| 1. |
- Barnes, Christopher, et al.
(author)
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High-spatial resolution dating of monazite and zircon reveals the timing of subduction–exhumation of the Vaimok Lens in the SeveNappe Complex (Scandinavian Caledonides)
- 2019
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In: Contributions to Mineralogy and Petrology. - : Springer Berlin/Heidelberg. - 0010-7999 .- 1432-0967. ; 174:1
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Journal article (peer-reviewed)abstract
- In-situ monazite Th–U–total Pb dating and zircon LA–ICP–MS depth-profiling was applied to metasedimentary rocks from the Vaimok Lens in the Seve Nappe Complex (SNC), Scandinavian Caledonides. Results of monazite Th–U–total Pb dating, coupled with major and trace element mapping of monazite, revealed 603 ± 16 Ma Neoproterozoic cores surrounded byrims that formed at 498 ± 10 Ma. Monazite rim formation was facilitated via dissolution–reprecipitation of Neoproterozoic monazite. The monazite rims record garnet growth as they are depleted in Y2O3 with respect to the Neoproterozoic cores. Rims are also characterized by relatively high SrO with respect to the cores. Results of the zircon depth-profiling revealed igneous zircon cores with crystallization ages typical for SNC metasediments. Multiple zircon grains also exhibit rims formedby dissolution–reprecipitation that are defined by enrichment of light rare earth elements, U, Th, P, ± Y, and ± Sr. Rims also have subdued Eu anomalies (Eu/Eu* ≈ 0.6–1.2) with respect to the cores. The age of zircon rim formation was calculated from three metasedimentary rocks: 480 ± 22 Ma; 475 ± 26 Ma; and 479 ± 38 Ma. These results show that both monazite and zircon experienced dissolution–reprecipitation under high-pressure conditions. Caledonian monazite formed coeval with garnet growth during subduction of the Vaimok Lens, whereas zircon rim formation coincided with monazite breakdown to apatite, allanite and clinozoisite during initial exhumation.
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| 2. |
- Barnes, Christopher J., et al.
(author)
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Timing of Paleozoic Exhumation and Deformation of the High-Pressure Vestgotabreen Complex at the Motalafjella Nunatak, Svalbard
- 2020
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In: Minerals. - : MDPI. - 2075-163X. ; 10:2
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Journal article (peer-reviewed)abstract
- The Vestgotabreen Complex exposed in the Southwestern Caledonian Basement Province of Svalbard comprises two Caledonian high-pressure units. In situ white mica 40Ar /39Ar and monazite Th-U-total Pb geochronology has resolved the timing of the tectonic evolution of the complex. Cooling of the Upper Unit during exhumation occurred at 476 2 Ma, shortly after eclogite-facies metamorphism. The two units were juxtaposed at 454 6 Ma. This was followed by subaerial exposure and deposition of Bullbreen Group sediments. A 430-400 Ma late Caledonian phase of thrusting associated with major sinistral shearing throughout Svalbard deformed both the complex and the overlying sediments. This phase of thrusting is prominently recorded in the LowerUnit, and is associated with a pervasive greenschist-facies metamorphic overprint of high-pressure lithologies. A c. 365-344 Ma geochronological record may represent an Ellesmerian tectonothermal overprint. Altogether, the geochronological evolution of the Vestgotabreen Complex, with previous petrological and structural studies, suggests that it may be a correlative to the high-pressure Tsakkok Lens in the Scandinavian Caledonides. It is suggested that the Vestgotabreen Complex escaped to the periphery of the orogen along the sinistral strike-slip shear zones prior to, or during the initial stages of continental collision between Baltica and Laurentia.
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| 3. |
- Barnes, Christopher J., et al.
(author)
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Zircon and monazite reveal late Cambrian/early Ordovician partial melting of the Central Seve Nappe Complex, Scandinavian Caledonides
- 2022
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In: Contributions to Mineralogy and Petrology. - : Springer. - 0010-7999 .- 1432-0967. ; 177:9
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Journal article (peer-reviewed)abstract
- The Seve Nappe Complex (SNC) comprises continental rocks of Baltica that were subducted and exhumed during the Caledonian orogeny prior to collision with Laurentia. The tectonic history of the central SNC is investigated by applying in-situ zircon and monazite (Th-)U-Pb geochronology and trace element analysis to (ultra-)high pressure (UHP) paragneisses in the Avardo and Marsfjallet gneisses. Zircons in the Avardo Gneiss exposed at Sippmikk creek exhibit xenocrystic cores with metamorphic rims. Cores show typical igneous REE profiles and were affected by partial Pb-loss. The rims have flat HREE profiles and are interpreted to have crystallized at 482.5 +/- 3.7 Ma during biotite-dehydration melting and peritectic garnet growth. Monazites in the paragneiss are chemically homogeneous and record metamorphism at 420.6 +/- 2.0 Ma. In the Marsfjallet Gneiss exposed near Kittelfjall, monazites exhibit complex zoning with cores enveloped by mantles and rims. The cores are interpreted to have crystallized at 481.6 +/- 2.1 Ma, possibly during garnet resorption. The mantles and rims provide a dispersion of dates and are interpreted to have formed by melt-driven dissolution-reprecipitation of pre-existing monazites until 463.1 +/- 1.8 Ma. Depletion of Y, HREE, and U in the mantles and rims compared to the cores record peritectic garnet and zircon growth. Altogether, the Avardo and Marsfjallet gneisses show evidence of late Cambrian/early Ordovician partial melting (possibly in (U)HP conditions), Middle Ordovician (U)HP metamorphism, and late Silurian tectonism. These results indicate that the SNC underwent south-to-north oblique subduction in late Cambrian time, followed by progressive north-to-south exhumation to crustal levels prior to late Silurian continental collision.
