Abstract The Southern North Sea Basin area, stretching from the UK to the Netherlands, has a rich hydrocarbon exploration and production history. The past, present and expected future hydrocarbon and geothermal exploration trends in this area are discussed for eight key lithostratigraphic intervals, ranging from the Lower Carboniferous to Cenozoic. In the period between 2007 and 2017, a total of 95 new hydrocarbon fields were discovered, particularly in Upper Carboniferous, Rotliegend and Triassic reservoirs. Nineteen geothermal systems were discovered in the Netherlands onshore, mainly targeting aquifers in the Rotliegend and Upper Jurassic/Lower Cretaceous formations. Although the Southern North Sea Basin area is mature in terms of hydrocarbon exploration, it is shown that with existing and new geological insights, additional energy resources are still being proven in new plays such as the basal Upper Rotliegend (Ruby discovery) for natural gas and a new Chalk play for oil. It is predicted that hydrocarbon exploration in the Southern North Sea Basin area will probably experience a slight growth in the coming decade before slowing down, as the energy transition further matures. Geothermal exploration is expected to continue growing in the Netherlands onshore as well as gain more momentum in the UK.

Abstract Seismic mapping of key Paleozoic surfaces in the East Irish Sea–North Channel region has been incorporated into a review of hydrocarbon prospectivity. The major Carboniferous basinal and inversion elements are identified, allowing an assessment of the principal kitchens for hydrocarbon generation and possible migration paths. A Carboniferous tilt-block is identified beneath the central part of the (Permian–Mesozoic) East Irish Sea Basin (EISB), bounded by carbonate platforms to the south and north. The importance of the Bowland Shale Formation as the key source rock is reaffirmed, the Pennine Coal Measures having been extensively excised following Variscan inversion and pre-Permian erosion. Peak generation from the Bowland source coincided with maximum burial of the system in late Jurassic–early Cretaceous time. Multiphase Variscan inversion generated numerous structural traps whose potential remains underexplored. Leakage of hydrocarbons from these into the overlying Triassic Ormskirk Sandstone reservoirs is likely to have occurred on a number of occasions, but currently unknown is how much resource remains in place below the Base Permian Unconformity. Poor permeability in the Pennsylvanian strata beneath the Triassic fields is a significant risk; the same may not be true in the less deeply buried marginal areas of the EISB, where additional potential plays are present in Mississippian carbonate platforms and latest Pennsylvanian clastic sedimentary rocks. Outside the EISB, the North Channel, Solway and Peel basins also contain Devonian and/or Carboniferous rocks. There have, however, been no discoveries, largely a consequence of the absence of a high-quality source rock and a regional seal comparable to the Mercia Mudstone Group and Permian evaporites of the Cumbrian Coast Group in the EISB.

Abstract The northwestern part of the Scandinavian Caledonides, formed by SE- to ESE-directed thrusting through the Neoproterozoic W. Baltica continental shelf, contains numerous small and often isolated outcrops of diamictite and associated strata. No precise biostratigraphic or isotopic data are available to constrain the age of these sediments, but, on the basis of their stratigraphic position, most are correlated with the Mortensnes Formation (Fm.) in E. Finnmark and also presumed to be of glaciogenic origin. The Mortensnes Fm. has been correlated with the 580 Ma Gaskiers glacial event on the basis of δ 13 C isotope studies. Structurally, the deposits occur in the Autochthon (below the Torneträsk Fm.), within an external imbricate zone (Lower Allochthon), within cover successions lying unconformably on allochthonous basement (Window Allochthon) palaeogeographically derived from below or outboard of the Lower Allochthon and, more rarely, within the Middle Allochthon, derived from outboard of the Window Allochthon. Evidence for a glaciogenic origin is typically poor or lacking. Only in the Komagfjord Antiformal Stack (Window Allochthon), where an up to 40-m-thick succession of three fining upwards cycles has been mapped, are the deposits comparable in thickness and complexity to the Mortensnes Fm. Other sequences are sometimes <1 m thick and unconformably overlain by post-‘glacial’ deposits. The Vakkejokk Breccia, a submarine slump in the Torneträsk area of the Autochthon closely underlies the correlative Precambrian–Cambrian lithostratigraphic boundary in E. Finnmark but overlies the first appearance of the boundary marker fossil Treptichnus pedum . Although sometimes interpreted as periglacial, this seems unlikely in view of the 30–50° palaeolatitude during deposition. Calcite nodules (<1 cm size) in the Vakkejokk Breccia have previously been interpreted as glendonite, but the microstructure and palaeolatitude makes this unlikely; they are likely a replacement of gypsum. Diamictites of uncertain origin have also been found in the Ediacaran Lower Siltstone Member of the Torneträsk Fm. and unconformably under the ?Lower Cambrian Lomvatn Fm. in the Komagfjord Antiformal Stack.

