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Irmeli Manttari - One of the best experts on this subject based on the ideXlab platform.

  • Evolution of a Palaeoproterozoic giant magmatic dome in the Finnish Svecofennian; New insights from U–Pb geochronology
    Precambrian Research, 2020
    Co-Authors: Anna Kotilainen, Irmeli Manttari, Pentti Holtta, Matti Kurhila, O. Tapani Rämö
    Abstract:

    Abstract The Svecofennian domain comprises a c. 800 km by 800 km area in Finland and Sweden, mainly composed of Palaeoproterozoic granitoids, schists and gneisses. In the central part of the domain in western Finland, the Vaasa complex hosts a sequence of high-grade metamorphic rocks and granites formed by crustal anatexis during the culmination of the ∼1.9 Ga Svecofennian orogeny. The Vaasa complex consists of a c. 8000 km 2 granitoid batholith surrounded by diatexitic and metatexitic migmatites as well as metasedimentary rocks. In order to enhance the perception of the crystallisation history, provenance, and maximum sedimentation age of the protoliths involved, nine granitoid-xenolith pairs and a palaeosome-neosome pair were collected from the main body of the Vaasa batholith and surrounding rocks, and zircon from them was U–Pb dated using the LA-MC-ICPMS method. The U–Pb zircon crystallisation ages of the granitoids are 1.88–1.87 Ga, which is in accordance with the few previous results from the Vaasa region, and confirms a relatively swift crystallisation of the granite core throughout the Finnish part of the complex. The samples from the central part of the batholith have younger zircon ages than those from batholith margin. The inherited zircon age distribution pattern of the granitoids resembles that of the metasedimentary xenoliths. Our new comprehensive data, combined with whole-rock geochemistry from previous studies, render an in situ origin of the Vaasa granite probable. The maximum sedimentation age of the supracrustal precursors of the Vaasa complex is 1.92 Ga. Some of the metasedimentary xenoliths from the Vaasa complex host zircon that is coeval with their host granitoids and register incipient melting. Based on these ∼1.88–1.86 Ga zircon grains, the maximum sedimentation age would be deemed too young. Therefore, our data calls for caution when determining maximum sedimentation ages of high-grade metasedimentary rocks.

  • three stages to form a large batholith after terrane accretion an example from the Svecofennian orogen
    Precambrian Research, 2016
    Co-Authors: Kaisa Nikkila, Olav Eklund, Mikko Nironen, Irmeli Manttari, Annakaisa Korja
    Abstract:

    Abstract The magmatic history of batholiths formed as the result of tectonic accretion mirrors the evolution of the underlying crust from island arcs to accretion and collapse. Chemical composition, age and structure give information about the magma source and emplacement depths. The target of this study is the Central Finland batholith (CFGC) that provides a magmatic record after terrane accretion during the Svecofennian orogeny followed by orogenic collapse. The crustal source of partial melting has changed during the crustal evolution and differentiation after the terrane accretion, and when the stress regime has changed from contraction to extension. Here we present a three-stage magmatic evolution model for accretional batholith in the Svecofennian orogen. In the first stage, the lower crust of the accreted crust melts partially and produces calcic tonalitic melts that are emplaced above the upper-middle crustal detachment zone (Group 1; ⩾1887 ± 3 Ma). In the second stage, the middle crust begins to melt producing calc-alkalic granodioritic melts that are emplaced close to the surface (Group 2; 1890–1886 Ma), and at both sides of the upper-middle crustal detachment zone (Group 2; 1884–1883 Ma). In the third stage, the lower crust remelts and produces bimodal, calc-alkalic gabbroic and alkali-calcic to alkalic granitic melts (Group 3; 1881–1880 Ma), which are emplaced above the upper-middle crustal detachment zone. This kind of crustal differentiation produces a mafic lower, an intermediate middle, and a felsic upper crust. The third stage represents the last magmatic event of the Svecofennian accretional orogeny, where the high-velocity lowermost crust is formed during this stage. Crustal thickening and widespread mid-crustal partial melting have inititated lateral flow after or concurrently with the emplacement of the Group 2 granodiorite. The lateral flow has reactivated large scale shear zones allowing the transportation of the Group 3 rocks from the lower crust to the upper-middle crustal detachment zone. The change in the degree of deformation at the exposed parts from undeformed, through local to pervasive is attributed to differences in the exhumation level.

  • Three stages to form a large batholith after terrane accretion – An example from the Svecofennian orogen
    Precambrian Research, 2016
    Co-Authors: Kaisa Nikkila, Olav Eklund, Mikko Nironen, Irmeli Manttari, Annakaisa Korja
    Abstract:

    Abstract The magmatic history of batholiths formed as the result of tectonic accretion mirrors the evolution of the underlying crust from island arcs to accretion and collapse. Chemical composition, age and structure give information about the magma source and emplacement depths. The target of this study is the Central Finland batholith (CFGC) that provides a magmatic record after terrane accretion during the Svecofennian orogeny followed by orogenic collapse. The crustal source of partial melting has changed during the crustal evolution and differentiation after the terrane accretion, and when the stress regime has changed from contraction to extension. Here we present a three-stage magmatic evolution model for accretional batholith in the Svecofennian orogen. In the first stage, the lower crust of the accreted crust melts partially and produces calcic tonalitic melts that are emplaced above the upper-middle crustal detachment zone (Group 1; ⩾1887 ± 3 Ma). In the second stage, the middle crust begins to melt producing calc-alkalic granodioritic melts that are emplaced close to the surface (Group 2; 1890–1886 Ma), and at both sides of the upper-middle crustal detachment zone (Group 2; 1884–1883 Ma). In the third stage, the lower crust remelts and produces bimodal, calc-alkalic gabbroic and alkali-calcic to alkalic granitic melts (Group 3; 1881–1880 Ma), which are emplaced above the upper-middle crustal detachment zone. This kind of crustal differentiation produces a mafic lower, an intermediate middle, and a felsic upper crust. The third stage represents the last magmatic event of the Svecofennian accretional orogeny, where the high-velocity lowermost crust is formed during this stage. Crustal thickening and widespread mid-crustal partial melting have inititated lateral flow after or concurrently with the emplacement of the Group 2 granodiorite. The lateral flow has reactivated large scale shear zones allowing the transportation of the Group 3 rocks from the lower crust to the upper-middle crustal detachment zone. The change in the degree of deformation at the exposed parts from undeformed, through local to pervasive is attributed to differences in the exhumation level.