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| 4. |
- Bukala, Michal, et al.
(author)
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U-Pb Zircon Dating of Migmatitic Paragneisses and Garnet Amphibolite from the High Pressure Seve Nappe Complex in Kittelfjäll, Swedish Caledonides
- 2020
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In: Minerals. - : MDPI AG. - 2075-163X. ; 10:4
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Journal article (peer-reviewed)abstract
- The Seve Nappe Complex exposed in the Kittelfjall area of the northern Scandinavian Caledonides comprises a volcano-sedimentary succession representing the Baltica passive margin, which was metamorphosed during the Iapetus Ocean closure. Garnet amphibolites, together with their host migmatitic paragneisses, record a potential (U)HP event followed by decompression-driven migmatization. The garnet amphibolites were originally thought to represent retrogressively altered granulites. The petrological and geochemical features of a studied garnet amphibolite allow for speculation about a peridotitic origin. Zirconium (Zr) content in rutile inclusions hosted in garnet in paragneisses points to near-peak temperatures between 738 degrees C and 780 degrees C, which is in agreement with the c. 774 degrees C obtained from the matrix rutile in the garnet amphibolite. The matrix rutile in multiple paragneiss samples records temperatures below 655 degrees C and 726 degrees C. Whereas the LA-ICP-MS U-Pb dating of zircon cores revealed the age spectrum from Paleoproterozoic to early Paleozoic, suggesting a detrital origin of zircon cores in paragneisses, the metamorphic zircon rims show an Early Ordovician cluster c. 475-469 Ma. Additionally, zircon cores and rims from the garnet amphibolite yielded an age of c. 473 Ma. The REE patterns of the Caledonian zircon rims from the paragneisses show overall low LREE concentrations, different from declining to rising trends in HREE (Lu-N/Gd-N = 0.49-38.76). Despite the textural differences, the cores and rims in zircon from the garnet amphibolite show similar REE patterns of low LREE and flat to rising HREE (Lu-N/Gd-N = 3.96-65.13). All zircon rims in both lithologies display a negative Eu anomaly. Hence, we interpret the reported ages as the growth of metamorphic zircon during migmatization, under granulite facies conditions related to exhumation from (U)HP conditions.
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| 5. |
- Carter, Isabel S. M., et al.
(author)
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Cambrian ages for metavolcanic rocks in the Lower Köli Nappes, Swedish Caledonides: implications for the status of the Virisen arc terrane
- 2023
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In: Journal of the Geological Society. - : Geological Society of London. - 0016-7649 .- 2041-479X. ; 180:6
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Journal article (peer-reviewed)abstract
- The Köli Nappe Complex (KNC) of the Scandinavian Caledonide orogen originated as oceanic terranes within the Iapetus Ocean. These terranes have characteristics of magmatic arcs and associated forearc or back-arc basins and underwent several periods of rifting and magmatism prior to their accretion to the Baltican margin. We present new U–Pb zircon ages from the Lower Köli Ankarede Volcanite Formation in Västerbotten, Sweden. U–Pb ages of magmatic zircon grains from metamorphosed dacitic to andesitic rocks show ages of 512 ± 3.5, 497 ± 2, 491 ± 1 and 488 ± 4 Ma. The three younger ages fit with previous ages for Lower Köli volcanic rocks, but the 512 Ma age is older than any previous age for this unit. These dates constrain the age of magmatism in an ensimatic arc system within Iapetus. We compare this evolution with published information from the other Köli nappes. Magmatic ages within the KNC overlap with ages for an early episode of ultrahigh-pressure (UHP) metamorphism within the underlying Seve Nappe Complex (SNC), supporting the hypothesis that attributes UHP metamorphism within the SNC to subduction beneath the island arc now preserved within the Lower Köli Nappes.