Abstract Multidisciplinary investigations of the western margin of the East European Craton (EEC) by EUROPROBE projects since 1992 have confirmed that the Trans-European Suture Zone (TESZ) is the most fundamental lithospheric boundary in Europe, extending 2000 km from the North Sea to the Black Sea-Crimean region. The crust of the EEC is thicker and denser than that of Phanerozoic-accreted Europe, and the base of the lithospheric mantle significantly deeper. These characteristics persist throughout the length of the TESZ, despite the variation in age of the accreted crust along strike. Geological studies of key deep borehole cores and the limited outcrop data confirm that the crust of Phanerozoic-accreted Central Europe comprises a number of terranes, each thought to be derived from Gondwana during several episodes of rifting, ocean formation, ocean destruction and sequential accretion to the EEC throughout Palaeozoic time. There is still much discussion about the identity, provenance and history of these orogenic terranes. The process of accretion led to the formation of terrane-bounding orogenic sutures, which may be marked in outcrop by ophiolitic and eclogitic relics. Recognition of concealed sutures is obviously more difficult, and relies on a variety of geophysical techniques, used in an integrated way by multidisciplinary teams; the evidence from deep seismic reflection and refraction surveys, teleseismic tomography, magnetotelluric experiments and from geophysical potential-field modelling is crucial for such studies. Since the European Geotraverse, much has been learnt about the geometry of the Thor, Iapetus, Rheic, Saxo-Thuringian and Moldanubian oceanic sutures, through the crust and sometimes into the mantle. This has led to a much better understanding of the 3D crustal structure of the Western Accretionary Margin of the EEC, and the lithospheric processes that have shaped it. From this, the influence of tectonic heterogeneities within the orogenic crust on the development of post-orogenic structures and basins can be much better constrained.

Abstract Recent work in Central Europe, combined with emerging information about basement massifs in SE Europe and NW Turkey, permits a new look at the relationships between crustal blocks abutting the East European Craton (EEC) along the Trans-European Suture Zone (TESZ). The simplest model indicates that the end-Cambrian establishment of the Bruno-Silesian, Lysogory and Malopolska terranes close to their present location on the SW margin of the EEC formed a major promontory on this margin of the continent. Moesia may also have formed part of this block. Both late Ordovician accretion of Avalonia and early Carboniferous accretion of the Armorican Terrane Assemblage (ATA) attached new continental material around the Bruno-Silesian Promontory (BSP). Palaeozoic faunal affinities and inherited isotopic signatures similar to those of Avalonia seen in the Istanbul block of NW Turkey, and in minor thrust slices in Moravia and Romania, suggest that easternmost Avalonia was severed, on collision with the BSP, and migrated east along the southern margin of the EEC. Likewise, the similarities to the ATA of the Balkan, Istranca, Sakarya and eastern Pontides blocks suggests that more easterly components of the ATA were detached at the BSP and migrated east. All the newly accreted blocks contain similar Neoproterozoic basement indicating a peri-Gondwanan origin; Palaeozoic plume-influenced metabasite geochemistry in the Bohemian Massif may explain their progressive separation from Gondwana before their accretion to the EEC. Inherited ages from Avalonia contain a 1.5 Ga ‘Rondonian’ component arguing for proximity to the Amazonian Craton at the end of the Neoproterozoic; Armorican terranes lack such a component, suggesting that they have closer affinities with the West African Craton. Models showing the former locations of these terranes and the larger continents from which they rifted, or later became attached to, must conform to both these constraints and those provided by palaeomagnetic data. In the late Neoproterozoic and Palaeozoic, these smaller terranes, some containing Neoproterozoic ophiolitic marginal basin and magmatic arc remnants, probably fringed the end-Proterozoic supercontinent as part of a ‘Pacific-type’ margin. When this margin fragmented, most resulting fragments accreted to the EEC.

