Sveconorwegian Orogeny Research Articles

Seismic imaging of upper crustal basement faults in the Skagerrak Sea

The continental upper crystalline crust appears almost non-reflective on many deep seismic reflection profiling sections. Typically, only the major faults and lithological boundaries are imaged, whereas smaller-scale faults are usually not identified. A deep seismic survey (0–16 s TWT) covering the Skagerrak Sea was undertaken in 1987. Although the northeastern part of the Skagerrak has only thin or no sediment cover, the data in the depth range 0–6 s TWT were reprocessed to commercial exploration standards. Close inspection of these high quality sections provides evidence of abundant, moderately steep dipping (20–50°) faults that can be traced to depths of 10–13 km. Fault geometry, which can be inferred at profile intersections, is in accordance with the general tectonic fabric observed on land and beneath the Skagerrak Sea. These areas were deformed during the Proterozoic Sveconorwegian orogeny and during the formation of the Permian Oslo Rift. Due to post-Permian erosion of the Skagerrak Sea proper, the relative age and movements of the basement faults could not be determined. This study shows that under favorable conditions, faults in the upper crystalline crust are mappable by seismic means. Such measurements have the potential for resolving variations in block geometry with depth and also recent seismotectonic movements.

Reintroduction of gold, other chalcophile elements and LILE during retrogression of depleted granulite, Tromøy, Norway

Several metamorphic and magmatic events were associated with the Sveconorwegian orogeny (∼ 1.1 Ga) that affected the Bamble shear belt, south Norway. Among the most important were (1) granuliteto amphibolite-facies metamorphism of the entire belt; (2) intrusion of mafic dykes (“hyperites”), followed by their localized metamorphism to amphibolite; (3) intrusion of granitic sheets, which in granulite terrane caused rehydration and retrogression. Previous studies have shown that rocks from across the belt metamorphosed to amphibolite and granulite grade during event (1) are strongly depleted in Au, Sb and As; while some granulites are also depleted in Rb, Cu and S. Gold and chalcophile elements were also lost during (2) amphibolization of hyperites. This paper is concerned with event (3), at which time the granulites had been uplifted and cooled. H 2OCO 2 fluids, at least in part derived from the granitic magma, caused localized rehydration and retrogression of granulite. This was accompanied by the variable reintroduction of the same elements (Au, As, Sb, Cu, S and Rb) that had earlier been depleted. The nature of the reintroduction of Au and other elements has relevance to the origin of mesothermal gold deposits.

Isotopic age determinations in South Norway III: Rb–Sr isotope systematics of the coronitic Vestre Dale Gabbro and its country rocks, Bamble Sector

Abstract Rb–Sr whole-rock isotope data of the coronitic Vestre Dale Gabbro and its country rocks are presented together with Rb–Sr and K–Ar isotope data of biotites and muscovites from the country rocks. The Rb–Sr whole-rock errorchron age of the Vestre Dale Gabbro, 1.26±0.09 Ga (87Sr/86Sr(I) = 0.70310±0.00010), falls within the error limits of the Sm–Nd whole-rock age and a Sm–Nd whole-rock–mineral age of this gabbro, suggesting that the Rb–Sr system remained closed during the Sveconorwegian orogeny, at least on hand-specimen scale. The leucocratic rocks, which constitute part of the agmatitic structures along the margins of the gabbro, yield a comparable errorchron age: 1.28±0.09 Ga (87Sr/86Sr(I) = 0.70516±0.00107). Emplacement of the gabbro disturbed the Rb–Sr systematics of the surrounding migmatites. It appears that complete homogenization of the Rb–Sr systematics was not achieved in these rocks, resulting in a poorly defined errorchron (MSWD = 151). Rb–Sr ages of the biotites (0.89 ± 0.02 Ga) and mu...

