Metamorphosed and deformed pillows from Losomäki: evidence of sub-aqueous volcanism in the Outokumpu association, eastern Finland

Pillow lavas, some highly deformed and now seen as banded diopside amphiboliites and tremolite-epidote-chlorite rocks (»barren skarn»), occur within the lower Proterozoic Outokumpu rock association at Losomäki, 50 km N.W. of Outokumpu. The occurrence of these sub-aqueous volcanic assemblages, together with the previously described serpentinite—metadolomite—non-detrital quartzite—cupriferous sulphide ore—black schist assemblage, is similar to those found in both Phanerozoic ophiolite complexes and the lower members of Archaean greenstone belts. The nature of this assemblage is of significance in assessing the lithospheric processes operative in early Proterozoic times as well as in elucidating the evolution of the Svecokarelides.