Abstract Palaeozoic Amalgamation of Central Europe summarizes recent research designed to clarify the timing, geometry and processes by which discrete terranes of Central Europe became amalgamated during the Palaeozoic Era. The area studied extends from the southern North Sea to Central Poland along the Trans-European Suture Zone, covering much of Germany, Denmark, Belgium, the Czech Republic and Poland. The 16 papers within the volume are divided into five sections: biostratigraphic/provenance evidence; isotopic constraints; petrological and geochemical evidence; structural evolution; seismic traverses and deep crustal structure. The first section contains papers summarizing continent-specific micropalaeontological and sediment provenance information backing current debates about microcontinent derivation and timing of their accretions to the proto-European continent, Baltica. The section on isotopic constraints discusses the use of isotopic dating to constrain the timing of accretions of rock units exposed in the northern Bohemian Massif, while the following section has more detailed studies of metamorphosed ophiolitic complexes adjoining palaeosutures in the same area. The two papers on the structural evolution of the area contrast a detailed review of the structural evolution of the Sudetes, with a broader, more regionally based hypothesis for the structural evolution of all Central Europe. The final section discusses models based on extensive seismic traverses in contrasting parts of the area - Belgium, the southern North Sea and Poland. This wide-ranging study thus encapsulates the most up-to-date ideas on the Palaeozoic amalgamation of Central Europe from the leading international researchers in the field. The volume will be of interest to those earth scientists in industry and academia with a broad-based interest in the construction of the European continent, primarily biostratigraphers, geophysicists, structural geologists and geochemists.

Abstract Multidisciplinary studies undertaken within the EU-funded PACE Network have permitted a new 3-D reassessment of the relationships between the principal crustal blocks abutting Baltica along the Trans-European Suture Zone ( TESZ ). The simplest model indicates that accretion was in three stages: end-Cambrian accretion of the Bruno-Silesian, Łysogóry and Małopolska terranes; late Ordovician accretion of Avalonia, and early Carboniferous accretion of the Armorican Terrane Assemblage ( ATA ), which had coalesced during Late Devonian — Early Carboniferous time. All these accreted blocks contain similar Neoproterozoic basement indicating a peri-Gondwanan origin: Palaeozoic plume-influenced metabasite geochemistry in the Bohemian Massif in turn may explain their progressive separation from Gondwana before their accretion to Baltica, although separation of the Bruno-Silesian and related blocks from Baltica during the Cambrian is contentious. Inherited ages from both the Bruno-Silesian crustal block and Avalonia contain a 1.5 Ga ‘Rondonian’ component arguing for proximity to the Amazonian craton at the end of the Neoproterozoic: such a component is absent from Armorican terranes, which suggests that they have closer affinities with the West African craton. Models showing the former locations of these terranes and the larger continents from which they rifted, or to which they became attached, must conform to the above constraints, as well as those provided by palaeomagnetic data. Hence, at the end of the Proterozoic and in the early Palaeozoic, these smaller terranes, some of which contain Neoproterozoic ophiolitic marginal basin and magmatic arc remnants, probably occurred within the end-Proterozoic supercontinent as part of a ‘Pacific-type’ margin, which became dismembered and relocated as the supercontinent fragmented.

