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  • 201. Jeon, H.
    et al.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    A Critical Evaluation of U–Pb Calibration Schemes Used in SIMS Zircon Geochronology.2015In: Geostandards and Geoanalytical Research, ISSN 1639-4488, E-ISSN 1751-908X, Vol. 39, p. 443-452Article in journal (Refereed)
    Abstract [en]

    Precision and accuracy in SIMS zircon geochronology strongly depend on the method of determination of the interelement ion ratios (e.g., 206Pb/238U) from the measured secondary ion ratios (206Pb+/238U+). Six possible U–Pb calibrations (Pb/U–UO2/U, Pb/U–UO/U, Pb/U–UO2/UO, Pb/UO–UO2/U, Pb/UO–UO/U, Pb/UO–UO2/UO) based on simple power law relationships, and Pb/UO2-related one- and two- (a power law) dimensional ones were compared using data acquired on the 91500 zircon reference material from one hundred measurement sessions, to determine the most statistically reliable scheme. Taking advantage of U oxide species (UO and UO2) over atomic U, due to their similar energy distribution to Pb and higher intensities, the data calibrated with Pb/UO–UO2/UO showed the smallest mean uncertainties and dispersions, and provided the best-fit calibration curve consistently. Although it was demonstrated with Temora 2 that the unknown zircon age was not changed significantly by different calibrations, its precision could be improved using the Pb/UO–UO2/UO calibration in zircon geochronology.

  • 202.
    Johansson, Åke
    Swedish Museum of Natural History, Department of Geology.
    35:e IGC i Kapstaden. Geologernas egen olympiad.2016In: Geologiskt forum, ISSN 1104-4721, no 92, p. 18-19Article in journal (Other (popular science, discussion, etc.))
  • 203.
    Johansson, Åke
    Swedish Museum of Natural History, Department of Geology.
    Berättelsen om ett jordeliv2014In: Geologiskt forum, ISSN 1104-4721, Vol. 21, no 84, p. 31-31Article in journal (Other (popular science, discussion, etc.))
  • 204.
    Johansson, Åke
    Swedish Museum of Natural History, Department of Geology.
    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 Editor2016In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 276, p. 233-235Article in journal (Other academic)
  • 205.
    Johansson, Åke
    Swedish Museum of Natural History, Department of Geology.
    Dokumentera underjorden innan det är för sent.2015In: Geologiskt forum, ISSN 1104-4721, Vol. 22, no 85, p. 31-Article in journal (Other (popular science, discussion, etc.))
  • 206.
    Johansson, Åke
    Swedish Museum of Natural History, Department of Geology.
    From Rodinia to Gondwana with the ‘SAMBA’ model—A distant viewfrom Baltica towards Amazonia and beyond2014In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 244, p. 226-235Article in journal (Refereed)
    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).

  • 207.
    Johansson, Åke
    Swedish Museum of Natural History, Department of Geology.
    Kilauea – besvikelse och överraskning2015In: Geologiskt forum, Vol. 22, no 87, p. 14-17Article in journal (Other (popular science, discussion, etc.))
  • 208.
    Johansson, Åke
    Swedish Museum of Natural History, Department of Geology.
    Timing of magmatism and migmatization in the 2.0–1.8 Ga accretionary Svecokarelian orogen, south-central Sweden.2017In: International journal of earth sciences, ISSN 1437-3254, E-ISSN 1437-3262, Vol. 106, no 3, p. 783-810Article in journal (Refereed)
    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.

  • 209.
    Johansson, Åke
    Swedish Museum of Natural History, Department of Geology.
    U-Pb SIMS dating of some granitoids from eastern Blekinge, southern Sweden2016In: GFF, ISSN 1103-5897, E-ISSN 2000-0863, Vol. 138, no 3, p. 430-444Article in journal (Refereed)
    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.

  • 210.
    Johansson, Åke
    Swedish Museum of Natural History, Department of Geology.
    Vegahallen, ett monument över svensk stenindustri2016In: Geologiskt forum, ISSN 1104-4721, no 92, p. 24-28Article in journal (Other (popular science, discussion, etc.))
  • 211.
    Johansson, Åke
    et al.
    Swedish Museum of Natural History, Department of Geology.
    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.2015In: GFF, ISSN 1103-5897, E-ISSN 2000-0863, Vol. 137, no 1, p. 74-82Article in journal (Refereed)
  • 212.
    Johansson, Åke
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Andersson, Ulf B.
    Uppsala University.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Petrogenesis and geotectonic setting of early Svecofennian arc cumulates in the Roslagen area, east-central Sweden2012In: Geological Journal, ISSN 0072-1050, E-ISSN 1099-1034, Vol. 47, p. 557-593Article in journal (Refereed)
  • 213.
    Johansson, Åke
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Palaeoproterozoic mafic intrusions along the Avesta-Östhammar belt, east-central Sweden: mineralogy, geochemistry and magmatic evolution2013In: International Geology Review, ISSN 0020-6814, E-ISSN 1938-2839, Vol. 55, p. 131-157Article in journal (Refereed)
  • 214.
    Johansson, Åke
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Kumpulainen, Risto
    Rantakokko, Nina
    Sveriges största granater?2018In: Geologiskt forum, ISSN 1104-4721, no 99, p. 6-9Article in journal (Other (popular science, discussion, etc.))
  • 215.
    Johansson, Åke
    et al.
    Swedish Museum of Natural History, Department of Geology.
    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 Fennoscandia2016In: Lithos, ISSN 0024-4937, E-ISSN 1872-6143, Vol. 244, p. 94-108Article in journal (Refereed)
    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.