The early evolution of the Southwest Swedish Gneiss Province: Geochronological and isotopic evidence from southernmost Sweden

Abstract The continental crust in southwestern Sweden has a complicated history of formation, apparently commencing ∼ 1.75 Ga ago and continuing until the end of the Sveconorwegian orogeny ∼ 0.9 Ga ago. Most of the rocks are polymetamorphic gneisses, but massifs of intrusive rocks can commonly be recognized. This study reports new UPb zircon ages from the province of Skane in the southernmost part of the region. Two gneiss samples and four samples of granitoid rocks were dated by the UPb zircon method. In the two gneiss samples, selected single zircon crystals were analyzed in addition to the standard multi-grain size fractions. The multigrain zircon analyses yielded an upper intercept age of 1613 ± 6 Ma for a grey gneiss from the central part of the province of Skane, and 1557−27+32 Ma for a red aplitic gneiss from southern Skane. Individual zircon crystals from these samples gave 207Pb 206Pb -ages between 1335 and 1669 Ma. For the grey gneiss, the individual zircons define a separate discordia with an upper-intercept age of 1640±16 Ma; in the red gneiss sample they scatter around a line with an upper intercept at 1675±25 Ma. Core-bearing zircons from a red gneissic granite in central Skane yielded an age of 1575−61+77 Ma, while similar zircons from a strongly foliated red granite from the Kullaberg horst in northwestern Skane gave an age of 1497−34+47 Ma. Core-free zircons from the Beden granodiorite in southern Skane have an age of 1449−11+23 Ma, and core-bearing zircons from a gneissic charnockite near Orkelljunga in northern Skane yielded an age of 1452−50+350 Ma. Although the latter age is poorly defined, it allows for similar intrusion ages of the Orkelljunga charnockite and the Beden granodiorite. SmNd isotopic analyses yield TDM ages of 1.84 o 1.99 Ga, and TCHUR ages of 1.48 to 1.60 Ga for these rocks, while RbSr analyses give TUR ages between 1.46 and 1.71 Ga. The combined evidence suggests that the main crust-forming episode in this part of southwestern Sweden occurred 1.6 to 1.7 Ga ago, with presumably subduction-related magmatism forming the protoliths of the red and grey gneisses. Around 1.5 to 1.6 Ga ago red anatectic granites were generated. The Beden granodiorite and the Orkelljunga charnockite, as well as the Varberg charnockite farther north, were all formed ∼ 1.45 Ga ago, possibly by mantle-generated anorogenic magmatism. Some 0.9 Ga ago, after the Sveconorwegian crustal thickening and high-pressure metamorphism, uplift within the Southwest Swedish Gneiss Province exposed lower- to mid-crustal granulitic and charnockitic rocks in its southern part.

Palaeomagnetism, mafic dykes and the Protogine Zone, southern Sweden

The Protogine Zone (PZ) forms the border between the Svecofennian and Sveconorwegian domains of southern Sweden. Intruded in the Zone are three generations of mafic dykes dated 1510 Ma, 1180 Ma and 930 Ma. A palaeomagnetic study of these dykes in the central and southern parts of the PZ yields two main directions of magnetization: ‘A’ ( D = 291°, I = −78° , N = 31) and ‘B’ ( D = 129°, I = 40°, N = 13). These directions give palaeopoles on the Sveconorwegian Loop of the Fennoscandian apparent polar wander path (APWP). A third, poorly defined group, ‘C’, yields a mean declinationof 185° and inclination of 9°, with the corresponding palaeopole situated on the c. 1500–1600 Ma part of the APWP. Two other sites yield palaeopoles located in the 1200 Ma part of the path. The data imply that the Sveconorwegian orogeny caused a remagnetization of the two older dyke generations and that this remagnetization was complete in the southern part of the PZ, while a few dykes retained their original magnetization in the central part of the Zone. Either the difference between the ‘A’ and ‘B’ directions record appreciable APW movement during differential cooling of the PZ, or the ‘A’ and ‘B’ directions may represent an asymmetric reversal of the Earth's magnetic field. In the latter case they may be contemporary and have implications for the size and form of the Sveconorwegian Loop of the Fennoscandian APWP.

