Abstract One of the main challenges facing geological storage is to identify cost-effective methodological workflows for characterizing and monitoring geological storage sites. In the framework of the ALGECO2 project, led by the IGME (Geological and Mining Institute, Spain), a preliminary study of the Lopín site in the NE of Spain indicated conditions were promising for geological storage of CO 2 . However, the poor quality of the legacy seismic reflection data precluded thorough characterization. Within the H2020 PilotSTRATEGY project, one of the possible selected target reservoirs was the Lopín structure. In order to characterize its geometry and physical properties as required to properly evaluate its storage potential, IGME applied a new emerging methodology that integrates reinterpreted reflection seismic data with newly acquired and interpreted gravity, passive seismic and petrophysical data. This methodology was successfully applied along one seismic profile. In this paper, we present the results of this integration as the first step towards characterizing the site and evaluating its suitability for storage.

Abstract In order to portray the main differences and similarities between the Northeastern Variscan segments (French Massif Central (FMC), Vosges, Black Forest and Bohemian Massif (BM)), we review their crustal-scale architectures, the specific rock associations and lithotectonic sequences, as well as the ages of the main magmatic and metamorphic events. This review demonstrates significant differences between the ‘Moldanubian’ domains in the BM and the FMC. On this basis we propose distinguishing between the Eastern and Western Moldanubian zones, while the Vosges/Black Forest Mountains are an intermediate section between the BM and the FMC. The observed differences are the result of, first, the presence in the French segment of an early large-scale accretionary system prior to the main Variscan collision and, second, the duration of Saxothuringian/Armorican subduction, which generated long-lived magmatic arc and back-arc systems in the Bohemian segment, while the magmatic activity in the FMC was comparably short-lived.

Abstract A geological synthesis of the Palaeozoic Vosges Mountains (NE France) is presented using existing observations and new data. The geodynamic evolution involves: (1) Early Palaeozoic sedimentation and magmatism; (2) Late Devonian subduction triggering back-arc spreading; (3) early Lower Carboniferous continental subduction, continent–continent collision and polyphase deformation and metamorphism of the orogenic root; and (4) late Lower Carboniferous orogenic collapse driven by thermal weakening of the middle crust. The evolution is integrated within the framework of the European Variscan Belt. The Northern Vosges comprise sediments of Rhenohercynian affinity separated from Teplá-Barrandian metasediments by a Lower Carboniferous magmatic arc. The latter is correlated with the Mid-German Crystalline Rise, and is ascribed to the south-directed subduction of the Rhenohercynian Basin. The Saxothuringian–Moldanubian suture is thought to be obliterated by the magmatic arc, while the Lalaye–Lubine Fault is interpreted as the Teplá-Barrandian–Moldanubian boundary. The Central Vosges are paralleled with the Moldanubian domain of the Bohemian Massif where identical lithologies record the Devonian–Carboniferous SE-directed subduction of the Saxothuringian passive margin below the Moldanubian upper plate. The Southern Vosges represent the upper Moldanubian crust and are linked to the southern Black Forest. The presence of an oceanic domain to the south of the Vosges–Black Forest remains unclear. Supplementary material: List of radiometric ages used for probability plots is available at http://www.geolsoc.org.uk/SUP18734 .

Abstract A correlation between allochthonous units exposed in the NW Iberian Massif and the southern Armorican Massif is carried out based on lithological associations, structural position, age and geochemistry of protoliths and tectonometamorphic evolution. The units on both sides of the Bay of Biscay are grouped into Upper, Middle and Lower allochthons, whereas an underlying allochthonous thrust sheet identified in both massifs is referred to as the Parautochthon. The Lower Allochthon represents a fragment of the outermost edge of Gondwana that underwent continental subduction shortly after the closure of a Palaeozoic ocean which, in turn, is represented by the Middle Allochthon. The latter consists of supra-subduction ophiolites and metasedimentary sequences alternating with basic, mid-ocean ridge basalt (MORB)-type volcanics, with inheritances suggesting the proximity of a continental domain. Seafloor spreading began at the Cambro-Ordovician boundary and oceanic crust was still formed during the Late Devonian, covering the lifetime of the Rheic Ocean, which is possibly represented by the Middle Allochthon. The opening of the oceanic domain was related to pulling apart the peri-Gondwanan continental magmatic arc, which is represented by the Upper Allochthon.

