a multi-ethnic European state in the Yugoslav wars, texts by Kiš or Ugrešić revisit and deconstruct patterns of the Habsburg myth. At the same time, Zivkovic's reading of Bachmann and Handke focuses on their Carinthian background and links to Slovenian culture, thus reversing traditional centre–periphery patterns in Austrian literature. Including Yugoslav literature in the Mitteleuropa debate revived in the 1980s by Kundera and Konrád opens up new perspectives on Europe as a cultural and political construct, as well as on the role of literature in this process. This not only applies to the widening of the Mitteleuropa discourse from a Balkan perspective. As Zivkovic points out in her conclusion, '[t]hrough an increased literary presence of Mitteleuropa in Ukrainian and Polish but also Croatian and Serbian literature over the last decade or so, the Central European margin is expanding further east and south' (p. 280). The impact of EU funding on promoting a specific vision of European collectivity is mentioned, as well as the role of exchanges with other Central European writers by means of networks, exile communities and literary festivals. It might also have been useful to discuss the role of literary awards in this context, as these play a major part in positioning authors in specific literary fields. The book also touches on what it means to write in a second language...

Rees and other critical raw materials in Cretaceous Mediterranean-type bauxite: The case of the Sardinian ore (Italy)

Mediterranean-type bauxite deposits in Sardinia formed during the Upper Cretaceous (Cenomanian–Turonian) due to the emergence of the south European margin of the Alpine Tethys in an area affected by monsoonal climate. The deposits were controlled by the structural frame formed in a transpressive tectonic regime and unconformably overlie carbonate rocks of different age and composition, which led to the formation of different bauxite types. In general, in the Sardinian bauxite deposits, boehmite is the main Al-phase, kaolinite is the main Si-rich mineral, and hematite as well as goethite are the Fe-rich phases. Secondary authigenic anatase and detrital rutile control the Ti contents. Eu/Eu* anomalies show that the bauxite types were derived from the Variscan basement. However, there are differences in Al2O3 and SiO2 contents, which suggest there was localised variability in the extent of epigenetic replacement of kaolinite by boehmite. R-mode factor analysis suggests that most critical raw materials (as defined by the devoted European Union working group), such as Sc, Ga, Nb, Hf, Ta, and W, covary with Al2O3 contents. In the Si-poor bauxite, these metals of economic interest are likely controlled by boehmite, whereas in the Si-rich bauxite they are mostly controlled by weathering-resistant minerals. Rare earth element (REE)-rich minerals, including fluorocarbonates and cerianite, are concentrated in the basal, illuvial horizon, especially in the silica-rich bauxite (ΣREE = 1006–2034 ppm). Cerianite formation required Ce oxidation, whereas fluorocarbonate formation involved mobilisation of trivalent REEs and further fluoride complexation. Both REE-rich mineral phases precipitated under alkaline pH conditions near to the carbonate bedrock. Our evaluation of the critical raw materials distribution in the Sardinian bauxite, coupled with the “economic importance” and “supply risk” parameters, indicate the ore contains large amounts of metals characterised by a “supply risk”, such as light and heavy REEs, and metals of “economic importance”, such as V and W. In this way, the Sardinian bauxite deposits could be reconsidered as a potential source of critical raw materials.

Are Past Sea-Ice Reconstructions Based on Planktonic Foraminifera Realistic? Study of the Last 50 ka as a Test to Validate Reconstructed Paleohydrography Derived from Transfer Functions Applied to Their Fossil Assemblages

Since its existence, paleoceanography has relied on fossilized populations of planktonic foraminifera. Except for some extreme environments, this calcareous protist group composes most of the silty-to-sandy fraction of the marine sediments, i.e., the foraminiferal oozes, and its extraction is probably the simplest among the currently existing set of marine fossil proxies. This tool has provided significant insights in the building of knowledge on past climates based on marine archives, especially with the quantification of past hydrographical variables, which have been a turning point for major comprehensive studies and a step towards the essential junction of modelling and paleodata. In this article, using the modern analog technique and a database compiling modern analogs (n = 1007), we test the reliability of this proxy in reconstructing paleohydrographical data other than the classical sea-surface temperatures, taking advantage of an update regarding a set of extractions from the World Ocean Atlas for transfer functions. Our study focuses on the last glacial period and its high climatic variability, using a set of cores distributed along the European margin, from temperate to subpolar sites. We discuss the significance of the reconstructed parameters regarding abrupt and extreme climate events, such as the well-known Heinrich events. We tested the robustness of the newly obtained paleodata by comparing them with older published reconstructions, especially those based on the complementary dinoflagellate cyst proxy. This study shows that the potential of planktonic foraminifera permits going further in reconstructions, with a good degree of confidence; however, this implies considering ecological forcings in a more holistic perspective, with the corollary to integrate the message of this fossil protist group, i.e., the obtained parameters, in light of a cohort of other data. This article constitutes a first step in this direction.