  • evolution of a palaeoproterozoic giant magmatic dome in the finnish Svecofennian new insights from u pb geochronology
    Precambrian Research, 2016
    Co-Authors: Anna Kotilainen, Irmeli Manttari, Pentti Holtta, Matti Kurhila, Tapani O Ramo
    Abstract:

    Abstract The Svecofennian domain comprises a c. 800 km by 800 km area in Finland and Sweden, mainly composed of Palaeoproterozoic granitoids, schists and gneisses. In the central part of the domain in western Finland, the Vaasa complex hosts a sequence of high-grade metamorphic rocks and granites formed by crustal anatexis during the culmination of the ∼1.9 Ga Svecofennian orogeny. The Vaasa complex consists of a c. 8000 km 2 granitoid batholith surrounded by diatexitic and metatexitic migmatites as well as metasedimentary rocks. In order to enhance the perception of the crystallisation history, provenance, and maximum sedimentation age of the protoliths involved, nine granitoid-xenolith pairs and a palaeosome-neosome pair were collected from the main body of the Vaasa batholith and surrounding rocks, and zircon from them was U–Pb dated using the LA-MC-ICPMS method. The U–Pb zircon crystallisation ages of the granitoids are 1.88–1.87 Ga, which is in accordance with the few previous results from the Vaasa region, and confirms a relatively swift crystallisation of the granite core throughout the Finnish part of the complex. The samples from the central part of the batholith have younger zircon ages than those from batholith margin. The inherited zircon age distribution pattern of the granitoids resembles that of the metasedimentary xenoliths. Our new comprehensive data, combined with whole-rock geochemistry from previous studies, render an in situ origin of the Vaasa granite probable. The maximum sedimentation age of the supracrustal precursors of the Vaasa complex is 1.92 Ga. Some of the metasedimentary xenoliths from the Vaasa complex host zircon that is coeval with their host granitoids and register incipient melting. Based on these ∼1.88–1.86 Ga zircon grains, the maximum sedimentation age would be deemed too young. Therefore, our data calls for caution when determining maximum sedimentation ages of high-grade metasedimentary rocks.

  • timing of accretion intra orogenic sedimentation and basin inversion in the paleoproterozoic Svecofennian orogen the pyhantaka area southern finland
    Precambrian Research, 2012
    Co-Authors: Mikko Nironen, Irmeli Manttari
    Abstract:

    Abstract The Pyhantaka area in southern Finland represents the accretionary Svecofennian orogen, presently exhumed to upper-mid crustal level. The post-1.87 Ga volcanic-sedimentary Pyhantaka formation is separated from underlying cordierite paragneiss (metagraywacke) by an unconformity, marked by an ancient weathering surface on top of the paragneiss and ultramature quartzite at the base of the Pyhantaka formation. Structural studies and U–Pb datings carried out in the paragneisses, metavolcanic rock interlayer and crosscutting granitoid rocks revealed four tectonic units, separated from each other by shear zones and representing different depositional ages (pre-1.87 Ga and post-1.87 Ga). Yet unidentified post-1.87 Ga rock sequences are anticipated in the Svecofennian orogen. The model of tectonothermal evolution in the Pyhantaka area includes contraction at 1.89 Ga causing rapid burial of graywackes (Harkala graywackes) to mid-crustal levels where they were metamorphosed into cordierite gneisses and intruded by syntectonic granite at 1875 Ma. Deposition of exhumation-related graywackes (Himattu graywackes) after 1.87 Ga, followed by development of a weathering surface and deposition of quartz sands, indicate gradual stabilization of the upper crust. A sequence of quartz sands, immature sands, volcaniclastic sands and basaltic rocks (the Pyhantaka formation), and graywackes on top (Kesua graywackes) were deposited in an intra-orogenic rift basin during crustal extension that may have initiated 1.85 Ga ago. Contraction at 1825 Ma caused basin inversion with thrusting and folding of the post-1.87 Ga sequence. All rocks in the Pyhantaka area were subject to a new high-grade metamorphic event that culminated at 1.82 Ga. Subsequent uplift of a pre-1.87 Ga rock sequence relative to the post-1.87 Ga sequence resulted in the present pattern of tectonic units. The inferred evolution at Pyhantaka conforms to several tectonic models presented for the Svecofennian orogen. However, the occurrence of an ancient weathering surface and ultramature quartzite, an evidence for a 10–20 Ma stable period, is more compatible with continental interior setting with outboard subduction than active continental margin setting during deposition of the Pyhantaka formation.

Mikko Nironen - One of the best experts on this subject based on the ideXlab platform.