The Proterozoic evolution of the Bamble Sector shear belt, southern Norway: correlations across southern Scandinavia and the Grenvillian controversy

The Bamble Sector contains a parautochthon, which is a southward continuation of the (now separate) Kongsberg Sector, and an autochthon, which is part of the Telemark Basement Gneiss Complex (TBGC), the northwest bounding block of the Kongsberg-Bamble shear belt. The parautochthon formed at ∼ 110 Ma in the Sveconorwegian Orogeny and produced a distinctive gravity anomaly. The shear belt originated in the Kongsbergian Orogeny (∼ 1700–1500 Ma). Supracrustal rocks (deposited at ∼ 1700–1650 Ma) were deformed by D1 (∼ 1650 ± 50 Ma), developing a bend from the north-south Kongsberg Sector to the NE-SW Bamble Sector. The shear belt (of the Bamble parautochthon and Kongsberg Sector) absorbed high strains relative to surrounding blocks, particularly around this bend. The Late-Kongsbergian, D3 angular shearing (∼ 1500 Ma), in the parautochthon, absorbed a dextral strike-slip past the TBGC. Magmatism of the Post-Kongsbergian anorogenic period (between 1500 and 1250 Ma) included large alkaline suite-augen gneiss complexes, intruded (before ∼ 1395 Ma) in a folded zone across the parautochthon. An Early-Sveconorwegian orogenic phase of deformation and granite intrusion (∼ 1250 Ma) was concentrated at the interface of the shear belt with the TBGC. The ensuing Sveconorwegian anorogenic phase of crustal extension (∼ 1200–1100 Ma) was localised in the shear belt, where much basic magma was intruded. The Main Sveconorwegian orogenic phase started (∼ 1100 Ma) with thrusting of the shear belt over the relatively cratonic, higher levels of the TBGC and Bamble autochthon, where later deformations and magmatism (ca. 1050–950 Ma) were concentrated. Controversy about the existence of Grenvillian (Sveconorwegian) orogenic effects in South Norway arose because of the shifting focus of successive events, which preserved a record of older effects in parts of the Bamble parautochthon. Other general features include the variation in response of different lithologies to one deformation phase, and the location of intrusions by earlier fold structures. The Bamble Sector also shows the reaction of deep crustal levels to a dextral strike-slip, which was absorbed by the development of large, overlapping domains of complementary angular shear. The sequence established in the Bamble Sector permits detailed correlations of Mid- and Late-Proterozoic events across southern Scandinavia.

Cataclastic rocks along the Nesodden Fault, Oslo Region, Norway: a reactivated Precambrian shear zone

The Nesodden Fault Segment (NFS) is the northern segment of the Oslofjorden Fault (OF), which separates the Precambrian rocks in the east from Palaeozoic rocks in the west. The NFS is characterized by two groups of fault rocks. Group 1 comprises a series of crush breccias to ultracataclasites containing material derived from the Precambrian basement. These fault rocks were formed at a depth greater than 5 km, by attrition brecciation and distributed crush brecciation, at some time between the Sveconorwegian orogeny (950 Ma) and the deposition of the Cambrian Alum shale (540-505 Ma). Group 2 comprises five crush breccias with a similar quartz matrix containing fragments of older rocks and Permian intrusive rocks. They were formed at a depth of less than 3.5 km by the interaction of cataclasis and hydrothermal percolation (attrition- and implosion-brecciation), during the formation of the Permo-Carbonifereous Oslo Rift (300-230 Ma). Evidence of repeated hydrothermal fluid flow and fluidization has been recognized in the youngest breccias. The seven different fault rocks emphasize the importance of fault reactivation and show that old fault zones commonly act as planes of weakness along which repeated deformation takes place and act as pathways for hydrothermal fluids.

Aluminous reaction textures in orthoamphibole‐bearing rocks: the pressure–temperature evolution of the high‐grade Proterozoic of the Bamble sector, south Norway

