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  • 1.
    Johansson, Åke
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    A refined U-Pb age for the Stockholm granite at Frescati, east-central Sweden2019Ingår i: GFF, ISSN 1103-5897, E-ISSN 2000-0863, Vol. 141, nr 1, s. 40-47Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A sample of fine-grained grey Stockholm granite from the Frescati area just north of central Stockholm, east-central Sweden, earlier dated to 1803 +23/−19 Ma by the U-Pb zircon method using TIMS on multigrain fractions, has been reanalyzed using the Nordsim ion microprobe. The new age obtained, 1792±4 Ma, is more precise, and replaces the earlier highly discordant date. It agrees well with other ages for the formation of the Stockholm-type granites and related pegmatites, indicating an age of around 1.79 Ga for this late-orogenic Svecofennian granite magmatism. The Stockholm granite thus formed toward the end of the 1.83–1.79 Ga late Svecofennian metamorphic phase, and crosscuts earlier formed migmatitic gneiss structures in a brittle manner at the present-day level of exposure.

  • 2.
    Johansson, Åke
    et al.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Karlsson, Andreas
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Hurgammal är Stockholmsgraniten? Vad säger forskningen och vad säger folket?2019Ingår i: Geologiskt forum, nr 101, s. 22-25Artikel i tidskrift (Övrig (populärvetenskap, debatt, mm))
  • 3.
    Kara, Jaakko
    et al.
    University of Turku.
    Väisänen, Markku
    University of Turku .
    Lahaye, Yann
    Geological Survey of Finland (GTK).
    O'Brien, Hugh
    Geological Survey of Finland (GTK).
    Eklund, Olav
    Åbo Akademi University.
    1.90-1.88 Ga arcmagmatism of central Fennoscandia: geochemistry, U-Pb geochronology, Sm-Nd andLu-Hf isotope systematics of plutonic-volcanic rocks from southern Finland.2018Ingår i: Geologica Acta, ISSN 1695-6133, E-ISSN 1696-5728, Vol. 16, nr 1, s. 1-23Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The earliest Svecofennian magmatism in southern Finland has been dated to 1.90-1.88Ga. As an example of this, the Orijärvi (ca. 1.89Ga) and Enklinge (ca. 1.88Ga) volcanic centres comprise bimodal plutonic batholiths surrounded by volcanic rocks of comparable ages and chemical compositions. The rock types range from gabbros to granites and indicate a subduction-related continental margin setting. The zircons from the Orijärvi granodiorite define an age of 1892±4Ma whereas the Enklinge granodiorite yields an age of 1882±6Ma. Several inherited ages of 2.25-1.95Ga as well as younger metamorphic ages of 1.86-1.80Ga were found in the Enklinge granodiorite. The initial εNd values of the mafic rocks from both locations fall in the range +1.1 to +2.9, whereas the felsic rocks exhibit initial εNd values of -0.4 to +1.2. The magmatic zircons from the Orijärvi and Enklinge granodiorites show average initial εHf values of -1.1 (at 1892Ma) and zero (at 1882Ma), respectively, both with a spread of about 7 ε-units. The initial εHf values for the inherited zircons from Enklinge range from +3.5 to +7.6 with increasing age. The Sm-Nd data indicate that the mafic rocks were derived from a “mildly depleted” mantle source while the felsi rocks show some crustal contribution. Also, the variation in ε Hf values indicates minor mixing between mildly depleted mantle-derived magmas and crustal sources. U-Pb ages and Hf isotopes for inherited zircons from the Enklinge granodiorite suggest the presence of juvenile Svecofennian “proto-crust” at depth