Abstract Geological mapping and structural investigations were carried out in the eastern rim of the Morais Allochthonous Complex in NE Portugal (NW Iberian Massif) along the first-order tectonic boundary between the lower part of the Galicia–Trás-os-Montes Zone (the parautochthonous Schistose Domain) and the autochthonous Central Iberian Zone. The aim was to correlate the Palaeozoic stratigraphic pile of both domains, and to establish their pre- and synorogenic Variscan evolution. An Early Palaeozoic volcanic complex forms part of the pre-orogenic record of the parautochthonous Schistose Domain. It includes two volcanic units, the oldest of which is described for the first time in this work and is named the Mora Volcanics. It is a bimodal volcanic suite with basic to acid rocks which has yielded a late Cambrian age ( c. 493 Ma). Above the Mora Volcanics, the Saldanha Volcanics show petrographic, geochemical and age ( c. 483 Ma) similarities to the Ollo de Sapo Formation, a volcano-detritic ensemble found in the autochthonous domain of NW and Central Iberia. The stratigraphic record and the geochemical signatures of both volcanic units indicate that they were originated by fast partial melting induced by extension along the northern Gondwana margin at the Cambro-Ordovician boundary, coeval with the opening of the Rheic Ocean.

Abstract The sediments of the Mauges Unit located in the internal zone provide an opportunity of studying the evolution of relief during Palaeozoic time. U–Pb dating on zircon and 39 Ar/ 40 Ar on white mica are used to constrain the age and nature of the sources. The first relief identified is marked by an Early Devonian unconformity interpreted as the opening of a northern back-arc basin. Detrital minerals are first reworked from underlying layers indicating a local supply. Magmatic zircons at c. 400 Ma then record the emergence of a magmatic arc. During the Middle Devonian, the gap in the sedimentary record is attributed to an emersion followed by the disappearance of the relief during the Late Devonian. At the Devonian–Carboniferous boundary, the main collision is followed by the onset of a relief. The continental sedimentation in the Ancenis Basin (late Tournaisian–Viséan) is a coarsening-upwards megasequence indicating an increasing and/or approaching relief. The detrital minerals record the progressive exhumation of Variscan metamorphic (mica at c. 350 Ma) and magmatic rocks (zircons at c. 390–340 Ma). The Serpukhovian–Bashkirian sedimentation records the erosion of a proximal metamorphic source (Champtoceaux with micas at c. 350–340 Ma) showing a much shorter drainage system. Supplementary material: Sample coordinates and U–Pb on zircon and 39 Ar/ 40 Ar on white mica analyses are available at http://www.geolsoc.org.uk/SUP18730 .

Abstract This paper summarizes the current knowledge on the nature, kinematics and timing of movement along major tectonic boundaries in the Bohemian Massif and demonstrates how the Variscan plutonism and deformation evolved in space and time. Four main episodes are recognized: (1) Late Devonian–early Carboniferous subduction and continental underthrusting of the Saxothuringian Unit beneath the Teplá–Barrandian Unit resulted in the orogen-perpendicular shortening and growth of an inboard magmatic arc during c. 354–346 Ma; (2) the subduction-driven shortening was replaced by collapse of the Teplá–Barrandian upper crust, exhumation of the high-grade (Moldanubian) core of the orogen at c. 346–337 Ma and by dextral strike-slip along orogen-perpendicular NW–SE shear zones; (3) following closure of a Rhenohercynian Ocean basin, the Brunia microplate was underthrust beneath the eastern flank of the Saxothuringian/Teplá–Barrandian/Moldanubian ‘assemblage’; this process commenced at c. 346 Ma in the NE and ceased at c. 335 Ma in the SW; and (4) late readjustments within the amalgamated Bohemian Massif included crustal exhumation and mainly S-type granite plutonism along the edge of the Brunia indentor at c. 330–327 Ma, and peripheral tectonothermal activity driven by strike-slip faulting and possibly mantle delamination around the consolidated Bohemian Massif's interior until late Carboniferous–earliest Permian times.