  • 216.
    Jonsson, Erik
    et al.
    Sveriges Geologiska Undersökning, Uppsala.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Mn3+-bearing pargasite from the Långban Fe-Mn oxide mineralisation, Bergslagen, Sweden2010In: GFF, ISSN 1103-5897, E-ISSN 2000-0863, Vol. 132, p. 167-172Article in journal (Refereed)
  • 217.
    Jonsson, Erik
    et al.
    Sveriges Geologiska Undersökning.
    Langhof, Jörgen
    Swedish Museum of Natural History, Department of Geology.
    Upptäckten av halvmetallen selen fyller 200 år2018In: Geologiskt Forum, ISSN 1104-4721, no 100, p. 24-27Article in journal (Other (popular science, discussion, etc.))
  • 218. Jordan, T.A.
    et al.
    Neale, R.F.
    Leat, P.T.
    Vaughan, A.P.M.
    Flowerdew, M.J,
    Riley, T.R.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Ferraccioli, F.
    Structure and evolution of Cenozoic arc magmatism on the Antarctic Peninsula; a high resolution aeromagnetic perspective2014In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 198, p. 1758-1774Article in journal (Refereed)
  • 219.
    Kasapoğlu, Bülent
    et al.
    The Graduate School of Natural and Applied Sciences, Dokuz Eylül University, TR-35160 İzmir, Turkey.
    Ersoy, Yalçın E.
    Department of Geological Engineering, Dokuz Eylül University, TR-35160 İzmir, Turkey.
    Uysal, İbrahim
    Department of Geological Engineering, Karadeniz Technical University, TR-61080 Trabzon, Turkey.
    Palmer, Martin R.
    School of Ocean and Earth Science, University of Southampton, National Oceanography Centre, European Way, Southampton SO14 3ZH, UK.
    Zack, Thomas
    Department of Earth Science, University of Gothenburg, Gothenburg, Sweden.
    Koralay, Ersin O.
    Department of Geological Engineering, Dokuz Eylül University, TR-35160 İzmir, Turkey.
    Karlsson, Andreas
    Swedish Museum of Natural History, Department of Geology.
    The petrology of Paleogene volcanism in the Central Sakarya, Nallıhan Region: Implications for the initiation and evolution of post-collisional, slab break-off-related magmatic activity2015In: Lithos, ISSN 0024-4937, E-ISSN 1872-6143, Vol. 246-247, p. 81-98Article in journal (Refereed)
    Abstract [en]

    Zircon ages, mineral chemistry, whole-rock major and trace element compositions, as well as Sr–Nd isotopic ratios of basaltic (basanite, basalt, and hawaiite with MgO = 3.90–10.06 and SiO2 = 43.18–48.16) to andesitic (SiO2 = 50.86–61.27) and rhyolitic (SiO2 = 71.11–71.13) volcanic rocks (E-W emplaced Nallıhan volcanics) in the Lower Eocene terrestrial sedimentary units in the Central Sakarya Zone were studied and compared with those of the northerly located E-W-trending Eocene volcanic rocks (the Kızderbent Volcanics with 52.7–38.1 Ma radiometric ages) that are thought to be related to slab break-off process following the continental collision in the NW Anatolia. Zircon U–Pb ages of the Nallıhan volcanics vary from 51.7 ± 4.7 to 47.8 ± 2.4 Ma.

    Clinopyroxene from the basaltic and andesitic rocks record crystallization conditions from ~ 7–8 kbars (~ 23 km) and ~ 1210 °C, to 4.5–1.5 kbars (~ 14–1.5 km) and 1110–1010 °C crystallization conditions, respectively. The olivine-bearing, high-MgO (up to 10 wt%) basaltic rocks of the Nallıhan volcanics have nepheline-normative and Na-alkaline compositions, while the andesitic to rhyolitic rocks show calc-alkaline affinity with mainly sodic character. This is the first time this type of volcanic rock has been described in this region. The initial Sr isotopic ratios of both basaltic and andesitic–rhyolitic samples from the Nallıhan volcanics are similar (~ 0.7040–0.7045), indicating that fractional crystallization processes were not accompanied by crustal contamination and that the magma chambers were likely stored within ophiolitic units. Trace element ratios suggest that the Nallıhan volcanics were derived from E-MORB- or OIB-like enriched mantle sources, while the Kızderbent volcanics had N-MORB-like depleted mantle sources. Both volcanic units were produced by partial melting of spinel-bearing (shallow) mantle sources that had undergone subduction-related enrichment processes, with the degree of enrichment having been greater for the Kızderbent volcanics.

    The geochemical features of both the Nallıhan and Kızderbent volcanics are best explained as the result of slab break-off, in which the Nallıhan volcanics (located closer to the original subduction front) were produced mainly by the melting of upwelling asthenospheric mantle. Further back from the subduction front, the upwelling interacted with more highly metasomatized sub-arc mantle that underwent partial melting to produce the Kızderbent volcanics. This geodynamic scenario can be used for understanding other post-collisional slab break-off-related magmatic activities.

  • 220.
    Kenny, Gavin G.
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Petrus, Joseph A.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Daly, J. Stephen
    Kamber, Balz S.
    Hf isotope evidence for effective impact melt homogenisation at the Sudbury impact crater, Ontario, Canada2017In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 215, p. 317-336Article in journal (Refereed)
    Abstract [en]

    We report on the first zircon hafnium-oxygen isotope and trace element study of a transect through one of the largest terrestrial impact melt sheets. The differentiated melt sheet at the 1.85 Ga, originally ca. 200 km in diameter Sudbury impact crater, Ontario, Canada, yields a tight range of uniform zircon Hf isotope compositions (εHf(1850) of ca. −9 to −12). This is consistent with its well-established crustal origin and indicates differentiation from a single melt that was initially efficiently homogenised. We propose that the heterogeneity in other isotopic systems, such as Pb, in early-emplaced impact melt at Sudbury is associated with volatility-related depletion during the impact cratering process. This depletion leaves the isotopic systems of more volatile elements more susceptible to contamination during post-impact assimilation of country rock, whereas the systems of more refractory elements preserve initial homogeneities. Zircon oxygen isotope compositions in the melt sheet are also restricted in range relative to those in the impacted target rocks. However, they display a marked offset approximately one-third up the melt sheet stratigraphy that is interpreted to be a result of post-impact assimilation of 18O-enirched rocks into the base of the cooling impact melt.

    Given that impact cratering was a more dominant process in the early history of the inner Solar System than it is today, and the possibility that impact melt sheets were sources of ex situ Hadean zircon grains, these findings may have significance for the interpretation of the early zircon Hf record. We speculate that apparent εHf-time arrays observed in the oldest terrestrial and lunar zircon datasets may be related to impact melting homogenising previously more diverse crust.

    We also show that spatially restricted partial melting of rocks buried beneath the superheated impact melt at Sudbury provided a zircon crystallising environment distinct to the impact melt sheet itself.

