Kursun ja Sallan kartta-alueiden kalliopera - arkisto.gsf.fi ...

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formations and three metasediment sequences .
The lowest, Salla formation, is composed of intermediate and felsic lavas and tuffs .
The overlying Mantyvaara formation is separated from the Salla formation by an Al-rich
weathering crust and a thin layer of sericite schist . Mantyvaara formation is composed
of high-Mg basalts, and komatiitic lavas and tuffs .
The metasediments of the Kelloselka formation are separated from the underlying volcanic
formations by a fault . They consist of dolomites, arkose quartzites and siltstones .
Tholeitic basalts of the about 50-150 m thick Tahkoselka formation rest on the
metasediments of the Kelloselka formation .
The overlying Matovaara formation is composed of carbonate-bearing siltstones, sericite
quartzites and orthoquartzites .
The uppermost formation in the Salla map-sheet area is the Aatsinginhauta formation .
It consists of dolomites, carbonate-rich metasediments, mica schist sulfide-bearing
graphite schists and jaspilites .
The mineral and chemical composition of the metadiabases, located near the western
border of the schist belt, are given in tables 2 and 3 .
Granite and migmatite area
Greatest part of the Kursu map-sheet area belongs to the large granitoid complex of
the Southern Lapland . Near the Salla schist complex the granites are homogeneous and
they penetrate the metadiabases and schists . Farther off the schist area the rocks are
migmatitic, reminiscent of Archaean gneisses . All the radiometric age determinations
made so far have given, however, Proterozoic ages (Lauerma 1982) .
Diabase dykes
The youngest rocks in the Kursu and Salla map-sheet areas are differentiated diabase
dykes . They have been previously described by Hackman (1914), Vaananen (1965),
Lauerma (1987) and Manninen (1991) . The length of the diabase swarm is about 130 km .
The width of the dykes is 60-100 m and they trend about N 60° W . The chemical and
mineral composition of the dykes is given in tables 2 and 3 .
Radiometric ages
Analytical data for zircons and titanites extracted from metadiabases and Salla diabase
dykes are given in table 5 and the concordia diagrams in Figs . 12-15 . According to them
the metadiabases intruded c . 2201-2210 Ma ago and the Salla dykes c . 1122 Ma ago .