Chapter 19 Regional context and tectonostratigraphic framework of the early–middle Paleozoic Caledonide orogen, northwestern Sweden

2020 ◽  
Vol 50 (1) ◽  
pp. 481-494 ◽  
Author(s):  
David G. Gee ◽  
Michael B. Stephens
Keyword(s):  
Foreland Basin ◽  
Metasedimentary Rocks ◽  
Mafic Intrusions ◽  
Late Cambrian ◽  
Iapetus Ocean ◽  
Nappe Complex ◽  
Middle Paleozoic ◽  
Thrust Sheets ◽  
Seve Nappe Complex ◽  
Augen Gneiss

AbstractThe 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.

Chapter 21 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 ◽  
Vol 50 (1) ◽  
pp. 517-548 ◽  
Author(s):  
David G. Gee ◽  
Iwona Klonowska ◽  
Per-Gunnar Andréasson ◽  
Michael B. Stephens
Keyword(s):  
Transition Zone ◽  
Foreland Basin ◽  
Ultrahigh Pressure ◽  
Dyke Swarm ◽  
Metasedimentary Rocks ◽  
Late Cambrian ◽  
Nappe Complex ◽  
Thrust Sheets ◽  
Augen Gneiss ◽  
Ocean Ridge

AbstractNappes 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.

scholarly journals Detrital zircon U-Pb geochronology of a metasomatic calc-silicate in the Tsäkkok Lens, Scandinavian Caledonides

2021 ◽  
Vol 47 (1) ◽  
pp. 21-31
Author(s):  
Christopher J. Barnes ◽  
Jarosław Majka ◽  
Michał Bukała ◽  
Erika Nääs ◽  
Sabine Rousku
Keyword(s):  
Detrital Zircon ◽  
Oscillatory Zoning ◽  
Similar Time ◽  
Metasedimentary Rocks ◽  
Tectonic Events ◽  
Scandinavian Caledonides ◽  
Iapetus Ocean ◽  
Nappe Complex ◽  
Seve Nappe Complex ◽  
Time Frames

The Tsäkkok Lens of the Seve Nappe Complex in the Scandinavian Caledonides comprises eclogite bodies hosted within metasedimentary rocks. These rocks are thought to be derived from the outermost margin of Baltica along the periphery of the Iapetus Ocean, but detrital records from the sedimentary rocks are lacking.Many metasedimentary outcrops within the lens expose both well-foliated metapelitic rocks and massive calc-silicates. The contacts between these two lithologies are irregular and are observed to trend at all angles to the high-pressure foliation in the metapelites. Where folding is present in the metapelites, the calc-silicate rocks are also locally folded. These relationships suggest metasomatism of the metapelites during the Caledonian orogenesis. Zircon U-Pb geochronology was conducted on sixty-one zircon grains from a calc-silicate sample to investigate if they recorded the metasomatic event and to assess the detrital zircon populations. Zircon grains predominantly show oscillatory zoning, sometimes with thin, homogeneous rims that have embayed contacts with the oscillatory-zoned cores. The zircon cores yielded prominent early Stenian, Calymmian, and Statherian populations with a subordinate number of Tonian grains. The zircon rims exhibit dissolution-reprecipitation of the cores or new growth and provide ages that span similar time frames, indicating overprinting of successive tectonic events. Altogether, the zircon record of the calc-silicate suggests that the Tsäkkok Lens may be correlated to Neoproterozoic basins that are preserved in allochthonous positions within the northern extents of the Caledonian Orogen.

scholarly journals Ba- and Ti-enriched dark mica from the UHP metasediments of the Seve Nappe Complex, Swedish Caledonides

Mineralogia ◽  
2015 ◽  
Vol 46 (1-2) ◽  
pp. 41-50
Author(s):  
Jarosław Majka ◽  
Łukasz Kruszewski ◽  
Åke Rosén ◽  
Iwona Klonowska
Keyword(s):  
Granulite Facies ◽  
Stability Field ◽  
Metasedimentary Rocks ◽  
High Pressure Metamorphism ◽  
Nappe Complex ◽  
Crystallochemical Formula ◽  
Seve Nappe Complex ◽  
The Mean ◽  
End Members ◽  
Parental Rock