  • Three stages to form a large batholith after terrane accretion – An example from the Svecofennian orogen
    Precambrian Research, 2016
    Co-Authors: Kaisa Nikkila, Olav Eklund, Mikko Nironen, Irmeli Manttari, Annakaisa Korja
    Abstract:

    Abstract The magmatic history of batholiths formed as the result of tectonic accretion mirrors the evolution of the underlying crust from island arcs to accretion and collapse. Chemical composition, age and structure give information about the magma source and emplacement depths. The target of this study is the Central Finland batholith (CFGC) that provides a magmatic record after terrane accretion during the Svecofennian orogeny followed by orogenic collapse. The crustal source of partial melting has changed during the crustal evolution and differentiation after the terrane accretion, and when the stress regime has changed from contraction to extension. Here we present a three-stage magmatic evolution model for accretional batholith in the Svecofennian orogen. In the first stage, the lower crust of the accreted crust melts partially and produces calcic tonalitic melts that are emplaced above the upper-middle crustal detachment zone (Group 1; ⩾1887 ± 3 Ma). In the second stage, the middle crust begins to melt producing calc-alkalic granodioritic melts that are emplaced close to the surface (Group 2; 1890–1886 Ma), and at both sides of the upper-middle crustal detachment zone (Group 2; 1884–1883 Ma). In the third stage, the lower crust remelts and produces bimodal, calc-alkalic gabbroic and alkali-calcic to alkalic granitic melts (Group 3; 1881–1880 Ma), which are emplaced above the upper-middle crustal detachment zone. This kind of crustal differentiation produces a mafic lower, an intermediate middle, and a felsic upper crust. The third stage represents the last magmatic event of the Svecofennian accretional orogeny, where the high-velocity lowermost crust is formed during this stage. Crustal thickening and widespread mid-crustal partial melting have inititated lateral flow after or concurrently with the emplacement of the Group 2 granodiorite. The lateral flow has reactivated large scale shear zones allowing the transportation of the Group 3 rocks from the lower crust to the upper-middle crustal detachment zone. The change in the degree of deformation at the exposed parts from undeformed, through local to pervasive is attributed to differences in the exhumation level.

  • three stages to form a large batholith after terrane accretion an example from the Svecofennian orogen
    Precambrian Research, 2016
    Co-Authors: Kaisa Nikkila, Olav Eklund, Mikko Nironen, Irmeli Manttari, Annakaisa Korja
    Abstract:

    Abstract The magmatic history of batholiths formed as the result of tectonic accretion mirrors the evolution of the underlying crust from island arcs to accretion and collapse. Chemical composition, age and structure give information about the magma source and emplacement depths. The target of this study is the Central Finland batholith (CFGC) that provides a magmatic record after terrane accretion during the Svecofennian orogeny followed by orogenic collapse. The crustal source of partial melting has changed during the crustal evolution and differentiation after the terrane accretion, and when the stress regime has changed from contraction to extension. Here we present a three-stage magmatic evolution model for accretional batholith in the Svecofennian orogen. In the first stage, the lower crust of the accreted crust melts partially and produces calcic tonalitic melts that are emplaced above the upper-middle crustal detachment zone (Group 1; ⩾1887 ± 3 Ma). In the second stage, the middle crust begins to melt producing calc-alkalic granodioritic melts that are emplaced close to the surface (Group 2; 1890–1886 Ma), and at both sides of the upper-middle crustal detachment zone (Group 2; 1884–1883 Ma). In the third stage, the lower crust remelts and produces bimodal, calc-alkalic gabbroic and alkali-calcic to alkalic granitic melts (Group 3; 1881–1880 Ma), which are emplaced above the upper-middle crustal detachment zone. This kind of crustal differentiation produces a mafic lower, an intermediate middle, and a felsic upper crust. The third stage represents the last magmatic event of the Svecofennian accretional orogeny, where the high-velocity lowermost crust is formed during this stage. Crustal thickening and widespread mid-crustal partial melting have inititated lateral flow after or concurrently with the emplacement of the Group 2 granodiorite. The lateral flow has reactivated large scale shear zones allowing the transportation of the Group 3 rocks from the lower crust to the upper-middle crustal detachment zone. The change in the degree of deformation at the exposed parts from undeformed, through local to pervasive is attributed to differences in the exhumation level.

  • the bothnian coupled oroclines of the Svecofennian orogen a palaeoproterozoic terrane wreck
    Terra Nova, 2014
    Co-Authors: Raimo Lahtinen, Stephen T Johnston, Mikko Nironen
    Abstract:

    The accretion of magmatic arcs gives rise to elongate, linear orogens and is a key process in forming new continental crust. Many Precambrian continents are, however, presently equidimensional or have large areas without any clear linearity, such as the central part of the Palaeoproterozoic Svecofennian Orogen (1.92–1.77 Ga). One way of forming an equidimensional continental domain is by buckling of a linear orogen about vertical axes of rotation into one or more coupled oroclines. Here, we reinterpret existing data and demonstrate the occurrence of coupled Bothnian oroclines in the Svecofennian Orogen. Palinspastic restoration of the southern and northern Bothnian oroclines brings a 1000-km-long segment of the Svecofennian Orogen into an originally linear, NW-striking geometry that restores the lithological belts, metamorphic zones and structural vergences to a common direction, and which indicates that the orogen consists of a SW-facing arc, which has been shortened along NE-verging folds and thrust faults.

  • timing of accretion intra orogenic sedimentation and basin inversion in the paleoproterozoic Svecofennian orogen the pyhantaka area southern finland
    Precambrian Research, 2012
    Co-Authors: Mikko Nironen, Irmeli Manttari
    Abstract:

    Abstract The Pyhantaka area in southern Finland represents the accretionary Svecofennian orogen, presently exhumed to upper-mid crustal level. The post-1.87 Ga volcanic-sedimentary Pyhantaka formation is separated from underlying cordierite paragneiss (metagraywacke) by an unconformity, marked by an ancient weathering surface on top of the paragneiss and ultramature quartzite at the base of the Pyhantaka formation. Structural studies and U–Pb datings carried out in the paragneisses, metavolcanic rock interlayer and crosscutting granitoid rocks revealed four tectonic units, separated from each other by shear zones and representing different depositional ages (pre-1.87 Ga and post-1.87 Ga). Yet unidentified post-1.87 Ga rock sequences are anticipated in the Svecofennian orogen. The model of tectonothermal evolution in the Pyhantaka area includes contraction at 1.89 Ga causing rapid burial of graywackes (Harkala graywackes) to mid-crustal levels where they were metamorphosed into cordierite gneisses and intruded by syntectonic granite at 1875 Ma. Deposition of exhumation-related graywackes (Himattu graywackes) after 1.87 Ga, followed by development of a weathering surface and deposition of quartz sands, indicate gradual stabilization of the upper crust. A sequence of quartz sands, immature sands, volcaniclastic sands and basaltic rocks (the Pyhantaka formation), and graywackes on top (Kesua graywackes) were deposited in an intra-orogenic rift basin during crustal extension that may have initiated 1.85 Ga ago. Contraction at 1825 Ma caused basin inversion with thrusting and folding of the post-1.87 Ga sequence. All rocks in the Pyhantaka area were subject to a new high-grade metamorphic event that culminated at 1.82 Ga. Subsequent uplift of a pre-1.87 Ga rock sequence relative to the post-1.87 Ga sequence resulted in the present pattern of tectonic units. The inferred evolution at Pyhantaka conforms to several tectonic models presented for the Svecofennian orogen. However, the occurrence of an ancient weathering surface and ultramature quartzite, an evidence for a 10–20 Ma stable period, is more compatible with continental interior setting with outboard subduction than active continental margin setting during deposition of the Pyhantaka formation.

  • u pb geochronological constraints of the late Svecofennian leucogranites of southern finland
    Precambrian Research, 2011
    Co-Authors: Matti Kurhila, Irmeli Manttari, Matti Vaasjoki, Tapani O Ramo, Mikko Nironen
    Abstract:

    Abstract The ∼500 km long zone of late Svecofennian leucogranites in southern Finland is characterized by felsic, in places migmatitic magmatism that crosscuts older Paleoproterozoic crustal segments. SIMS and ID-TIMS U–Pb isotopic data on zircon and monazite from 15 granite and migmatite samples show that the emplacement of individual leucogranite plutons took place between ∼1.85 Ga and ∼1.79 Ga. This is a considerably longer period than what has traditionally been assigned to these granites. The youngest ages are found in the eastern part of the zone, which is the target area of this study. Significant age differences between granite plutons imply that the granites were emplaced in various depths and/or in various stages of the late Svecofennian, in support of a multi-stage accretionary history of the arc complexes of southern and western Finland. The late Svecofennian granites represent recycled crustal material and therefore commonly contain inherited zircons. The problem posed by the heterogeneity of zircon ages is overcome to some extent by the fact that the youngest zircons are invariably as old as the monazites, and thus monazite can be used as an emplacement age indicator. Zircon inheritance patterns vary somewhat between the different plutons within the granite zone. Archean inherited ages range from ∼2.8 Ga to ∼2.5 Ga and Paleoproterozoic 2.1–2.0 Ga inheritance is also commonplace, despite the lack of known exposed source rocks of this age. The contrasting age distribution of inherited zircons suggests that both sedimentary and igneous rocks provided source material for these granites.

Fernando Corfu - One of the best experts on this subject based on the ideXlab platform.

  • Penetrative ductile deformation and amphibolite-facies metamorphism prior to 1851Ma in the western part of the Svecofennian orogen, Fennoscandian Shield
    Precambrian Research, 2020
    Co-Authors: Tobias Hermansson, Michael B Stephens, Fernando Corfu, Jenny Andersson, Laurence Page
    Abstract:

    The Svecofennian orogen in the Fennosandian Shield consists of several Palaeoproterozoic meta-igneous provinces that generally young progressively southwards and westwards. The understanding of the tectonic evolution of these different provinces is linked to the ability to constrain the timing of ductile deformation and metamorphism within them. In the western part of the orogen, in central Sweden, ductile deformation and metamorphism is conventionally thought to have occurred after 1.85 Ga and mainly around 1.82-1.80 Ga. At Forsmark in central Sweden, we have dated two undeformed granite dykes that cross-cut the tectonic fabric in their host rocks to 1851 +/- 15 and 1855 +/- 6 Ma, respectively. Since the former shows an unequivocal field relationship with respect to the tectonic fabric, we establish that penetrative ductile deformation under amphibolite-facies metamorphic conditions occurred prior to 1851 +/- 5 Ma. This U-Pb zircon minimum age for the timing of ductile deformation is supported by a U-Pb titanite age of 1844 +/- 4 Ma. These data as well as the field relationships at Forsmark indicate that an early phase of penetrative deformation and metamorphism affected the Svecofennian bedrock in the western part of the Fennoscandian Shield and was overprinted, after 1851 +/- 5 Ma, by spatially more confined deformational events. In conjunction with earlier results, our data help to establish the presence of tectonic domains with contrasting tectonothermal histories in the western part of the Svecofennian orogen. (c) 2006 Elsevier B.V. All rights reserved

  • multiple post Svecofennian 1750 1560 ma pegmatite dykes in archaean palaeoproterozoic rocks of the west troms basement complex north norway geological significance and regional implications
    Precambrian Research, 2015
    Co-Authors: Steffen G Bergh, Fernando Corfu, Nadezhda Priyatkina, Kare Kullerud, Per Inge Myhre
    Abstract:

    Abstract The West Troms Basement Complex, North Norway, consist of Meosarchaean, Neoarchaean and Palaeoproterozoic crust which likely represent the continuation of the Karelian craton of the Fennoscandian Shield beneath and across the Caledonian nappes. The complex is transected by several meta-sedimentary/volcanic belts with ages from ca. 2.7 to 1.9 Ga, and linear ductile shear zones that record polyphase deformation after emplacement of several late-Svecofennian plutonic complexes (1.80–1.79 Ga). The Astridal supracrustal belt of the Senja shear zone was intruded by various generations of granite pegmatite dykes, which yield zircon and titanite U–Pb ages ranging between 1758 and 1562 Ma, with evidence of a weak Caledonian overprint at about 400 Ma that formed or reset some, but not all, titanites. The age range indicates that formation of the pegmatites occurred after termination of the main Svecofennian orogeny (1.92–1.79 Ga) of the Karelian craton. Comparison within the larger scale context of the Fennoscandian Shield suggests that emplacement of these pegmatites may have been caused by late-stage reactivation of intracratonic shear zones, possibly reflecting distal effects of deeper magmatic processes such as intrusion of coeval aged rapakivi granite suites (ca. 1.65–1.5 Ga) in Finland, and/or the Mesoproterozoic Gothian orogeny and magmatism affecting the southwestern parts of Fennoscandia. The Mesoproterozoic ages, however, also correspond to late Laxfordian (ca. 1.7–1.6 Ga) tectonic events in the Lewisian basement on the Laurentian margin of Scotland, suggesting a potential early link between these basement complexes.