Abstract In central Europe, three crustal units, i.e. the Małopolska, the Łysogóry and the Bruno-Silesia, can be recognized by basement data, faunas and provenance of clastic material in the Cambrian clastic rocks. They are now situated within the Trans-European Suture Zone, a tectonic collage of continental terranes bordering the Tornquist margin of the palaeocontinent of Baltica, but during the Cambrian their position in relation to each other and to Baltica was different from today. These units are exotic terranes in respect to Baltica and are interpreted as having been derived from the Cadomian margin of Gondwana. Their detachment is probably related to the final break-up of the supercontinent Rodinia at c. 550–590 Ma. New detrital zircon and muscovite age data provide evidence that Małopolska was derived from the segment of the Cadomian orogen that bordered the Amazonian Craton. It must have already separated from Gondwana in Early Cambrian time (some 40–50 Ma before Avalonia became detached and began its rapid drift). The accretion of Małopolska to Baltica occurred between late mid-Cambrian and Tremadocian times. Both palaeontological and provenance evidence demonstrate that Małopolska and not Avalonia was the first terrane to join the Baltica palaeocontinent. This event initiated the progressive crustal growth of the European lithosphere, which continued during Phanerozoic times and led to the formation of modern Europe.

Abstract Following recognition of the Vendian to mid-Ordovician rotation of Baltica, with more than 55° of that rotation occurring in the Upper Cambrian and Lower Ordovician, the Tornquist Margin of Baltica must have faced northwards towards Laurentia and the Panthalassic Ocean, rather than, as now, southwestwards towards Gondwana (including Avalonia). Unequivocally Baltic endemic trilobite, brachiopod and other faunas are known from both the Cambrian and the Ordovician of the Holy Cross Mountains, Poland, and from both parts of them, i.e. the Małopolska Block and the Łysogóry Block. Whether or not these two blocks were united into a single terrane or were separate as two terranes is equivocal from the faunal evidence, and there is no faunal evidence of substantial strikeslip faulting of the blocks in relation to the main Baltic craton: they are perceived as having made up part of the margin of Baltica itself. However, both Holy Cross Mountain blocks were different and palaeogeographically separate from the Bruno-Silesian Block, whose continental origins are yet to be finally determined. The Ordovician clastic sediments at both Rügen, north Germany, and Pomerania, NW Poland, have yielded no macrofossils other than graptolites, but microfossils (acritarchs and chitinozoa) are interpreted as having been deposited at relatively high palaeolatitudes, i.e. at a higher palaeolatitude than Baltica, and may have been deposited in an ocean basin within the Tornquist Ocean between Baltica and Avalonia.

