| 1. |
- Bergström, Ulf, et al.
(författare)
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Polyphase (1.6–1.5 and 1.1–1.0 Ga) deformation and metamorphism of Proterozoic (1.7–1.1 Ga) continental crust, Idefjorden terrane, Sveconorwegian orogen
- 2020
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Ingår i: Sweden. - : Geological Society of London. ; , s. 397-434
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Bokkapitel (övrigt vetenskapligt/konstnärligt)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.
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| 2. |
- Gee, David G., et al.
(författare)
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Lower thrust sheets in the Caledonide orogen, Sweden: Cryogenian–Silurian sedimentary successions and underlying, imbricated, crystalline basement
- 2020
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Ingår i: Sweden. - : Geological Society of London. ; , s. 495-515
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Bokkapitel (övrigt vetenskapligt/konstnärligt)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.
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| 3. |
- Gee, David G., et al.
(författare)
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Middle thrust sheets in the Caledonide orogen, Sweden: the outer margin of Baltica, the continent–ocean transition zone and late Cambrian–Ordovician subduction–accretion
- 2020
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Ingår i: Sweden. - : Geological Society of London. - 9781786204608 ; 50:1, s. 517-548
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Bokkapitel (övrigt vetenskapligt/konstnärligt)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.
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| 4. |
- Gee, David G., et al.
(författare)
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Regional context and tectonostratigraphic framework of the early–middle Paleozoic Caledonide orogen, northwestern Sweden
- 2020
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Ingår i: Sweden. - : Geological Society of London. ; , s. 481-494
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Bokkapitel (övrigt vetenskapligt/konstnärligt)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.
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| 5. |
- Ripa, Magnus, et al.
(författare)
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Continental magmatic arc and siliciclastic sedimentation in the far-field part of a 1.7 Ga accretionary orogen
- 2020
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Ingår i: Sweden. - : Geological Society of London. ; , s. 253-268
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Trachyandesitic to trachybasaltic lavas, interlayered siliciclastic sedimentary rocks and subaerial ignimbrites with a rhyolitic to trachydacitic composition lie unconformably above metamorphic rocks in west-central Sweden. These volcanic rocks erupted at 1711 + 7/−6 to 1691 ± 5 Ma and belong to a high-K, calc-alkaline to shoshonitic suite deposited in a continental arc setting. Positive ɛNd values and Nb/Yb ratios in the trachyandesitic to trachybasaltic rocks indicate an enriched mantle source. Coeval, 1710 ± 11 to 1681 ± 16 Ma plutonic and subvolcanic rocks are mainly granitic or quartz syenitic in composition. Subordinate components include quartz monzonite, quartz monzodiorite and monzogabbro or gabbro. ɛNd values in the range −1.0 to + 1.1 overlap with those in the inferred 1.9–1.8 Ga source rocks. All these rocks belong to the youngest phase of the lithodemic unit referred to as the Transscandinavian Igneous Belt. This magmatic province extends in a roughly NNW direction for at least 900 km, variably deformed and metamorphosed equivalents occurring inside and beneath younger orogenic belts to the south (Sveconorwegian) and north (Caledonian). The part of the province in west-central Sweden addressed here represents a far-field and shallow crustal component in this 1.7 Ga accretionary orogenic system.
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| 6. |
- Ripa, Magnus, et al.
(författare)
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Dolerites (1.27–1.25 Ga) and alkaline ultrabasic dykes (c. 1.14 Ga) related to intracratonic rifting
- 2020
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Ingår i: Sweden. - : Geological Society of London. ; , s. 315-323
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Doleritic sills, lopoliths and dykes were emplaced into the Paleoproterozoic craton in central Sweden at 1271–1264, 1259–1256 and c. 1247 Ma, a complex temporal zonation occurring in a WSW–ENE direction. The dolerites are subalkaline to alkaline and show predominantly gabbroic, with a trend towards monzogabbroic and quartz monzodioritic, compositions. Positive ɛNd and ɛHf values suggest a significant depleted mantle component in the source volume of the parental magmas. Dyke orientations indicate extension, at least locally, in a northwesterly direction, consistent with a magma flow direction determined using the anisotropy of magnetic susceptibility values. Intracratonic rifting linked to the break-up of the supercontinent Columbia, back-arc extension above a subduction boundary in a westwards-retreating mode or a mantle plume tail above a continental hotspot have all been proposed for the tectonic setting. Renewed intracratonic rifting at c. 1.14 Ga in the coastal area in northeasternmost Sweden resulted in the emplacement of alkaline ultrabasic dykes, including carbonatites (beforsites), silico-carbonatites and lamprophyres, in a north–south direction along an older shear belt. The broader tectonic setting of this extensional event is not known.