  • Multiple post-Svecofennian 1750–1560 Ma pegmatite dykes in Archaean-Palaeoproterozoic rocks of the West Troms Basement Complex, North Norway: Geological significance and regional implications
    Precambrian Research, 2015
    Co-Authors: Steffen G Bergh, Fernando Corfu, Nadezhda Priyatkina, Kare Kullerud, Per Inge Myhre
    Abstract:

    Abstract The West Troms Basement Complex, North Norway, consist of Meosarchaean, Neoarchaean and Palaeoproterozoic crust which likely represent the continuation of the Karelian craton of the Fennoscandian Shield beneath and across the Caledonian nappes. The complex is transected by several meta-sedimentary/volcanic belts with ages from ca. 2.7 to 1.9 Ga, and linear ductile shear zones that record polyphase deformation after emplacement of several late-Svecofennian plutonic complexes (1.80–1.79 Ga). The Astridal supracrustal belt of the Senja shear zone was intruded by various generations of granite pegmatite dykes, which yield zircon and titanite U–Pb ages ranging between 1758 and 1562 Ma, with evidence of a weak Caledonian overprint at about 400 Ma that formed or reset some, but not all, titanites. The age range indicates that formation of the pegmatites occurred after termination of the main Svecofennian orogeny (1.92–1.79 Ga) of the Karelian craton. Comparison within the larger scale context of the Fennoscandian Shield suggests that emplacement of these pegmatites may have been caused by late-stage reactivation of intracratonic shear zones, possibly reflecting distal effects of deeper magmatic processes such as intrusion of coeval aged rapakivi granite suites (ca. 1.65–1.5 Ga) in Finland, and/or the Mesoproterozoic Gothian orogeny and magmatism affecting the southwestern parts of Fennoscandia. The Mesoproterozoic ages, however, also correspond to late Laxfordian (ca. 1.7–1.6 Ga) tectonic events in the Lewisian basement on the Laurentian margin of Scotland, suggesting a potential early link between these basement complexes.

  • migratory tectonic switching western Svecofennian orogen central sweden constraints from u pb zircon and titanite geochronology
    Precambrian Research, 2008
    Co-Authors: Tobias Hermansson, Michael B Stephens, Fernando Corfu, Laurence Page, Jenny Andersson
    Abstract:

    Abstract The Forsmark area, in the western part of the Svecofennian orogen, central Sweden, is situated between two major Palaeoproterozoic tectonic domains that show contrasting histories with respect to timing of igneous activity, ductile deformation and metamorphism. Geological features common to both the adjacent domains are found at Forsmark, which, consequently, is a key area for understanding the tectonic evolution of the Svecofennian orogen in this region. New SIMS and TIMS geochronological data from several samples in a limited area at Forsmark constrain the timing of igneous activity, ductile deformation and metamorphism in this area. U/Pb zircon dating, in combination with field studies, reveals the existence of two calk-alkaline igneous suites at Forsmark. The older and most voluminous plutonic suite intruded at 1.89–1.87 Ga and is affected by penetrative, yet variably intense ductile deformation, with the development of a ductile grain-shape fabric under amphibolite facies metamorphic conditions and folding. The younger and less voluminous hypabyssal suite intruded at 1.86–1.85 Ga, during the waning stages of this penetrative deformational phase. Furthermore, U/Pb titanite dating shows that the area has been affected by one or more tectonothermal events after regional fabric development, and possibly even after 1.83 Ga. The deformation during these events involved more restricted strain along discrete zones. The Forsmark data, in combination with a compilation and evaluation of available geochronological data from the time interval 1.91–1.84 Ga in central Sweden, points to the existence of at least two major tectonic cycles in this region. Each cycle is characterised by igneous activity associated at least partly with extension, a short interval of compressional deformation and migration of the tectonic activity. In this paper, we discuss two highly contrasting tectonic models that may explain the cyclic tectonic evolution of the western part of the Svecofennian orogen in central Sweden. The favoured model involves continuous subduction, with a constant polarity, beneath a single active continental margin, combined with alternating subduction hinge retreat and advance. The model involves migration of what has been described as tectonic switching in the younger, accretionary orogenic systems of eastern Australia (Palaeozoic Lachlan orogen) and New Zealand.

  • penetrative ductile deformation and amphibolite facies metamorphism prior to 1851 ma in the western part of the Svecofennian orogen fennoscandian shield
    Precambrian Research, 2007
    Co-Authors: Tobias Hermansson, Michael B Stephens, Fernando Corfu, Jenny Andersson, Laurence Page
    Abstract:

    The Svecofennian orogen in the Fennosandian Shield consists of several Palaeoproterozoic meta-igneous provinces that generally young progressively southwards and westwards. The understanding of the tectonic evolution of these different provinces is linked to the ability to constrain the timing of ductile deformation and metamorphism within them. In the western part of the orogen, in central Sweden, ductile deformation and metamorphism is conventionally thought to have occurred after 1.85 Ga and mainly around 1.82-1.80 Ga. At Forsmark in central Sweden, we have dated two undeformed granite dykes that cross-cut the tectonic fabric in their host rocks to 1851 +/- 15 and 1855 +/- 6 Ma, respectively. Since the former shows an unequivocal field relationship with respect to the tectonic fabric, we establish that penetrative ductile deformation under amphibolite-facies metamorphic conditions occurred prior to 1851 +/- 5 Ma. This U-Pb zircon minimum age for the timing of ductile deformation is supported by a U-Pb titanite age of 1844 +/- 4 Ma. These data as well as the field relationships at Forsmark indicate that an early phase of penetrative deformation and metamorphism affected the Svecofennian bedrock in the western part of the Fennoscandian Shield and was overprinted, after 1851 +/- 5 Ma, by spatially more confined deformational events. In conjunction with earlier results, our data help to establish the presence of tectonic domains with contrasting tectonothermal histories in the western part of the Svecofennian orogen. (c) 2006 Elsevier B.V. All rights reserved. (Less)

Ian S Williams - One of the best experts on this subject based on the ideXlab platform.

