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  • 1
    Electronic Resource
    Electronic Resource
    Detrital zircon ages from the Loch Maree Group, Lewisian Complex, NW Scotland: confirmation of a Palaeoproterozoic Laurentia—Fennoscandia connection (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Terra nova 9 (1997), S. 0 
    Details
    ISSN: 1365-3121
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Ion-microprobe U-Pb zircon ages of detrital zircons from a metasediment of the Loch Maree Group, Lewisian Complex, NW Scotland show striking similarities to those in coeval Palaeoproterozoic belts of Laurentia and Fennoscandia, and confirm previous suggestions of a connection between them. Late-Archaean zircons (3.06–2.48 Gyr old) represent derivation from Lewisian quartzofeldspathic gneisses, andlor a contemporaneous terrane. Palaeoproterozoic zircons (2.2–2.0 Gyrold) place a maximum age constraint upon deposition. An appropriate quartzofeldspathic source for these latter zircons is not presently known, either in the Lewisian or the wider Laurentia-Fennoscandia region, although its requirement would be consistent with a development of the Loch Maree Group, together with juvenile magmatic arc rocks, at an active margin which was probably removed by lateral tectonics. Comparisons are made with contemporaneous supracrustal sequences throughout the Laurentia–Fennoscandia region, which exhibit marked similarities in source region age characteristics, lithologies, and inferred depositional environment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3121.1997.tb00025.x
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  • 2
    Electronic Resource
    Electronic Resource
    Subduction-flip during Iapetus Ocean closure and Baltica–Laurentia collision, Scandinavian Caledonides (2003)
    Oxford, UK : Blackwell Science Ltd
    Terra nova 15 (2003), S. 0 
    Details
    ISSN: 1365-3121
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Evidence is presented here from the northern Scandinavian Caledonides for development of an extensional basin of Ashgill to Mid Llandovery age along the Baltoscandian margin immediately prior to Baltica–Laurentia collision. U/Pb multigrain and ion microprobe zircon dating of plagiogranites in the Halti Igneous Complex complement previous baddeleyite and zircon dating of a dolerite dyke, and zircon dating of anatectic granite; they demonstrate that this dunite, troctolite, gabbro, sheeted-dyke complex ranges in age from c. 445 to 435 Ma. The dolerite dykes intruded and melted arkoses of inferred Neoproterozoic age. This evidence, taken together with previous documentation of ophiolites (Solund–Stavfjord), ophiolite-like associations (Sulitjelma Igneous Complex) and several other mafic suites (e.g. Råna, Artfjället) of Ashgill to Llandovery age further south in the northern Scandinavian Caledonides, implies that Scandian collisional orogeny along this nearly 2000-km-long mountain belt was immediately preceeded by development of short-lived marginal basins. The latter developed during the final closure of the Iapetus Ocean and are inferred to be of back-arc origin, some (perhaps all) related to E-dipping subduction. Collision of the continents at c. 435 Ma is inferred to have induced a flip in subduction polarity, leading to underthrusting of Laurentia by Baltica.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3121.2003.00486.x
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  • 3
    Electronic Resource
    Electronic Resource
    Pb–Pb systematics of Lewisian gneisses—implications for crustal differentiation (1986)
    [s.l.] : Nature Publishing Group
    Nature 319 (1986), S. 488-489 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The Lewisian Complex of mainland north-west Scotland is divided into three main regions which are considered to have originally occupied different crustal levels4. The central region, between Loch Laxford and Gruinard Bay, preserves granulite fades gneisses from the Scourian metamorphism which has ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/319488a0
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  • 4
    Electronic Resource
    Electronic Resource
    Crust formation in the Lewisian (1995)
    [s.l.] : Nature Publishing Group
    Nature 375 (1995), S. 366-366 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] SIR - Burton et al1 have presented U-Pb and Sm-Nd mineral regression ages on rocks from the Lewisian complex at Gruinard Bay, which apparently require that "the history of crustal development in the Lewisian complex will have to be radically rethought"2. They1 ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/375366a0
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  • 5
    Electronic Resource
    Electronic Resource
    Granulite fades Nd-isotopic homogenization in the Lewisian complex of northwest Scotland (1988)
    [s.l.] : Nature Publishing Group
    Nature 331 (1988), S. 705-707 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The late-Archaean (~ 2,900 Myr) Lewisian complex of main-land NW Scotland is divided into three main regions: the granulite facies central region and the amphibolite facies northern and southern regions. The present disposition of these regions is generally interpreted in terms of juxtaposed ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/331705a0
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  • 6
    Electronic Resource
    Electronic Resource
    Hercynian, Pan-African, Proterozoic and Archean ion-microprobe zircon ages for a Betic-Rif core complex, Alpine belt, W Mediterranean – consequences for its P-T-t path (1999)
    Springer