AbstractWe report on the occurrence of peculiar Ba- and Ti-enriched dark mica in metasedimentary rocks that underwent high-pressure metamorphism in the diamond stability field followed by decompression to granulite facies conditions. The mica occurs as well-developed preserved laths in a quartzofeldspathic matrix. The mean concentrations of BaO and TiO2in the mica are 11.54 and 7.80wt%, respectively. The maximum amounts of these components are 13.38wt% BaO and 8.45wt% TiO2. The mean crystallochemical formula can be expressed as (K0.54Ba0.39Na0.02Ca0.01)Σ0.96(Fe1.37Mg0.85Ti0.50Al0.29Mn0.01Cr0.01)Σ3.03(Si2.59Al1.41)Σ4.00O10(OH1.30O0.66F0.02S0.01)Σ1.99, withoxyannite,oxy-ferrokinoshitaliteand siderophyllite as dominating end-members. Based on the petrographical observations, it is proposed that the dark mica was formed at a rather late stage in the evolution of the parental rock, i.e. under granulite facies conditions.

Thermal history of thrust sheets in an orogenic wedge: 40Ar/39Ar data from the polymetamorphic Seve Nappe Complex, northern Swedish Caledonides

2000 ◽  
Vol 137 (4) ◽  
pp. 437-446 ◽  
Author(s):  
OLAF M. SVENNINGSEN
Keyword(s):  
Shear Zones ◽  
Passive Margin ◽  
Fault System ◽  
Dyke Swarm ◽  
Slow Cooling ◽  
Nappe Complex ◽  
Thrust Sheets ◽  
Seve Nappe Complex ◽  
The Baltic ◽  
The Individual

The Seve Nappe Complex in the Scandinavian Caledonides contains the fragmented late Precambrian continent–ocean transition between Baltica and the Iapetus Ocean. This passive margin was fragmented and thrust eastwards over the Baltic Shield during Caledonian orogenesis. The individual thrust sheets in the Seve Nappe Complex went through different P–T–t evolutions, resulting in dramatic metamorphic contrasts: eclogite-bearing nappes are juxtaposed with nappes showing no evidence of Caledonian deformation or metamorphism in their interiors. Strain localization to the marginal parts of the thrust sheets left records of both pre-orogenic (rift) and early orogenic (subduction and subsequent uplift) processes in the thrust sheets of the Seve Nappe Complex. Even though it has been transported several hundred kilometres, only the margins of the eastern part of the Sarektjåkkå Nappe are affected by penetrative Caledonian deformation. This part of the Sarektjåkkå Nappe is dominated by pristine tholeiitic dykes and cross-bedded sandstones. The dykes are 608±1 Ma old and make up 70–80% of the nappe. Widely spaced thin shear zones of the Ruopsok fault system represent the only Caledonian penetrative deformation in the interior of the nappe. Previously published Ar–Ar dates indicate cooling below the closure temperature of hornblende at c. 470 Ma, but numerous ages have been recorded. Ar dating of biotite and muscovite from a cross-laminated metapsammite in the Sarektjåkkå Nappe gave well-defined ages of 428.5±3.6 and 432.4±3.8 Ma, respectively. Muscovite from a shear zone in the Ruopsok Fault System gave 428.2±4.0 Ma, whereas hornblende from the same locality did not yield interpretable data. The results indicate that these rocks were completely degassed at some unknown time, presumably at the emplacement of the dyke swarm. No subsequent excess argon contamination can be detected. A likely candidate for the degassing event is the emplacement of the dykes at 608 Ma. The interior of the nappe, and thus the entire nappe complex, cooled below ∼ 350 °C at around 430 Ma. Cooling from more than 500 °C at c. 470 Ma to 350 °C at c. 430 Ma suggests an average cooling rate of [les ] 4 °C/Ma. A prolonged period of slow cooling (≈exhumation?) following the initial, rapid uplift of the eclogite-bearing nappes and Early Ordovician construction of the Seve Nappe Complex is suggested.

scholarly journals Revised Timing of Cenozoic Atlantic Incursions and Changing Hinterland Sediment Sources during Southern Patagonian Orogenesis

Lithosphere ◽  
2020 ◽  
Vol 2020 (1) ◽  
pp. 1-18 ◽  
Author(s):  
Julie C. Fosdick ◽  
R. A. VanderLeest ◽  
J. E. Bostelmann ◽  
J. S. Leonard ◽  
R. Ugalde ◽  
...  
Keyword(s):  
Detrital Zircon ◽  
Atlantic Coast ◽  
Foreland Basin ◽  
Late Eocene ◽  
Coarse Grained ◽  
Plate Convergence ◽  
Metasedimentary Rocks ◽  
Sediment Routing ◽  
Thrust Sheets ◽  
Major Shift