Aluminous reaction textures in orthoamphibole‐bearing rocks from the Froland area, Bamble, south Norway, record the prograde pressure–temperature path of the high‐grade Kongsbergian Orogeny (c. 1600–1500 Ma) and the low–mid amphibolite facies overprint during the Sveconorwegian Orogeny (c. 1100–1000 Ma). The rocks contain anthophyllite/gedrite, garnet, cordierite, biotite, quartz, andalusite, kyanite, Cr‐rich staurolite, tourmaline, ilmenite, rutile and corundum in a variety of parageneses. The P–T path is deduced from petrographic observations, mineral chemistry and zoning, geothermometry and (N)FMASH equilibria. The results indicate the sequence of metamorphic stages outlined below. (a) An M1 phase characterized by the presence of strongly deformed andalusite, gedrite and tourmaline.(b) An M2 phase with the development of kyanite after andalusite and the growth of staurolite associated with strong Na–Al–Mg zoning in orthoamphibole, indicating an increase in pressure (4 8 kbar) and temperature (500° 650°C).(c) Pressure decrease at high P (6–7 kbar) and high T (600–700 °C) during M3a with the production of cordierite ° Corundum between kyanite, staurolite and orthoamphibole and cordierite growth between corundum and orthoamphibole.(d) Temperature increase to 740 ± 60 °C and 7 kbar; static growth of garnet (M3b) at the metamorphic climax (peak T). The heat supply necessary to explain the temperature increase between the M3a and M3b phases is correlated with synkinematic enderbitic–charnockitic and basic intrusions in the Arendal granulite facies terrain.(e) M3b metamorphic conditions were followed by an initial isobaric cooling path (early M4) and late‐stage pressure decrease (late M4). Early M4 conditions of 6–7 kbar and 550–600 °C, assuming PH2O < Ptotal are indicated by a retrograde talc–kyanite–quartz assemblage in late quartz–cordierite veins. Late M4 conditions of 3–4 kbar and 420–530 °C are inferred from a kyanite–andalusite–chlorite–quartz assemblage in vein‐cordierite. The M1–M3 stages are interpreted as being the result of the same metamorphic P–T path, which was caused by both tectonic and magmatic thickening. A prolonged crustal residence time is proposed for the Bamble sector before uplift during the later stages of M4 occurred.

Crustal reflections underneath Lake Vänern, Sweden

SUMMARY In conjunction with airgun profiles on Lake Vanern, 48-channel seismic recordings were made along a 7 km long profile on the northern peninsula, Varmlandsnas. This peninsula lies in the Mylonite Zone which runs through SW Sweden. Four airgun profiles were recorded, two on the eastern side of the Mylonite Zone and two on the western side, each profile being on the order of 20-30 km long. These profiles have been processed using the method of common data point (CDP) stacking which resulted in a total of approximately 50 km of sub-surface coverage. We have interpreted the data in the context of the regional geology and results from other geophysical studies in the area. Important results are the imaging of lower crustal reflectors and Moho at near-vertical incidence angles. The dips and depths of these reflectors are in fair agreement with other studies. The upper crust on the eastern side of the Mylonite Zone appears to be considerably more reflective. This may be due to the presence of mafic intrusions or to the reworking of the crust during the Sveconorwegian orogeny. A brief comparison with results from the GLIMPCE profiles over the Grenville province is also made.

Crustal evolution of Fennoscandia—palaeomagnetic constraints

Palaeomagnetic poles from Fennoscandia, ranging in age from Archaean to Tertiary, are compiled and graded using a modified Briden-Duff classification scale. An new “filtering” technique is applied to select only the most reliable poles for analysis. The filtering takes into account the following information: 1.(1) source block of rock unit,2.(2) age of rock,3.(3) age of magnetization component,4.(4) scatter of palaeomagnetic directions,5.(5) information from multicomponent analysis of natural remanent magnetization (NRM),6.(6) whether the pole considered belongs to a cluster or subcluster of poles,7.(7) magnetic polarity and8.(8) the author's original assignment of results.Data are still insufficient for the drawing of separate Apparent Polar Wander Paths (APWP) for different blocks or cratons of Fennoscandia. Treating Fennoscandia as a single plate, a new APWP from Archaean to Permian is constructed. From the five previously drawn APWP loops (or “hairpins”), only one, the Jatulian loop (2200-2000 Ma), disappears in filtering. The loops during 1925-1700 Ma and during 1100-800 Ma ago are linked to Svecofennian and Sveconorwegian orogenies, respectively. Palaeomagnetic data support the concept that these orogenies took place episodically; three distinct orogenic pulses (early, middle and late) can be distinguished in the cluster plots of palaeopoles.The drift history of Fennoscandia from Archaean to Permian is presented. During most of geological history, Fennoscandia has occupied low to moderate latitudes and undergone considerable latitudinal shifts and rotations. The Svecofennian and Sveconorwegian orogenies have different kinematic characteristics. During the Svecofennian orogeny, Fennoscandia drifted slowly while rotating a large amount in an anticlockwise sense. During the Sveconorwegian orogeny, it drifted rapidly and rotated first clockwise and then anticlockwise. The most striking feature in the drift velocity curves is, however, the pronounced maxima in the latitudinal drift and rotation rates (~ 9 cm/yr and ~ 0.8°/Ma, respectively) during the late Subjotnian-Jotnian anorogenic magmatism and rifting phase (~1450-1250 Ma ago), possibly reflecting the passage of Fennoscandia across a thermal upwelling (hotspot) at equatorial latitudes.The use of palaeomagnetism in delineating and dating movements between blocks is demonstrated with three examples from the POLAR Profile area, the northernmost section of the European Geotraverse.

