evolution of Fennoscandian Shield. The main source components and implications for the tec-
tonic evolution of the central Fennoscandian shield are given with emphasis on proposed su-
tures. Notes on the crustal evolution and Ar- chaean – Proterozoic transition in general, and on
Ba depletion are also given. As all the studied sedimentary rocks are metamorphosed, the prefix
’meta’ has been dropped. The data set is available on request from the author.
2. Sampling and analytical methods
Sampling was done with a mini-drill with dia- mond bit. Each sample comprised four to six
subsamples altogether 1 – 1.5 kg from the same lithological unit, if detection of unit boundaries
was possible sometimes this was impossible, e.g. in some migmatites. In the case of turbidites, the
whole Bouma A, AB or ABC was sampled in most cases. A composite sample was taken from
Fig. 1. Simplified geological map of Finland and surrounding areas modified from Sorjonen-Ward 1993, Korsman et al. 1997. The study area is outlined see Fig. 2.
Fig. 2. Simplified geological map of the study area Fig. 1 modified from Korsman et al. 1997. Sample locations are also indicated.
veined migmatites and pelitic rocks where layers were B 5 cm thick and a more homogeneous unit
was not available. The analytical work was done in the laborato-
ries of the Geological Survey of Finland. Samples were jaw crushed and splits were pulverized in a
tungsten carbide bowl for X-ray fluorescence XRF analysis, and in a carbon steel bowl for
inductively coupled plasma mass spectrometry ICP-MS. Major elements and Cl, V, Cr, Ni, Zn,
Rb, Sr, Y, Zr, Nb and Ba were determined by XRF, C
Graf.
by Leco CR-12 carbon analyzer, F by ion selective electrode, aqua regia leachable S and
Cu by ICP-AES, and aqua regia leachable Au, Pd, Te, As, Ag, Bi, Sb and Se by GAAS Sand-
stro¨m, 1996. REE, Co, Nb, Hf, Rb, Sc, Ta, Th and U were determined by ICP-MS after dissolu-
tion of the sample 0.2 g with hydrofluoric acid- perchloricacid treatment completed by a lithium
metaboratesodium perborate fusion Rautiainen et al., 1996. The estimated uncertainty is 1 – 5
for major elements and 3 – 10 for trace elements.
3. General geology
The cratonic part of the study area Fig. 1 includes rocks from Archaean mainly 2.76 – 2.73
Ga; Vaasjoki et al., 1993 and Palaeoproterozoic cratonic stage 2.5 – 2.1 Ga with coeval and sub-
sequent multiple rifting e.g. Vuollo, 1994; Ko- honen, 1995 in which the latest phase led to
formation of ophiolitic sequences 1.95 Ga; Pel- tonen et al., 1996. The cratonic cover in the
Ho¨ytia¨inen and Suvasvesi areas Fig. 2 are domi- nated by autochthonous and allochthonous rocks,
respectively. The Ho¨ytia¨inen area or rift basin Ward, 1987 includes the Tohmaja¨rvi volcanic
complex 2105 9 15 Ma; Huhma, 1986 and asso- ciated coarse clastic deposits but is dominated by
mica schists representing metamorphosed thinly laminated pelites to massive turbidites Ward,
1987; Kohonen, 1995. The formal lithostrati- graphic procedure has been applied only to the
autochthonous Sariola, Jatuli and Ludian groups in the eastern margin of the Ho¨ytia¨inen area
Pekkarinen, 1979; Pekkarinen and Lukkarinen, 1991; Kohonen and Marmo, 1992; Karhu, 1993.
Otherwise lithostratigraphy and chronostratigra- phy of the Ho¨ytia¨inen area are not resolved Ko-
honen, 1995 but depositional ages from 2.1 to about 1.9 Ga are inferred.
The Suvasvesi area is characterized by the ‘Up- per Kaleva’ Kontinen and Sorjonen-Ward, 1991
or Western Kaleva Kohonen, 1995 a term adopted in this study greywackes that occur as
allochthonous units in thrust complexes charac- terized by associated ophiolites and related rocks
Koistinen, 1981 and references therein though evidence for local deposition upon Archaean
basement has also been noted Ward, 1987. The increase in metamorphic grade from east to west
Fig. 2 is seen as an increase in quartz veins and the onset of segregational banding quartz +
feldspar leading finally to migmatites.
The boundary zone BZ includes migmatitic sedimentary rocks Korsman et al., 1984 and a
1.93 – 1.91 Ga volcano-plutonic formation Lahti- nen, 1994 and references therein. The Svecofen-
nian is divided into the central Svecofennian including the Central Finland Granitoid Complex
CFGC and Bothnian Belt BB, and the south- ern Svecofennian including the Rantasalmi –
Haukivuori
area RH.
The tentative
sedimentation ages for the central Svecofennian, based on data available from the Tampere Schist
Belt Lahtinen, 1996 and references therein, are ]
1.91 and 1.89 – 1.87 Ga for rocks correlated to basement- and arc-related groups in the Tampere
Schist Belt, respectively. The southern Svecofen- nian, including the Rantasalmi – Haukivuori area,
is characterized by granite migmatites, which is a clear difference to the central Svecofennian,
boundary zone and Suvasvesi area, which are characterized by tonalite migmatites Korsman et
al., 1999 and references therein.
4. Results