Abstract A review is given of recently published and new data on Avalonia east of the Midlands Microcraton. The three megasequences from Cambrian to mid Devonian described in Wales and Welsh Borderland are also present east of the Midlands Microcraton (Brabant Massif, Condroz, Ardennes, Remscheid and Ebbe inliers, Krefeld high). The three megasequences are caused by a tectonic driving mechanism and are explained by three different geodynamic contexts: an earlier phase with extensional basins or rifting and rather thick sequences, when Avalonia was still attached to Gondwana; a second phase with a shelf basin with moderately thin sequences when Avalonia was a separate continent and a later phase with a shelf or foreland basin development and thick sequences. Deformation of the megasequences 1 and 2 or 1 to 3 varies between areas. In Wales and the Lake District the Acadian phase is long-lived and active from early to mid Devonian. In the Ardennes inliers a deformation is active between the late Ordovician and the Silurian (Ardennian Phase), with a similar intensity as the core of the Brabant Massif, when present erosion levels are compared. The Brabant Massif is partly deformed by the long-lived Brabantian Phase from late Silurian till early mid Devonian. Both the Ardennes inliers and the Brabant Massif are not classic orogenic belts, only slate belts where no more than the epizone is reached at present erosion levels. Areas supposedly close to the microcraton or basement are nearly undeformed (SW Brabant Massif and central Condroz). A model of anticlockwise rotation of Avalonia of about 55° from Caradoc to Emsian is proposed to explain the deposition setting of megasequence 3 and the subsequent Acadian and Brabantian deformation. Immediately after the Avalonian microcontinent touched Baltica in Caradoc times it created a short-lived subduction magmatic event from The Wash to the Brabant Massif and soon after the magmatism ended a foreland basin developed. Possibly during and after that development a long-lived and slow compressional event occurred, leading to the deformation of the Anglo-Brabant Deformation Belt. In the early Devonian, contemporaneous with the shortening of the Anglo-Brabant Deformation Belt, extension occurred in the Rheno-Hercynian Zone, possibly caused by the same slow rotation of Avalonia. More evidence emerges that Avalonia east of the Midlands Microcraton comprises not one but probably two terranes: the remnant of the palaeocontinent Avalonia, and what is called the palaeocontinent Far Eastern Avalonia; the latter is only occasionally observed in the few deep boreholes into the Heligoland-Pomerania Deformation Belt, in southern Denmark, NE Germany and NW Poland, with scant available indirect data in between indicating only Proterozoic basement and no Caledonian deformation. For Far Eastern Avalonia a similar palaeogeographical history is postulated as Avalonia, with rifting from Gondwana in Arenig or earlier times, collision with Baltica before the mid-Ashgill and deformation between the late Ordovician and latest Silurian. The Avalonia concept might need to be expanded to an ‘Avalonian Terrane Assemblage’ with cratonic cores and small short-lived oceans as in the Armorican Terrane Assemblage.

Abstract Tectonically disturbed Ordovician rocks penetrated by deep drillholes in Pomerania, NW Poland (Koszalin-Chojnice Zone) belong to the Heligoland-Pomerania Deformation Belt. Earlier data demonstrate that the Avalonia-Baltica collision occurred in Late Ordovician times, but in Pomerania, the timing of convergence has not been ascertained, and it is uncertain if the rocks underneath the Koszalin-Chojnice Zone belong to Avalonia or Baltica. Data from chitinozoans, organic-walled Palaeozoic microfossils with applications in biostratigraphy and palaeobiogeography, were assessed from ten boreholes (Brda 2; Brda 3; Chojnice 5; Karsina 1; Kościernica 1; Nowa Wieś 1; Okunino 1; Sarbinowo 1; Skibno 1; Wyszebórz 1) to address these problems. The results improve the biostratigraphy of the cores and demonstrate that the youngest Ordovician rocks are of a Burrellian (early mid Caradoc) to Cheneyan (late mid Caradoc) age. Because these rocks are interpreted as forming part of the deformation belt, the obtained ages put a lower age limit on the initiation of foreland basin sedimentation on the foreland of the orogeny, i.e. the Baltic platform. Quantitative comparison of chitinozoan assemblages demonstrates a high level of similarity between Pomerania and Avalonia. Together, Pomerania and Avalonia show greater similarity to Baltoscandia than to North Gondwana, supporting the idea that the Tornquist Ocean had narrowed significantly in early Caradoc times.

Abstract Strongly tectonized Ordovician rocks appear in the Ebbe Anticline (Rheinisches Schiefergebirge), West Germany. These fine-grained detrital rocks of the Herscheider Schichten are divided into the Plettenberger Bänderschiefer. Unterer (Kiesberter) Tonschiefer, (Rahlenberger) Grauwackenschiefer, and the Oberer (Solinger) Tonschiefer. The scope of this investigation was to improve the dating of the entire Ordovician succession. but especially the Oberer (Solinger) Tonschiefer. We used chitinozoans. Palaeozoic microfossils of high biostratigraphic value, and Nd isotopes, which previously have been used for correlation and terrane affinity analysis. Chitinozoan preservation is poor, but some taxa could be confidentially identified to the species level. The εNd(t) values obtained from the Ordovician succession range from -8.0 to -9.2. Joint evaluation of chitinozoan and Nd isotope data together with previously known age-ranges suggest the following ages for the Herscheider Schichten: Plettenberger Bänderschiefer (early Abereiddian, earliest Llanvirn), Unterer (Kiesberter) Tonschiefer (early to mid Abereiddian, early Llanvirn). (Rahlenberger) Grauwackenschiefer (Aurelucian, earliest Caradoc), and Oberer (Solinger) Tonschiefer (late Caradoc). The Ebbe εNd(t) values are most readily compared with εNd(t) values from Avalonia. and we therefore support the inclusion of the Ordovician rocks of the Ebbe Anticline in that palaeocontinent.