  • 221.
    Kenny, G.G.
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Balz, B.S
    Differentiated impact melt sheets may be a potential source of Hadean detrital zircon.2016In: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 44, p. 431-434Article in journal (Refereed)
    Abstract [en]

    Constraining the origin and history of very ancient detrital zircons has unique potential for furthering our knowledge of Earth’s very early crust and Hadean geodynamics. Previous applications of the Ti-in-zircon thermometer to >4 Ga zircons have identified a population with relatively low crystallization temperatures () of ~685 °C. This could possibly indicate wet minimum-melting conditions producing granitic melts, implying very different Hadean terrestrial geology from other rocky planets. Here we report the first comprehensive ion microprobe study of zircons from a transect through the differentiated Sudbury impact melt sheet. The new zircon Ti contents and corresponding  fully overlap with those of the Hadean zircon population. Previous studies, which measured Ti in impact melt sheet zircons did not find this wide range because they analyzed samples only from a restricted portion of the melt sheet and because they used laser ablation analyses that can overestimate true Ti content. It is important to note that internal differentiation of the impact melt is likely a prerequisite for the observed low  in zircons from the most evolved rocks. On Earth, melt sheet

  • 222.
    Kenny, G.G.
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Kamber, B.S.
    Differentiated impact melt sheets may be a potential source of Hadean detrital zircon: Reply2016In: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 44, article id e399Article in journal (Refereed)
  • 223.
    Kielman, Ross
    et al.
    Swedish Museum of Natural History, Department of Geology. Stockholm University.
    Nemchin, Alexander
    Curtin University.
    Whitehouse, Martin
    Swedish Museum of Natural History, Department of Geology.
    Pidgeon, Robert
    Curtin University.
    Bellucci, Jeremy
    Swedish Museum of Natural History, Department of Geology.
    U-Pb age distribution recorded in zircons from Archean quartzites in the Mt. Alfred area, Yilgarn Craton, Western Australia2018In: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 310, p. 278-290Article in journal (Refereed)
    Abstract [en]

    The U-Th-Pb isotopic data from detrital zircon grains from five samples of Archean quartzite from the Mt. Alfred area of the Illaara greenstone belt in the Yilgarn Craton of Western Australia are presented in this study. The zircon grains are typically fractured and contain both irregular and oscillatory zoned internal structures as revealed by cathodoluminescence imaging. Concordant 207Pb/206Pb ages range between 3109 ± 17 and 3918 ± 16 Ma (2σ), with three main age peaks at ca. 3640, 3690 and 3760 Ma. Older 207Pb/206Pb ages up to 4067 ± 5 Ma are strongly affected by at least one recent disturbance event, however one single-grain discordia yields an upper intercept age of 4107 ± 12 (MSWD = 1.2). A further sixteen zircon grains with multiple analyses define discordia that suggest U-Pb disturbance events in the Neoarchean and the Mesozoic, the latter as a result of invasive low temperature weathering solutions. The notable lack of grains with ages less than ∼3.6 Ga in the Mt. Alfred detrital zircon population differentiates it from other quartzite samples from both the Illaara Formation and the Eoarchean zircon-bearing metasedimentary rocks of the Narryer Terrane. Also, the limited spread of zircon ages between 3640 and 3760 Ma suggests a relatively uniform and possibly local source region. However, no rocks of this age have been found in the Youanmi Terrane. This implies either the distal transport of similarly aged clastic sediments at 3.1 Ga from the Narryer Gneiss Complex (NGC) to the Mt. Alfred area, or the previous existence of NGC-like rocks near the Illaara greenstone belt that are either not currently recognised or have since been destroyed.

  • 224.
    Kielman, Ross
    et al.
    Swedish Museum of Natural History, Department of Geology. Stockholm University.
    Whitehouse, Martin
    Swedish Museum of Natural History, Department of Geology.
    Nemchin, Alexander
    Curtin University.
    Kemp, Anthony
    University of Western Australia.
    A tonalitic analogue to ancient detrital zircon2018In: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 499, p. 43-57Article in journal (Refereed)
    Abstract [en]

    A zircon population from an Archean tonalite sample from southern West Greenland hasbeen used as a source analogue in order to test common methods and approaches applied toancient detrital zircon populations. Measurements of U-Th-Pb, oxygen and Lu-Hf isotopes aswell as rare earth element and Ti concentrations were made in these zircon crystals and,where possible, in multiple areas within a single grain. The population is dominated by oscillatory zoned cores aged 3.82 Ga with an isotopically and compositionally distinct rims that formed at 3.59 Ga. We demonstrate that multiple age components may be erroneously inferred from within these oscillatory zoned zircon cores, both from the total population and within individual grains. This has bearing on other zircon-hosted geochemical systems, as temporal correlations may be incorrectly assigned. Oxygen and Lu-Hf isotope compositions are relatively consistent through the population with only a small number of outliers. Ranges in rare earth element and Ti abundances are evident from the total population, from which apparent inverse cooling trends may be inferred. Additionally, we show that even with enhanced filtering of Ti concentrations using light rare earth element abundances,crystallisation temperatures derived from zircon grains of a single, hand sample sized rockcan yield both wide and bimodal results. Since even simple, single “source rock” zirconpopulations may, without careful scrutiny, portray artificially complex results, particular caremust be taken in the interpretation of complex ancient detrital zircon populations.

    The full text will be freely available from 2020-11-05 15:37
  • 225. Klawonn, I.
    et al.
    Nahar, N.
    Walve, J.
    Andersson, B.
    Olofsson, M.
    Svedén, J.B.
    Littmann, S.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Kuypers, M.M.M.
    Ploug, H.
    Cell-specific nitrogen- and carbon-fixation of cyanobacteria in a temperate marine system (Baltic Sea).2016In: Environmental Microbiology Reports, ISSN 1758-2229, E-ISSN 1758-2229Article in journal (Refereed)
    Abstract [en]

    We analysed N2- and carbon (C) fixation in individual cells of Baltic Sea cyanobacteria by combining stable isotope incubations with secondary ion mass spectrometry (SIMS). Specific growth rates based on N2- and C-fixation were higher for cells of Dolichospermum spp. than for Aphanizomenon sp. and Nodularia spumigena. The cyanobacterial biomass, however, was dominated by Aphanizomenon sp., which contributed most to total N2-fixation in surface waters of the Northern Baltic Proper. N2-fixation by Pseudanabaena sp. and colonial picocyanobacteria was not detectable. N2-fixation by Aphanizomenon sp., Dolichospermum spp. and N. spumigena populations summed up to total N2-fixation, thus these genera appeared as sole diazotrophs within the Baltic Sea's euphotic zone, while their mean contribution to total C-fixation was 21%. Intriguingly, cell-specific N2-fixation was eightfold higher at a coastal station compared to an offshore station, revealing coastal zones as habitats with substantial N2-fixation. At the coastal station, the cell-specific C- to N2-fixation ratio was below the cellular C:N ratio, i.e. N2 was assimilated in excess to C-fixation, whereas the C- to N2-fixation ratio exceeded the C:N ratio in offshore sampled diazotrophs. Our findings highlight SIMS as a powerful tool not only for qualitative but also for quantitative N2-fixation assays in aquatic environments.

