Abstract The Scandian mountains in northwestern Sweden are dominated by the eastern part of the Scandinavian Caledonides, an orogen that terminated during the middle Paleozoic with Himalayan-style collision of the ancient continents of Baltica and Laurentia. In this foreland region, far-transported higher allochthons from an exotic continental margin (Rödingsfjället Nappe Complex) and underlying mostly oceanic-arc basin character (Köli Nappe Complex) were emplaced at least 700 km onto the Baltoscandian margin of Baltica. The thrust sheets below the Iapetus Ocean terranes were derived from the transition zone to Baltica (Seve Nappe Complex), comprising mainly siliciclastic metasedimentary rocks, hosting abundant metamorphosed c. 600 Ma mafic intrusions. They preserve evidence of subduction (eclogites, garnet peridotites and microdiamonds in host paragneisses), starting in the late Cambrian; exhumation continued through the Ordovician. Underlying allochthons derived from the outer margin of Baltica are less-metamorphosed Neoproterozoic sandstone-dominated successions, also intruded by Ediacaran dolerite dykes (Särv Nappes); they are located tectonically above similar-aged metasandstone and basement slices, devoid of dykes (Offerdal and Tännäs Augen Gneiss nappes and equivalents). Lowermost allochthons (Jämtlandian Nappes and equivalents), from the inner Baltoscandian margin, provide evidence of Cryogenian rifting, Ediacaran–Cambrian drifting and platformal sedimentation, followed by foreland basin development in the Ordovician and Silurian.

Abstract The Jämtlandian Nappes and their equivalents further north, belonging to the lower thrust sheets in the Caledonide orogen of Sweden, comprise a mega-duplex of Cryogenian–Silurian sedimentary rocks sandwiched between structurally higher allochthons and a basal décollement. Further west towards the hinterland, crystalline basement is increasingly involved in this thrusting, imbricate stacking occurring beneath the décollement in antiformal windows. The sedimentary successions were derived from the Cryogenian rifted margin of Baltica, the Ediacaran–Cambrian drifted margin, and Ordovician and Silurian foreland basins. During the Early–Late Ordovician (Floian–Sandbian), hinterland-derived turbidites were deposited in response to early Caledonian accretion of subducted complexes belonging to the outermost margin of Baltica, now preserved in the higher allochthons. Following a quiescent period during the Late Ordovician (Hirnantian) and early part of the Llandovery, collision of Laurentia and Baltica reactivated the foreland basins, with flysch and molasse deposition during the Llandovery–Wenlock. Collisional shortening during this Scandian orogenic episode continued into the Devonian. High- and ultrahigh-pressure (HP/UHP) metamorphism accompanied Baltica's underthrusting of Laurentia in the deep hinterland, and prominent basement-cored antiforms developed towards the foreland during the advance of the orogenic wedge over the foreland basin onto the Baltoscandian platform.

Abstract Nappes of continental outer and outermost margin affinities (Middle Allochthon) were transported from locations west of the present Norwegian coast and thrust eastwards onto the Baltoscandian foreland basin and platform. They are of higher metamorphic grade than underlying thrust sheets and most are more penetratively deformed. These allochthons are treated here in three groups. The lower thrust sheets comprise Paleoproterozoic crystalline basement (e.g. Tännäs Augen Gneiss Nappe) and greenschist facies, Neoproterozoic, siliciclastic metasedimentary rocks (e.g. Offerdal Nappe). These are overthrust by a Cryogenian−Ediacaran succession intruded by c. 600 Ma dolerites (Baltoscandian Dyke Swarm) with an affinity to mid-ocean ridge basalt containing normal to enriched incompatible element contents (Särv Nappes). The upper sheets are dominated by higher-grade allochthons (Seve Nappe Complex) with similar, mainly siliciclastic sedimentary protoliths, more mafic magmatism and some solitary ultramafic bodies. Within this early Ediacaran continent−ocean transition zone (COT) assemblage, generally metamorphosed in amphibolite facies, some nappes experienced migmatization, and eclogites are present. Evidence of ultrahigh-pressure metamorphism has been obtained from garnet peridotites and eclogites; recently, microdiamonds have been discovered in paragneisses. Subduction of the COT started by the late Cambrian and accretion continued through the Ordovician, prior to the Baltica–Laurentia collision. Thrusting of all these Middle allochthons onto the foreland basin exceeds a distance of 400 km.

