Age (U-Pb, SHRIMP-II), Geochemistry of Zircon, and Conditions of the Formation of Sapphirine-Bearing Rocks of the Central Kola Granulite-Gneiss Area

摘要

Sapphirine-bearing rocks are observed in the central part of the Central Kola granulite-gneiss area (CKGGA), ～10 km to the west of the Kitsa railway station, where two types of rocks are abundant, namely orthopyroxene-biotite orthogneiss separated by aluminous garnet-biotite and garnet-cordierite-sillimanite-biotite plagiogneisses related to the Kola Series. The contacts between the two rock types are tectonic. Several outcrops of sapphirine-bearing rocks occur in the shear zone of the contact between the Vezhetundra orthogneiss body and aluminous gneiss. Sapphirine-bearing rocks often compose elongated veinlike bodies with a length of ＞100 m and a thickness of ＜n m. In each area sapphirine-bearing rocks are quite variable by the structure and mineral composition: from acid rocks enriched in quartz to quartz-free melanocratic rocks with a remarkable content of sapphirine, spinel, and corundum.