  • 226. Kleine, B. I.
    et al.
    Stefánsson, A.
    Halldórsson, S. A.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Jónasson, K.
    Silicon and oxygen isotopes unravel quartz formation processes in the Icelandic crust2018In: Geochemical Perspectives Letters, Vol. 7, p. 5-11Article in journal (Refereed)
    Abstract [en]

    Quartz formation processes in the Icelandic crust were assessed using coupled δ18O and δ30Si systematics of silica deposits formed over a wide temperature range (<150 to >550 °C). Magmatic quartz reveals δ18O (-5.6 to +6.6 ‰) and δ30Si (-0.4 ± 0.2 ‰) values representative of mantle- and crustally-derived melts in Iceland. Hydrothermal quartz and silica polymorphs display a larger range of δ18O (-9.3 to +30.1 ‰) and δ30Si (-4.6 to +0.7 ‰) values. Isotope modelling reveals that such large variations are consistent with variable water sources and equilibrium isotope fractionation between fluids and quartz associated with secondary processes occurring in the crust, including fluid-rock interaction, boiling and cooling. In context of published δ18O and δ30Si data on hydrothermal silica deposits, we demonstrate that large ranges in δ30Si values coupled to insignificant δ18O variations may result from silica precipitation in a hydrothermal fluid conduit associated with near-surface cooling. While equilibrium isotope fractionation between fluids and quartz seems to prevail at high temperatures, kinetic fractionation likely influences isotope systematics at low temperatures.

  • 227. Kleinhanns, I.C.
    et al.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Nolte, N.
    Baero, W.
    Wilsky, F.
    Hansen, B.T.
    Schoenberg, R.
    Mode and timing of granitoid magmatism in the Västervik area (SE Sweden, Baltic Shield): Sr-Nd isotope and SIMS U-Pb age constraints.2015In: Lithos, ISSN 0024-4937, E-ISSN 1872-6143, Vol. 212-215, p. 321-337Article in journal (Refereed)
    Abstract [en]

    Observed geochemical and geophysical signatures in the southern Svecofennian domain (SD) and the Transscandinavian Igneous Belt (TIB) are explained through a model of tectonic cycling and episodic south-westward migration of a subduction zone system. The Västervik area is located between these two major tectonic domains and as such has received much attention. Granitoids of the Västervik area were recently re-grouped and classified within the context of this larger regional tectonic model, but a discrepancy between previous relative age estimations and the few available granitoid age determinations was noted. To address this issue, we have dated 13 granitoid samples using a high spatial resolution secondary ion mass spectrometry (SIMS) U–Pb technique. Our new results constrain the intrusion of the majority of granitoids to 1819–1795 Ma, thus placing them into the TIB-1 period. This age range also encompasses our new ages from the central granodiorite belt and the Örö-Hamnö pluton, demonstrating a previous overestimation of older granitoid generations in the Västervik area. Nonetheless, it is shown that Askersund/TIB-0 magmatism, represented by an augen gneiss sample dated to 1846 Ma, is unambiguously present as far south as the Västervik region. The anatectically generated leucogranites reveal TIB-1 ages and, as expected, older inherited zircon derived from the parental metasedimentary Västervik formation. By simple Sr–Nd isotope modeling it is further possible to deduce that most TIB-1 granitoids follow a simple (assimilation-) fractional crystallization petrogenetic trend. The youngest granitoid generation was produced through low-pressure fluid-absent crustal melting. In conclusion, granitoids of the Västervik area fit well into the proposed model for south-westward migration of a subduction zone system active in the Svecofennian domain and represent a new tectonic cycle. It is therefore possible to link the Svecofennian domain and the Transscandinavian Igneous Belt within a single evolutionary scenario explaining the observed granitoid petrology, geochemistry and geochronology. The study area is located at the edge of a particularly long-lived active continental margin that started to operate during the supercontinent Columbia at ca. 1.8 Ga and the presented model explains how this margin initiated at its eastern end.

  • 228.
    Kooijman, Ellen
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Smit, Matthijs
    Ratschbacher, Lothar
    Kylander-Clark, Andrew
    A view into crustal evolution at mantle depths2017In: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 465, p. 59-69Article in journal (Refereed)
    Abstract [en]

    Crustal foundering is an important mechanism in the differentiation and recycling of continental crust. Nevertheless, little is known about the dynamics of the lower crust, the temporal scale of foundering and its role in the dynamics of active margins and orogens. This particularly applies to active settings where the lower crust is typically still buried and direct access is not possible. Crustal xenoliths derived from mantle depth in the Pamir provide a unique exception to this. The rocks are well-preserved and comprise a diverse set of lithologies, many of which re-equilibrated at high-pressure conditions before being erupted in their ultrapotassic host lavas. In this study, we explore the petrological and chronological record of eclogite and felsic granulite xenoliths. We utilized accessory minerals – zircon, monazite and rutile – for coupled in-situ trace-element analysis and U–(Th–)Pb chronology by laser-ablation (split-stream) inductively coupled plasma mass spectrometry. Each integrated analysis was done on single mineral zones and was performed in-situ in thin section to maintain textural context and the ability to interpret the data in this framework. Rutile thermo-chronology exclusively reflects eruption (), which demonstrates the reliability of the U–Pb rutile thermo-chronometer and its ability to date magmatic processes. Conversely, zircon and monazite reveal a series of discrete age clusters between 55–11 Ma, with the youngest being identical to the age of eruption. Matching age populations between samples, despite a lack of overlapping ages for different chronometers within samples, exhibit the effectiveness of our multi-mineral approach. The REE systematics and age data for zircon and monazite, and Ti-in-zircon data together track the history of the rocks at a million-year resolution. The data reveal that the rocks resided at 30–40 km depth along a stable continental geotherm at 720–750 °C until 24–20 Ma, and were subsequently melted, densified, and buried to 80–90 km depth – 20 km deeper than the present-day Moho – at . The material descended rapidly, accelerating from 0.9–1.7 mm yr−1to 4.7–5.8 mm yr−1 within 10–12 Myr, and continued descending after reaching mantle depth at 14–13 Ma. The data reflect the foundering of differentiated deep-crustal fragments (2.9–3.5 g cm−3) into a metasomatized and less dense mantle wedge. Through our new approach in constraining the burial history of rocks, we provided the first time-resolved record of this crustal-recycling process. Foundering introduced vestiges of old evolved crust into the mantle wedge over a relatively short period (c. 10 Myr). The recycling process could explain the variability in the degree of crustal contamination of mantle-derived magmatic rocks in the Pamir and neighboring Tibet during the Cenozoic without requiring a change in plate dynamics or source region.