Abstract Caledonian collision of continents Laurentia and Baltica, with at least 1000 km of lateral shortening, dominates the bedrock along the northern margins of the North Atlantic Ocean. Scandian (Silurian–Devonian) underthrusting of Laurentia by Baltica resulted in stacking of the main orogenic wedge and its migration onto the platform edge of Baltica. Complementary thrust sheets, exposed in northeastern Greenland, telescoped the Laurentian continental margin. The Swedish part of the Caledonides, comprising the foreland segment along the central half of this mountain belt, includes the key components of: (1) the Baltoscandian inner margin, including Ordovician and Silurian foreland basins; (2) the Neoproterozoic extended outer margin dominated by mafic magma and continent–ocean transition zone; (3) Iapetus oceanic terranes; and (4) evidence that substantial parts of the outermmost Baltoscandian margin experienced deep subduction and high- and ultrahigh-pressure (HP/UHP) metamorphism during late Cambrian–Ordovician accretion. This evidence, integrated with the Norwegian Caledonides, defines an orogenic pro-wedge comparable to that in the Himalaya today. Orthogonal Scandian collision, lasting for about 60 million years ( c. 440–380 Ma), involved late Silurian–Early Devonian HP/UHP metamorphism of the underthrusting Baltoscandian basement. By the Middle Devonian, the hinterland was experiencing orogen-parallel folding and axial extension, accompanying exhumation, while the orogenic pro-wedge continued to migrate eastwards on to the platform.

Abstract In central parts of the Scandinavian Caledonides, detrital zircon signatures provide evidence of the change in character of the Baltoscandian crystalline basement, from the characteristic Late Palaeoproterozoic granites of the Transscandinavian Igneous Belt (TIB, c. 1650–1850 Ma) in the foreland Autochthon to the typical, mainly Mesoproterozoic-age profile ( c. 950–1700 Ma) of the Sveconorwegian Orogen of southwestern Scandinavia in the hinterland. Late Ediacaran to Early Cambrian shallow-marine Vemdal quartzites of the Jämtlandian Nappes (Lower Allochthon) provide strong bimodal signatures with TIB (1700–1800 Ma) and Sveconorwegian, sensu stricto (900–1150 Ma) ages dominant. Mid-Ordovician turbidites (Norråker Formation) of the Lower Allochthon in Sweden, sourced from the west, have unimodal signatures dominated by Sveconorwegian ages with peaks at 1000–1100 Ma, but with subordinate components of older Mesoproterozoic zircons (1200–1650 Ma). Latest Ordovician shallow-marine quartzites also yield bimodal signatures, but are more dispersed than in the Vemdal quartzites. In the greenschist facies lower parts of the Middle Allochthon, the Fuda (Offerdal Nappe) and Särv Nappe signatures are either unimodal or bimodal (950–1100 and/or 1700–1850 Ma), with variable dominance of the younger or older group, and subordinate other Mesoproterozoic components. In the overlying, amphibolite to eclogite facies lower part of the Seve Nappe Complex, where the metasediments are dominated by feldspathic quartzites, calcsilicate-rich psammites and marbles, most units have bimodal signatures similar to the Särv Nappes, but more dispersed; one has a unimodal signature very similar to the Ordovician turbidites of the Jämtlandian Nappes. In the overlying Upper Allochthon, Lower Köli (Baltica-proximal, Virisen Terrane), Late Ordovician quartzites provide unimodal signatures dominated by Sveconorwegian ages ( sensu stricto ). Further north in the Scandes, previously published zircon signatures in quartzites of the Lower Allochthon are similar to the Vemdal quartzites in Jämtland. Data from the Kalak Nappes at 70°N are in no way exotic to the Sveconorwegian Baltoscandian margin. They do show a Timanian influence (ages of c. 560–610 Ma), as would be expected from the palinspastic reconstructions of the nappes. Thus the detrital zircon signatures reported here and published elsewhere provide supporting evidence for a continuation northwards of the Sveconorwegian Orogen in the Neoproterozoic, from type areas in the south, along the Baltoscandian margin of Baltica into the high Arctic. Supplementary material: LA-ICP-MS U–Pb analyses are available at http://www.geolsoc.org.uk/SUP18699 .

