Tutkimusraportti 192 - arkisto.gsf.fi - Geologian tutkimuskeskus

Mäkitie, H. 2011. Puumalan kartta-alueen kallioperä. Summary: Pre-Quaternary
rocks of the Puumala map sheet area. Geological Survey of Finland,
Report of Investigation 192, 52 pages, 33 figures, 3 tables and 3 appendices.
This report gives the results of lithological and geochemical bedrock studies
in the Puumala map sheet area in southeastern Finland. In the map sheet
area, geological studies were made at several sites during the 1960s, 1970s and
1980s. Limited fieldwork was also carried out during 2007–2008. A bedrock
map at 1:100 000 scale is appended.
The main rocks in the map sheet area are Svecofennian (1.9–1.8 Ga) migmatitic
(phlebitic) biotite paragneisses and various granitic intrusions. These
gneisses, possibly turbiditic in origin, commonly have psammitic intercalations
and contain garnet, cordierite and K-feldspar porphyroblasts. Mafic
metavolcanic rocks, quartz-feldspar schists and quartzitic rocks, which are
part of the Tiirismaa Suite, occur in a narrow, irregular, east-west trending
belt across the map sheet area. In the SW part of the map sheet area there are
graphite-sulphide paraschists. The largest granitoid pluton in the area is the
Käkövesi granodiorite (110 km 2 ), which is probably synorogenic in age (~1.88
Ga). There are also smaller tonalitic intrusions. Moreover, the biotite para-
gneisses typically contain many granite pegmatite dykes and some larger S-type
granitoid bodies. The generation of these dykes and bodies are connected with
a Svecofennian late-orogenic 1.84–1.81 Ga thermotectonic event (amphibolite
to granulite grade metamorphism) in southern Finland.
The biotite paragneisses are rich in aluminium (17–21 wt% Al 2 O 3 ). The
metavolcanic rocks of the Tiirismaa Suite are mafic to intermediate and predominantly
range from trachybasalts to andesites. Chemically they are tholeiitic
to calc-alkaline, locally with slightly elevated alkali contents. Most of the
studied granitoids are peraluminous.
The map sheet area includes two small metallic mineral deposits: a Ni-Cu
occurrence in a norite body at Kitula, south of the Puumala municipal centre,
and a Cu-Mo occurrence in the western part of the Käkövesi granodiorite.
Both occurrences were studied in the 1960s, 1970s and 1980s, but were considered
to have no economic value.
Keywords (GeoRef Thesaurus, AGI): areal geology, explanatory text, bedrock,
metamorphic rocks, plutonic rocks, geochemistry, economic geology,
Paleoproterozoic, Svecofennian, Puumala, Finland
Hannu Mäkitie
Geological Survey of Finland
P.O. Box 96
FI-02151 Espoo
FINLAND
E-mail: hannu.makitie@gtk.fi
ISBN 978-952-217-168-9 (PDF)
ISSN 0781-4240