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| 6. |
- Rzeski, Wojciech, et al.
(author)
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Alpha-ketoglutarate (AKG) inhibits proliferation of colon adenocarcinoma cells in normoxic conditions
- 2012
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In: Scandinavian Journal of Gastroenterology. - : Informa UK Limited. - 1502-7708 .- 0036-5521. ; 47:5, s. 565-571
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Journal article (peer-reviewed)abstract
- Background and objective. Alpha-ketoglutarate (AKG), a key intermediate in Krebs cycle, is an important biological compound involved in the formation of amino acids, nitrogen transport, and oxidation reactions. AKG is already commercially available as a dietary supplement and its supplementation with glutamine, arginine, or ornithine alpha-ketoglutarate has been recently considered to improve anticancer immune functions. It is well documented that AKG treatment of Hep3B hepatoma cells in hypoxia induced HIF-alpha (hypoxia-inducible factor) degradation and reduced vascular endothelial growth factor (VEGF) synthesis. Moreover, AKG showed potent antitumor effects in murine tumor xenograft model, inhibiting tumor growth, angiogenesis, and VEGF gene expression. However, the mechanisms of its anticancer activity in normoxia have not been examined so far. Results. Here, we report that in normoxia, AKG inhibited proliferation of colon adenocarcinoma cell lines: Caco-2, HT-29, and LS-180, representing different stages of colon carcinogenesis. Furthermore, AKG influenced the cell cycle, enhancing the expression of the inhibitors of cyclin-dependent kinases p21 Waf1/Cip1 and p27 Kip1. Moreover, expression of cyclin D1, required in G1/S transmission, was decreased, which accompanied with the significant increase in cell number in G1 phase. AKG affected also one the key cell cycle regulator, Rb, and reduced its activation status. Conclusion. In this study for the first time, the antiproliferative activity of AKG on colon adenocarcinoma Caco-2, HT-29, and LS-180 cells in normoxic conditions was revealed. Taking into consideration an anticancer activity both in hypoxic and normoxic conditions, AKG may be considered as a new potent chemopreventive agent.
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| 7. |
- Walczak, Katarzyna, et al.
(author)
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Late Neoproterozoic extended continental margin development recorded by the Seve Nappe Complex of the northern Scandinavian Caledonides
- 2022
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In: Lithos. - : Elsevier. - 0024-4937 .- 1872-6143. ; 416
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Journal article (peer-reviewed)abstract
- The Scandinavian Caledonides comprise nappe stacks of far-travelled allochthons that record the opening and closure of the Iapetus Ocean, culminating with the collision of Baltica and Laurentia. The Seve Nappe Complex (SNC) of the Scandinavian Caledonides comprises relics of the outermost Baltoscandian passive margin that were subducted to mantle depths during ocean closure. Subduction of these rocks overprinted much of the Neoproterozoic record for Iapetus Ocean formation, and as a result, much of the work conducted in the SNC has focused solely on the Caledonian orogenic history.& nbsp;In this study, we combined petrological and geochronological work to expand the knowledge about the Neoproterozoic metamorphic history of the Baltoscandian margin in the understudied Vaivancohkka-Salmmecohkat region of the northern Scandinavian Caledonides. The work focused on rocks that belong to the upper gneiss unit, which constitutes part of SNC in the region. The unit comprises migmatitic paragneisses and garnet-mica schist containing metamafic bodies. U-Pb zircon and Th-U-total Pb monazite dating of the migmatitic paragneiss yielded consistent age of metamorphism in 602 +/- 5 Ma and 599 +/- 3 Ma, respectively. A similar U-Pb age of 604 +/- 8 Ma was obtained for the zircon from the leucocratic vein transecting the amphibolite within the studied gneiss. Interestingly, no Caledonian ages were identified. Likewise, no evidence for high or ultra-high pressure conditions was found, neither in the gneisses/schists nor in the metamafic rocks. Petrographic observations and calculated metamorphic P-T conditions indicate that rocks belonging to upper gneiss unit underwent upper-amphibolite facies metamorphism in a melt stability field; 8.0-10.5 kbar at 750-790 degrees C.& nbsp;Since the studied rocks underwent high-grade metamorphism in the Ediacaran and lack obvious evidence for Caledonian high-pressure metamorphism, the studied part of the SNC offers an extraordinary insight into the Late Neoproterozoic history of the hot, extended Baltoscandian margin.
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| 8. |
- Walczak, Katarzyna, et al.