RbSr isotopic equilibrium during Sveconorwegian (= Grenville) deformation and metamorphism of the Orust dykes, S.W. Sweden

The Orust dykes and their regional correlatives are an important time marker in the polymetamorphic Östfold-Marstrand belt of S.E. Norway and S.W. Sweden. They were deformed and metamorphosed in the amphibolite facies during the Sveconorwegian (= Grenville) orogeny. Three narrow strongly deformed dykes yield RbSr whole-rock ages (1106 ± 52 m.y., 1062 ± 90 m.y., 1000 ± 153 m.y.). The weighted mean age (1087 m.y.) is interpreted as the age of the first post-dyke deformation and the accompanying amphibolite facies metamorphism. High initial 87Sr/ 86Sr ratios (0.7074 ± 9, 0.710 ± 2, 0.713 ± 3, respectively) and other geochemical evidence point to considerable exchange of mobile elements between the dykes and the country rocks. The emplacement age is not known precisely. However, the dykes may be correlated with widespread mafic magnatism which accompanied crustal instability in the N. Atlantic region early in the Sveconorwegian (= Grenville) orogeny about 1200 m.y. ago.

The effects of penetrative Sveconorwegian deformations on RbSr isotope systems in the Römskog-Aurskog-Höland Area, SE Norway

Abstract The area investigated consists of five granitoid complexes which range over more than 900 Ma (?1850-925 Ma RbSr whole rock) in age as well as an old series of layered para- and orthogneiss. The relative ages of the old gneiss series and the oldest granitoid complex, which is a series of augen gneisses (?1850-1710 Ma), are uncertain. The layered para- and orthogneisses were however definitely gneissified before the intrusion of a 1631 Ma old grey orthogneiss. Deformational activity took place several times during the geological evolution. The major structures developed mainly after the intrusion of both a 1277 ± 20 Ma old red granitic orthogneiss and the mafic dykes that transsect it. The post-1277 Ma structures resulted from the following: a foliation-forming event with migmatization; a fold phase giving E–W-directed folds; a fold phase giving N–S-directed folds which affect the southern part of the area only; and finally, a large-scale overthrusting towards the east along the western limit of the area. The upper age limit of the folding activity is established by a 925 Ma old undeformed granite. The post-1277 Ma structures are regarded as constituting the infrastructure of the Sveconorwegian orogeny in the area. Possible correlation with the suprastructure of this orogeny in the Dalsland area further south is discussed. Although the dated rocks have suffered from high-grade metamorphism, we argue that the RbSr whole-rock ages mark the ages of intrusion (crystallization) of the plutonic complexes.

The Sveconorwegian structures of the Norwegian part of the Kongsberg-Bamble-Østfold segment

Abstract The Kongsberg-Bamble-Østfold segment within the Sveconorwegian province is bounded by the Kristiansand-Bang shear zone and the Dalsland Boundary Thrust. The pre-Sveconorwegian basement rocks in this segment were involved in tectono-metamorphic reworking during the Sveconorwegian orogeny, which produced the main regional structures. These structures and opposite thrusting along the eastern and western margins of the segment suggest a large amount of Sveconorwegian crustal shortening in an E-W direction.

