Browsing by Subject "Scandinavian Caledonides"

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Access status: Open Access ,
Detrital zircon U-Pb geochronology of a metasomatic calc-silicate in the Tsäkkok Lens, Scandinavian Caledonides
(Wydawnictwa AGH, 2021) Barnes, Cristopher J.; Majka, Jarosław ; Bukała, Michał; Nääs, Erika; Rousku, Sabine
The Tsäkkok Lens of the Seve Nappe Complex in the Scandinavian Caledonides comprises eclogite bodies hosted within metasedimentary rocks. These rocks are thought to be derived from the outermost margin of Baltica along the periphery of the Iapetus Ocean, but detrital records from the sedimentary rocks are lacking. Many metasedimentary outcrops within the lens expose both well-foliated metapelitic rocks and massive calc-silicates. The contacts between these two lithologies are irregular and are observed to trend at all angles to the high-pressure foliation in the metapelites. Where folding is present in the metapelites, the calc-silicate rocks are also locally folded. These relationships suggest metasomatism of the metapelites during the Caledonian orogenesis. Zircon U-Pb geochronology was conducted on sixty-one zircon grains from a calc-silicate sample to investigate if they recorded the metasomatic event and to assess the detrital zircon populations. Zircon grains predominantly show oscillatory zoning, sometimes with thin, homogeneous rims that have embayed contacts with the oscillatory-zoned cores. The zircon cores yielded prominent early Stenian, Calymmian, and Statherian populations with a subordinate number of Tonian grains. The zircon rims exhibit dissolution-reprecipitation of the cores or new growth and provide ages that span similar time frames, indicating overprinting of successive tectonic events. Altogether, the zircon record of the calc-silicate suggests that the Tsäkkok Lens may be correlated to Neoproterozoic basins that are preserved in allochthonous positions within the northern extents of the Caledonian Orogen.
Access status: Restricted ,
Metamorphic evolution of the Seve Nappe Complex in the Scandinavian Caledonides of west-central Sweden
(Data obrony: 2012-09-12) Klonowska, Iwona
Wydział Geologii, Geofizyki i Ochrony Środowiska
The Seve Nappe Complex in the Caledonides of western Jämtland (Sweden) is composed of high grade metamorphic rocks, mainly amphibolite facies metasediments and granulite facies gneisses, locally migmatized, with rare eclogites and peridotites. Within ?reskutan Nappe of west-central Jämtland (studied area), kyanite-bearing leucogranulites are found. Conventional geothermobarometry and thermodynamic modeling were utilized to constrain metamorphic conditions. Phg (Si apfu), Grt-Phg, Grt-Phg-Ky-Qtz geothermobarometers and modeled phase equilibria for high pressure assemblages (garnet, phengite) in NCKFMMnASH system indicate peak pressure conditions of 24-32 kbar at temperature of ~700°C. The decompression stage together with partial melting is inferred from GASP barometer, ternary feldspar modeling, kyanite-sillimanite transition, assemblages of biotite-plagioclase and melt occurrence (phase diagrams). Decompression to pressures of ~5kbar is simultaneous with increase of temperature to ~800-820°C and partial melting initiated by micas, what was followed by cooling and crystallization of melt. Geothermobarometry and modeling approach connected with field work observations and microtextures analysis show the innovative conception of ?reskutan’s Nappe HP and HT history. It enabled getting a more complete picture of the SNC evolution during Caledonies orogeny formation.
Access status: Open Access ,
Microdiamonds in paragneisses from the allochthonous unit of the Swedish Caledonides - precious testimony of the UHP metamorphism
(Wydawnictwa AGH, 2015) Klonowska, Iwona
The highest metamorphic grade allochthonous unit in the Scandinavian Caledonides is represented by the Seve Nappe Complex (SNC) that belongs to the Middle Allochthon.