  • 4. Kornprobst, Jacques
    et al.
    Abalos, Benito
    Barbey, Pierre
    Boullier, Anne-Marie
    Burg, Jean-Pierre
    Capdevila, Ramon
    Claesson, Stefan
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Cordani, Umberto
    Corrigan, David
    Gabrielsen, Roy H
    Gil-Ibarguchi, José I
    Johansson, Åke
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Letsch, Dominik
    Le Vigouroux, Phillipe
    Upton, Brian
    Boris Choubert: Unrecognized visionarygeologist, pioneer of the global tectonics.2018Ingår i: BSGF - Earth Science Bulletin, Vol. 189, nr 2, s. 1-15, artikel-id 7Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This work is a review of Boris Choubert’s paper (1935), which was published in French under the rather devalorizing title: “Research on the Genesis of Palaeozoic and Precambrian Belts.” Despite its innovative content, this article had no impact either at the time of its publication or even later. It begins with the construction of a remarkable fit of the circum-Atlantic continents. This was based on the 1.000 meters isobath instead of the shoreline. Thirty years before Bullard et al. (1965), it demonstrated in an indisputable way the reality of the continents motion on the surface of the Earth. Therefore, Choubert designated Wegener’s “continental drift” as the main cause of tectonics. Even going beyond Wegener’s theory, he argued that this mechanism was efficient well before the formation of the Triassic Pangæa, during the whole Palaeozoic to result in the building of the Caledonian and Hercynian mountains. Although he was still encumbered by the vocabulary of the time regarding geosynclines, Boris Choubert described tectonics based on the horizontal mobility of the Precambrian continental blocks. Oddly enough, he did not apply this model to the Precambrian structures, which he attributed to the effects of the Earth’s rotation on the continental crust during its solidification. At the time of its publication, this paper was a very important step towards understanding global tectonics. Unfortunately, Choubert’s contemporaries did not generally recognize its significance.

  • 5.
    Johansson, Åke
    et al.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Kumpulainen, Risto
    Rantakokko, Nina
    Sveriges största granater?2018Ingår i: Geologiskt forum, ISSN 1104-4721, nr 99, s. 6-9Artikel i tidskrift (Övrig (populärvetenskap, debatt, mm))
  • 6.
    Johansson, Åke
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Timing of magmatism and migmatization in the 2.0–1.8 Ga accretionary Svecokarelian orogen, south-central Sweden.2017Ingår i: International journal of earth sciences, ISSN 1437-3254, E-ISSN 1437-3262, Vol. 106, nr 3, s. 783-810Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Palaeoproterozoic (2.0–1.8 Ga) Svecokarelian orogen in central Sweden consists of a low-pressure, predominantly medium-grade metamorphic domain (central part of Bergslagen lithotectonic unit), enclosed to the north and south by low-pressure migmatite belts. Two periods of metamorphism (1.87–1.85 and 1.83–1.79 Ga) are known in the migmatite belts. In this study, new U–Th–Pb ion microprobe data on zircon and monazite from twelve samples of locally migmatized gneisses and felsic intrusive bodies determine both protolith and metamorphic ages in four sample areas north of Stockholm, inside or immediately adjacent to the medium-grade metamorphic domain. Two orthogneiss samples from the Rimbo area yield unusually old protolith ages of 1909 ± 4 and 1908 ± 4 Ma, while three orthogneisses from the Skutskär and Forsmark areas yield more typical protolith ages between 1901 ± 3 and 1888 ± 3 Ma. Migmatized paragneiss samples from this and two earlier studies contain a significant detrital component sourced from this 1.9 Ga magmatic suite. They are interpreted to be deposited contemporaneously with or shortly after this magmatism. Migmatization of the paragneiss at Rimbo was followed by intrusion of leucogranite at 1846 ± 3 Ma. Even in the other sample areas to the north (Hedesunda-Tierp, Skutskär and Forsmark), metamorphism including migmatization is constrained to the 1.87–1.85 Ga interval and penetrative ductile deformation is limited by earlier studies in the Forsmark area to 1.87–1.86 Ga. However, apart from a metamorphic monazite age of 1863 ± 1 Ma, precise ages were not possible to obtain due to the presence of only partially reset recrystallized domains in zircon, or highly discordant U-rich metamict and altered metamorphic rims. Migmatization was contemporaneous with magmatic activity at 1.87–1.84 Ga in the Bergslagen lithotectonic unit involving a mantle-derived component, and there is a spatial connection between migmatization and this magmatic phase in the Hedesunda-Tierp sample area. The close spatial and temporal interplay between ductile deformation, magmatism and migmatization, the PT metamorphic conditions, and the continuation of similar magmatic activity around and after 1.8 Ga support solely accretionary rather than combined accretionary and collisional orogenic processes as an explanation for the metamorphism. The generally lower metamorphic grade and restricted influence of the younger metamorphic episode, at least at the ground surface level, distinguishes the central part of the Bergslagen lithotectonic unit from the migmatite belts further north and south.