(author)
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U–Pb zircon age dating of diamond-bearing gneiss from Fjørtoft reveals repeated burial of the Baltoscandian margin during the Caledonian Orogeny
- 2019
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In: Geological Magazine. - Cambridge : Cambridge University Press. - 0016-7568 .- 1469-5081. ; 156:11
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Journal article (peer-reviewed)abstract
- The first find of microdiamond in the Nordøyane ultra-high-pressure (UHP) domain of the Western Gneiss Region (WGR) of the Scandinavian Caledonides reshaped tectonic models for the region. Nevertheless, in spite of much progress regarding the meaning and significance of this find, the history of rock that the diamonds were found in is complex and still largely ambiguous. To investigate this, we report U–Pb zircon ages obtained from the exact crushed sample material in which metamorphic diamond was first found. The grains exhibit complicated internal zoning with distinct detrital cores overgrown by metamorphic rims. The cores yielded a range of ages from the Archaean to the late Neoproterozoic / early Cambrian. This detrital zircon age spectrum is broadly similar to detrital signatures recorded by metasedimentary rocks of the Lower and Middle allochthons elsewhere within the orogen. Thus, our dating results support the previously proposed affinity of the studied gneiss to the Seve–Blåhø Nappe of the Middle Allochthon. Metamorphic rims yielded a well-defined peak at 447 ± 2 Ma and a broad population that ranges between c. 437 and 423 Ma. The data reveal a prolonged metamorphic history of the Fjørtoft gneiss that is far more complex then would be expected for a UHP rock that has seen a single burial and exhumation cycle. The data are consistent with a model involving multiple such cycles, which would provide renewed support for the dunk tectonics model that has been postulated for the region.
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| 9. |
- Walczak, Katarzyna, et al.
(author)
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Zircon age depth-profiling sheds light on the early Caledonian evolution of the Seve Nappe Complex in west-central Jämtland
- 2022
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In: Geoscience Frontiers. - : Elsevier. - 1674-9871. ; 13:2
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Journal article (peer-reviewed)abstract
- The Scandinavian Caledonides comprise nappe stacks of far-travelled allochthons that record closure of the Iapetus Ocean and subsequent continental collision of Baltica and Laurentia. The Seve Nappe Complex (SNC) of the Scandinavian Caledonides includes relics of the outermost Baltoscandian passive margin that were subducted to mantle depths. The earliest of the deep subduction events has been dated to ca. 500-480 Ma. Evidence of this event has been reported from the northern exposures of the SNC. Farther south in the central and southern segments of the SNC, (ultra)high-pressure rocks have yielded younger ages in the range of ca. 470-440 Ma. This study provides the first record of the early Caledonian event in the southern SNC. The evidence has been obtained by depth profiling of zircon grains that were extracted from the Tvaraklumparna microdiamond-bearing gneiss. These zircon grains preserve eclogite facies overgrowths that crystallized at 482.6 +/- 3.8 Ma. A second, chemically-distinct zircon overgrowth records granulite facies metamorphism at 439.3 +/- 3.6 Ma, which corroborates previous geochronological evidence for granulite facies metamorphism at this time. Based on these results, we propose that the entire outer margin of Baltica was subducted in the late Cambrian to early Ordovician, but the record of this event may be almost entirely eradicated in the vast majority of lithologies by pervasive late Ordovician to early Silurian metamorphism.
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| 10. |
- Ziemniak, Grzegorz, et al.
(author)
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Th–U–total Pb monazite geochronology records Ordovician (444 Ma) metamorphism/partial melting and Silurian (419 Ma) thrusting in the Kåfjord Nappe, Norwegian Arctic Caledonides
- 2019
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In: Geologica Carpathica. - Bratislava : Walter de Gruyter GmbH. - 1335-0552 .- 1336-8052. ; 70:6, s. 494-511
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Journal article (peer-reviewed)abstract
- The northern extent of the Scandinavian Caledonides includes the Skibotn Nappe Complex of still debatedstructural position. This paper is focused on part of this complex and presents new U–Th–total Pb monazite dating resultsfor the migmatitic gneiss of the Kåfjord Nappe. The rocks show mineral assemblage of garnet + plagioclase + biotite +white mica + kyanite + rutile ± K-feldspar ± sillimanite. Thermodynamic modelling suggests that garnet was stable at P–Tconditions of ca. 680–720 °C and 8–10 kbars in the stability field of kyanite and the rocks underwent partial meltingduring exhumation following a clockwise P–T path. This episode is dated to 444 ± 12 Ma using chemical Th–U–total Pbdating of the Y-depleted monazite core. Second episode highlighted by growth of secondary white mica resulted fromsubsequent overprint in amphibolite and greenschist facies. Fluid assisted growth of the Y-enriched monazite rim at419 ± 8 Ma marks the timing of the nappe emplacement. Age of migmatization and thrusting in the Kåfjord Nappe issimilar to the Kalak Nappe Complex, and other units of the Middle Allochthon to the south. Nevertheless, the obtainedresults do not allow for unambiguous definition of the tectonostratigraphic position of the Skibotn Nappe Complex.
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