Abstract The study of complex orogenic belts commonly begins in the frontal regions with well-defined tectonostratigraphy, and relatively simple structure and metamorphism, and proceeds into the progressively more complex hinterland, which nevertheless may contain the best geochronological record of the most intense orogenic events. The northern part of the Western Gneiss Region in the hinterland of the Scandian orogen contains a robust U–Pb zircon geochronological framework on rocks subjected to high-pressure (HP) and ultra-high-pressure (UHP) metamorphism that has implications for tectonic development both there and towards the foreland. HP and UHP eclogite crystallization occurred at 415–410 Ma (Early Devonian, Lochkovian to Pragian), followed by pegmatite crystallization at c. 395 Ma (Late Emsian) during exhumation and return to amphibolite-facies conditions, thus limiting the process to 15–20 myr. The nature and sequence of events are much more complex than in the foreland, causing difficulty in correlation, yet the combined tectonics in the two regions provides the necessary context to explain, for example, how rocks were subjected to deep-seated, high-temperature metamorphism and then exhumed to shallower levels. Here, we suggest how a recently recognized extensional detachment fault and a recently recognized out-of-sequence thrust might be linked to the timing of HP metamorphism and later exhumation. The postulated Agdenes extensional detachment in its footwall has basement gneisses containing Mesoproterozoic igneous titanite fully reset at 395 Ma, as well as Devonian pegmatites, and in the hanging wall Ordovician to Early Silurian granitoids of the Støren Nappe containing igneous titanite barely influenced by Devonian recrystallization and no evidence of post-Ordovician melts. This implies removal of a significant crustal section on a large-scale detachment. Rocks both above and below are overprinted by the same late, subhorizontal, sinistral ductile extensional fabric, obscuring any fabrics produced during development of the detachment itself. Eastern Trollheimen escaped the late, strong, subhorizontal overprint, and shows: (1) early emplacement of thrust nappes of Lower and Middle Allochthons over Baltican basement and its Late Neoproterozoic quartzite cover; (2) major, SE-directed, recumbent folding of the entire thrust-imbricated sequence; and (3) major, out-of-sequence, SE-directed thrusting (Storli Thrust), for an 80 km minimum transport across-strike, of the recumbent-folded sequence over deeper, less deformed, lower basement gneisses and unconformable Neoproterozoic quartzite cover. The upper basement contains boudins of eclogite and garnet-corona gabbro lacking in the lower basement. Similar basement imbrications occurred in the Tømmerås window, the Skarddøra Antiform, the Mullfjället Antiform and the Grong–Olden Culmination, up to 240 km NE of Trollheimen, as well as in the Reksdalshesten antiform 100 km west, all within the postulated minimum 400×180 km area of the Agdenes detachment.

Abstract The scientific drilling project COSC (Collisional Orogeny in the Scandinavian Caledonides), designed to study key questions concerning orogenic processes, aims to drill two fully cored boreholes to depths of c. 2.5 km each at carefully selected locations in west-central Sweden. The first of these, COSC-1, is scheduled for start late spring 2014 and will target the Seve Nappe Complex, characterized by inverted metamorphism and with parts that have evidently been subjected to hot ductile extrusion. In this study available seismic sections have been combined with surface geology to produce a 3D interpretation of the tectonic structures in the vicinity of the COSC-1 borehole. Constrained 3D inverse gravity modelling over the same area supports the interpretation, and the high-density Seve Nappe Complex stands out clearly in the model. Interpretation and models show that the maximum depth extent of the Seve Nappe Complex is less than 2.5 km, consistent with reflection seismic data. The gravity modelling also requires underlying units to comprise low-density material, consistent with the Lower Allochthon, but the modelling is unable to discern the décollement separating the allochthons from the crystalline Precambrian basement.