The Sveconorwegian orogenic belt, a case of late-proterozoic plate-collision

A geotetctonic model is proposed for the Sveconorwegian orogeny (1200-850 Ma), based on compilation of lithological and structural evidence. This analysis suggests a N—S trending, asymmetrical orogenic belt with longitudinal zonation. In the western-most core zone, synkinematic intrusions dominate, while the central zone consists primarily of reworked basement with subordinate intrusions and metasediments. In the easternmost marginal zone, series of pre-Sveconorwegian mega-units are separated by thrust zones and finally bordered by the Sveconorwegian frontal thrust towards the east. Graben formation in the Telemark area preserves the deposits of previous epicratonic stages and marks the initiation of Sveconorwegian activities at about 1190 Ma. The subsequent orogenic development, associated with lithospheric subduction, shows tight folding about N—S axes with steep axial planes in the west, and more open NW—SE folding with gentle westward dipping axial planes towards the east. Regional metamorphism of low-P, high-T conditions imply steep geothermal gradients and suggests hercynotype crustal evolution, in agreement with a Cordilleran-type plate collision. In the Bamble district, important structural alignment forms a zone of crustal anisotropy which was repeatedly reactivated and ultimately became the site for Permian rifting forming the Oslo Graben. The lithological and structural characters as well as the crustal evolution for the Sveconorwegian orogeny show strong similarities with the Grenville development in southeastern Canada. Structural vergence and orogenic zonation suggest that the Sveconorwegian front and the Grenville front are equivalent and form different parts of a single orogenic belt, permitting a tentative reconstruction of the Late-Proterozoic, North-Atlantic Shield.

The Central Scandinavian Dolerite Group in Jämtland, central Sweden

Abstract Inz north central Sweden, the ca. 1250-Ma old Central Scandinavian Dolerite Group mainly comprises large flat-lying sheets essentially of alkali-basaltic olivine dolerite. The content of incompatible elements is somewhat lower than is average in alkali basalts. Geochemically, the dolerites are rather homogeneous and follow a liquid-descent line which is modified somewhat by the cumulation of early olivine. Mineralogical control of crystallization is particularly obvious in the Ni/Cr and K/Rb distributions. The contents and proportions of minor chemical constituents are discussed in relation to systems proposed for tectonic classification. The intrusion of the Central Scandinavian Dolerite Group was an intra-plate event coinciding in time with the early stages of the Sveconorwegian orogeny in western Scandinavia.

A uranium and thorium enriched province of the Fennoscandian shield in southern Norway

The Precambrian Flå, Iddefjord, and Bohus granites lie along a line striking roughly northwest which crosses the Permian Oslo Province to the southwest of Oslo. Radioelement investigations in the three bodies show they all contain abnormally high thorium and uranium concentrations relative to the published literature on average radioelement contents of granitic rocks. Trend surface analysis of the radioelement distribution in the Iddefjord granite suggests there was relative movement of uranium to the east with respect to thorium, possibly as the result of Permian activity in the adjacent rocks. Geological considerations, radiometric evidence and published gravimetric data suggest that the 3 granites represent a continuous belt enriched in thorium and uranium during the Sveconorwegian orogeny. A portion of the belt was later involved in the Permian igneous activity which produced the igneous Oslo Province. There is some evidence that the Permian Drammen and Finnemarka granites represent that part of the belt which was modified in Permian time.

The structural setting and geochronology of basal granitic gneisses in the Caledonides of part of Nordland, Norway

Rb–Sr whole rock isochron dates of 1780 ± 43 m.y. and 1731 ± 73 m.y. (λ 87 Rb 1.39 × 10 −11 yr −1 ) have been measured on basal granitic gneisses which underlie Caledonian metamorphic rocks in the Glomfjord-Nasafjåll tract of Norway. Rb–Sr data from a part of the region can be interpreted in terms of localized Sr isotope homogenization at around 1200 m.y., but severe Caledonian deformation and metamorphism has had little apparent effect on the whole rock systems on the scale of sampling. The dates are discussed in the context of published Rb–Sr and U–Pb dates from the Baltic Shield, of which a distribution map is given. It is concluded that the gneisses investigated attained their pre-Caledonian form during the Svecofennian orogeny, but may have been affected in part by the Sveconorwegian orogeny.