  • late Svecofennian sedimentary basins in the crystalline basement of ne poland and adjacent area of lithuania ages major sources of detritus and correlations
    Geological Quarterly, 2010
    Co-Authors: Ewa Krzeminska, Janina Wiszniewska, Grazina Skridlaite, Ian S Williams
    Abstract:

    The Precambrian basement of Lithuania and NE Poland, much of which is metasedimentary paragneiss, can be accessed only by cores from deep boreholes. Ion microprobe dating of detrital zircons from samples of these metasediments and the geochemical signatures of the rocks provide new insights into their age and provenance. Detrital zircons from metasediments from Jastrzbna and Moki have Pb isotopic ages in the ranges 3.14-1.83 and 3.53-1.82 Ga, respectively. Similar results have been obtained from the Lithuanian Lazdijai and Bliudziai paragneisses. About 30% of the analysed Polish detrital zircon cores are of Late Archaean age (2.90-2.60 Ga) and about 70% are Palaeoproterozoic (2.10-1.90 Ga), similar to the age distributions of detrital zircon from Svecofennian metasediments exposed in Central Sweden and Southern Finland. The youngest detrital zircon sub-groups indicate maximum deposition ages of about 1.86 Ga, similar to the ages of exposed Svecofennian sedimentary basins. Possible source rocks of comparable ages and affinities can be found within Fennoscandia, Greenland and Sarmatia.

  • an extension of the Svecofennian orogenic province into ne poland evidence from geochemistry and detrital zircon from paleoproterozoic paragneisses
    Precambrian Research, 2009
    Co-Authors: Ian S Williams, Ewa Krzeminska, Janina Wiszniewska
    Abstract:

    Abstract The Precambrian crystalline rocks of northern Poland are known only from deep drill cores. Drilling at Jastrzebna and Monki, in the Mazowsze Domain, NE Poland, has intersected a monotonous sequence of grey paragneisses superficially similar to the paragneisses of the Svecofennian Domain exposed in Sweden and Finland. Petrographically, geochemically and isotopically the rocks from the two regions are in fact almost the same. The Jastrzebna paragneiss is an immature metasediment characterised by depleted HREE and Y, indicative of derivation from a source dominated by TTG-type rocks. The Monki metasediment, in contrast, is more mature and chemically uniform, with a REE pattern very similar to average Post-Archean Australian Shale (PAAS). Both metasediments have La–Sc–Th compositions characteristic of active continental margin or continental arc settings. The detrital zircon populations in the two Polish metasediments have the same age distributions; a dominant Paleoproterozoic population at 2.1–1.9 Ga, a subordinate late Archean population at 2.9–2.7 Ga, and rare early Archean grains up to 3.4 Ga. Both samples have very few zircons in the age range 2.6–2.1 Ga. This age distribution is extremely similar to the age distributions of detrital zircon from Svecofennian metasediments exposed in Sweden and Finland. It is highly likely that the Polish metasediments are derived from the same source region as the ‘classical’ Svecofennian, and were deposited in the same basin or basin system. The ages of the detrital zircons do not match the ages of any known igneous rocks currently exposed in the Baltic Shield. However, they do match the ages of rocks within the Osnitsk–Mikashevichi Igneous Belt on the western margin of Sarmatia, plus Archean rocks of the adjacent Ukrainian Shield. It is likely that detritus eroded from this region at ca. 1.93–1.86 Ga, during a period of rapid uplift, was deposited in a continental marginal basin system adjacent to the Archean craton. The Polish metasediments were metamorphosed up to lower amphibolite facies at ca. 1.83 Ga.

  • a regional 1 92 ga tectonothermal episode in ostrobothnia finland implications for models of Svecofennian accretion
    Precambrian Research, 2008
    Co-Authors: Ian S Williams, R Roye W Rutland, Jukka Kousa
    Abstract:

    Abstract The mostly metasedimentary Svecofennian Western Pohjanmaa belt in Ostrobothnia, Finland, can be divided into two stratigraphic groups separated by a major unconformity that reflects deformation following regional metamorphism. The western Lappfors group, interpreted as a Svionian basement complex, has strong W-trending folding and aeromagnetic signatures that contrast with the overlying eastern Evijarvi group, interpreted as lower Bothnian, which has more open N-trending folding and magnetic patterns. Several lines of evidence date the unconformity at ∼1.92 Ga. Detrital zircons from two samples of Lappfors group metasediment, and a sample of the basal Nivala gneisses in the Eastern Pohjanmaa belt, have 1.92–1.91 Ga post-depositional low-Th/U metamorphic overgrowths. The maximum deposition age of the Lappfors sedimentary protoliths, based on detrital zircon ages, is between ∼1.99 and ∼1.95 Ga. Three samples of Bothnian sediments lack pervasive ∼1.91 Ga overgrowths, instead having a variety of detrital zircons as young as ∼1.95–1.91 Ga, reflecting recycling of the underlying basement complex. The maximum deposition age of the Bothnian sedimentary protoliths is inferred to be ∼1.91 Ga. The Niska granitoid, which intrudes the Evijarvi group and is deformed only by the younger tectonic episode affecting that sequence, has a zircon age of 1896 ± 6 Ma. That episode, which established the present relationships between basement and cover, is dated by ∼1.88 Ga metamorphic zircon overgrowths in both the Svionian and Bothnian samples, and by 1878 ± 4 Ma metamorphic monazite from a metasediment from the Savo belt, east of the Nivala district. The post-1.91 Ga volcanic sequences of the Svecofennian Province are unlikely to represent arc accretion. The Svionian metamorphic sequences are probably the remnants of a widespread marginal basin that formed between ∼1.97 and 1.92 Ga, then was accreted to the craton during an Early Svecofennian (∼1.92–1.91 Ga) orogenic phase, forming the basement on which the Bothnian volcano-sedimentary sequences were subsequently deposited.