  • 7.
    Johansson, Åke
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    35:e IGC i Kapstaden. Geologernas egen olympiad.2016Ingår i: Geologiskt forum, ISSN 1104-4721, nr 92, s. 18-19Artikel i tidskrift (Övrig (populärvetenskap, debatt, mm))
  • 8.
    Johansson, Åke
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Comments to ”Detrital zircon signatures of the Baltoscandian margin along the Arctic Circle Caledonides in Sweden: The Sveconorwegian connection” by Gee et al. (2015).: Letter to the Editor2016Ingår i: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 276, s. 233-235Artikel i tidskrift (Övrigt vetenskapligt)
  • 9.
    Johansson, Åke
    et al.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Waight, Tod
    University of Copenhagen.
    Andersen, Tom
    University of Oslo.
    Geochemistry and petrogenesis of Mesoproterozoic A-type granitoids from the Danish island of Bornholm, southern Fennoscandia2016Ingår i: Lithos, ISSN 0024-4937, E-ISSN 1872-6143, Vol. 244, s. 94-108Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Granitoids and gneisses from the Danish island of Bornholm have been investigated using whole rock geochemistry, Sr and Nd isotope geochemistry and Hf isotopes in zircon. Recent U-Pb dating shows that the rocks were formed during a short time interval at 1.45 to 1.46 Ga, penecontemporaneous with ongoing deformation. The strong similarity in geochemical signatures indicate that they all belong to a single igneous suite composed of alkali-calcic biotite-hornblende quartz monzonites to more evolved biotite granites, albeit with an apparent gap in SiO2 content at around 70 wt%, dividing the suite into an intermediate and a felsic part. These dominantly metaluminous rocks are strongly ferroan and potassic, and with highly elevated concentrations of many trace elements, traits that are typical for A-type granitoids. The presence of magnetite and titanite indicates relatively oxidized compositions, and Nb/Y ratios designate them to the A2 subtype. Initial whole rock eNd values range between +1 and -2 (with one outlier at +4), and initial zircon eHf values between +3 and -4. These values may be explained by melting of relatively juvenile crust similar to that forming the Transscandinavian Igneous Belt alone, but the spread in Hf and Nd isotope compositions to values overlapping with the Svecofennian mantle at 1.45 Ga suggests involvement of a mantle-derived component. This indicates the magmatism was associated with juvenile crustal growth. There are no systematic differences in isotope or trace element characteristics between the orthogneisses and the less deformed granitoids, suggesting similar origins for both rock types, and no systematic changes in isotopic composition with SiO2concentration. 

    Trace element compositions indicate a within-plate setting, similar to other 1.45 Ga granites in southwest Fennoscandia, in spite of the close relation between magmatism and deformation on Bornholm. We therefore suggest intracratonic A-type magmatism within an active continental shear zone as a tentative model for the Mesoproterozoic magmatism on Bornholm. However, a close relationship to the nearby Hallandian tectono-magmatic activity in southern Sweden, attributed to continental margin orogenic processes, is also evident. Intermediate magmas presumably formed by ponding of enriched mantle-derived basic magma at the crust-mantle boundary or within the lower crust, causing extensive partial melting and assimilation of mafic to intermediate crustal rocks related to the Transcandinavian Igneous Belt. The magmas then evolved to granitic compositions by removal of an assemblage similar to that seen petrographically, i.e. plagioclase, amphibole, magnetite, titanite, and late-stage K-feldspar.

