Abstract The Småland lithotectonic unit in the 2.0−1.8 Ga Svecokarelian orogen, southeastern Sweden, is dominated by a c. 1.81−1.77 Ga alkali–calcic magmatic suite (the Transscandinavian Igneous Belt or TIB-1). At least in its central part, the TIB-1 suite was deposited on, or emplaced into, c. 1.83–1.82 Ga calc-alkaline magmatic rocks with base metal sulphide mineralization and siliciclastic sedimentary rocks (the Oskarshamn–Jönköping Belt). Ductile deformation and metamorphism under low- to medium-grade conditions affected the Oskarshamn–Jönköping Belt prior to c. 1.81 Ga. Both suites were subsequently affected by low-grade ductile deformation, mainly along steeply dipping, east–west to NW–SE shear zones with dip-slip and dextral strike-slip displacement. Sinistral strike-slip NE–SW zones are also present. In the northern part of the lithotectonic unit, 1.9 Ga magmatic rocks, c. 1.87–1.81 Ga siliciclastic sedimentary rocks and basalt, and c. 1.86–1.85 Ga granite show fabric development, folding along steep NW–SE axial surfaces and medium- or high-grade metamorphism prior to c. 1.81 Ga and, at least partly, at c. 1.86–1.85 Ga; base metal sulphide, Fe oxide and U or U–REE mineralizations also occur. Magmatism and siliciclastic sedimentation along an active continental margin associated with subduction-related, accretionary tectonic processes is inferred over about 100 million years.

Abstract Accretionary processes contributed to major continental growth in Fennoscandia during the Palaeoproterozoic, mainly from 2.1 to 1.8 Ga. The composite Svecofennian orogen covers c . 1×10 6 km 2 and comprises the Lapland–Savo, Fennia, Svecobaltic and Nordic orogens. It is a collage of 2.1–2.0 Ga microcontinents and 2.02–1.82 Ga island arcs attached to the Archaean Karelian craton between 1.92 and 1.79 Ga. Andean-type vertical magmatic additions, especially at c . 1.89 and c . 1.8 Ga, were also important in the continental growth. The Palaeoproterozoic crust is the end product of accretionary growth, continental collision and orogenic collapse. Preserved accretional sections are found in areas where docking of rigid blocks has prevented further shortening. The Pirkanmaa belt represents a composite accretionary prism, and other preserved palaeosubduction zones are identified in the Gulf of Bothnia and the Baltic Sea areas. In the southern segment of the Lapland–Savo orogen collision between the Archaean continent (lower plate) and the Palaeoproterozoic arc–microcontinent assembly (upper plate) produced a special type of lateral crustal growth: the Archaean continental edge decoupled from its mantle during initial collision and overrode the arc and its mantle during continued collision.

Abstract Sub-ophitic, equigranular or plagioclase-phyric dolerite dykes, referred to as the Blekinge–Dalarna dolerite (BDD) swarm, were emplaced during the time span 0.98–0.95 Ga and trend NNE–NNW in an arcuate fashion, parallel to and east of the Sveconorwegian orogen. Dolerite sills are locally present. These rocks are subalkaline to alkaline with a monzogabbroic or gabbroic composition and show a predominantly within-plate tectonic affinity. ɛ Nd and ɛ Hf values fall in the range −2 to +4 and +1 to +5, respectively. Siliciclastic sedimentary rocks (Almesåkra Group) in a small outlier in southern Sweden were deposited in an aeolian to fluviatile or lacustrine environment and an arid or semi-arid warm palaeoclimate, coevally with the dolerite sills. Smaller occurrences of sandstone with peperitic field relationships to the BDD dykes are known from other localities. The spatial distribution, orientation and age of the BDD magmatic suite suggest roughly east–west extension in the eastern, cratonic foreland to the Sveconorwegian orogen during the latest phase of this mountain-building event, the age data tentatively suggesting a younging to the east. The siliciclastic sedimentary rocks represent an erosional relict of a larger and spatially much more extensive early Tonian foreland basin to this orogen, as proposed earlier on the basis of fission-track thermochronology.

Abstract An intimate lithostratigraphic and lithodemic connection between syn-orogenic rock masses inside the different lithotectonic units of the 2.0–1.8 Ga (Svecokarelian) orogen, Sweden, is proposed. A repetitive cyclic tectonic evolution occurred during the time period c. 1.91–1.75 Ga, each cycle lasting about 50–55 million years. Volcanic rocks ( c. 1.91–1.88 Ga) belonging to the earliest cycle are host to most of the base metal sulphide and Fe oxide deposits inside the orogen. Preservation of relict trails of continental magmatic arcs and intra-arc basins is inferred, with differences in the depth of basin deposition controlling, for example, contrasting types of base metal sulphide deposits along different trails. The segmented geometry of these continental magmatic arcs and intra-arc basins is related to strike-slip movement along ductile shear zones during transpressive events around and after 1.88 Ga; late orogenic folding also disturbed their orientation on a regional scale. A linear northwesterly orogenic trend is suggested prior to this structural overprint, the strike-slip movement being mainly parallel to the orogen. A solely accretionary orogenic model along an active margin to the continent Fennoscandia, without any trace of a terminal continent–continent collision, is preferred. Alternating retreating and advancing subduction modes that migrated progressively outboard and southwestwards in time account for the tectonic cycles.

