U-Pb and Rb-Sr systematics of the Suomussalmi Archean greenstone belt (Eastern Finland)

https://doi.org/10.1016/0016-7037(80)90201-XGet rights and content

Abstract

The greenstone belt of Suomussaimi is composed of a lower volcanic sequence of komatiitic and tholeiitic composition, a middle sedimentary unit and a upper volcanic sequence that is mainly andesitic-rhyodacitic in composition. These series have been folded and then intruded by granitic to granodioritic plutons. The surrounding basement is mainly composed of migmatitic gneisses which have undergone a complex tectonometamorphic history.

The Pb-Pb and Rb-Sr systematics reveal that

  • 1.

    (1) All these rocks have been emplaced at about 2.65 b.y. and are therefore Archean in age;

  • 2.

    (2) all the events in the basement and the belt lasted not more than the analytical uncertainties, that is 0.2 b.y.;

  • 3.

    (3) all the rocks probably originated from source regions (the mantle and its derived basic rocks) characterized by similar isotopic compositions; the involvement of much older continental rocks was negligible;

  • 4.

    (4) the basement gneisses have low calculated second stage μ values (1→ 7) and high calculated Th/U ratios (5 → 20); in contrast, the belt rocks (with the exception of komatiitic basalts) have second stage μ values from 6 to 18 and Th/U ratios from 2 to 5. These features can be interpreted as the result of U-depletion in a high grade metamorphism prior to the belt formation or due to the melting of underlying granulite facies crust;

  • 5.

    (5) K-feldspars Pb-Pb systematics and biotites Rb-Sr ages show the influence of the 1.7 b.y. Svecokarelian thermal event;

  • 6.

    (6) almost all the rocks have undergone a very strong recent U. depletion.

References (34)

  • M. Tatsumoto

    Isotopic composition of lead in oceanic basalt and its implication to mantle evolution

    Earth Planet. Sci. Lett.

    (1978)
  • J.M. Bertrand et al.

    Précisions sur l'évolution structurale de l'Archéen de Karélie (Finlande)

    C.R. Acad. Sci. Paris

    (1978)
  • E.V. Bibikova et al.

    Geochronology of the White Sea Block

  • S. Blais et al.

    Les grands traits géologiques de la ceinture archéenne de roches vertes de Suomussalmi-Kuhmo (Finlande orientale)

    Bull. Soc. Géol. France

    (1977)
  • D.R. Bowes

    Archean Crustal History in the Baltic Shield

  • E.J. Catanzaro et al.

    Absolute isotopic abundance ratios of Common, equal atom and radiogenic lead isotopic standards

    J. Res. Natl. Bur. Stand.

    (1968)
  • J.H. Chen

    Uranium-Lead isotope ages from the Southern Sierra Nevada Batholith and adjacent areas, California

  • Cited by (55)

    • Lead isotope planetary profiling (LIPP): Summation-depiction of Earth's many reservoirs

      2006, Chemical Geology
      Citation Excerpt :

      Of 26 isochrons in this report six appear to concur on an intersection with a MTL composition (denoted here R4). These are the isochrons of the Amîtsoq gneiss of Greenland (3.73 Ga line B in Tera, 2003), Africa's Barberton komatiite (3.40 Ga, Brévart et al., 1986) and Belingwe komatiite (2.69 Ga, Dupré and Arndt, 1990), Australia's Ruth Well komatiite (2.64 Ga; Dupré and Arndt, 1990), Australia's Kambalda volcanics (2.55 Ga, Roddick, 1984), and Finland's Suomussalmi greenstone belt (2.66 Ga, Vidal et al., 1980). The case of the Amîtsoq gneiss is detailed in Tera (2003, Fig. 21), and that of Belingwe is discussed in Section 3.2 of this work.

    • Chapter 2 Archean rocks

      2005, Developments in Precambrian Geology
    View all citing articles on Scopus
    View full text