  • pre 1 91 ga deformation and metmorphism in the palaeo proterozoic vammala migmatite belt southern finland and implications for Svecofennian tectonics
    Bulletin of The Geological Society of Finland, 2004
    Co-Authors: R Roye W Rutland, Ian S Williams, Kalevi Korsman
    Abstract:

    A metamorphic event in the Vammala Migmatite Belt (VMB) at ~1.92 Ga, revealed by SHRIMP U-Pb analyses of both zircon overgrowths and monazite ,i s interpreted as post-depositional and is correlated with the development of the early high-grade schistosity .N either this Early Svecofennian deformation and metamorphism, nor the associated complex folding, is present in the overlying Ta mpere Schist Belt (TSB) sequence, consistent with the VMB being part of a pre-1.91 Ga basement complex. The ~1.92 Ga event provides a maximum deposition age for the TSB ,c onfirm ing earlier age estimates. Earlier stratigraphic correlations between parts of the VMB and TSB ,a nd associated tectonic interpretations, can no longer be sustained.The crustal thickening seen in the VMB ,a nd previously attributed to arc accretion at ~1.89 Ga, is now attributed to accretion of a large Svionian marginal basin during the ‘Early Svecofennian’ orogenic phase at ~1.92 Ga.This is of similar age to the deformation and metamorphism associated with collision in the Lapland-Kola Orogen to the north of the Karelian Province. The well-known post-TSB orogenic phase was also identified in the VMB by a monazite age of 1881±6 Ma. A granitoid intrusion gave an emplacement age of 1888±5 Ma, comparable to the age of granitoid clasts in the upper part of the TSB succession. The detrital zircon data are interpreted to suggest that deposition of the precursor VMB sediments probably took place soon after an earlier pre-depositional metamorphism at ~1.98 Ga, which affected igneous source complexes dated at ~1.99 Ga and ~2.01 Ga. Mafic rocks in the southern part of the VMB ,a nd probably also the Haveri basalts, represent a renewed episode of extensional magmatism, which might correlate with the 1.96–1.95 Ga Jormua and Outokumpu ophiolites. A pre-1.96 Ga older stage basin has an expression in Sweden and complexes of similar age occur in the concealed Palaeoproterozoic basement south of the Gulf of Finland. Similar rocks, deformed and metamorphosed before ~1.96 Ga, might be present beneath the Central Finland granitoid complex and the late Svecofennian granite-migmatite zone ,a nd were possibly more local sources for both the younger stage Svionian basin sediments and the post-1.91 Ga Bothnian Basin sediments. The TSB and other post-accretionary volcanic sequences, and the associated plutonism, are interpreted to reflect a ~40 m.y .e xtensional period, inboard of the contemporaneous active margin, between orogenic phases at ~1.92 Ga and ~1.88 Ga.This interpretation provides a more satisfactory explanation of the major heat input to the crust over a very wide area than does the arc accretion hypothesis.The tectonic evolution of the Svecofennian Province has strong similarities to that of the Palaeozoic Lachlan Fold Belt in eastern Australia.

  • Svecofennian detrital zircon ages implications for the precambrian evolution of the baltic shield
    Precambrian Research, 1993
    Co-Authors: Stefan Claesson, Hannu Huhma, P D Kinny, Ian S Williams
    Abstract:

    Metasediments intruded by 1.90-1.87 Ga old plutonic rocks form the oldest major Proterozoic crustal component in the Svecofennian Domain of the Baltic (Fennoscandian) Shield. Their NdTDM model ages and conventional multigrain zircon UPb ages between 2.4 and 2.1 Ga have previously been interpreted either as mixing ages between ∼ 1.9 Ga old juvenile materials and a minor Archaean component, or as actual rock and protolith ages. To resolve the ensuing controversy, 120 individual detrital zircons from Svecofennian metasediments in Sweden and Finland were analysed using the SHRIMP ion microprobe. The oldest materials in this array are a 3.44 Ga old zircon from the Tampere Schist Belt in Finland and a 3.32 Ga old crystal from southeastern Sweden. About 30% of the analysed crystals are 2.97-2.60 Ga old, while ∼ 65% have ages between 2.12 and 1.88 Ga. Thus there is no evidence of 2.6-2.1 Ga old protoliths, but the age range of the Proterozoic zircons indicates that a major area of 2.1-1.9 Ga old crust was in erosional position 1.9 Ga ago. This implies that the formation of Palaeoproterozoic crust in the Baltic Shield or its one-time close neighbourhood must have commenced 100–200 Ma earlier than hitherto assumed. In conjunction with previously obtained isotopic data, the youngest detritus ages of the present study constrain the age of Svecofennian sedimentation. It can also be concluded that the Archaean zircons found in quartzites from southern Sweden may have been derived from source areas to the southwest of the central-Svecofennian marine depositional basin, the so-called Bothnian Basin, separating southern Sweden from the Archaean craton in the northeastern part of the Shield.