    Contributions to mineralogy and petrology 134 (1999), S. 134-149 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Ion-microprobe analysis of zircons from an andalusite-bearing orthogneiss within the major Alpujárride nappe complex in the central part of the Betic Cordilleras has yielded a Hercynian age of 285 ± 5 (2σ) Ma for euhedral rims, interpreted as the magmatic age of the andalusite-bearing biotite granite parent rock for the gneisses. Zircon age zoning systematics suggest a Paleozoic sedimentation age for the parent material for the anatectic source rock. Zircon cores represent several groups of ages: (1) Archean, c. 2.7 Ga; (2) Early Proterozoic, 2.2–2.0 Ga; (3) Middle Proterozoic, 1.1–0.9 Ga; (4) Pan-African, 0.8–0.5 Ga; including a well-defined event at 612 ± 13 (2σ) Ma. Paragenetic and textural relations indicate that gneissification took place during a high-P (12–13 kbar) low-T (450–500 °C) collisional event during which the primary Alpine nappe pile was produced. The second and final Alpine tectono-metamorphic event led to reorganization of the primary nappe pile by extensional tetonics with coeval very fast rock uplift and cooling (from c. 8? to c. 1 kbar and c. 600 to 100 °C within the period 19.5–18.5 Ma). The fast uplift/cooling stage was triggered by slab break-off which is thought to have induced diapiric underplating by high-T asthenospheric material. This may have heated the collisional wedge, causing thermal weakening which might have advanced the late stage fast uplift/cooling. The Alpine events did not leave a zircon crystallization record. The inherited, Archean–Pan-African zircon age pattern corresponds to that established for the Hercynian basement in central and southern Europe which is considered as reworked Gondwana crust. Deeper levels of core complexes within the Betic-Rif belt thus belong to the pre-Triassic basement of the Tethyan realm (Betic-Ligurian lithosphere) and represent reworked material ultimately derived from Archean and Proterozoic rock complexes from the Gondwana crustal domain. This study implies that thermobarometry of rock complexes which went through several phases of tectono-metamorphic reworking may render ambiguous results if based upon field observations and petrography alone. Zircon ion-microprobe dating may provide additional constraints required to arrive at a feasible tectono-metamorphic history, that is P-T-t trajectory, for such rock complexes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004100050474
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  • 7
    Electronic Resource
    Electronic Resource
    Detrital zircon ages from southern Norway – implications for the Proterozoic evolution of the southwestern Baltic Shield (1997)
    Springer
    Contributions to mineralogy and petrology 130 (1997), S. 47-58 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract An ion-microprobe (SIMS) U-Pb zircon dating study on four samples of Precambrian metasediments from the high-grade Bamble Sector, southern Norway, gives the first information on the timing of discrete crust-forming events in the SW part of the Baltic Shield. Recent Nd and Pb studies have indicated that the sources of the clastic metasediments in this area have crustal histories extending back to 1.7 to 2.1 Ga, although there is no record of rocks older than 1.6 Ga in southern Norway. The analysed metasediments are from a sequence of intercalated, centimetre to 10-metre wide units of quartzites, semi-metapelites, metapelites and mafic granulites. The zircons can be grouped in two morphological populations: (1) long prismatic; (2) rounded, often flattened. The BSE images reveal that both populations consist of oscillatory zoned, rounded and corroded cores (detrital grains of magmatic origin), surrounded by homogeneous rims (metamorphic overgrowths). The detrital zircons have 207Pb/206Pb ages between 1367 and 1939 Ma, with frequency maxima in the range 1.85 to 1.70 Ga and 1.60 to 1.50 Ga. There is no correlation between crystal habit and age of the zircon. One resorbed, inner zircon core in a detrital grain is strongly discordant and gives a composite inner core-magmatic outer core 207Pb/206Pb age of 2383 Ma. Two discrete, unzoned zircons have 207Pb/206Pb ages of 1122 and 1133 Ma, representing zircon growth during the Sveconorwegian high-grade metamorphism. Also the μm wide overgrowths, embayments in the detrital cores and apparent “inner cores” which represent secondary metamorphic zircon growth in deep embayments in detrital grains, are of Sveconorwegian age. The composite-detrital-metamorphic zircon analyses give generally discordant 206Pb/238U versus 207Pb/235U ratios and maximum 207Pb/206Pb ages of 1438 Ma. These data demonstrate the existence of a protocrust of 1.7 to 2.0 Ga in the southwestern part of the Baltic Shield, implying a break in the overall westward younging trend of the Precambrian crust, inferred from the southeastern part of the Baltic Shield.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004100050348
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  • 8
    Electronic Resource
    Electronic Resource
    Sr-Nd-Pb isotope data for ultramafic xenoliths from Hierro, Canary Islands: Melt infiltration processes in the upper mantle (1995)
    Springer