  • 229. Kornprobst, Jacques
    et al.
    Abalos, Benito
    Barbey, Pierre
    Boullier, Anne-Marie
    Burg, Jean-Pierre
    Capdevila, Ramon
    Claesson, Stefan
    Swedish Museum of Natural History, Department of Geology.
    Cordani, Umberto
    Corrigan, David
    Gabrielsen, Roy H
    Gil-Ibarguchi, José I
    Johansson, Åke
    Swedish Museum of Natural History, Department of Geology.
    Letsch, Dominik
    Le Vigouroux, Phillipe
    Upton, Brian
    Boris Choubert: Unrecognized visionarygeologist, pioneer of the global tectonics.2018In: BSGF - Earth Science Bulletin, Vol. 189, no 2, p. 1-15, article id 7Article in journal (Refereed)
    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.

  • 230. Kotková, J.
    et al.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Schaltegger, U.
    D'Azbac, F.-X.
    The fate of zircon during UHT–UHP metamorphism: isotopic (U/Pb, δ18O, Hf) and trace element constraints.2016In: Journal of Metamorphic Geology, ISSN 0263-4929, E-ISSN 1525-1314, Vol. 34, p. 719-739Article in journal (Refereed)
    Abstract [en]

    Garnet–clinopyroxene ultra-high-pressure (UHP) rocks from the northern Bohemian Massif contain zircon with micro-diamond inclusions. Trace element concentrations, oxygen and hafnium isotopic composition and U–Pb age of distinct textural domains in zircon characterize their growth conditions and temporal evolution. Diamond-bearing zircon mantle domains with relicts of oscillatory zoning have uniform Th/U ratios (~0.1–0.2), high-Ti contents (110–190 ppm, corresponding to temperatures of at least 1100 °C), and some (two of 17 mantle analyses) preserve steep heavy rare earth element (HREE) patterns with YbN/GdN = 10–11, with a weak negative Eu anomaly. These signatures are consistent with crystallization from a melt under UHP/ultra-high-temperature (UHT) conditions. Some of the bright-cathodoluminscence (CL) rims preserve Th/U and Ti values characteristic of the zircon mantles, but others show elevated Th/U ratios of ~0.3–0.4 and lower Ti contents (20–40 ppm; only 13 ppm in a rare low-CL outer rim). As they feature flat HREE patterns and negative Eu anomalies and commonly make embayments and truncate the mantle zoning, we suggest that they have formed through recrystallization in the solid state during exhumation of the rock, when both garnet and plagioclase were stable. The three zircon domains, that is, cores, mantles and rims, yield U–Pb concordia ages of 340.9 ± 1.5, 340.3 ± 1.5 and 341.2 ± 3.4 Ma respectively. When linked to the previously reconstructed P–T path of the rock, the error limits of the zircon mantle and rim ages constrain the exhumation of the rocks from depth of ~140 km (UHP) to ~80 km (HP) to a minimum rate of 1.5 cm yr−1. The zircon cores are heterogeneous in terms of Th/U ratio (below 0.1 but also above 0.2) and REE characteristics, and their εHf values scatter between −15.7 and +4.8 with similar values for individual domains within a single zircon grain suggesting a very localized control on hafnium isotope composition on a grain scale. The non-equilibrated εHf values as well as a large range of the Hf-depleted mantle model ages possibly reflect the presence of a heterogeneous population of old zircon. Consequently, the uniform and young 238U/206Pb ages may represent (near-)complete resetting of the U–Pb geochronometer during the UHP–UHT event at c. 340 Ma through dissolution–reprecipitation process. In contrast to Hf, the oxygen isotope composition of zircon is homogeneous, ranging between 7.8‰ and 9.6‰ VSMOW, reflecting a source containing upper crustal material and homogenization at UHP–UHT conditions. Our study documents that continental crust was subducted to mantle depths at c. 340 Ma during the Variscan orogeny and was subsequently very rapidly exhumed, implying that the sequence of events was faster than can be resolved by the secondary ion mass spectrometry technique.

  • 231.
    Krall, Lindsay
    et al.
    The Swedish Nuclear Fuel and Waste Management Company.
    Trezzi, Giada
    Universitat Autònoma de Barcelona.
    Garcia-Orellana, Jordi
    Universitat Autònoma de Barcelona.
    Valenti, Rodellas
    CEREGE, Aix-Marseille Université.
    Mörth, Magnus
    Department of Geological Sciences Stockholm University.
    Andersson, Per
    Swedish Museum of Natural History, Department of Geology.
    Submarine groundwater discharge at Forsmark, Gulf of Bothnia, providedby Ra isotopes2017In: Marine Chemistry, ISSN 0304-4203, E-ISSN 1872-7581, Vol. 196, p. 162-172Article in journal (Refereed)
    Abstract [en]

    Submarine groundwater discharge (SGD) to the Gulf of Bothnia, Baltic Sea, has been believed to be insignificant from hydrological models, yet geochemical investigations of SGD in this basin are limited. In this study, 223Ra, 224Ra, 226Ra, and 228Ra have been complemented by stable δ18O and d2H isotopes to characterize and quantify SGD rates from the coast of Forsmark, Sweden to Öregrundsgrepen Strait (Gulf of Bothnia). In shallow bays, SGD has been traced using relations between Ra, d2H and d18O isotopes and salinity. Zonal SGD from deformation zones, expressed as hydraulically conductive fractures, overlain by the Börstilåsen esker, a strip of conductive gravel sediment, have been traced through offshore 224Raxs and 226Ra trends. On the basis of a 224Raxs mass balance, the SGD flow rate ranges from (5.5 ± 3.0) · 103 m3 d-1 to (950 ± 520) · 103 m3 d-1. These rates are up to two orders of magnitude higher than those determined from local hydrological models, which consider only the fresh component of SGD. From the divergence between the hydrological and 224Raxs models, it is inferred that the site is influenced by a component of recirculated seawater.

  • 232.
    Kristiansson, Per
    et al.
    Lunds universitet.
    Borysiuk, Maciek
    Lunds universitet.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Mosenfelder, Jed
    Caltech, Pasadena, CA, USA.
    Ros, Linus
    Lunds universitet.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Abdel, Naseem
    Lunds universitet.
    Elfman, Mikael
    Lunds universitet.
    Nilsson, Charlotta
    Lunds universitet.
    Pallon, Jan
    Lunds universitet.
    The implementation of a DSSSD in the upgraded boron analysis at LIBAF for applications in geochemistry2014In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 332, p. 207-211Article in journal (Refereed)
  • 233.
    Kumpulainen, Risto A.
    et al.
    Stockholms universitet.
    Bergman, Stefan
    Sveriges geologiska undersökning.
    Claesson, Stefan
    Swedish Museum of Natural History, Department of Geology.
    Sweden to review its geological nomenclatureArticle in journal (Refereed)
    Abstract [en]

    All geoscientists working with the geology of Sweden are invited to join a common effort to review Swedish geological nomenclature and the naming of geological units and other features. A new guide, the Guide for geological nomenclature in Sweden, provides advice for this review process. The Geological Survey of Sweden will set up a new open and freely accessible database for geological names, and a dedicated name committee with mandate to formally approve proposed names will supervise the naming process. The success of this vital long-term commitment will depend on active participation of the geoscientific community at large.