Abstract New evidence is presented for ultra-high-pressure metamorphism of kyanite–garnet pelitic gneiss in the Åreskutan Nappe of the Seve Nappe Complex, in the central part of the Scandinavian Caledonides. Modelled phase equilibria for a peak pressure assemblage garnet+phengite+kyanite+quartz (coesite) in the NCKFMMnASH system record pressure and temperature conditions of c. 26–32 kbar at 700–720 °C, possibly up to ultra-high-pressure conditions. Subsequent decompression, simultaneous with an increase of temperature to c. 800–820 °C, led to partial melting largely owing to the dehydration and breakdown of phengite. Based on existing isotope age data, we conclude that the Middle Seve Nappe in central Jämtland experienced deep subduction in the late(st) Ordovician, prior to decompression and partial melting of the pelitic protoliths during Early Silurian extrusion, giving way in the Mid to Late Silurian to thrusting on to the Baltoscandian platform. Nappe emplacement probably continued into and through the Early Devonian.

Abstract Secondary ionization mass spectrometry (SIMS) U–Pb dating of zircons from the Åreskutan Nappe in the central part of the Seve Nappe Complex of western central Jämtland provides new constraints on the timing of granulite–amphibolite-facies metamorphism and tectonic stacking of the nappe during the Caledonian orogeny. Peak-temperature metamorphism in garnet migmatites is constrained to c. 442±4 Ma, very similar to the ages of leucogranites at 442±3 and 441±4 Ma. Within a migmatitic amphibolite, felsic segregations crystallized at 436±2 Ma. Pegmatites, cross-cutting the dominant Caledonian foliation in the Nappe, yield 428±4 and 430±3 Ma ages. The detrital zircon cores in the migmatites and leucogranites provide evidence of Late Palaeoproterozoic, Mesoproterozoic to Early Neoproterozoic source terranes for the metasedimentary rocks. The formation of the ductile and hot Seve migmatites, with their inverted metamorphism and thinning towards the hinterland, can be explained by an extrusion model in which the allochthon stayed ductile for a period of at least 10 million years during cooling from peak-temperature metamorphism early in the Silurian. In our model, Baltica–Laurentia collision occurred in the Late Ordovician–earliest Silurian, with emplacement of the nappes far on to the Baltoscandian platform during the Silurian and early Devonian, Scandian Orogeny lasting until c. 390 Ma.

Abstract The metamorphic evolution of the Tjeliken eclogite, occurring within the Seve Nappe Complex of northern Jämtland (Swedish Caledonides), is presented here. The prograde part of the pressure and temperature ( P–T ) path is inferred from the mineral inclusions (pargasitic amphibole) in garnet and intracrystalline garnet exsolutions in omphacite. Peak metamorphic conditions of 25–26 kbar at 650–700 °C are constrained from geothermobarometry for the peak-pressure assemblage garnet+omphacite+phengite+quartz+rutile, using the garnet–clinopyroxene Fe–Mg exchange thermometer in combination with the net-transfer reaction (6 diopside+3 muscovite=3 celadonite +2 grossular+pyrope) geobarometer, the average P–T method of Thermocalc and pseudosection modelling. Quartz inclusions with well-developed radial cracks were identified within omphacite, which suggest that the studied rock could have been buried down to the coesite stability field. Post-peak P–T evolution is inferred from diopside–plagioclase symplectites and amphibole coronas around garnet. Previous studies in northern Jämtland suggest a substantial gap between the P–T conditions of the Lower and Middle Seve nappes: 14–16 kbar and 550–680 °C and 20–30 kbar and 700–800 °C, respectively. The Tjeliken eclogite has been considered previously to be a part of Lower Seve by most authors, but the new P–T data suggest that it may be an isolated klippe of Middle Seve.

Abstract Europe provides on outstanding field laboratory for studying lithospheric processes through time: for tracing the results of plate movements from the present back into the early Precambrian. This book has been designed to focus on tectonic processes in the European lithosphere through these three billion years and how they may have changed during this time. Two things are particularly striking: the importance of plate tectonics far back through the Proterozoic into the Archaean, and the significance of tectonic inheritance, older structures and rheologies guiding, even defining, the younger evolution. Basement structure has a profound influence on subsequent basin evolution and the distribution of geo-resources. The economic importance of understanding these processes cannot be overestimated.