Montlivaltia multiformis Toula (Scleractinia) from the Aptian of the Prebetic Domain (SE Spain)

Montlivaltia multiformis Taula (Scleractinia, Faviina, Montlivaltidae), formerly reported from the Carpatho Balkanic domain is described from Lower Aptian beds of the Prebetic Domain (SE Spain). Taxonomic attributes include the organisation of radial elements, septal trabeculae, carinae and endothecal elements while the external morphology of the coralla is fairly variable. The sedimentological context suggests a circalittoral environment also supported by palaecological features of the surrounding fauna. Owing to its stratigraphic position in the Carpatho-Balkanic region and in Spain, Montlivaltia multiformis appears as a potential marker for both shallow carbonate or outer shelf settings of the Lower Aptian Tethys European margin.

Extension and early orogenic inversion along the basal detachment of a hyper-extended rifted margin: an example from the Central Pyrenees (France)

The North Pyrenean Zone inverts remnants of an Aptian–Cenomanian rifting during which subcontinental mantle was exhumed. These remnants contain a synrift HT–LP metamorphic domain, the Internal Metamorphic Zone. New field data, Raman spectroscopy on carbonaceous material data and structural cross-sections constrain the structural and metamorphic relationships between the Internal Metamorphic Zone and the underlying low-grade North Pyrenean Zone. The Internal Metamorphic Zone is a tectonic nappe that overthrusts the European margin along the 3M Fault. Along this contact, the Tuc de Haurades peridotite is surrounded by tectonic breccia composed of ductilely deformed carbonate and sparse lherzolite clasts that passes upward into foliated marbles. Marbles contain top-to-south ductile shear, recording continuing extensional deformation that marks the onset of HT metamorphism. During Early Cretaceous rifting, European Mesozoic sedimentary cover metamorphosed and its base brecciated as it slid basinward on Triassic salt onto exhumed mantle. As the exhumed mantle domain closed during early convergence, the detached metamorphosed cover was transported northward and thrust onto the distal European margin, sampling lherzolite tectonic lenses. This triggered the first tectonic loading on the European plate. This study highlights the role of the Internal Metamorphic Zone in the early Pyrenean orogenic phase and gives new insights into the east–west diversity of structural setting of the North Pyrenean Zone peridotites. Supplementary material : A table with Raman spectroscopy on carbonaceous material temperatures and original and high-quality photographs of the samples are available at https://doi.org/10.6084/m9.figshare.c.5539260

Geochemistry and paleogeographic implications of Permo-Triassic metasedimentary cover from the Tauern Window (Eastern Alps)

Abstract. The chemical composition of metasediments is a valuable source of paleogeographic information about the protolith's sedimentary environment. Here, we compile major- and trace-element whole-rock data, including B contents, and 10/11B-isotope ratios from the Permo-Triassic metasedimentary cover of the Pfitsch–Mörchner basin, overlying the Variscan basement in the western Tauern Window, Eastern Alps (Austria and Italy). The basement consists of orthogneiss (“Zentralgneis”, metamorphosed Variscan granitoids with intrusion ages between 305 and 280 Ma), and the roof pendant consists of granites (amphibolites, paragneiss, and minor serpentinites). The Zentralgneis is partly hydrothermally altered into pyrite quartzite with high Al–S contents, low Na–Sr–Ca–Mg contents, and very strong depletion of the light rare earth elements. Comparison with published detailed mapping of this and other time-equivalent basins in the western Tauern Window, with radiometric age data in the literature, and with unmetamorphosed basins in the South Alpine realm yields a late Permian to Early Triassic age of sedimentation. Although during Alpine metamorphism all rocks were strongly deformed, the whole-rock chemical compositions of the metasediments were not pervasively changed during deformation. We show that the sediments were deposited in a small, probably lacustrine–fluviatile, intramontane basin, under arid to semi-arid climatic conditions. The sequence starts with metaconglomerates, which can be interpreted as a mixture of the different basement rocks, based on a combination of major-element ratios Na2O / (Na2O + K2O) and MgO / (MgO + Fe2O3) with concentrations of trace elements Cr, V, and Ni. The sequence is overlain by a fining-upwards sequence of clastic sediments, in which the behavior of K, Rb, and Sr allows the reconstruction of intense diagenetic K–B metasomatism, which raised the K2O contents up to ∼ 10 wt %. The average B content of 218 µg g−1 is well above the B content of common sediments, and the B-isotope composition reaches extremely low values of down to −33 ‰ δ11B. The top of the sequence is a lazulite quartzite, interpreted as a former conglomeratic phosphatic sandstone, which marks the transition from a closed Permian basin to an open Triassic basin. Within the clastic sequence, the presence of hydrothermal tourmalinite veins documents a hydrothermal event after deposition but before the onset of Alpine metamorphism. A metamorphosed mafic dike swarm in the orthogneiss indicates a post-Variscan event of basaltic magmatism, and this event is tentatively correlated with increased heat flow in the Triassic basin and hydrothermal activity. A consistent conceptual model of this basin and its diagenetic modifications, based on a combination of geochemical data with petrographical and field information, provides the geodynamic context of the European margin at the onset of the Alpine orogeny.