Abstract New detrital zircon U-Pb geochronology data from the Cenozoic Magallanes-Austral Basin in Argentina and Chile ~51° S establish a revised chronostratigraphy of Paleocene-Miocene foreland synorogenic strata and document the rise and subsequent isolation of hinterland sources in the Patagonian Andes from the continental margin. The upsection loss of zircons derived from the hinterland Paleozoic and Late Jurassic sources between ca. 60 and 44 Ma documents a major shift in sediment routing due to Paleogene orogenesis in the greater Patagonian-Fuegian Andes. Changes in the proportion of grains from hinterland thrust sheets, comprised of Jurassic volcanics and Paleozoic metasedimentary rocks, provide a trackable signal of long-term shifts in orogenic drainage divide and topographic isolation due to widening of the retroarc fold-thrust belt. The youngest detrital zircon U-Pb ages confirm timing of Maastrichtian-Eocene strata but require substantial age revisions for part of the overlying Cenozoic basinfill during the late Eocene and Oligocene. The upper Río Turbio Formation, previously mapped as middle to late Eocene in the published literature, records a newly recognized latest Eocene-Oligocene (37-27 Ma) marine incursion along the basin margin. We suggest that these deposits could be genetically linked to the distally placed units along the Atlantic coast, including the El Huemul Formation and the younger San Julián Formation, via an eastward deepening within the foreland basin system that culminated in a basin-wide Oligocene marine incursion in the Southern Andes. The overlying Río Guillermo Formation records onset of tectonically generated coarse-grained detritus ca. 24.3 Ma and a transition to the first fully nonmarine conditions on the proximal Patagonian platform since Late Cretaceous time, perhaps signaling a Cordilleran-scale upper plate response to increased plate convergence and tectonic plate reorganization.

The subduction, exhumation, and deformation history of the Vaimok Lens, Seve Nappe Complex, Scandinavian Caledonides

2021 ◽  
Author(s):  
Christopher Barnes ◽  
Jarosław Majka ◽  
David Schneider ◽  
Mattia Gilio ◽  
Matteo Alvaro ◽  
...  
Keyword(s):  
Weighted Average ◽  
White Mica ◽  
Garnet Growth ◽  
Prograde Metamorphism ◽  
Early Ordovician ◽  
Metasedimentary Rocks ◽  
Scandinavian Caledonides ◽  
Nappe Complex ◽  
History Of ◽  
Seve Nappe Complex

<p>            The Seve Nappe Complex (SNC) of the Scandinavian Caledonides represents portions of the Baltican margin that were subducted to mantle depths. Eclogite-bearing sub-units of the SNC provide a record of this important step in orogen development. One such sub-unit is the Vaimok Lens of the SNC in southern Norrbotten. The Vaimok Lens constitutes eclogites hosted within metasedimentary rocks that reached ultra-high pressure (UHP) conditions in the Cambrian/Early Ordovician period. The metasedimentary rocks are typically composed of quartz, white mica, garnet, plagioclase, biotite, clinozoisite, apatite and titanite, and show a pervasive ‘S2’ foliation that developed during exhumation. Garnet is recognized as a relic of prograde metamorphism during subduction, whereas the other minerals represent retrogressive metamorphism during exhumation. To resolve the timing of prograde metamorphism, Lu-Hf geochronology was conducted on metasediment-hosted garnet that preserves prograde, bell-shaped Mn-zoning with a chemical formula of Alm<sub>69-59</sub>Grs<sub>32-24</sub>Sps<sub>13-2</sub>Prp<sub>5-2</sub>. The results indicate garnet growth at 495.3 ± 2.6 Ma. Quartz-in-garnet (QuiG) elastic geobarometry was also conducted on garnet from the same sample, providing pressures of 0.9-1.3 GPa, calculated at 500-700°C. Six samples were obtained for in-situ <sup>40</sup>Ar/<sup>39</sup>Ar geochronology, targeting white mica defining the S2 foliation. Samples can be classified as: 1) low-strain (n: 3), with large (>400 µm width), undeformed micas that are chemically homogeneous (X<sub>Cel</sub>: 0.24-0.35), which yielded a weighted average <sup>40</sup>Ar/<sup>39</sup>Ar population of 470.5 ± 5.9 Ma; 2) high-strain (n: 3), with small (<300 µm width) mica fish with heterogeneous chemistry (X<sub>Cel</sub>: 0.03-0.27), which provided weighted average <sup>40</sup>Ar/<sup>39</sup>Ar populations of 447.6 ± 2.6 Ma and 431.1 ± 4.1 Ma. An additional sample from the basal thrust of the lens that contains large (>300 µm width), homogeneous (X<sub>Cel</sub>: 0.24-0.34) mica was also dated, yielding a population of 414.1 ± 5.8 Ma. Altogether, the data indicates that the Vaimok Lens was subducting by c. 495 Ma. The lens underwent post-decompression cooling at c. 470 Ma, possibly decompressing to 0.9-1.3 GPa by this time. This would equate to an exhumation rate of 3-9 mm/yr. Imbrication of the SNC in southern Norrbotten is taken to be c. 447 Ma. Scandian deformation was active by c. 431 Ma and led to overthrusting of the SNC onto subjacent nappes by latest c. 414 Ma. Both the timescale for subduction and the rates of exhumation for the Vaimok Lens reflect subduction-exhumation dynamics of large UHP terranes. Furthermore, the timing of imbrication and Scandian deformation in southern Norrbotten is similar to estimates along strike of the SNC. These results indicate that the SNC acted as a large UHP terrane that underwent a ~25 Myr cycle of subduction and exhumation during the late Cambrian/Early Ordovician, before being deformed and partially dismembered in subsequent accretionary and collisional events.</p><p> </p><p>Research funded by National Science Centre (Poland) project no. 2014/14/E/ST10/00321 to J. Majka.</p>

