Timing of Palaeoproterozoic crustal shearing in the central Fennoscandian Shield according to U-Pb data from associated granitoids, Finland

Vaasjoki, Matti; Kärki, Aulis; Laajoki, K.

doi:10.17741/bgsf/73.1-2.007

Cited by 11 publications

(8 citation statements)

References 26 publications

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“…Recent works by e.g. Lahtinen & Huhma (1997), Nironen (1997), Elliot et al (1998), Korsman et al (1999), Vaasjoki et al (2001), Nironen et al (2002) and Väisänen (2002) have considerably improved our understanding of these events. Zircon ion microprobe studies by Huhma et al (1991) and Claesson et al (1993), and later by Lindh et al (2001), Väisänen et al (2002), Rutland et al (2001aRutland et al ( , 2001bRutland et al ( and 2003, and Weihed et al (2002), indicate the existence of a pre-1.95 Ga Palaeoproterozoic continental crust in different parts of the shield.…”

Section: Introductionmentioning

confidence: 99%

Timing of Svecofennian crustal growth and collisional tectonics in Åland, SW Finland

Ehlers¹,

Skiöld²,

Vaasjoki³

2004

Bull Geol Soc Finland

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In an effort to quantify the time parameter in the tectonomagmatic evolution of what has been called the Southern Svecofennian Arc Complex (SSAC) of SW Finland, advanced radiometric dating techniques have here been applied to rock groups of key importance in that area. In this paper we report the results of 131 high-resolution ion microprobe spot analyses (SIMS) of zircons, and 33 measurements using isotope dilution mass spectrometry (ID-TIMS) on zircon, monazite and titanite,and employing both large-sample multi-grain as well as single-grain techniques.The To rsholma area of the Åland archipelago,situated between southern Finland and central Sweden, is a key structural area significant to resolve the time dimension in Svecofennian tectonics.There a collage of imbricated rock slabs was formed by tectonic shortening representing the culmination of large-scale penetrative Svecofennian deformation. Another structurally significant feature investigated is the South Finland Shear Zone (SFSZ) that transects the southwest-Finnish archipelago and further east follows the southern coast of Finland.This shear zone forms the southern limit of the c. 1830 Ma Late Svecofennian Granite and Migmatite Zone (LSGM) and also features deformations of a later stage when the considered region of Svecofennian crust was consolidated.The obtained age results and theirt ectonic analysis can be summarized as follows. The Enklinge volcanic sequence (1885±6 Ma) is within error limits coeval with the intrusion of abundant early-kinematic gneissose granodiorites whose average age of 1884±5 Ma marks the formation of new crust in this region.Some of these geisses contain a significant amount of 2000-2080 Ma zircon. Although many Svecofennian granitoids are known to contain heterogeneous zircon populations, mainly formed c. 1890 Ma ago but also containing an inherited component, the Kökar gneiss is, to the best of our knowledge,the first case where inheritance from c. 2030 Ma sources has been unequivocally demonstrated in a syntectonic Svecofennian intrusive rock.At To rsholma,granodiorites (1879±6 Ma) have similarly intruded the supracrustal series, but there they were later metamorphosed into granulite orthogneisses.The mesoscopic recumbent folds and subhorizontals chistosityo ft heseg neisses were transected by a set of steep amphibolitic dykes indicating an episode of extension. During a preceding stage,these gneisses had been sandwiched like an allochthonous slab unit between the supracrustal rocks. Yo unger sheet-like granodioritic intrusions (1861±19 Ma) with associated dykes (1865±7 Ma) reflect an even later stage of collisional thrusting. Altogether this tectonic evolution lasted for approximately 15 Ma (c. 1875-1860 and records a period of significant deformations during the Svecofennian orogeny. Monazites and zircon rims yield concordant U-Pb ages of c. 1830 Ma.This is in agreement with previously obtained ages of late Svecofennian granites and migmatites in the LSGM zone in S Finland.Weaklyd eformed pegmatites and even-grained granit...

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Section: Introductionmentioning

confidence: 99%

Timing of Svecofennian crustal growth and collisional tectonics in Åland, SW Finland

Ehlers¹,

Skiöld²,

Vaasjoki³

2004

Bull Geol Soc Finland

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“…The peak-T conditions are considered to have occurred between ca. 1.87 Ga and 1.85 Ga, although the heating was protracted, with temperatures falling below ~500 ºC only after 1.80 Ga (Kontinen et al, 1992;Peltonen et al, 1996;Tuisku, 1997;Vaasjoki et al, 2001). Blastomylonite textures are characteristic features in sheared rocks of the area, indicating that peak-T conditions were reached under static conditions after the main Svecofennian deformations, which were over before ca.…”