Exploring the extent to which fluctuations in ice‐rafted debris reflect mass changes in the source ice sheet: a model–observation comparison using the last British–Irish Ice Sheet

ABSTRACTThe British and Irish Ice Sheet (BIIS) was highly dynamic during the Late Quaternary, with considerable regional differences in the timing and extent of its change. This was reflected in equally variable offshore ice‐rafted debris (IRD) records. Here we reconcile these two records using the FRUGAL intermediate complexity iceberg–climate model, with varying BIIS catchment‐level iceberg fluxes, to simulate change in IRD origin and magnitude along the western European margin at 1000‐year time steps during the height of the last BIIS glaciation (31–6 ka bp). This modelled IRD variability is compared with existing IRD records from the deep ocean at five cores along this margin. There is general agreement of the temporal and spatial IRD variability between observations and model through this period. The Porcupine Bank off northwestern Ireland was confirmed by the modelling as a major dividing line between sites possessing exclusively northern or southern source regions for offshore IRD. During Heinrich events 1 and 2, the cores show evidence of a proportion of North American IRD, more particularly to the south of the British Isles. Modelling supports this southern bias for likely Heinrich impact, but also suggests North American IRD will only reach the British margin in unusual circumstances.

Deep Tectonics in the Eastern Hellenides Uncovered: The Record of Variscan Continental Amalgamation, Permo‐Triassic Rifting, and Early Alpine Collision in Pre‐Variscan Continental Crust in the W‐Rhodope (Vertiscos‐Ograzden Complex, N‐Greece)

AbstractThe Vertiskos‐Ograzden metamorphic complex (VOC; W‐Rhodope Metamorphic Domain, RMD) is a key area for reconstructing the geodynamic history of the Hellenides. We distinguish four metamorphic events: (1) an (U)HP eclogite facies metamorphism, succeeded by partial melting during decompression, amphibolite facies reequilibration in the kyanite stability field, and injection of muscovite pegmatites; (2) a LP‐HT event, associated with partial melting within the stability field of sillimanite, cordierite, and K‐feldspar (andalusite at subsolidus conditions) and magmatic intrusions; (3) a prograde moderate high‐pressure (MHP) metamorphism within the kyanite stability field increasing to the NE from epidote amphibolite to upper amphibolite facies; and (4) in the easternmost VOC, a LP amphibolite facies event (new cordierite and andalusite). Considering existing geochronological data, the VOC formed part of successive tectonic settings: (1) the “Variscan” collision zone between “East‐Avalonian” and Armorican continental fragments; (2) the Triassic middle crust of a continental rift zone, (leading to formation of oceanic crust, in the eastern VOC); (3) late Jurassic‐early Cretaceous closure of the oceanic basin and accretion of the VOC to southern European margin and northeastward polarity of subduction/collision; (4) late Cretaceous extension and crustal thinning. Then, subduction of the Neo‐Tethys and Apulian plate underneath Europe occurred, and the VOC plus the upper units of the RMD were part of the upper (European) plate. Large‐scale north dipping low‐angle normal detachments exhumed the VOC from the vicinity of a magmatic arc presently situated in the north RMD and Sredna Gora and Strandja zones and drag it into its present position.