Abstract Based on an integrated study of geological and geophysical data, a tectonic model for the Palaeoproterozoic evolution of the Svecofennian orogen within the Fennoscandian Shield at the northwestern corner of the East European Craton is proposed. The Svecofennian orogen is suggested to have formed during five, partly overlapping, orogenies: Lapland-Savo, Lapland-Kola, Fennian, Nordic and Svecobaltic. The Svecofennian orogen evolved in four major stages, involving microcontinent accretion (1.92–1.88 Ga), large-scale extension of the accreted crust (1.87–1.84 Ga), continent-continent collision (1.87–1.79 Ga) and finally gravitational collapse (1.79 and 1.77 Ga). The stages partly overlapped in time and space, as different processes operated simultaneously in different parts of the plates. In the Lapland-Savo and Fennian orogenies, microcontinents (suspect terranes) and island arcs were accreted to the Karelian microcontinent, which itself was accreting to Laurentia in the Lapland-Kola orogeny. The formation of the Svecofennian orogen was finalized in two continental collisions producing the Nordic orogen in the west (Fennoscandia-Amazonia) and Svecobaltic orogen in the SSW (Fennoscandia-Sarmatia). The collisions were immediately followed by gravitational collapse.

Abstract Current models for the growth of Fennoscandia, including the eastern part of the Sveconorwegian Province, are largely based on U–Pb data and do not discriminate between juvenile and reworked crust. Here we present new combined U–Pb and Hf isotopic data, from the Eastern Segment and the Idefjorden terrane of the Sveconorwegian Province, and suggest a revised model of crustal growth. Most of the crystalline basement in this part of the shield formed by mixing of a 2.1–1.9 Ga juvenile component and Archaean crust. Archaean reworking decreases between 1.9 and 1.7 Ga and a mixed Svecofennian crustal reservoir is generated. Succeeding magmatism between 1.7 and 1.4 Ga indicates reworking of this reservoir with little or no crust generation. At c. 1.2 Ga, an influx of juvenile magma is recorded by granite to quartz-syenite magmatism with mildly depleted (ɛ Hf 1.18 Ga of c. 3) signatures. The amount of recycled crust in the 1.9–1.7 Ga arc system is in contrast to previously proposed models for the growth of the southwestern part of the Fennoscandian Shield. This model agrees with long-term subduction along the western margin of Fennoscandia, but suggests substantial reworking of existing crust and decreasing amounts of <1.9 Ga crustal growth. Supplementary material: The analytical method, U–Pb SIMS table, U–Pb LA-SF-ICP-MS table and Lu–Hf table are available at www.geolsoc.org.uk/SUP18648

Abstract The Eastern Segment in the Sveconorwegian orogen comprises Paleoproterozoic–Mesoproterozoic magmatic suites, which formed along an active continental margin, and Mesoproterozoic suites emplaced during intracratonic extension. Zn–Pb sulphide and Fe oxide mineralizations in 1.9 Ga metavolcanic rocks form a significant mineral resource cluster in the northeastern part. Deformation and metamorphism under low-pressure (≤5 kbar) and variable-temperature conditions, including anatexis and granulite facies, prevailed during 1.9–1.8 Ga (Svecokarelian) and 1.5–1.4 Ga (Hallandian) accretionary orogenies. Sveconorwegian tectonothermal reworking initiated at c. 0.99–0.98 Ga in structurally lower levels. Crustal shortening, underthrusting with eclogite facies metamorphism (18 kbar), exhumation by eastwards thrusting (D 1 ) during continued shortening and high-pressure granulite (8–12 kbar) to upper amphibolite facies metamorphism prevailed. Anatexis and folding around east–west axial surfaces with west-northwesterly constrictional strain (D 2 ) followed at c. 0.98–0.95 Ga, being consanguineous with crustal extension. Structurally higher levels, northwards and eastwards, consist of high-pressure (10–12 kbar) orthogneisses, not affected by anatexis but also showing polyphase deformation. Sveconorwegian convergence ceased with upright folding along north–south axial surfaces and, in the uppermost frontal part, greenschist facies shearing with top-to-the-foreland normal followed by reverse displacement after 0.95 Ga. The normal shearing detached the upper compartment from the underlying gneisses.