Abstract
Several komatiite and komatiitic basalt occurrences have been found in the greenstone successions of the eastern part of the Baltic shield (Soviet Karelia), with both Archaean and Proterozoic ages being represented. Some flows exhibit internal layering with well-developed spinifex textures similar to those described from the classic komatiite provinces of Canada and Australia. Marked differences have been found in the trace-element geochemistry of these rocks. Some Archaean volcanics exhibit flat REE distributions with approximately chondritic ratios of Ca, Ti, Al, Zr, V and Y whereas others show depletion in LREE and Zr. Proterozoic komatiitic basalts differ from the Archaean ones by their relative LREE. Ba and Sr enrichment. These geochemical features are ascribed to an established heterogeneity in the Archaean mantle source and its further development by the Proterozoic. Major- and trace-element variations suggest relative immobility, during metamorphism, of all the analyzed elements except volatiles and alkalis. These trends being adequately explained by olivine with minor chromite fractionation.
Published Version
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