Destructive episodes and morphological rejuvenation during the lifecycles of tectonically active seamounts: Insights from the Gorringe Bank in the NE Atlantic

Seamounts are spectacular bathymetric features common within volcanic and tectonically active continental margins. During their lifecycles, they evolve through stages of construction and destruction. The latter are marked by variable magnitude flank collapses that often interrupt the evolution of seamounts and constitute a major source of hazard. The Southwest Iberian Margin is a tectonically complex region with moderate to high seismicity where numerous seamounts occur. On such a setting, earthquake-triggered collapses on seamount flanks are common, leading to the deposition of Mass-Transport Deposits (MTDs) on the surrounding abyssal plains. Using a wealth of 2D seismic reflection profiles, we investigate the lifecycle of the tectonic Gorringe Bank (GB), the largest submarine seamount offshore European margins, based on the magnitude and recurrence patterns of MTDs along the active thrust flank. Eight MTDs with relevant expression on the seismic data were analysed, four of estimated Miocene age and four on a Pliocene-Quaternary interval. Miocene MTDs are overall larger and correlate with the main uplift stages of the GB structure. Their distribution and relative timing suggest that failure-triggering earthquakes were common along the whole length of the GB. Pliocene to Quaternary MTDs tend to cluster along the northern half of the GB flank and are generally smaller. Overall, the size and magnitude of the mass-waste events is directly relatable to the magnitude of the uplift stages. Given the lack of indicators of large MTDs on the modern GB morphology, we propose that the lifecycle of tectonic seamounts is marked by morphological rejuvenation driven by thrust fault activity in between major collapse events or cycles. Tectonic-driven rejuvenation is thus key to hinder or obliterate evidence of past high-magnitude destructive events on tectonic seamount morphology.

Mediatising Violence and Renegotiating Commonality: Bosnian Muslim Press Reporting on the Italo-Turkish War (1911–1912)

This article presents a case study concerning Bosnian Muslim press reporting on the Italo-Turkish War in 1911 and 1912. It discusses the impact of mediatised violence and emotions on the imagination of space, commonality and future. The case under scrutiny is situated at the Eastern European margins of what was, during the course of the long nineteenth century, increasingly conceptualised and perceived as the ‘Muslim world’. This process of imagining the Muslim world as a politically meaningful entity engendered the constitution and transformation of mental maps which played, as this article argues, a key role in local processes of making modernity in a Transottoman setting.

Anatomy and evolution of the Astoin diapiric complex, sub-Alpine fold-and-thrust belt (France)

The structure of the southwestern branch of the Alpine orogen is affected by the extensive Late Triassic evaporites. These evaporites have been involved in polyphased salt tectonics since the early Liassic, coeval with the Tethyan rifting, and are the décollement level for thrusts in the external parts during Alpine orogeny. The role of salt tectonics in this branch of the Alpine arc is re-evaluated in order to determine the relative importance of early deformation related to salt motion with respect to deformation related to main Alpine compressional events. This paper focuses on one structure identified as diapiric since the 1930’s: the Astoin diapir (Goguel, 1939). Analysis of geological maps together with new field work have allowed to better define diapirism in the Upper Triassic evaporites outcrops around Astoin. Study of the diapir and the surrounding depocenters reveals a major involvement of salt in the structuration of the area, since the Liassic. Several salt ridges are linked to a main diapiric structure, explaining why we call it the “diapiric complex” of Astoin. Salt tectonics was initiated during the Liassic rifting, and a few locations show evidence of reactive diapirism whereas in others evidence of passive diapirism as early as the Liassic is seen. Passive diapirism continued during the post-rift stage of Alpine margin history in the Late Jurassic and Cretaceous when an allochthonous salt sheet was emplaced. Diapirism also occurred during the Oligocene while the Alpine foreland basin was developing in this part of the European margin of the Alps. Serial interpretative cross-sections have been drawn in order to illustrate the lateral variations of diapirism and structural style. Sequential evolutions for each cross-section are proposed to reconstruct the diapiric complex evolution through time. The Astoin diapir shows a complex structural framework with an important along-strike variation of diapiric activity. Most of the geometries are inherited from salt tectonics that occurred during extension, and in some places these early structures are overprinted by Alpine compressional structures.

