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The supracrustal rocks of the Kuovila area in the Palaeoproterozoic Svecofennian Uusimaa Belt, southern Finland, consist mainly of volcaniclastic rocks associated with banded iron formations (BIFs) and marbles. Small ZnS and PbS mineralizations are occasionally located within the marbles. Some primary features are well preserved in the sedimentary and volcanic rocks, including lamination in tuffites and banded iron formations. Geochemical results show that the volcanism was bimodal and it mainly had volcanic arc affinity. Specific geochemical indicators suggesting a volcanic arc origin for the Kuovila volcanic rocks include: 1) Enrichment of LILE over the HFSE elements and 2) Distinctly low Nb and Ta contents in relation to Th, Ce and LREE. Geochemistry of the Kuovila area volcanic rocks is very similar to those of the Orijärvi and Kisko formations, located ~15 km NE of Kuovila. Felsic tuff in the Kuovila area was dated at 1891±4 Ma by the U-Pb system on zircons. Consequently volcanism was contemporaneous with magmatism in the adjacent Orijärvi area, thus representing the earliest identified volcanic stage in the southern Svecofennian Uusimaa Belt. Early deformation structures within the Kuovila area are suggested to relate to lowmetamorphic or localized low-angle thrusting during D 1 . F 1 folds were recumbent and the S 1 cleavages are generally weak. Thrusting was followed by approximately N–S contraction with upright, peak-metamorphic F 2 folding overprinting D 1 structures and defining the Kuovila synform. Two separate intrusive phases include a synvolcanic granodiorite-dioritegabbro association and a weakly S 2 -foliated syn-D 2 granodiorite. Anatectic granites and associated migmatizing veins are absent, therefore suggesting that D 2 pre-dates the ~1.84– 1.82 Ga metamorphic event in the Southern Svecofennian Arc Complex (SSAC). D 2 structures in the Kuovila area are suggested to correlate with the early structures with associated axial planar cleavages in the Orijärvi area. D 2 strain is localized into axial planar high strain zones and the curvilinear patterns of the B 2 fold axes probably result from vertical stretching during D 2 .

Supracrustal rocks in the Kuovila area, Southern Finland: Structural evolution, geochemical characteristics and the age of volcanism