  • 234. Kusebauch, C.
    et al.
    John, T.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Engvik, A.
    Apatite as probe for the halogen composition of metamorphic fluids (Bamble Sector, SE Norway)2015In: Contributions to Mineralogy and Petrology, ISSN 0010-7999, E-ISSN 1432-0967, Vol. 170, p. 1-20, article id 34Article in journal (Refereed)
    Abstract [en]

    Halogen composition of replaced apatite formed during a regional metasomatic event (Bamble Sector, SE Norway) reveals information about the composition and evolution of the hydrothermal fluid. Infiltration and pervasive fluid flow of highly saline fluids into gabbroic bodies lead to scapolitization and amphibolitization, where magmatic Cl-rich apatite reacts with the hydrothermal fluid to form OH- and/or F-rich apatite. Apatite from highly altered samples adjacent to the shear zone has highest F (up to 15,000 µg/g) and lowest Br (4–25 µg/g) concentrations, whereas apatite from least altered samples has very low F (30–200 µg/g) and high Br (30–85 µg/g). In addition, individual replaced apatite grains show a zonation in F with high concentrations along rims and cracks and low F in core regions. Iodine concentrations remain rather constant as low values of 0.18–0.70 µg/g. We interpret all observed compositional features of replaced apatite to be the result of a continuous evolution of the fluid during fluid–rock interaction. Due to its high compatibility, F from the infiltrating fluid is incorporated early into recrystallized apatite (close to shear zone and rims of individual apatite grains). In contrast, Br as an incompatible halogen becomes enriched in the fluid and is highest in the most evolved fluid. Using experimental partition data between replaced apatite and fluid, we calculated F concentrations of the evolving fluid to decrease from 60 to <1 µg/g and Br to increase from ~1200 to ~5000 µg/g; I concentrations of the fluid are constant in the order of 370 µg/g. Although Cl is expected to show a similar behavior as Br, replaced apatite has constant Cl concentrations throughout the alteration sequence (~1 wt.%), which is likely the result of a rather constant Cl activity in the fluid. Chlorine stable isotope values of individual apatite grains are heterogeneous and range from −1.2 to +3.7 ‰. High δ 37Cl values are generally correlated with OH-rich zones of replaced apatite, whereas low δ 37Cl values are measured in F-rich zones of replaced apatite and in Cl-apatite of probably magmatic origin. Though apatite δ 37Cl values follow the general bulk trend, the individual δ 37Cl signature seems to reflect the highly localized composition of interfacial fluid at the reaction front. Our observations suggest that apatite can be used as a fluid probe for F, Br, and I to detect a compositional evolution of the fluid, which can be quantified by using experimentally derived partition coefficients. Partitioning of Cl and Cl stable isotopes between highly saline fluids and apatite is complex and likely controlled by more unknown factors than just the Cl concentration.

  • 235. Kusebauch, C.
    et al.
    John, T.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Klemme, S.
    Putnis, A.
    Distribution of halogens between fluid and apatite during fluid-mediated replacement processes.2015In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 170, p. 1-18Article in journal (Refereed)
    Abstract [en]

    Apatite (Ca5(PO4)3(OH, F, Cl)) is one of the main host of halogens in magmatic and metamorphic rocks and plays a unique role during fluid–rock interaction as it incorporates halogens (i.e. F, Cl, Br, I) and OH from hydrothermal fluids to form a ternary solid solution of the endmembers F-apatite, Cl-apatite and OH-apatite. Here, we present an experimental study to investigate the processes during interaction of Cl-apatite with different aqueous solutions (KOH, NaCl, NaF of different concentration also doped with NaBr, NaI) at crustal conditions (400–700 °C and 0.2 GPa) leading to the formation of new apatite. We use the experimental results to calculate partition coefficients of halogens between apatite and fluid. Due to a coupled dissolution–reprecipitation mechanism new apatite is always formed as a pseudomorphic replacement of Cl-apatite. Additionally, some experiments produce new apatite also as an epitaxial overgrowth. The composition of new apatite is mainly governed by complex characteristics of the fluid phase from which it is precipitating and depends on composition of the fluid, temperature and fluid to mineral ratio. Furthermore, replaced apatite shows a compositional zonation, which is attributed to a compositional evolution of the coexisting fluid in local equilibrium with the newly formed apatite. Apatite/fluid partition coefficients for F depend on the concentration of F in the fluid and increase from 75 at high concentrations (460 μg/g F) to 300 at low concentrations (46 μg/g F) indicating a high compatibility of F in apatite. A correlation of Cl-concentration in apatite with Cl concentration of fluid is not observed for experiments with highly saline solutions, composition of new apatite is rather governed by OH concentration of the hydrothermal fluid. Low partition coefficients were measured for the larger halogens Br and I and vary between 0.7 * 10−3–152 * 10−3 for Br and 0.3 * 10−3–17 * 10−3 for I, respectively. Br seems to have D values of about one order of magnitude higher than I. These data allow an estimation of the D values for the other halogens based on a lattice strain model which displays a sequence with DF of ∼120, DOH of ∼100, DCl of ∼2.3 DBr ∼0.045, and DI ∼0.0025. Results from this experimental study help to better understand fluid–rock interaction of an evolving fluid, as it enables the composition of hydrothermally derived apatite to be used as a fluid probe for halogens at crustal conditions. It further shows the importance of mineral replacement as one of the key reactions to generate apatite of different composition.

