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- Johansson, Åke, et al.
(författare)
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A geochronological review of magmatism along the external margin of Columbia and in the Grenville-age orogens forming the core of Rodinia
- 2022
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Ingår i: Precambrian Research. - : Elsevier BV. - 0301-9268 .- 1872-7433. ; 371, s. 1-43
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Tidskriftsartikel (refereegranskat)abstract
- A total of 4344 magmatic U-Pb ages in the range 2300 to 800 Ma have been compiled from the Great Proterozoic Accretionary Orogen along the margin of the Columbia / Nuna supercontinent and from the subsequent Grenvillian collisional orogens forming the core of Rodinia. The age data are derived from Laurentia (North America and Greenland, n = 1212), Baltica (NE Europe, n = 1922), Amazonia (central South America, n = 625), Kalahari (southern Africa and Dronning Maud Land in East Antarctica, n = 386), and western Australia (n = 199). Laurentia, Baltica, and Amazonia (and possibly other cratons) most likely formed a ca. 10 000-km-long external active continental margin of Columbia from its assembly at ca. 1800 Ma until its dispersal at ca. 1260 Ma, after which all cratons studied were involved in the Rodinia-forming Grenvillian orogeny. However, the magmatic record is not smooth and even but highly irregular, with marked peaks and troughs, both for individual cratons and the combined data set. Magmatic peaks typically range in duration from a few tens of million years up to around hundred million years, with intervening troughs of comparable length. Some magmatic peaks are observed on multiple cratons, either by coincidence or because of paleogeographic proximity and common tectonic setting, while others are not. The best overall correlation, 0.617, is observed between Baltica and Amazonia, consistent with (but not definitive proof of) their being close neighbours in a SAMBA-like configuration at least in Columbia, and perhaps having shared the same peri-Columbian subduction system for a considerable time. Correlation factors between Laurentia and Baltica, or Laurentia and Amazonia, are below 0.14. Comparison between the Grenville Province in northeastern Laurentia and the Sveconorwegian Province in southwestern Fennoscandia (Baltica) shows some striking similarities, especially in the Mesoproterozoic, but also exhibits differences in the timing of events, especially during the final Grenville-Sveconorwegian collision, when the Sveconorwegian evolution seems to lag behind by some tens of million years. Between the other cratons, the evolution before and during the final Grenvillian collision is also largely diachronous. After 900 Ma, magmatic activity had ceased in all areas investigated, attesting to the position of most of them within the stable interior of Rodinia.
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| 2. |
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| 3. |
- Lahtinen, R., et al.
(författare)
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New geochronological and Sm-Nd constraints across the Pajala shear zone of northern Fennoscandia : Reactivation of a Paleoproterozoic suture
- 2015
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Ingår i: Precambrian Research. - : Elsevier BV. - 0301-9268 .- 1872-7433. ; 256, s. 102-119
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Tidskriftsartikel (refereegranskat)abstract
- Altogether 1130 U-Pb analyses on zircons from 25 samples across the Pajala shear zone in northern Fennoscandia were performed by LA-ICPMS methodology to study the origin of the zone. The samples were also analyzed for their Sm-Nd isotope systematics and geochemically. The new data is tested with existing geological information to elaborate the provenance and maximum depositional ages, the stratigraphic position of studied samples, and finally to assess the tectonic evolution in the Pajala shear zone area. Chromium-enriched metasedimentary rocks are found within and to the east and west of the N-S trending Pajala shear zone. No material originating from Proterozoic felsic igneous (zircons) or mafic (Sm-Nd) rocks was found in these rocks and thus, only Neoarchean or very early Paleoproterozoic ages of