Abstract Crust generated during an accretionary orogeny at 1.66–1.52 Ga (Gothian), and later during crustal extension at c. 1.51–1.49, c. 1.46, c. 1.34–1.30 Ga and after c. 1.33 Ga, dominate the Idefjorden terrane. Metamorphism under greenschist to, locally, high-pressure granulite facies, emplacement of syn-orogenic pegmatite and granite, and polyphase deformation followed at 1.05–1.02 Ga (Agder tectonothermal phase, Sveconorwegian orogeny). Sinistral transpressive deformation, including foreland-directed thrusting, preceded top-to-the-west movement and large-scale open folding along north–south axial trends during the younger orogeny. Crustal extension with emplacement of dolerite and lamprophyre dykes, norite–anorthosite, and a batholithic granite took place at c. 0.95–0.92 Ga (Dalane phase, Sveconorwegian orogeny). Ductile shear zones divide the Idefjorden terrane into segments distinguished by the character of the Gothian crustal component. Orthogneisses with c. 1.66 and c. 1.63–1.59 Ga protoliths occur in the Median segment; c. 1.59–1.52 Ga gneissic intrusive rocks and 1.6 Ga paragneisses with relicts of Gothian deformation and migmatization at c. 1.59 Ga and at c. 1.56–1.55 Ga occur in the Western segment. Mineral resources include stratabound Cu–Fe sulphides hosted by sandstone deposited after c. 1.33 Ga, and polymetallic quartz vein mineralization locally containing Au.

Abstract The Eastern Segment in the Sveconorwegian orogen, southwestern Sweden, is dominated by 2.0–1.8, 1.7 and 1.5–1.4 Ga crust; and the overlying Idefjorden terrane by 1.6–1.5 Ga crust. Assuming reorganization of a subduction system prior to 1.5–1.4 Ga and applying a sinistral transpressive component of disruption during the subsequent Sveconorwegian orogeny (1.1–0.9 Ga), the Idefjorden terrane is inferred to be indigenous outboard rather than exotic with respect to the continental plate Fennoscandia (Baltica). The geological record then records successive westwards shift of accretionary orogens along a convergent plate boundary for at least 500 million years. Sveconorwegian foreland-younging tectonic cycles at c. 1.05 (or older)–1.02 Ga (Idefjorden terrane) and at c. 0.99–0.95 Ga (Eastern Segment) prevailed. Crustal thickening and exhumation during oblique convergence preceded migmatization, magmatic activity and a changeover to an extensional regime, possibly triggered by delamination of continental lithosphere, in each cycle. Convergence after 0.95 Ga involved antiformal doming with extensional deformation at higher crustal levels (Eastern Segment) and continued magmatic activity (Idefjorden terrane). An overriding plate setting is inferred during either accretionary orogeny or, more probably, protracted continent–continent collision. Continuity of the erosional fronts in the Grenville and Sveconorwegian orogens is questioned.

Abstract The 1.1–0.9 Ga Sveconorwegian orogen in southwestern Scandinavia belongs to the global system of mountain belts established during the assembly of the supercontinent Rodinia. An overall north–south structural trend and five lithotectonic units bounded by crustal-scale shear zones characterize this orogen. In Sweden, the Eastern Segment abuts the orogen's cratonic foreland eastwards and is separated from the Idefjorden terrane westwards by a ductile shear zone, up to 5 km thick, displaying a sinistral transpressive component. These two lithotectonic units differ on the basis of their pre-Sveconorwegian accretionary tectonic evolution, and the timing of Sveconorwegian high-pressure metamorphism, anatexis and polyphase deformation. High-pressure granulites and migmatites formed at c. 1.05–1.02 Ga in the Idefjorden terrane; eclogites, high-pressure granulites and migmatites at c. 0.99–0.95 Ga in the Eastern Segment. Magmatic activity and crustal extension progressed westwards at c. 0.98–0.92 Ga. Prior to or at 0.93–0.91 Ga, greenschist facies shear deformation with top-to-the-foreland movement affected the frontal part of the orogen. Geodynamic uncertainties concern the affinity of the Idefjorden terrane relative to Fennoscandia (Baltica), the character of the Sveconorwegian orogenesis, and the contiguous or non-contiguous nature of the erosional fronts of the late Mesoproterozoic–early Neoproterozoic orogens in Sweden and Canada.