    Contributions to mineralogy and petrology 119 (1995), S. 239-246 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  We present here Sr, Nd, and Pb-isotopic data from harzburgite (group I) and dunite–pyroxenite (group II) suite mantle xenoliths from the island of Hierro, one of the youngest and westernmost of the Canary Islands. A progressive leaching technique has been developed and applied to the whole-rock powder samples in order to identify and remove as far as possible any recent additions (host basalt and/or seawater). Isotopic analyses of the leached residues show significant systematic differences between these two suites. Dunite–pyroxenite suite xenoliths (olivine pyroxenites, dunites and wehrlites) exhibit a relatively small range of isotopic compositions (87Sr/86Sr from 0.70292 to 0.70315; 143Nd/144Nd from 0.51295 to 0.51302; 206Pb/204Pb from 19.18 to 19.40) compared to the harzburgite suite (87Sr/86Sr from 0.70295 to 0.70320; 143Nd/144Nd from 0.51285 to 0.51296; 206Pb/204Pb from 18.85 to 19.41). In all isotope correlation diagrams the leached dunite–pyroxenite suite xenoliths plot between the Hierro basalt field and a hypothetical depleted mantle suggesting that these xenoliths may have been strongly infiltrated by Hierro-type basalt. Progressive leaching of this suite of samples showed removal of a component with more enriched Sr (higher 87Sr/86Sr relative to depleted mantle) and Nd (lower 143Nd/144Nd) isotopic compositions that is probably host basalt glass. The leached harzburgite suite xenoliths extend to more enriched Sr and Nd isotopic compositions than Hierro-type basalt but always have more depleted Pb. This relationship can best be explained if this suite has been subject to infiltration by earlier magmas of the Canary Island suite (in particular, those from Gran Canaria show appropriate compositional ranges), although additional infiltration by Hierro basalt cannot be ruled out. The leaching experiments for this suite mostly show removal of a radiogenic Sr component only (? seawater) which supports the interpretation of early infiltration and subsequent recrystallisation and equilibration prior to the Hierro event. Isotopic data presented in this study show that complex interaction with percolating basaltic melts of varying composition was occurring in the upper mantle beneath Hierro prior to and during the volcanic event and was probably related to the generation of earlier Canary Island magmas.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00307284
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  • 9
    Electronic Resource
    Electronic Resource
    Sr-Nd-Pb isotope data for ultramafic xenoliths from Hierro, Canary Islands: Melt infiltration processes in the upper mantle (1995)
    Springer
    Contributions to mineralogy and petrology 119 (1995), S. 239-246 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract We present here Sr, Nd, and Pb-isotopic data from harzburgite (group I) and dunite-pyroxenite (group II) suite mantle xenoliths from the island of Hierro, one of the youngest and westernmost of the Canary Islands. A progressive leaching technique has been developed and applied to the whole-rock powder samples in order to identify and remove as far as possible any recent additions (host basalt and/or sea-water). Isotopic analyses of the leached residues show significant systematic differences between these two suites. Dunite-pyroxenite suite xenoliths (olivine pyroxenites, dunites and wehrlites) exhibit a relatively small range of isotopic compositions (87Sr/86Sr from 0.70292 to 0.70315; 143Nd/144Nd from 0.51295 to 0.51302; 206Pb/204Pb from 19.18 to 19.40) compared to the harzburgite suite (87Sr/86Sr from 0.70295 to 0.70320; 143Nd/144Nd from 0.51285 to 0.51296; 206Pb/204Pb from 18.85 to 19.41). In all isotope correlation diagrams the leached dunite-pyroxenite suite xenoliths plot between the Hierro basalt field and a hypothetical depleted mantle suggesting that these xenoliths may have been strongly infiltrated by Hierro-type basalt. Progressive leaching of this suite of samples showed removal of a component with more enriched Sr (higher 87Sr/86Sr relative to depleted mantle) and Nd (lower 143Nd/144Nd) isotopic compositions that is probably host basalt glass. The leached harzburgite suite xenoliths extend to more enriched Sr and Nd isotopic compositions than Hierro-type basalt but always have more depleted Pb. This relationship can best be explained if this suite has been subject to infiltration by earlier magmas of the Canary Island suite (in particular, those from Gran Canaria show appropriate compositional ranges), although additional infiltration by Hierro basalt cannot be ruled out. The leaching experiments for this suite mostly show removal of a radiogenic Sr component only (? seawater) which supports the interpretation of early infiltration and subsequent recrystallisation and equilibration prior to the Hierro event. Isotopic data presented in this study show that complex interaction with percolating basaltic melts of varying composition was occurring in the upper mantle beneath Hierro prior to and during the volcanic event and was probably related to the generation of earlier Canary Island magmas.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00307284
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  • 10
    Electronic Resource
    Electronic Resource
    Distribution and abundance of seabirds and fur seals near the Antarctic Peninsula during the austral winter, 1986 (1994)
    Springer
    Polar biology 14 (1994), S. 325-330 
    Details
    ISSN: 1432-2056
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Twenty one species of seabirds plus fur seals were observed at sea near the Antarctic Peninsula, between 60 °–68 °S, in May and June 1986, a season for which few published observations of marine animals are available for this area. Here we describe and quantify the importance of fishing activities as well as sea-ice cover and other environmental variables to the distribution patterns of birds and seals. The most striking aspect of the winter avifauna was its pronounced concentration near fishing trawlers operating on the continental shelf to the north and west of Elephant Island, and its temporal shift in response to the seasonal advance of the ice edge.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00238448
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