Abstract The West Sudetes (NE margin of the Bohemian Massif) consist of a complex mosaic of several tectonometamorphic units juxtaposed during the Variscan orogeny. The polyphase Variscan tectonothermal development of the West Sudetes was determined by 40 Ar/ 39 Ar ages of single grains and mineral concentrates. Late Famennian (359 Ma) mica ages from the high-grade Góry Sowie Block suggest continuous uplift after a Late Devonian high temperature-low pressure (HT-LP) event contemporaneous with the end of subduction-related high pressure-low temperature (HP-LT) metamorphism in the East Krkonoše Complex. Mid-Late Devonian high pressure events in the Krkonoše-Jizera Terrane and Orlica-Śnieżnik Dome are followed by coeval high temperature events between 345 and 335 Ma (Viséan). The latter are interpreted as consequence of uplift, and decompression during overthrusting of both complexes on their forelands. Subsequent small- to large-scale shear movements dated at around 325–320 Ma (early Namurian) affected the Orlica-Śnieżnik Dome, Krkonoše-Jizera Terrane, including the Intra-Sudetic Fault, and also the eastern Lusatian Granitoid Complex. They were accompanied by contemporaneous emplacement of the Krkonoše-Jizera pluton. The upper limit of the tectonometamorphic and magmatic activity is dated at 314–312 Ma (Namurian/Westphalian boundary). The final juxtaposition of the diversified tectonometamorphic units, which constitute the West Sudetes, took place in early Namurian times.

Abstract The West Sudetes, NE Bohemian Massif, comprises several suspect terranes accreted to the margins of Laurussia during Variscan orogenesis. Whole rock REE and Sm-Nd isotope data for seven separate provinces (Izera, Kaczawa, Rudawy Janowickie and Kłodzko complexes; Fore-Sudetic and Góry Sowie Blocks; Slęża Ophiolite) suggest involvement of a variety of crustal and mantle sources. Felsic metasedimentary rocks (εNd(t) = −8.3 to −5.0) have two stage T DM ages of 1.9 to 1.5 Ga, whereas acidic metavolcanic rocks and granite gneisses (εNd(t) = −5.4 to +0.8) have two stage T DM ages of 1.5 to 1.0 Ga. A range of sources is implicated: predominantly Archaean and Palaeoproterozoic sources for the metasedimentary rocks, and Archaean. Palaeoproterozoic and Neoproterozoic to early Palaeozoic sources for the meta-igneous felsic lithologies. LREE depleted tholeiitic metabasites ((Ce/Yb) N = 0.8 to 3.4) generally have εNd(t) = +4.0 to +9.1, indicating derivation from depleted mantle asthenosphere. LREE enriched meta-alkali basalts ((Ce/Yb) N = 4.6 to 10.1) with εNd(t) between +3.1 and +7.0 implicate utilization of enriched mantle asthenosphere. Analogous lithologies from elsewhere in the Sudetes, North Bohemian Massif and the Armorican Terrane Assemblage have similar REE abundances, εNd values and T DM ages. Complexes previously considered to have had disparate Neoproterozoic to early Palaeozoic histories may be integrated into a unifying geodynamic model of derivation from the North Gondwanan (North African) margin during a widespread episode of continental margin break-up.