Evidence of decoupled deformation during Jurassic rifting and Cenozoic inversion phases in the salt-rich Corbières-Languedoc Transfer Zone (Pyreneo-Provençal orogen, France)

A detailed field study of Jurassic tectono-stratigraphic architecture of the southwestern part of the Corbières-Languedoc Transfer Zone (CLTZ, NE-SW oriented), between the Pyrenean and Provençal orogenic segments (N110 oriented) in SE France, document for the first time variations in thickness and stratigraphic geometries in relation to oblique extensional cover structures (NE-SW and N110 oriented). These structures (low-dip normal faults, salt rollers, rollovers, forced folds) formed during a Jurassic extension phase with strong decoupling between basement and cover on the Keuper pre-rift salt (Carnian-Norian evaporites). Some of these structures such as the Treilles Fault, the Valdria and the Terres Noires fold pairs, were previously interpreted as compressional and Pyrenean in origin (Late Santonian-Bartonian). Our study instead shows that these are Jurassic extensional and salt related structures, which were later affected by Pyrenean compression and Oligo-Miocene extension. Evidence of Jurassic extension is still observable in the field despite later rectivations, making these good field analogs for gently inverted extensional salt structures. During the Jurassic the interference between oblique structures above Keuper, leads to the formation of three dimensional growth strata observable at kilometric scale. Despite the mechanical decoupling effect of Keuper, we infer that their formation was linked to a strong interaction between oblique basement structures (NE-SW and N110) as the area lies during the Jurassic at the intersection between the eastern part of the Pyrenean E-W trending rift system and the NE-SW trending European margin of the Alpine Tethys rift. The decoupled deformation and the strong segmentation above and below Keuper detachement are here identified as Jurassic structural inheritence for later tectonic events, notably for the Nappe des Corbières Orientales emplaced at the end of Pyrenean orogenesis. Associated to previous works, this study highlights that the CLTZ is a key area to better understand Pyreneo-Provençal system evolution along its whole Wilson cycle and to better understand the processes that govern the formation of a salt-rich transfer zone in a strongly pre-structured crust, its multiple reactivations and the decoupling role of salt.

Development of coral\u2013sponge\u2013microbialite reefs in a coated grain-dominated carbonate ramp (Upper Jurassic, eastern Sardinia, Italy)

The Late Jurassic is a peak time of diversification of reefs with corals, stromatoporoids, calcareous and siliceous sponges, and microbialites during the Phanerozoic. This study focuses on the Callovian–Kimmeridgian carbonate succession of eastern Sardinia, deposited at tropical latitudes on the European passive margin that recorded from the late Oxfordian the evolution from a coated grain-dominated to a reef-bearing carbonate ramp. The coated grain-dominated carbonate ramp (phase 1; Callovian–middle Oxfordian) includes inner ramp ooidal shoals and peloidal packstone in the middle-to-outer ramp. The overlying reef-bearing ramp (phase 2; late Oxfordian–late Kimmeridgian) is characterized by three types (1–3) of bioconstructions. The distribution of these build-ups along the middle-to-outer ramp depositional profile reflects bathymetric parameters, related to the interplay of water energy and light penetration. Type 1 build-ups developed in the proximal middle ramp and consist of 45 m thick, 100 m wide, coral-stromatoporoid boundstone associated with coral–stromatoporoid rudstone–grainstone. Type 2 build-ups, colonizing deeper environments in the middle ramp, are lens-shaped coral–calcareous sponge–diceratid boundstone including stromatoporoids and chaetetid sponges, 1–2 m thick and 3–4 m wide, associated with bioclastic packstone–grainstone. Type 3 lens-shaped calcareous and siliceous sponge–coral–microbialite boundstone build-ups (1 m thick and a few metres wide) formed in lower energy, distal middle-to-outer ramp settings. The evolution of the eastern Sardinian carbonate ramp reflects the Oxfordian–Kimmeridgian spread of the coral–sponge-microbialite reefs along the Tethyan European passive margin.

Comparative geochemical study on Furongian–earliest Ordovician (Toledanian) and Ordovician (Sardic) felsic magmatic events in south-western Europe: underplating of hot mafic magmas linked to the opening of the Rheic Ocean

