The early Proterozoic Saari-Kiekki greenstone belt: A representative of the Sariola Group at Kuhmo, Eastern Finland

• Published in: Bulletin of the Geological Society of Finland
• Main Author: E.J. Luukkonen
• Format: Article in Journal/Newspaper
• Language: English
• Published: Geological Society of Finland 1989
• Subjects: greenstone belts; stratigraphy; metavolcanic rocks; metasedimentary rocks; chemical composition; deformation; absolute age; Proterozoic; Sariolian; Saari-Kiekki; Kuhmo; Finland; Geology; QE1-996.5; Saari; Latvalampi; karelia*
• Online Access: https://doi.org/10.17741/bgsf/61.2.003; https://doaj.org/article/12aa276b67624e0eb2ae2da37cb27b4e

The early Proterozoic Saari-Kiekki greenstone belt in Kuhmo, eastern Finland, is the deformed remnant of a NW‒SE-trending elongate structural basin c. 15 km long and up to 3 km wide. It is correlated with the Sariola Group in eastern and northeastern Finland as well as with the Sumi-Sariola Group in Soviet Karelia, and is thus one representative of this oldest unit of the Karelia Supergroup preserved in Central Finland. The volcano-sedimentary sequence of the belt was deposited in terrestial to fluvial environments on late Archaean granitoids and migmatites, in a fault-bounded basin. The basin-margin faults belong to a regional system of dextral strike-slip faults, which were active both prior to (= late Archaean time), during and after the basin formation (= early Proterozoic time). Locally the marginal zones of the basin are characterized by tectonic‒eluvial granitoid breccia hundreds of metres thick, which contain some arkosic layers (= Latvalampi Formation). Subaereal or partly subaqueous basalts, basaltic andesites and andesites were deposited longitudinally in the centre of the basin (= Kaita-Kiekki Formation). In many places the volcanic suite is overlain by the sublitharenites, arkosic sandstones‒conglomerates and polymictic conglomerates (= Pötsölampi Formation). The whole belt is cut by NW‒SE- or NNW‒SSE-trending early Proterozoic metadiabase dykes. U-Pb zircon and titanite isotopic data for the metadiabase dyke indicate that the Saari-Kiekki greenstone belt was deposited before 2209 + 11 Ma. The problematic calc-alkaline trend of the Kaita-Kiekki intermediate volcanites associated with the intracratonic strike-slip fault system is interpreted to be a consequence of late Archaean crustal contamination of basaltic magma at depth during its uprise. Regional dextral E‒SE-trending strike-slip faulting, overthrusting from west to east, open to tight folding, a strong west plunging lineation and the development of the Saari-Kiekki greenstone belt, record an important stage of early Proterozoic reactivation ...