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| 7. |
- Ripa, Magnus, et al.
(författare)
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Magmatism (1.6–1.4 Ga) and Mesoproterozoic sedimentation related to intracratonic rifting coeval with distal accretionary orogenesis
- 2020
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Ingår i: Sweden. - : Geological Society of London. ; , s. 269-288
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Separate pulses of magmatic activity involving the emplacement of plutons with predominantly granitic or bimodal granitic and gabbroic composition, as well as dolerite dykes, occurred in a cratonic setting in eastern Sweden at c. 1.59–1.58 Ga, c. 1.53–1.50 Ga and c. 1.47–1.44 Ga; anorthosite, monzodiorite and syenitoid rocks are locally present. Most of the granites have been compared with rapakivi granites in Finland and elsewhere. Isotopic data (Hf in zircons and ɛNd values) from the plutons in north-central Sweden show contamination by an Archean source. Siliciclastic rocks dominated by aeolian or deltaic sandstones overlie c. 1.58 Ga or c. 1.50 Ga plutons, are intercalated with 1.46 Ga basaltic lavas and were deposited prior to the emplacement of 1.27–1.25 Ga dolerites. The magmatic rocks are subalkaline (tholeiitic) to alkaline and the mafic components have been compared with continental flood basalts, suggesting an intracratonic, rift-related tectonic setting for the magmatism and sand deposition. These rocks constitute the westerly part of a late Paleoproterozoic to early Mesoproterozoic magmatic province in northern Europe, located along roughly north–south- and WSW–ENE-trending linear belts. This tectonic development was coeval with accretionary orogenic activity further to the west and SW.
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| 8. |
- Ripa, Magnus, et al.
(författare)
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Siliciclastic sedimentation in a foreland basin to the Sveconorwegian orogen and dolerites (0.98–0.95 Ga) related to intracratonic rifting
- 2020
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Ingår i: Sweden. - : Geological Society of London. ; , s. 325-333
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Bokkapitel (övrigt vetenskapligt/konstnärligt)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. ɛNd and ɛHf 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.
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| 9. |
- Skyttä, Pietari, et al.
(författare)
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Paleoproterozoic (2.0–1.8 Ga) syn-orogenic sedimentation, magmatism and mineralization in the Bothnia–Skellefteå lithotectonic unit, Svecokarelian orogen
- 2020
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Ingår i: Sweden. - : Geological Society of London. ; , s. 83-130
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Bokkapitel (refereegranskat)abstract
- The Bothnia–Skellefteå lithotectonic unit is dominated by turbiditic wacke and argillite (Bothnian basin), deposited at 1.96 (or older)–1.86 Ga, metamorphosed generally under high-grade conditions and intruded by successive plutonic suites at 1.95–1.93, 1.90–1.88, 1.87–1.85 and 1.81–1.76 Ga. In the northern part, low-grade and low-strain, 1.90–1.86 Ga predominantly magmatic rocks (the Skellefte–Arvidsjaur magmatic province) are enclosed by the basinal components. Subduction-related processes in intra-arc basin and magmatic arc settings, respectively, are inferred. Changes in the metamorphic grade and the relative timing of deformation and structural style across the magmatic province are linked to major shear zones trending roughly north–south and, close to the southern margin, WNW–ESE. Zones trending WNW–ESE and ENE–WSW dominate southwards. Slip along the north–south zones in an extensional setting initiated synchronously with magmatic activity at 1.90–1.88 Ga. Tectonic inversion steered by accretion to a craton to the east, involving crustal shortening, ductile strain and crustal melting, occurred at 1.88–1.85 Ga. Deformation along shear zones under lower-grade conditions continued at c. 1.8 Ga. Felsic volcanic rocks (1.90–1.88 Ga) host exhalative and replacement-type volcanogenic massive sulphide deposits (the metallogenic Skellefte district). Other deposits include orogenic Au, particularly along the ‘gold line’ SW of this district, porphyry Cu–Au–Mo, and magmatic Ni–Cu along the ‘nickel line’ SE of the ‘gold line’.
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| 10. |
- Stephens, Michael B., et al.
(författare)
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Accretionary orogens reworked in an overriding plate setting during protracted continent–continent collision, Sveconorwegian orogen, southwestern Sweden
- 2020
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Ingår i: Sweden. - : Geological Society of London. ; , s. 435-448
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Bokkapitel (övrigt vetenskapligt/konstnärligt)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.
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