Regional geology and tectonic framework of the Southern Indian domain, Trans-Hudson Orogen, Manitoba

2021 ◽  
Author(s):  
Tania Martins ◽  
Nicole Rayner ◽  
David Corrigan ◽  
Paul Kremer
Keyword(s):  
Regional Scale ◽  
Foreland Basin ◽  
Geological Mapping ◽  
Metasedimentary Rocks ◽  
Mafic Intrusions ◽  
Plume Magmatism ◽  
Tectonic Framework ◽  
Lynn Lake ◽  
Clastic Sedimentary ◽  
Polymictic Conglomerate

The collaborative federal-provincial Southern Indian Lake project in north-central Manitoba covered an area of more than 3500 km2 of the Trans-Hudson orogen. Regional-scale geological mapping, sampling, and lithogeochemical, isotopic and geochronological studies resulted in the identification of distinct assemblages of supracrustal rocks and varied episodes of plutonism. A granodiorite gneiss dated at ca. 2520 Ma is interpreted to represent the basement of the Southern Indian domain and is considered a separate crustal domain, named the Partridge Breast block. The Churchill River assemblage is composed of juvenile pillow basalt with intervening clastic sedimentary rocks, possibly a reflection of plume magmatism related to initial rifting of the Hearne craton margin. The Pukatawakan Bay assemblage consists mainly of massive to pillowed, juvenile metabasaltic rocks and associated basinal metasedimentary rocks. The Partridge Breast Lake assemblage is dominated by continental-arc volcanic and volcaniclastic rocks associated with basinal metasedimentary rocks. The Strawberry Island assemblage, consisting of arenite and polymictic conglomerate, is interpreted to have been deposited in a foreland-basin basin or intra-orogen pull-apart basin environment. The Whyme Bay assemblage is characterized by fluvial-alluvial orogenic sediments and is temporally linked to the Sickle Group rocks in the Lynn Lake greenstone belt. Granitoid rocks, dominantly monzogranite and granodiorite, range in age from ca. 1890 to 1830 Ma and occur throughout the Southern Indian domain, and intermediate and mafic intrusions of similar ages are also present. In this paper we integrate these new data into a tectonic framework for the Southern Indian domain of the Trans-Hudson orogen in Manitoba.

scholarly journals U-Pb Zircon Dating of Migmatitic Paragneisses and Garnet Amphibolite from the High Pressure Seve Nappe Complex in Kittelfjäll, Swedish Caledonides

Minerals ◽  
2020 ◽  
Vol 10 (4) ◽  
pp. 295 ◽  
Author(s):  
Michał Bukała ◽  
Jarosław Majka ◽  
Katarzyna Walczak ◽  
Adam Włodek ◽  
Melanie Schmitt ◽  
...  
Keyword(s):  
Granulite Facies ◽  
Passive Margin ◽  
Metamorphic Zircon ◽  
Garnet Amphibolite ◽  
Iapetus Ocean ◽  
Icp Ms ◽  
Nappe Complex ◽  
The Matrix ◽  
Seve Nappe Complex ◽  
Ree Patterns

