The Archean of the Baltic Shield: Geology, Geochronology, and Geodynamic settings

Geotectonics (Impact Factor: 0.75). 01/2006; 40(6):409-433. DOI: 10.1134/S001685210606001X

ABSTRACT The Archean provinces and lithotectonic complexes of the Baltic (Fennoscandian) Shield are considered. The supracrustal complexes
are classified by age: <3.2, 3.10–2.90, 2.90–2.82, 2.82–2.75, and 2.75–2.65 Ga. The data on Archean granitoid complexes and
metamorphic events are mentioned briefly, whereas the recently found fragments of the Archean ophiolitic and eclogite-bearing
associations are discussed in more detail. The Paleoarchean rocks and sporadic detrital grains of Paleoarchean zircons have
been found in the Baltic Shield; however, the relatively large fragments of the continental crust likely began to form only
in the Mesoarchean (3.2–3.1 Ga ago), when the first microcontinents, e.g., Vodlozero and Iisalmi, were created. The main body
of the continental crust was formed 2.90–2.65 Ga ago. The available information on the Paleoarchean complexes of the Baltic
Shield is thus far too scanty for judgment on their formation conditions. The geologic, petrologic, isotopic, and geochronological
data on the Meso-and Neoarchean lithotectonic complexes testify to their formation in the geodynamic settings comparable with
those known in Phanerozoic: subduction-related (ensialic and ensimatic), collisional, spreading-related, continental rifting,
and the setting related to mantle plumes.

  • Doklady Earth Sciences 09/2013; 452(1):930-935. · 0.39 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Data on processes that occurred at contacts of large agpaitic syenite intrusions and basement gneisses obtained by the authors by studying and sampling profiles across the contacts and involve the composition of minerals, analysis of mineral assemblages, isotopic dating of the processes, and analysis of the behavior of major, volatile, and trace elements in rocks near the contact. The contact zones of the massifs were determined to consist of products of contact interaction during the early and late magmatic stages and provide a record of successive stages of a continuous process of gneiss transformations, starting with the filling of the magmatic reservoir with melt and ending with late- and postmagmatic processes related to the development of a system of alkaline veins and pegmatite bodies in the gneisses. Early alkaline metasomatic processes in the Khibina Massif were local, controlled by diffusion, and were induced by the immediate thermal and chemical effect of alkaline melts on the gneisses. In the Lovozero Massif, metasomatism was related predominantly to the development of postmagmatic veins at 359 ± 5 Ma, was controlled by infiltration, and proceeded immediately after the consolidation of the main intrusive series. The metasomatic transformations during the early and late magmatic stages under the effect of agpaitic melts on gneisses predetermined different closure conditions and, correspondingly, different behaviors of the Rb-Sr and Sm-Nd isotopic systems during the contact processes: while the interaction of agpaitic melts with gneisses has modified the (87Sr/86Sr)(T = 370 Ma) ratio via the enrichment of radiogenic Sr in the host Archean rocks, the Sm-Nd isotopic characteristics of the syenites in the inner contact zone and veins preserved their mantle values, which corresponded to the average ones for rocks in the central parts of the intrusion. Experimental data, model simulations, and natural observations testify that Nb, Ta, Zr, Hf, and REE were mobile in the contact interaction zone with agpaitic melts. With regard for data on the fluid regime of the agpaitic melts and the concentrations of volatile components in the contact zones, we believe that the main role in the transfer of REE and HFSE during contact metasomatism could be played by their ligands with F−, Cl−, and SO42−.
    Petrology 01/2011; 19(2):109-133. · 0.99 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The Scandinavian Caledonides have been viewed as resulting from either a single Silurian (i.e. Scandian) event or from polycyclic orogenies involving several collisions on the margin of Baltica. Early studies of the Kalak Nappe Complex (KNC) in Finnmark, Arctic Norway, led to the hypothesis of an Early Cambrian-Early Ordovician (520-480 Ma) Finnmarkian Orogeny, though the nature of this tectonic event remains enigmatic. In this contribution we have employed in situ UV laser ablation Ar-Ar dating of fine-grained phyllite and schist from the eastern Caledonides of Arctic Norway to investigate the presence of pre-Scandian tectonometamorphic events. U-Th-Pb detrital zircon and whole rock Sm-Nd analyses have been used to test the regional stratigraphic correlations of these metasedimentary rocks. These results indicate that the Berlevåg Formation within the Tanafjord Nappe, previously assumed to be part of the KNC, was deposited after 1872 Ma and prior to a low temperature hydrothermal event at 555 ± 15 Ma. It has a likely provenance on the Baltica continent, lacks any Grenville-Sveconorwegian detrital zircons, and thus cannot be part of the KNC which contains abundant detritus in this age range. Instead the Berlevåg Formation is interpreted as part of the Laksefjord Nappe Complex, which structurally underlies the KNC. Laser-ablation argon-argon dating also shows that late Caledonian (i.e. Scandian) tectonometamorphism affected both the KNC and its immediate footwall at c. 425 ± 15 Ma. This is corroborated by a step-heating argon-argon muscovite age of 424 ± 3 Ma which is interpreted as dating cooling. However, within two samples from the KNC, an earlier (Middle-Late Cambrian) metamorphic event is also recorded. A biotite-grade schist yielded an Ar-Ar inverse isochron age of 506 ± 17 Ma from whole rock surfaces, in which the mineral domains are too fine-grained to date individually. An early generation of muscovite from a coarser-grained amphibolite-facies sample yielded an inverse isochron of 498 ± 13 Ma. Both isochron ages have atmospheric argon intercept values. Previous studies have documented similar Cambrian ages in the Caledonian nappes below the KNC. These results suggest correlative tectonometamorphic events in the eastern KNC and its footwall at c. 500 Ma. This Cambrian event may reflect the arrival of the Kalak Nappe Complex as a previously constructed exotic mobile belt onto the margin of Baltica. Combined with recent studies from the western Kalak Nappe Complex, the results do not support the traditional constraint on the Finnmarkian Orogeny sensu stricto. However they vindicate classic tectonic models involving a Cambrian accretion event.
    Tectonophysics 09/2008; 460:158–177. · 2.68 Impact Factor