deposition are possible. Our new results indicate that the bimodal 1.99-1.97 Ga supracrustal rocks of the Rovaniemi Supersuite cover a large area east of the Pajala shear zone. Based on the absence of Archean zircons typical of the metasedimentary rocks covering the Archean basement, it seems that the basement and its sedimentary cover were not exposed at the time of deposition of the Rovaniemi Supersuite. The metasedimentary rocks of the Uusivirka Supersuite, located within the Pajala shear zone, vary from hornblende-bearing metasedimentary rocks, metapelite, and meta-arkose to orthoquartzite. Their characteristic features include a dominant Proterozoic zircon population (65-87%), with a high proportion of analyzed grains yielding ages between 1.96 Ga and 1.91 Ga, and maximum depositional ages of 1.92-1.91 Ga. We record at least three metamorphic events; at ca. 1.92-1.90 Ga, ca. 1.85 Ga and at 1.82-1.78 Ga, of which the youngest can possibly be separated into two events at 1.83-1.82 Ga and 1.79-1.77 Ga, respectively. We propose a tectonic model in which continental breakup occurred at 2.1-2.05 Ga, followed by the development of a magmatic arc (Kittila arc) at ca. 2.0 Ga above a subduction zone. Two Archean continental units (Norrbotten and Karelia) collided at ca. 1.92-1.91 Ga, the Kittila arc was obducted upon the Karelia continent as a foreland fold and thrust belt, and the metasedimentary rocks of the Uusivirka Supersuite were emplaced as foreland deposits. The proposed tectonic model is based on the absence of 2.44 Ga layered intrusions, and especially 2.06 Ga rocks and 1.99-1.97 Ga rocks of the Rovaniemi Supersuite that are found only east of the Pajala shear zone. In our model the Pajala shear zone originated as a divergent plate boundary, and was multiply reactivated after continental collision with both lateral and vertical movements.
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| 4. |
- Lahtinen, R., et al.
(författare)
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Paleoproterozoic magmatism across the Archean-Proterozoic boundary in central Fennoscandia: Geochronology, geochemistry and isotopic data (Sm–Nd, Lu–Hf, O).
- 2016
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Ingår i: Lithos. - : Elsevier BV. - 0024-4937 .- 1872-6143. ; 262, s. 507-525
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 5. |
- Woodard, J., et al.
(författare)
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Zircon and monazite geochronology of deformation in the Pielavesi Shear Zone, Finland: multistage evolution of the Archaean–Proterozoic boundary in the Fenoscandian Shield.
- 2017
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Ingår i: Journal of the Geological Society. - : Geological Society of London. - 0016-7649 .- 2041-479X. ; 174, s. 255-267
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Tidskriftsartikel (refereegranskat)abstract
- The Raahe–Ladoga Shear Complex is a major crustal structure representing the Archaean–Palaeoproterozoic boundary in the Fennoscandian Shield. The complex developed during the Svecofennian Orogeny (c. 1.9 – 1.8 Ga) beginning with regional thrust tectonic phases D1 and D2, followed by large-scale shearing events D3 and D4. The Pielavesi Shear Zone is a vertical north–south-trending shear zone within the Raahe–Ladoga Shear Complex formed during regional D3 shearing and later reactivated during the regional D4 phase. Three north–south-trending elongate granitoid intrusions were selected as representative of silicic melts that intruded the transtensional Pielavesi Shear Zone during the regional D3 phase. The oriented magmatic fabric of the granitoids indicates that they intruded coeval to the deformation event. The zircon U–(Th)–Pb secondary ionization mass spectrometry (SIMS) ages of these intrusions (1888 ± 4, 1884 ± 6 and 1883 ± 5 Ma) overlap within error and provide a direct age for the regional D3 deformation. εHf(T)(−1.1 to +3.4) and εNd(T) (−1.2 to +0.4) values from these granitoids are both consistent with a predominantly juvenile source affected by a minor Archaean component. U–(Th)–Pb SIMS analyses of metamorphic monazite formed within a crosscutting blastomylonite provide an age for the regional D4phase and associated fluid activity of 1793 ± 3 Ma.
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