Abstract. A geochemical comparison of early Palaeozoic felsic magmatic episodes throughout the south-western European margin of Gondwana is made and includes (i) Furongian–Early Ordovician (Toledanian) activities recorded in the Central Iberian and Galicia–Trás-os-Montes zones of the Iberian Massif, and (ii) Early–Late Ordovician (Sardic) activities in the Eastern Pyrenees, Occitan Domain (Albigeois, Montagne Noire and Mouthoumet massifs) and Sardinia. Both phases are related to uplift and denudation of an inherited palaeorelief, and stratigraphically preserved as distinct angular discordances and paraconformities involving gaps of up to 22 million years. The geochemical features of the predominantly felsic Toledanian and Sardic activities point to a predominance of magmatic byproducts derived from the melting of metasedimentary rocks, rich in SiO2 and K2O and with a peraluminous character. Zr ∕ TiO2, Zr ∕ Nb, Nb ∕ Y and Zr vs. Ga ∕ Al ratios, and rare-earth element (REE) and εNd(t) values suggest the contemporaneity, for both phases, of two geochemical scenarios characterized by arc and extensional features evolving to distinct extensional and rifting conditions associated with the final outpouring of mafic tholeiite-dominant lava flows. The Toledanian and Sardic magmatic phases are linked to neither metamorphism nor penetrative deformation; on the contrary, their unconformities are associated with foliation-free open folds subsequently affected by the Variscan deformation. The geochemical and structural framework precludes subduction-generated melts reaching the crust in a magmatic arc-to-back-arc setting and favours partial melting of sediments and/or granitoids in the lower continental crust triggered by the underplating of hot mafic magmas related to the opening of the Rheic Ocean.

Evolution of a salt-rich transtensional rifted margin, eastern North Pyrenees, France

In this field study we reinterpret the narrow eastern North Pyrenean Zone, France, as an inverted salt-rich transtensional rift system based on identification of halokinetic depositional sequences across rift platform to distal rift margin domains with a cumulative throw of >2.8 km on steep Cretaceous faults. The rift platform records extension on detached rotational faults above Triassic evaporites from Jurassic to Aptian with uplift and erosion during the Albian. Transtensional Aptian–Albian minibasins align along the salt-rich rift margin fault zone. In the Aptian–Albian main rift large en echelon synclinal minibasins developed between salt walls, although Jurassic diapiric evolution is likely. Upper Cretaceous units locally record continuing diapirism. The Boucheville and Bas Agly depocentres, altered by synrift HT metamorphism, form the distal rift domain terminating south against the North Pyrenean Fault. The narrowness of the Pyrenean rift, shape of minibasins, en echelon oblique synclinal depocentres and folds coupled with a discontinuous distribution and intensity of HT metamorphism support a transtensional regime along the Iberia–Europe plate margin during late Early and early Late Cretaceous. In this model, the distal European margin comprises deep faults limiting laterally discontinuous crustal domains and ‘hot’ pull-apart basins with mantle rocks directly beneath sedimentary cover. Supplementary material : A table summarizing the stratigraphy of the NE Pyrenees and an interpreted Google Earth view of the Quillan syncline and minibasin are available at https://doi.org/10.6084/m9.figshare.c.5100036

Reconstructing the pre-Variscan puzzle of Cambro-Ordovician basement rocks in the southwestern European margin of Gondwana

Abstract A Cambro-Ordovician palaeogeographical restoration of the southwestern European margin of Gondwana is proposed based on the relative positions of Variscan tectonostratigraphic units. Four palaeogeographical proximal–distal transects are recognized and comprise: (i) the Cantabrian, West Asturian-Leonese, Central Iberian/Central Armorican and Ossa-Morena/North Armorican zones and domains of the Iberian and Armorican massifs, respectively; (ii) the South Armorican Domain and its lateral prolongation into the Thiviers-Payzac unit and the Occitan Domain, including the transect from the Axial, southern and northern Montagne Noire, and the Albigeois-southern Cévennes unit; (iii) the southern and northern sides of the Canigó Massif in the Eastern Pyrenees; and (iv) the External Zone and the External and Internal nappes of Sardinia. Two geodynamic scenarios are recognized controlled by the presence/absence of: (i) the Furongian–Early Ordovician (Toledanian or ‘lacaune normande’) break-up unconformity across the Ossa-Morena/North Armorican and Central Iberian/Central Armorican belts; (ii) the Early–Late Ordovician (Sardic) Phase across the Occitan and Pyrenean domains and SW Sardinia; and (iii) the migration of peaks in trilobite and cinctan (echinoderm) diversity. Other similar palaeogeographical shifts are recognized in zircon provenance patterns, the occurrence of climatically sensitive subtropical facies and mineral indicators across platform–basinal transects along the Gondwana margin. This multidisciplinary framework is proposed as a preliminary step in the quest to produce more tightly constrained Early Paleozoic reconstructions along southwestern Europe.