  • 236. Kusiak, M.A.
    et al.
    Dunkley, D.J.
    Wirth, R.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Wilde, S.A.
    Marquardt, K.
    Metallic lead nanospheres discovered in ancient zircons.2015In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 112, p. 4958-4963Article in journal (Refereed)
    Abstract [en]

    Zircon (ZrSiO4) is the most commonly used geochronometer, preserving age and geochemical information through a wide range of geological processes. However, zircon U–Pb geochronology can be affected by redistribution of radiogenic Pb, which is incompatible in the crystal structure. This phenomenon is particularly common in zircon that has experienced ultra-high temperature metamorphism, where ion imaging has revealed submicrometer domains that are sufficiently heterogeneously distributed to severely perturb ages, in some cases yielding apparent Hadean (>4 Ga) ages from younger zircons. Documenting the composition and mineralogy of these Pb-enriched domains is essential for understanding the processes of Pb redistribution in zircon and its effects on geochronology. Using high-resolution scanning transmission electron microscopy, we show that Pb-rich domains previously identified in zircons from East Antarctic granulites are 5–30 nm nanospheres of metallic Pb. They are randomly distributed with respect to zircon crystallinity, and their association with a Ti- and Al-rich silica melt suggests that they represent melt inclusions generated during ultra-high temperature metamorphism. Metallic Pb is exceedingly rare in nature and previously has not been reported in association with high-grade metamorphism. Formation of these metallic nanospheres within annealed zircon effectively halts the loss of radiogenic Pb from zircon. Both the redistribution and phase separation of radiogenic Pb in this manner can compromise the precision and accuracy of U–Pb ages obtained by high spatial resolution methods.                           

  • 237. Kusiak, Monika A.
    et al.
    Dunkley, Daniel J.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Wilde, Simon A.
    Sałacińska, Anna
    Konečný, Patrík
    Szopa, Krzysztof
    Gawęda, Aleksandra
    Chew, David
    Peak to post-peak thermal history of the Saglek Block of Labrador: A multiphase and multi-instrumental approach to geochronology2018In: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 484, p. 210-223Article in journal (Refereed)
    Abstract [en]

    The Saglek Block of coastal Labrador forms the western margin of the North Atlantic Craton, where Archean gneisses and granulites have been reworked during the Paleoproterozoic. Previous work has established that the block is a composite of Eoarchean to Mesoarchean protoliths metamorphosed to upper amphibolite and granulite facies at around 2.8–2.7Ga. New in-situ microbeam dating of accessory minerals in granoblastic gneisses reveals a complex peak to post-peak thermal history. Zircon growth at ca. 3.7–3.6Ga provides the age of formation of the tonalitic protoliths to the gneisses. Further zircon growth in syn-tectonic granitic gneiss and monazite growth in a variety of orthogneisses confirm peak metamorphic conditions at ca. 2.7Ga, but also reveal high-temperature conditions at ca. 2.6Ga and 2.5Ga. The former is interpreted as the waning stages of the 2.7Ga granulite event, whereas the latter is associated with a younger phase of granitic magmatism. In addition, apatite ages of ca. 2.2Ga may represent either cooling associated with the 2.5Ga event or a previously unrecognized greenschist-facies metamorphism event that predates the Torngat Orogeny.

  • 238.
    Kutscher, Liselott
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Mörth, Carl-Magnus
    Stockholm University.
    Porcelli, Don
    University of Oxford.
    Hirst, Catherine
    Swedish Museum of Natural History, Department of Geology.
    Maximov, Trofim
    North Eastern Federal University, Yakutsk, Russia.
    Petrov, Roman
    North Eastern Federal University, Yakutsk, Russia.
    Andersson, Per
    Swedish Museum of Natural History, Department of Geology.
    Spatial variation in concentration and sources of organic carbon in the Lena River, Siberia2017In: Journal of Geophysical Research - Biogeosciences, ISSN 2169-8953, E-ISSN 2169-8961, Vol. 122Article in journal (Refereed)
    Abstract [en]

    Global warming in permafrost areas is expected to change fluxes of riverine organic carbon (OC) 22 to the Arctic Ocean. Here OC concentrations, stable carbon isotope signatures (δ13C) and carbon-23 nitrogen ratios (C/N) are presented from 22 sampling stations in the Lena River and 40 of its 24 tributaries. Sampling was conducted during two expeditions: the first in July 2012 in the south 25 and southeastern region and the second in June 2013 in the northern region of the Lena basin. 26 The data showed significant spatial differences in concentrations and major sources of OC. Mean 27 sub-catchment slopes were correlated with OC concentrations, implying that mountainous areas 28 in general had lower concentrations than lowland areas. δ13C and C/N data from tributaries 29 originating in mountainous areas indicated that both dissolved and particulate OC (DOC and 30 POC) were mainly derived from soil organic matter (SOM). In contrast, tributaries originating in 31 lowland areas had larger contributions from fresh vegetation to DOC, while aquatically produced 32 OC was the major source of POC. We suggest that these differences in dominant sources 33 indicated differences in dominant flow pathways. Tributaries with larger influence of fresh 34 vegetation probably had surficial flow pathways, while tributaries with more SOM influence had 35 deeper water flow pathways. Thus, the future export of OC to the Arctic Ocean will likely be 36 controlled by changes in spatial patterns in hydroclimatology and the depth of the active layers 37 influencing the dominant water flow pathways in Arctic river basins.

  • 239. Käpyaho, A.
    et al.
    Molnár, F.
    Sorjonen-Ward, P.
    Mänttäri, I.
    Sakellaris, G.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    New U-Pb age constraints for the timing of gold mineralization at the Pampalo gold deposit, Archaean Hattu schist belt, Eastern Finland, obtained from hydrothermally altered and recrystallised zircon.2017In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 289, p. 48-61Article in journal (Refereed)
    Abstract [en]

    In this paper we present new U-Pb data on zircon and titanite from the host rocks of the Pampalo gold deposit located within the Neoarchaean Hattu schist belt in eastern Finland. We also present new U-Pb data on nearby plutonic rocks. Plagioclase porphyries at the mine site demonstrate inheritance from 2.82–2.83 Ga sources while a suggestive intrusive age is at c. 2.76 Ga. Zircon grains extracted from the altered felsic units hosting the gold ore show complex alteration and recrystallisation textures and demonstrate Zr mobility. This mobility is most probably related to the alteration event although direct link to gold mineralization remains to be shown. The preserved or recrystallized parts of the altered zircon grains, texturally homogeneous grain aggregates and some overgrowths yield heterogeneous ages which cluster between ca. 2.73 and 2.70 Ga, with a mean age of 2.71 Ga. This age is considered to place a new constraint on the timing of mobility of Au at the Pampalo. This event postdates the known crustal formation event at 2.76–2.73 Ga in the area as recorded by the adjacent plutonic rocks and volcanoclastic rocks within the Hattu schist belt. The Naarva tourmaline granite, 10 km NW of Pampalo, is 2.69 Ga and is thus temporally associated with known regional crustal anatexis and metamorphism in the Archaean of eastern Finland. Whether this crustal reworking event played a role in the genesis of the gold in eastern Finland needs to be further studied.