  • 10.
    Johansson, Åke
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    U-Pb SIMS dating of some granitoids from eastern Blekinge, southern Sweden2016Ingår i: GFF, ISSN 1103-5897, E-ISSN 2000-0863, Vol. 138, nr 3, s. 430-444Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Zircons from seven granitoids in eastern Blekinge have been dated using secondary ion mass spectrometry. The analyzed rocks include one Småland granitoid from north of the Småland-Blekinge Deformation Zone (SBDZ), two samples of megacrystic “Filipstad-type” granite from south of that zone, and one sample each of the “Småland-type” Rödeby, Almö, Tjurkö and Jämjö granites. The results yield a crystallization age of 1776 ± 6 Ma for the Småland granitoid, and crystallization ages between 1770 ± 4 and 1758 ± 6 Ma for the other granitoids, in most cases substantially older than previous TIMS ages. These data show that the “Småland-type” granitoids in eastern Blekinge are similar in age to the surrounding Tving granitoids, and the more felsic of them may represent late-stage differentiates belonging to the same magmatic suite. As the Tving granitoids show differences both in degree of deformation, in geochemistry and possibly in age, when compared with the Småland granitoids north of the SBDZ, it is suggested that these represent two separate but closely related igneous suites, which could both be included within a TIB-1 supersuite.

    The investigated zircons showed very limited signs of metamorphic overgrowths, and no metamorphic ages could be determined. However, the combined evidence from field observations combined with earlier U-Pb geochronology would suggest the presence of two separate metamorphic episodes in Blekinge, one in close connection with the formation of these rocks at 1.76 – 1.75 Ga, and one connected to the intrusion of the Karlshamn granitoid suite at around 1.45 Ga.

  • 11.
    Johansson, Åke
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Vegahallen, ett monument över svensk stenindustri2016Ingår i: Geologiskt forum, ISSN 1104-4721, nr 92, s. 24-28Artikel i tidskrift (Övrig (populärvetenskap, debatt, mm))
  • 12.
    Johansson, Åke
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Dokumentera underjorden innan det är för sent.2015Ingår i: Geologiskt forum, ISSN 1104-4721, Vol. 22, nr 85, s. 31-Artikel i tidskrift (Övrig (populärvetenskap, debatt, mm))
  • 13. Armands, Gösta
    et al.
    Claesson, Stefan
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Johansson, Åke
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Lundqvist, Thomas
    En pionjär inom svensk isotopgeologi. In memoriam, Eric Welin, 1923-20142015Ingår i: Geologiskt forum, Vol. 22, nr 85, s. 26-27Artikel i tidskrift (Övrig (populärvetenskap, debatt, mm))
  • 14.
    Johansson, Åke
    et al.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Andersen, Tom
    Universitetet i Oslo.
    Simonsen, Siri L.
    Universitetet i Oslo.
    Hafnium isotope characteristics of late Palaeoproterozoic magmatic rocks from Blekinge, southeast Sweden: possible correlation of small-scale Hf and Nd isotope variations in zircon and whole-rocks.2015Ingår i: GFF, ISSN 1103-5897, E-ISSN 2000-0863, Vol. 137, nr 1, s. 74-82Artikel i tidskrift (Refereegranskat)
  • 15.
    Johansson, Åke
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Kilauea – besvikelse och överraskning2015Ingår i: Geologiskt forum, Vol. 22, nr 87, s. 14-17Artikel i tidskrift (Övrig (populärvetenskap, debatt, mm))
  • 16.
    Johansson, Åke
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Berättelsen om ett jordeliv2014Ingår i: Geologiskt forum, ISSN 1104-4721, Vol. 21, nr 84, s. 31-31Artikel i tidskrift (Övrig (populärvetenskap, debatt, mm))
  • 17.
    Johansson, Åke
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    From Rodinia to Gondwana with the ‘SAMBA’ model—A distant viewfrom Baltica towards Amazonia and beyond2014Ingår i: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 244, s. 226-235Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A refined model of the late Mesoproterozoic to Neoproterozoic supercontinent Rodinia is presented, with Baltica, Amazonia and West Africa attached to eastern Laurentia as in the SAMBA model (Johansson, 2009), East Antarctica, Australia and India to western Laurentia in a SWEAT configuration (Moores, 1991), and northern Siberia attached to northern Laurentia as proposed by Condie and Rosen (1994). In such a model, the Proto-Andean margin of South America would form the conjugate margin of Laurentia’s Grenville margin. With the Kalahari craton attached to SW Laurentia and East Antarctica, as proposed by Loewy et al. (2011), followed by the Congo and Tanzania cratons in Africa and the Sao Fransisco and Rio de la Plata cratons in South America, all these cratons would be part of Rodinia, but would still be separated from Amazonia by a wide Brasiliano (Clymene) ocean embayment. By rotating the African and eastern South American cratons ca 90° counterclockwise around a pole located close to the Laurentia – Kalahari junction, and East Antarctica, Australia and India ca 120° counterclockwise around a pole located inside the Kalahari craton, all relative to a fixed Laurentia, these cratons will move from a Rodinia to a Gondwana configuration. These rotations will open up the Proto-Pacific ocean, close the Brasiliano (Clymene) ocean, and both open and close the intervening Adamastor and Mozambque oceans, creating the various Brasiliano and Pan-African fold belts in the ensuing collisions. The maximum plate velocity, ca 7.5 cm/year (15 000 km in 200 m.y.), will occur along the outer periphery of this rotation, thereby explaining the formation of large amounts of juvenile Neoproterozoic continental crust within the oceanic Arabian – Nubian sector of the Pan-African Orogen. Rather than being an example of ‘introversion’ or ‘extroversion’, the change from Rodinia to Gondwana in this model would be more like the 90º ‘orthoversion’ model proposed by Mitchell et al. (2012).