Abstract The Mariánské-Lázně Complex is a Cambro-Ordovician terrane of oceanic affinity tectonically emplaced between the Saxothuringian Zone and Teplá-Barrandian Unit, NW Czech Republic. It forms a SE-dipping allochthonous body that comprises the largest contiguous exposure of metamorphosed basic and ultrabasic lithologies in the Bohemian Massif. Petrographic evidence indicates that a significant proportion of protoliths underwent eclogite facies metamorphism (570 to 720°C, 1.44 to 2.10 GPa), followed by an increase in temperature (up to around 800°C) and a subsequent widespread retrograde amphibolite facies event (550 to 680 °C, 0.75 to 1.20 GPa). New major and trace element geochemical analyses of metamorphosed basic and ultrabasic lithologies indicate that they exhibit geochemical characteristics attributable to a sea floor origin. The metabasites were generated at a spreading centre that interacted with deep-seated upwelling mantle asthenosphere. Separate, independently fractionating basic melt batches existed: these were derived from depleted and enriched asthenosphere and depleted sub-continental lithosphere sources. Geochemical correlation of the Mariánské-Lázně Complex with other early Palaeozoic metabasic provinces facilitates comparison of metabasic lithologies occurring in tectonically dislocated nappe pile thrust sheets, and allows delineation of important suture zones in the European Variscides.

Abstract The Ślęża Ophiolite is one of several thrust-bounded crustal slices dominated by metabasites in the western Sudetes. The apparent field association of serpentinites, gabbros and amphibolitic components led previous workers to consider that this lithological assemblage represented an ophiolite sequence. Fieldwork suggests that the ophiolite is now highly inclined, partly overturned, so that an ophiolitic pseudostratigraphy can be deduced, grading from serpentinites and gabbros in the south to metabasite lavas in the north. The recent discovery of pillow lava structures (at Gozdnica Hill, to the west of Sobótka town) confirms that the volcanic top of the ophiolite lies in the northern section, as might be expected from the ophiolite model. The gabbros have undergone greenschist facies metamorphism with the random development of low-grade amphibole. The volcanic portion of the sequence comprise metamorphosed dolerites and basalts partly within the contact aureole of the Variscan Strzegom-Sobótka granite. Previous work dated plagiogranites associated with the gabbros at about 400–420 Ma (U-Pb zircon ages). Geochemical data suggest that the gabbros are distinct and apparently not comagmatic with the volcanic section of sheeted dykes and lavas. The gabbros, in particular, although very depleted in incompatible elements are dissimilar to supra-subduction zone ophiolites, exhibiting instead N-MORB-like light REE depleted patterns. Depletion is both a feature of the cumulate character of many of the gabbros, as well as a source effect (especially the uniformly low Nb content). The metabasalts and metadolerites, on the other hand, are a well-evolved single comagmatic suite with high incompatible element contents, Zr/Y approximately 3–4, and generally flat to light REE-depleted patterns. The geochemical dichotomy of the plutonic and volcanic segments calls into question a simple interpretation of the body as a single-stage coherent stratiform ophiolite. Chemical comparison with Sudetic metabasites from within the nearby Rudawy-Janowickie and Kacazawa Complexes shows that the Ślęża metabasites have a number of features in common, including the presence of both low-Ti (gabbros) and high-Ti (dykes and lavas) chemical groups. The correlation of the gabbros, dykes and lavas with the low-Ti and high-Ti (Main Series) metatholeiites respectively, seen throughout the Bohemian Massif, as well as the Sudetes, places them within the regional collage of Palaeozoic crustal blocks separated by the Saxothuringian Seaway. Comparison with Bohemian Massif metabasites also indicates that sediment contamination of the Ślęża Ophiolite sources was not an important process and that an enriched plume source played no part in the generation of the ophiolitic melts. The two Ślęża chemical groups were derived from variably depleted asthenospheric mantle sources. Simple modelling suggests that the volcanic segment could have been derived by 10–15% partial melting of a depleted N-MORB source, whereas the plutonic segment represents around 30% partial melting of a more depleted source. To develop varying degrees of depletion in an oceanic environment, the two sources could be related via incremental partial melting of a shallow MORB-type source.