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  • the bothnian coupled oroclines of the Svecofennian orogen a palaeoproterozoic terrane wreck
    Terra Nova, 2014
    Co-Authors: Raimo Lahtinen, Stephen T Johnston, Mikko Nironen
    Abstract:

    The accretion of magmatic arcs gives rise to elongate, linear orogens and is a key process in forming new continental crust. Many Precambrian continents are, however, presently equidimensional or have large areas without any clear linearity, such as the central part of the Palaeoproterozoic Svecofennian Orogen (1.92–1.77 Ga). One way of forming an equidimensional continental domain is by buckling of a linear orogen about vertical axes of rotation into one or more coupled oroclines. Here, we reinterpret existing data and demonstrate the occurrence of coupled Bothnian oroclines in the Svecofennian Orogen. Palinspastic restoration of the southern and northern Bothnian oroclines brings a 1000-km-long segment of the Svecofennian Orogen into an originally linear, NW-striking geometry that restores the lithological belts, metamorphic zones and structural vergences to a common direction, and which indicates that the orogen consists of a SW-facing arc, which has been shortened along NE-verging folds and thrust faults.

  • the Svecofennian orogen a collage of microcontinents and island arcs
    Geological Society London Memoirs, 2006
    Co-Authors: Annakaisa Korja, Raimo Lahtinen, Mikko Nironen
    Abstract:

    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.

  • detrital zircons in late Svecofennian metasandstones in central sweden and southern finland
    2006
    Co-Authors: Stefan Bergman, Mikko Nironen, Karin Hogdahl, Håkan Sjöström, Lena Lundqvist, E Ogenhall, Raimo Lahtinen
    Abstract:

    Deformed and metamorphosed quartz-rich sandstones in southern Finland and east-central Sweden were presumed to be deposited in late Svecofennian time (30 Ma between the volcanism and sand depositio ...

  • sources of Svecofennian granitoids in the light of ion probe upb measurements on their zircons
    Precambrian Research, 2003
    Co-Authors: Matti Vaasjoki, Raimo Lahtinen, Hannu Huhma, Jessica Vestin
    Abstract:

    Abstract The presence of 1.91–1.93 Ga old granitoids at the Archean–Proterozoic boundary along the Raahe–Ladoga zone in Finland has been demonstrated on various occasions. These rocks have been considered to represent juvenile crustal material, as their e Nd values are markedly positive. However, as Svecofennian metasediments contain detrital zircons derived from a ca. 2 Ga old source, the possibility has existed that the 1.92 Ga age may have been a mixture between 2 and 1.89 Ga old zircon populations, as such mixing would not markedly affect their neodymium isotopic properties. Also, some syntectonic 1.89 Ga old Svecofennian granitoids contain heterogeneous zircon populations, but it has been impossible to determine the age and origin of the older zircons by conventional methods. NORDSIM ion probe results on three samples from the 1.92 Ga age group confirm the earlier conclusions. Especially important is that no zircons older than 1.95 Ga were detected in the 1.92 Ga group samples. Thus, the 1.92 Ga event was the beginning of the formation of new continental crust in the primitive Svecofennian island arc and these granitoids formed by partial melting of basaltic magmas derived from a depleted mantle source. One sample also contains a younger zircon population formed during the orogenic culmination at 1.89 Ga. In contrast, one grain from a sample representing the 1.89 Ga age group contains an Archean core, which is considered to represent sedimentary detritus assimilated during either magma formation or intrusion. While the results prove the true igneous nature of the 1.92 Ga event, they also rule out these rocks as a possible provenance for the ca. 2 Ga old zircons encountered in the Svecofennian metaturbidites. Thus, there is still no direct evidence from granitoid rocks for an extensive Svecofennian protocrust, the existence of which has been postulated on the basis of geochemical and SmNd isotopic data.

  • contrasting source components of the paleoproterozoic Svecofennian metasediments detrital zircon u pb sm nd and geochemical data
    Precambrian Research, 2002
    Co-Authors: Raimo Lahtinen, Hannu Huhma, Jukka Kousa
    Abstract:

    Abstract The Paleoproterozoic Svecofennian Orogen in the Fennoscandian shield can be regarded as one entity or as a collage of several accretionary units. To test for the possible occurrence of a suture zone dividing the Svecofennian Orogen into Central and Southern parts, we report new ion microprobe data on clastic zircons of nine samples of metasediments. Whole-rock Sm–Nd and geochemical data were acquired to characterize the source components of the metasediments. The Central Svecofennian metasediments in Finland can be divided to lower and upper types with inferred deposition ages at 1.92–1.91 and 1.90–1.88 Ga, respectively. Both types are immature and show a derivation from an unweathered orogenic source. The lower Central Svecofennian metasediments show a dominant Proterozoic age population at 1.93–2.02 Ga and a variation in eNd (1.9) values from about −3 to −0.5, which is mainly explained by variable amounts of Archean detritus (30–45%). The upper Central Svecofennian metasediments have eNd (1.9) at about 0, similar to values obtained from adjacent volcanic and plutonic arc rocks. One meta-arkose is tentatively classified as a molasse-type sediment with a source dominated by earlier Svecofennian sediments. Southern Svecofennian metasediments can be divided into mature and less mature types with dominant deposition ages at 1.90–1.88 Ga and eNd (1.9) values from −3 to +1. Mature quartzites seem to occur at least in two stratigraphic levels where the upper quartzites have maximum deposition ages at 1.87–1.86 Ga. A characteristic feature of some Southern Svecofennian metasediments is a dominant Proterozoic age population at 2.0–2.1 Ga. Coincident deposition of mature and immature sediments and volcaniclastic rocks indicate that different sources, weathered and non-weathered ‘basement’, and syn-depositional volcanic centers, produced simultaneously detritus to a large subsiding basin. Mature pelites and quartzites suggest a long residence time and stable passive margin or cratonic environment. The tectonic setting and possible provenance areas for the Central and Southern Svecofennian metasediments are also discussed. As a conclusion, the metasediments from the Central and Southern parts of the Svecofennian Orogen show different lithological characteristics and have contrasting source components. The presented isotope data indicate a different evolution of these parts prior to 1.89 Ga and the existence of a suture zone between them as proposed in earlier studies.