  • 18.
    Dahlin, Peter
    et al.
    Uppsala Universitet.
    Johansson, Åke
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Andersson, Ulf Bertil
    LKAB.
    Source character, mixing, fractionation and alkali metasomatism in Palaeoproterozoic greenstone dykes, Dannemora area, NE Bergslagen region, Sweden2014Ingår i: Geological Magazine, ISSN 0016-7568, E-ISSN 1469-5081, Vol. 151, nr 4, s. 573-590Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The geochemical and isotopic characteristics of metamorphosed Svecofennian mafic dykes from the Dannemora area in the NE part of the Bergslagen region in central Sweden were investigated and compared to mafic intrusive rocks in their vicinity. The dykes, with an inferred age of c. 1860–1870 Ma, are calc-alkaline, sub-alkaline and basaltic in composition and have a mixed subduction and within-plate geochemical affinity. They are the result of mixing of at least three mantle source components with similar basaltic major element composition, but different concentrations of incompatible trace elements. Magma M1 is strongly enriched both in Rare Earth Elements (REE) and High-Field-Strength Elements (HFSE); magma M2 is highly enriched in Large-Ion Lithophile Elements (LILE, except Sr) with only moderate enrichment in HFSE and REE (particularly low in Heavy Rare Earth Elements); and magma M3 is enriched in Sr and has a flat REE profile. Magma M3 also has a somewhat more positive (depleted) initial εNd value of +1.8, compared to +0.4 to +0.5 for magmas M1 and M2. The magma evolution was controlled by a mixture of fractionation (mainly affecting the compatible elements) and mixing, best seen in the incompatible element concentrations and the Nd isotope data. The basaltic overall composition indicates little or no wholesale contamination by upper continental crust, but the dykes have undergone later metasomatic changes mainly affecting the alkali elements.

  • 19.
    Johansson, Åke
    et al.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Hålenius, Ulf
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Palaeoproterozoic mafic intrusions along the Avesta-Östhammar belt, east-central Sweden: mineralogy, geochemistry and magmatic evolution2013Ingår i: International Geology Review, ISSN 0020-6814, E-ISSN 1938-2839, Vol. 55, s. 131-157Artikel i tidskrift (Refereegranskat)
  • 20.
    Johansson, Åke
    et al.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Andersson, Ulf B.
    Uppsala University.
    Hålenius, Ulf
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Petrogenesis and geotectonic setting of early Svecofennian arc cumulates in the Roslagen area, east-central Sweden2012Ingår i: Geological Journal, ISSN 0072-1050, E-ISSN 1099-1034, Vol. 47, s. 557-593Artikel i tidskrift (Refereegranskat)
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