The Seve Nappe Complex exposed in the Kittelfjäll area of the northern Scandinavian Caledonides comprises a volcano-sedimentary succession representing the Baltica passive margin, which was metamorphosed during the Iapetus Ocean closure. Garnet amphibolites, together with their host migmatitic paragneisses, record a potential (U)HP event followed by decompression-driven migmatization. The garnet amphibolites were originally thought to represent retrogressively altered granulites. The petrological and geochemical features of a studied garnet amphibolite allow for speculation about a peridotitic origin. Zirconium (Zr) content in rutile inclusions hosted in garnet in paragneisses points to near-peak temperatures between 738 °C and 780 °C, which is in agreement with the c. 774 °C obtained from the matrix rutile in the garnet amphibolite. The matrix rutile in multiple paragneiss samples records temperatures below 655 °C and 726 °C. Whereas the LA-ICP-MS U-Pb dating of zircon cores revealed the age spectrum from Paleoproterozoic to early Paleozoic, suggesting a detrital origin of zircon cores in paragneisses, the metamorphic zircon rims show an Early Ordovician cluster c. 475–469 Ma. Additionally, zircon cores and rims from the garnet amphibolite yielded an age of c. 473 Ma. The REE patterns of the Caledonian zircon rims from the paragneisses show overall low LREE concentrations, different from declining to rising trends in HREE (LuN/GdN = 0.49–38.76). Despite the textural differences, the cores and rims in zircon from the garnet amphibolite show similar REE patterns of low LREE and flat to rising HREE (LuN/GdN = 3.96–65.13). All zircon rims in both lithologies display a negative Eu anomaly. Hence, we interpret the reported ages as the growth of metamorphic zircon during migmatization, under granulite facies conditions related to exhumation from (U)HP conditions.

Chapter 23 Swedish Caledonides: key components of an early–middle Paleozoic Himalaya-type collisional orogen

2020 ◽  
Vol 50 (1) ◽  
pp. 577-599 ◽  
Author(s):  
David G. Gee
Keyword(s):  
North Atlantic Ocean ◽  
Mafic Magma ◽  
Ultrahigh Pressure ◽  
Uhp Metamorphism ◽  
Foreland Basins ◽  
The North ◽  
Late Cambrian ◽  
Orogenic Wedge ◽  
Middle Paleozoic ◽  
Thrust Sheets

AbstractCaledonian 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.

Chapter 22 Upper and uppermost thrust sheets in the Caledonide orogen, Sweden: outboard oceanic and exotic continental terranes

2020 ◽  
Vol 50 (1) ◽  
pp. 549-575 ◽  
Author(s):  
Michael B. Stephens
Keyword(s):  
Continental Margin ◽  
Amphibolite Facies ◽  
Magmatic Activity ◽  
Volcanic Arcs ◽  
Late Cambrian ◽  
Marine Sedimentation ◽  
Nappe Complex ◽  
Thrust Sheets ◽  
Tectonothermal Event ◽  
Gabbroic Pluton

AbstractThree separate stacks of thrust sheets (Köli Nappe Complex) constitute the Upper Allochthon in the Caledonide orogen, Sweden. This thrust complex is dominated by late Cambrian–Ordovician successions deposited in subduction-related, marginal oceanic basins. Magmatic activity at c. 488 Ma (Lower Köli) and c. 492–476 Ma (Middle Köli) is linked to rifted volcanic arcs and Zn–Cu–Fe–(Pb–Au–Ag) sulphide mineralization; serpentinite bodies with talc deposits are also conspicuous. Renewed magmatic activity, both plutonic (Upper and Middle Köli) and mafic volcanic (Middle and Lower Köli), occurred at c. 440–434 Ma during crustal extension. Late Ordovician shallow-marine sedimentation, deepening upwards into an early Silurian succession also prevailed (Lower Köli). Silurian (c. 430 Ma and later) folding, eastwards-vergent thrusting and greenschist or lower amphibolite facies metamorphism preceded upright, orogen-parallel and orogen-transverse open folding. Juxtaposition of an arc-related terrane to an ancient continental margin, comprising slices of gneiss and marble, in the Middle Köli occurred prior to c. 437 Ma and the eastwards-vergent thrusting; remnants of an Ordovician amphibolite facies tectonothermal event are also preserved in the Upper Köli. The tectonic roof to the Köli complex contains amphibolite facies mica schist, gneiss and marble, derived from the Laurentian continental margin, and a major gabbroic pluton (Rödingsfjället Nappe Complex, Uppermost Allochthon).

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