  • 240. Lahtinen, R.
    et al.
    Huhma, H.
    Lahaye, Y.
    Lode, S.
    Heinonen, S.
    Sayab, M.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Paleoproterozoic magmatism across the Archean-Proterozoic boundary in central Fennoscandia: Geochronology, geochemistry and isotopic data (Sm–Nd, Lu–Hf, O).2016In: Lithos, ISSN 0024-4937, E-ISSN 1872-6143, Vol. 262, p. 507-525Article in journal (Refereed)
    Abstract [en]

    The central Fennoscandia is characterized by the Archean-Proterozoic (AP) boundary and the Central Finland Granitoid Complex (CFGC), a roundish area of approximately 40,000 km2 surrounded by supracrustal belts. Deep seismic reflection profile FIRE 3A runs across these units, and we have re-interpreted the profile and crustal evolution along the profile using 1.92–1.85 Ga plutonic rocks as lithospheric probes. The surface part of the profile has been divided into five subareas: Archean continent (AC) in the east, AP, CFGC, boundary zone (BZ) and the Bothnian Belt (BB) in the west. There are 12 key samples from which zircons were studied for inclusions and analyzed (core-rim) by ion probe for U–Pb dating and oxygen isotopes, followed by analyzes for Lu–Hf by LA–MC–ICP–MS.

    The AC plutonic rocks (1.87–1.85 Ga) form a bimodal suite, where the proposed mantle source for the mafic rocks is 2.1–2.0 Ga metasomatized lower part of the Archean subcontinental lithospheric mantle (SCLM) and the source for the felsic melts is related plume-derived underplated mafic material in the lower crust. Variable degrees of contamination of the Archean lower crust have produced “subduction-like” Nb–Ta anomalies in spidergrams and negative εNd (T) values in the mafic-intermediate rocks. The felsic AC granitoids originate from a low degree melting of eclogitic or garnet-bearing amphibolites with titanite ± rutile partly prevailing in the residue (Nb–Ta fractionation) followed by variable degree of assimilation/melting of the Archean lower crust. The AP plutonic rocks (ca. 1.88 Ga) can be divided into I-type and A-type granitoids (AP/A), where the latter follow the sediment assimilation trend in ASI diagram, have high δ18O values (up to 8‰) in zircons and exhibit negative Ba anomalies (Rb–Ba–Th in spidergram), as found in sedimentary rocks. A mixing/assimilation of enriched mantle-derived melts with melts from already migmatized sedimentary rocks ± amphibolites is proposed. The CFGC is characterized by both I-type and A-type (CFGC/A) intermediate and felsic granitoids. The I-type granitoids are divided into two groups at ≥ 1885 Ma and ≤ 1882 Ma, where the latter overlap in age with the CFGC/A granitoids. Both I-type CFGC and CFGC/A granitoids are interpreted to have formed from mixing of Paleoproterozoic SCLM-derived melts with crustal melts from hydrous and dry intermediate-felsic igneous sources, respectively. The geochemistry, dominantly δ18O values below 6.5‰ in zircons and TDM (2.11–2.42 Ga) of the CFGC granitoids favor the occurrence of older crust (ca. 2.1–2.0 Ga) in their genesis. The BZ granitoids are similar in age but more juvenile with TDM ages between 1.94 Ga and 2.16 Ga. The 1.92 Ga granodiorite in the BB is correlated with juvenile gneissic tonalites and granodiorites found from the AP boundary.

    We suggest that the present high-velocity lower crust under the CFGC is composed of melt-extracted granulites (crustal source age ≥ 2.0 Ga) and mafic cumulates which both formed during 1.90–1.88 Ga arc magmatism. The ≤ 1.88 Ga stage represents the end of compression/transpression and is followed by 1.87–1.86 Ga buckling, forming the Bothnian Oroclines.

  • 241.
    Langhof, Jörgen
    Swedish Museum of Natural History, Department of Geology.
    Anton Sögren och Hugo V. Tiberg - två smålänningar i den värmländska förskingringen2015In: Värmland förr och nu/ 2015: Värmlands Museum - Långban gruv- och kulturby / [ed] Andreas Hansen, Karlstad: Värmlands Museum , 2015, p. 104-117Chapter in book (Other (popular science, discussion, etc.))
  • 242.
    Langhof, Jörgen
    Swedish Museum of Natural History, Department of Geology.
    Eric Thomas Svedenstierna2017In: Svenskt biografiskt lexikon, Vol. 169, p. 512-517Article in journal (Other academic)
  • 243.
    Langhof, Jörgen
    Swedish Museum of Natural History, Department of Geology.
    Herman Sundholm2014In: Svenskt Biografiskt Lexikon, Vol. 34, no 167, p. 268-271Article in journal (Other academic)
  • 244.
    Langhof, Jörgen
    Swedish Museum of Natural History, Department of Geology.
    Jacob Berzelius och norsk mineralogi2009In: Kongsberg mineralsymposium, ISSN 0800-1855, no 41, p. 50-53Article in journal (Other academic)
  • 245.
    Langhof, Jörgen
    Swedish Museum of Natural History, Department of Geology.
    Karl Sundberg2014In: Svenskt Biografiskt Lexikon, Vol. 34, no 167, p. 213-215Article in journal (Other academic)
  • 246.
    Langhof, Jörgen
    Swedish Museum of Natural History, Department of Geology.
    Knut Styffe2013In: Svenskt biografiskt lexikon SBL, Vol. 34, no 166, p. 127-130Article in journal (Other academic)
  • 247.
    Langhof, Jörgen
    Swedish Museum of Natural History, Department of Geology.
    Kolsva fältspatgruva: En av Skandinaviens största fältspatgruvor och Europas största Be-mineralisering2015In: Litofilen, ISSN 1651-6117, Vol. 32, no 4, p. 21-40Article in journal (Other (popular science, discussion, etc.))
  • 248.
    Langhof, Jörgen
    Swedish Museum of Natural History, Department of Geology.
    Mineralfynd vid Nordmarksberg - en historisk överblick2015In: Historien om Nordmarksbergs gruvor / [ed] Jan Kruse, Mjölby: Atremi AB , 2015, 750, p. 174-176Chapter in book (Other (popular science, discussion, etc.))
  • 249.
    Langhof, Jörgen
    Swedish Museum of Natural History, Department of Geology.
    Nils Sundius2014In: Svenskt Biografiskt Lexikon, Vol. 34, no 167, p. 274-279Article in journal (Other academic)
  • 250.
    Langhof, Jörgen
    Swedish Museum of Natural History, Department of Geology.
    Personporträtt - Erik Ygberg2014In: Långbansnytt, ISSN 1650-4968, Vol. 20, no 2, p. 4-6Article in journal (Other (popular science, discussion, etc.))
2345678 201 - 250 of 418
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