Abstract This volume was conceived during EUROPROBE's investigations into the dynamic evolution of the Palaeozoic Uralide Orogen and relationships northwards into the Eurasian high Arctic. During these European Science Foundation studies, the preservation of Neoproterozoic deformation over large regions of northern Europe became increasingly apparent. This mainly Vendian tectonic event is referred to as the Timanian Orogeny and became the focus of many recent and on-going investigations. Much progress has been made in understanding Timanian Orogeny and a Memoir synthesizing our current knowledge is not only timely, but also relevant to Neoproterozoic global tectonic reconstructions. The type area for the Timanide Orogen is located in the Timan Range of northwestern Russia, which separates the East European Craton from the Pechora Basin and Polar Urals. The orogen extends over a distance of at least 3000 km, from the southern Ural Mountains of Kazakhstan to the Varanger Peninsula of northernmost Norway, flanking the eastern margin of the older craton (Fig. 1 ). From the Timan Range, it reaches northeastwards below the thick Phanerozoic successions of the Pechora Basin and Barents Shelf ( O’Leary et al. 2004 ), and reappears in the Polar Ural Mountains and northwards through Pai Khoi to Novaya Zemlya. Timanian orogeny thus influenced a vast region of northwestern Russia. The Phanerozoic cover, Arctic shelf areas and, further east, Uralian deformation, obscure the importance of this orogenic event for the geodynamic evolution of Europe. The Timanide Orogen has been referred to by various other names, most frequently as the ‘Baikalides’. The term ‘Baikalian Orogeny’

Abstract Neoproterozoic, slope-to-basin, lithostratigraphic successions are discontinuously exposed within the Timan Range, in NW Russia, NE of a faulted basinal margin that marks the outer edge of a former, fluvial to shallow-marine, pericratonic domain. The Mid to Late Riphean, deep-water depositional systems of the Kanin Peninsula, and northern and central Timan attain considerable thicknesses, up to 10 000 m in the case of Kanin Peninsula. Basements to these successions are nowhere exposed. Although the successions accumulated along a comparatively stable, passive margin of Baltica, there are notable differences in sedimentary facies from area to area. Whereas the successions in northern and central Timan preserve a record of relative stability, with sedimentation keeping pace with subsidence, the nearby Kanin succession shows evidence of repeated faulting. This may reflect a non-contemporaneity of the diverse successions or a segmentation of the basin margin. Comparisons are also made with deep-water, turbidite-fan systems in northwestern parts of the Timan-Varanger Belt, on the Rybachi and Varanger Peninsulas. The lateral differences in sedimentary facies in these areas, seen in relation to the situation in Timan and Kanin, do, in fact, suggest that the 1800 km long Timanian Basin margin may have been segmented, and possibly into sub-basinal domains.

Abstract The northeastern and eastern margin of the East European Craton exposes numerous Riphean and Vendian (Meso- and Neoproterozoic) sedimentary successions that were deposited in alluvial and shallow-marine environments in intra- and pericratonic basins. A review is presented of the lithostratigraphy, sedimentary environments and architectural style of these sedimentary sequences in the Southern, Middle, Subarctic and Polar Urals, on the Poludov Range, and in the Volga-Urals and Timan-Pechora regions. The Riphean sequences are subdivided into three major sedimentary units: Lower, Middle and Upper, based on type areas in the Bashkirian Anticlinorium. During the Early and Middle Riphean, in the Southern Urals there were several short episodes of ‘diffuse’ and linear rifting and long intervals of more stable development in intracratonic sedimentary basins. During the Late Riphean, in the territory under review, larger shallow marine basin developed. Two laterally connected zones existed along the eastern periphery of the East European Craton: one in the Southern and Middle Urals, with a predominance of shallow marine arkosic deposits, and the other, with moderately deep marine (continental slope and rise) turbidities in the Timan-Pechora region. Subsequent Vendian successions were largely shallow marine and deposited in epicratonic basins; they generally give way upwards in the Late Vendian into non-marine clastic formations, derived from the east.