Abstract The ‘Mylonite Zone’ (MZ) forms a major, arcuate terrane boundary in the Precambrian Sveconorwegian orogen of SW Scandinavia. SE-directed thrusting along this curvilinear shear zone emplaced the higher-grade Idefjorden Terrane to the west onto the lower-grade Eastern Segment terrane to the east. Detailed structural characterization of the MZ mylonites in two different localities (Värmlandsnäs and Bua peninsulas) reveals a complex three-dimensional strain pattern. Inclined transpression is inferred on the basis of coexisting (and broadly coeval) foliation-parallel oblique shearing (resolvable in a strike-slip and dip-slip component) and across-foliation shortening. The former accommodated the transpressive component of the MZ, and its kinematics is either sinistral or dextral depending on the local strike of the MZ with respect to the regional thrust shortening vector. The latter led to pure-shear shortening perpendicular to the thrust sheet and subsequent lateral extrusion parallel to the mylonitic foliation via the development of antithetic displacements. No significant strain partitioning is observed at the meso-scale and strain is thus truly triclinic. The example described is an outstanding case of triclinic deformation, confirms theoretical analyses of complex strain models and adds valuable natural field constraints to our knowledge of deformation in the crust.

Abstract Re–Os dating of a suite of nine molybdenite samples from two small Cu–Mo mineral occurrences in the epidote-amphibolite facies Sæsvatn supracrustal sequence provides a temporal record of Sveconorwegian metamorphism and deformation. The sequence is situated in the western allochthonous lithotectonic domain of the Sveconorwegian orogen, the Rogaland–Hardangervidda terrane of south Norway. Onset of metamorphism occurred at about 1047 ± 2 Ma, as recorded in small gash veinlets, followed by a deformational peak at about 1032 ± 2 Ma, as recorded in mineralized breccia and mineralized metagabbro comprising a ductile shear zone constituting the Langvatn deposit. Deformation waned significantly by about 1017 ± 2 Ma, based on mineralization hosted in a brittle fault zone within stratigraphically higher metabasalts exposed at the Kobbernuten deposit. The origin of the mineralization at both deposits is most probably metamorphic with ore constituents provided by metasomatism of hosting basalt and gabbro. A metamorphic origin is supported by an array of Re–Os ages that can be related to structural features and the stratigraphic sequence, the absence of plutons related in time and space, the confinement of ore occurrences to mafic sequences in a bimodal supracrustal package that includes rhyolites and clastic units, and clear evidence for Cu mobility in mafic units. The ‘main’ Sveconorwegian orogenic event, probably a continent–continent collision involving imbrication, stacking, and burial of terranes took place at about 1.05 Ga and thereafter. Peak deformation in the Sæsvatn supracrustal sequence in the western part of the Sveconorwegian orogen (South Norway) may correlate with thermal metamorphism in the Idefjorden terrane in the eastern part of the orogen (SW Sweden), with a timing of about 1.03 Ga for both regions. The results of this study indicate that comparatively low grade domains in the orogen (greenschist to epidote-amphibolite facies), corresponding to upper crust, were deformed in a ductile fashion at about 1.03 Ga and were affected by brittle deformation as early as 1.025–1.015 Ga. In the high-grade domains (amphibolite to granulite facies), corresponding to middle and lower crust, ductile deformation is younger, beginning at about 1.025 Ga and persisting until 0.97 Ga.

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 This paper summarizes the main geochronological features of the Caledonian nappes in southern Norway, discusses their similarities and differences, and reports new U–Pb isotope dilution thermal ionization mass spectrometry data. The latter include ages of 1670 Ma for orthogneiss from the Upper Finse Nappe, 1500, 1250 and 950 Ma for intrusive rocks from the Hallingskarvet Nappe, and 1037 and 997 Ma for volcanic units from the Suldal and Lower Finse nappes. The Caledonian nappes can be subdivided into units formed at 1700–1600 Ma, having an affinity with Gothian crust, and units formed at about 1500 Ma, correlating with Telemarkian crust. A Sveconorwegian tectonometamorphic overprint is ubiquitous, but with large differences in the intensity and relative timing of the overprint. Some complexes (such as Kvitenut–Dyrskard) were affected at around 1000 Ma and others (such as Jotun and Lindås) between 970 and 930 Ma. There is also considerable variety in the Caledonian effects. Ordovician events affected some nappes (Jæren, Revsegg), thought to be of exotic origin, while Silurian and Devonian events of variable intensity are observed in all nappes. The emerging patterns offer the basis for a qualitative discussion of the provenance of the nappes that can eventually be combined with quantitative structural criteria to reconstruct pre-Caledonian palaeogeographies.