U-PB AGES OF ZIRCON FROM THE KOLVITSA GABBRO-ANORTHOSITE COMPLEX, SOUTHERN KOLA-PENINSULA, RUSSIA

Anorthosite of the highly deformed Kolvitsa gabbro-anorthosite complex, tectonically emplaced into high-grade mafic gneisses on the shore of Kandalaksha Bay, contains two generations of zircon differing both physically and in age. Prismatic zircon of igneous aspect gives a concordia upper intercept age of 2462 +7/-6 Ma, which is considered to be the crystallization age of the anorthosite. Irregular to rounded zircon fragments have an essentially concordant age of 1905 +/- 20 Ma, interpreted as the time of a tectono-metamorphic overprint. The Early Proterozoic protolith age is slightly older than recently determined crystallization ages of 2.45 Ga from gabbro-anorthosite massifs (including the Kolvitsa complex) in the western Kola Peninsula and from basic-ultrabasic rocks intruding the Archean craton south of the Kola Peninsula. The 1.9 Ga metamorphic age along with the lithologies and tectonic setting of the Kolvitsa complex and its host rocks support a correlation with the Tanaelv Belt of Finland.