Abstract Bodies of coronitic metagabbro occur in the SW Mariánské Lázně Complex (MLC) and the adjacent Teplá Crystalline Unit (TCU) on the western margin of the Teplá-Barrandian Unit (TBU), Bohemian Massif. The characteristic structural, geochemical, petrographic, and metamorphic features of five groups of metagabbros and related rocks are presented, compared with other metabasites of the MLC and Zone of Erbendorff-Vohenstrauss (ZEV), and used to constrain the tectonometamorphic evolution of the western part of the TBU. The metagabbros are considered to be a younger intrusive member of the complicated lower crustal tectonic stack of Upper Proterozoic to Early Palaeozoic age which is formed by the Mariánské Lázně Complex and the Teplá Crystalline Unit together. It is proposed that a significant part of the metamorphic evolution of some parts of these units took place before the emplacement of metagabbros and granitoids at around 496–516 Ma. The sequence of metamorphic events is interpreted to have been as follows. Deep burial of primitive MORB type tholeiitic rocks (a) metamorphosed up to eclogite facies, followed by (b) uplift to lower crustal levels so that the partially exhumed rocks were juxtaposed with other lower/middle crustal rocks. Thermal relaxation (c) followed, with an episode of extension recorded in L-tectonites of amphibolite facies. Once this lithologically variegated stack was welded together, it was intruded by the Upper Cambrian-Lower Ordovician granitoids and gabbros (d). This pre-Variscan metamorphic event may be expressed at the supracrustal level by an unconformity between Upper Cambrian and Lower Ordovician rocks in the Barrandian. The final configuration of the units was established during the Variscan collision of the Teplá Barrandian terrane with Saxothuringia (e) in which the rocks of the MLC and TCU were thrust to the NW over the Saxothuringian para-autochthon. The accompanying metamorphic event reached upper amphibolite facies. The thermally relaxed rocks cooled rapidly, and pre-existing thrust planes were re-activated during the final extensional collapse.

Abstract A synthesis of published and new data is used to interpret the Sudetic segment of the Variscan belt as having formed by the accretion of four major and two or three minor terranes. From west to east the major terranes are (1) Lusatia-Izera Terrane, exposing Armorican continental basement reworked by Ordovician plutonism and Late Devonian-Carboniferous collision, showing Saxothuringian affinities; (2) composite Góry Sowie-Kłodzko Terrane characterized by multistage evolution (Silurian subduction, mid- to late Devonian collision, exhumation and extension, Carboniferous deformational overprint), with analogues elsewhere in the Bohemian Massif, Massif Central and Armorica; (3) Moldanubian (Gföhl) Terrane comprising the Orlica-Śnieżnik and Kamieniec massifs, affected by Early Carboniferous high-grade metamorphism and exhumation and (4) Brunovistulian Terrane in the East Sudetes, set up on Avalonian crust and affected by Devonian to late Carboniferous sedimentation, magmatism and tectonism. The main terranes are separated by two smaller ones squeezed along their boundaries: (1) Moravian Terrane, between the Moldanubian and Brunovistulian, deformed during Early Carboniferous collision, and (2) SE Karkonosze Terrane of affinities to the Saxothuringian oceanic realm, sandwiched betwen the Lusatia-Izera and Góry Sowie-Kłodzko (together with Teplá-Barrandian) terranes, subjected to high pressure-metamorphism and tectonized during Late Devonian-Early Carboniferous convergence. The Kaczawa Terrane in the NW, of oceanic accretionary prism features, metamorphosed and deformed during latest Devonian-Early Carboniferous times, may either be a distinct unit unrelated to closure of the Saxothuringian Ocean or represent a continuation of the SE Karkonosze Terrane.