Section: Geologic Settingmentioning

confidence: 99%

“…Blastomylonite textures are characteristic features in sheared rocks of the area, indicating that peak-T conditions were reached under static conditions after the main Svecofennian deformations, which were over before ca. 1.85 Ga (Pajunen & Poutiai nen, 1999;Vaasjoki et al, 2001;Kontinen & Paavola, 2006;Kontinen et al, 2013b,c). The most plausible explanation to the observed Svecofennian heating is tectonic burial of the presently exposed rocks to depths of 15-20 km in association with the 1.9-1.8 Ga folding and thrusting event, although igneous underplating could have been an additional factor (Kontinen et al, 1992(Kontinen et al, , 2013bTuisku, 1997;Korsman et al, 1999;Pajunen & Poutiainen, 1999;Kontinen, 2002;Kontinen & Paavola, 2006;Lahtinen et al, 2010Lahtinen et al, , 2015…”

Section: Geologic Settingmentioning

confidence: 99%

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Geology, geochronology and geochemistry of the 2.05 Ga gneissic A1-type granites and related intermediate rocks in central Finland: implication for the tectonic evolution of the Karelia craton margin

Kärenlampi¹,

Kontinen²,

Huhma³

et al. 2019

Bull Geol Soc Finland

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The 2.05 Ga Otanmäki suite represents a globally rare occurrence of Paleoproterozoic non-orogenic A1-type magmatism. It consists of a broad variety of A-type felsic and intermediate igneous rocks including monzodiorites, monzonites, syenites and peralkaline to peraluminous granites, containing both plutonic and subvolcanic members. The suite has chemical characteristics similar to those of A1-type suites formed in intraplate hotspots or continental rifts by differentiation of variably crustally contaminated, mafic mantle-derived magmas. However, compared to the Otanmäki rocks, most A1-type suites are considerably younger. Unraveling the original geologic setting of the Otanmäki suite is challenging because the suite was disintegrated, deformed and metamorphosed under amphibolite facies conditions (T ~550-600 ºC, P ~4 kbar) during the Svecofennian collisional orogeny (ca. 1900 Ma), i.e., 150-200 Ma after its initial emplacement. As a result, Otanmäki suite rocks are now found as pervasively foliated rocks within two nappe units sandwiched between Archean granitoid gneiss complexes and Paleoproterozoic supracrustal belts. The occurrence of slivers of 1950 Ma ocean-continent-transition ophiolitic rocks in the same thrust belt and the proximity of the Otanmäki suite to the Karelia-Svecofennia margin suggest that the suite records an early stage of a slow, ca. 100-Ma-long extension-rifting process which, at ca. 1950 Ma, eventually led to the final break-up of the Karelia craton and formation of the nascent ocean basin witnessed by the Jormua ophiolite complex.

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“…The last major deformation in the OSZ took place at 1.86–1.80 Ga (Kärki ), with 1.80 Ga marking the end of the orogenic evolution in the region (Vaasjoki et al. ). However, the old ductile structures were later reactivated as faults, likely related to the shield‐wide postorogenic extension episodes, including the latest orogenic event affecting the Shield, i.e., the Caledonian (Scandian) orogeny, at 430–400 Ma (e.g., Windley ; Holma, personal communication).…”

Section: Geologic Background and Previous Studiesmentioning

confidence: 99%

Shock metamorphic features in quartz grains from the Saarijärvi and Söderfjärden impact structures, Finland

Öhman¹,

Preeden²

2013

Meteorit & Planetary Scien

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Abstract-Shock metamorphic features at the Saarija¨rvi (D > 2 km) and So¨derfja¨rden (D = 6.5 km) structures in Finland have so far only been studied tentatively, although both are considered to be proven impact structures. This work presents the first detailed universal stage study of planar deformation features (PDFs), feather feature lamellae (FFL), and planar fractures (PFs) in quartz grains from a polymict impact breccia dike from So¨derfja¨rden, and from sedimentary crater-fill rocks from Saarija¨rvi. Planar microstructures, particularly PDFs, are very rare and poorly developed or preserved in Saarija¨rvi, whereas in So¨derfja¨rden they are much more common and well defined. Miller-Bravais indices of the planar microstructures in both Saarija¨rvi and So¨derfja¨rden are indicative of relatively lowshock pressure but high shear conditions, only compatible with an impact origin for these structures. Although a Proterozoic age for Saarija¨rvi cannot be ruled out, the observations of shock features throughout the sedimentary crater-fill sequence and a brecciated sedimentary dike below the crater floor are more consistent with a Lower Cambrian (or younger) impact age.

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Timing of Palaeoproterozoic crustal shearing in the central Fennoscandian Shield according to U-Pb data from associated granitoids, Finland

Cited by 11 publications

References 26 publications

Timing of Svecofennian crustal growth and collisional tectonics in Åland, SW Finland

Timing of Svecofennian crustal growth and collisional tectonics in Åland, SW Finland

Geology, geochronology and geochemistry of the 2.05 Ga gneissic A1-type granites and related intermediate rocks in central Finland: implication for the tectonic evolution of the Karelia craton margin

Shock metamorphic features in quartz grains from the Saarijärvi and Söderfjärden impact structures, Finland

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