Abstract Middle Devonian–Permian magmatic rocks from the northern Vosges Mountains show temporal and chemical variations which are linked to the continuous subduction of the Rhenohercynian oceanic crust and the Avalonian Devonian passive margin underneath the Saxothuringian continental crust. Major and trace elements and Sr–Nd isotopes of the northern Vosges basic to acidic magmatic rocks show that they evolved through time from: (1) Middle Devonian tholeiitic to calc-alkaline volcanic Rabodeau–Schirmeck sequence derived from partial melting of a depleted mantle, with these primary magmas having triggered anatexis of young crustal material of the Saxothuringian crust; (2) calc-alkaline Bande Médiane volcanic belt ( c. 334 Ma), diorite and Hohwald granodiorite intrusion ( c. 329 Ma) originated from enriched mantle contaminated and metasomatized by fluids expelled from a subduction zone; (3) high-K calc-alkaline Belmont granite ( c. 318 Ma), whose chemical signature suggests magma-mixing between enriched mantle-derived melts and magmas from a young crustal source; (4) Mg–K Younger granite ( c. 312 Ma) might be related to partial melting of enriched mantle which interacted with juvenile crustal material; and (5) Kagenfels S-type granite and Permian volcanic rocks generated by anatexis of meta-igneous and minor metasedimentary rocks. Supplementary material: Chemical analyses of biotite and amphibole of the northern Vosges rocks are available at http://www.geolsoc.org.uk/SUP18740 .

Abstract The Variscan metamorphic evolution of the autochthonous domain of NW and Central Iberia is characterized by a Barrovian gradient followed by a high-temperature–low-pressure (HT/LP) event associated with voluminous granite magmatism. The structural, metamorphic and magmatic histories of the region are described briefly and the relations between them are explained. A coherent model for evolution of the continental crust is proposed using published radiometric ages, thermal models and seismic reflection profiles. The metamorphic evolution, including the high-temperature event, is explained by crustal thickening resulting from the Gondwana–Laurussia collision followed by a period of thermal relaxation and a long-lasting extensional stage. The fact that the highest temperatures were reached in the core of the Central Iberian arc, partly occupied by remnants of a huge allochthonous nappe stack, is discussed in relation to both the emplacement of the allochthon and subsequent oroclinal bending. The overburden provided by the allochthonous pile was decisive in triggering the high-temperature event. Orocline development mostly occurred later and had no significant effect on the metamorphic evolution, although it was important for the present localization of gneiss domes and granitoids. The possible role of the mantle in supplying additional heat to explain the HT/LP event is also discussed. It would seem that little mantle contribution was needed and there are no strong arguments for mantle delamination, although some kind of mantle–crust interaction is expected beneath the hot regions presently occupying the core of the Central Iberian arc.

Abstract Variscan massifs of NE Iberia occur along the Pyrenees, Catalan Coastal Ranges, Iberian Range and Minorca. Despite the effects of the Alpine cycle, which involve localized reworking, tilting, translation of basement units and blocks drifting, the Variscan evolution can be reconstructed. Geological features evidence significant differences across the zones in the north, with high-grade metamorphic rocks, structural domes and syntectonic plutons more internal than the zones in the south, where unmetamorphosed and low-grade rocks are present along with undeformed late- to post-tectonic plutons. This setting contradicts existing schemas where this part of the Variscan belt is located in an external foreland. Variscan structures evidence bulk transpression gradually evolving from a NNW–SSE-directed crustal shortening to NW–SE wrench-dominated tectonics. The low-pressure–high-temperature (LP/HT) metamorphic peak and magmatism coincide with the latest stages of the NNW–SSE event. There is no field evidence based on penetrative structures for a widespread late orogenic extensional collapse.

Abstract The Variscan segment of the Pyrenees is well suited to study the timing of crustal-scale deformations as crustal flow and gneiss dome formation. This has been constrained from a synthesis of available structural and geochronological data of intrusive rocks, as well as new zircon U–Pb age determinations via laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). After a stage of moderate thickening by fold–thrust belt development in the upper crust between 323 and 308 Ma, the Variscan segment of the Pyrenees experienced crustal flow at c. 306 Ma and then gneiss dome formation at c. 304 Ma. Localization of the deformation along reverse-dextral shear zones occurred at c. 300 Ma. The Variscan segment of the Pyrenees recorded a high-temperature regime, which allowed crustal flow of the middle crust, but with limited amounts of heat which induced rapid cooling. The development of this enigmatic orogenic segment of the Variscan belt is closely contemporaneous with the formation of the Cantabrian Orocline and could correspond to a lithospheric-scale shear zone that accommodated buckling of the orocline. Late Variscan lithospheric delamination and asthenospheric upwelling associated with buckling in the core of the Cantabrian Orocline could explain the short-period high-temperature regime in the Variscan segment of the Pyrenees. Supplementary material: Review of published U–Th–Pb, Ar–Ar and K–Ar ages of granites from the Axial Zone of the Pyrenees; LA-ICP-MS U–Pb dating methodology (Clermont-Ferrand, France); and zircon LA-ICP-MS U–Pb data for Ax-les-Thermes, Carançà, Mont-Louis and Cauterets granites are available at http://www.geolsoc.org.uk/SUP18729 .