ISOTOPE DATA ON THE AGE AND GENESIS OF LAYERED BASIC-ULTRABASIC INTRUSIONS IN THE KOLA-PENINSULA AND NORTHERN KARELIA, NORTHEASTERN BALTIC SHIELD

New U-Pb zircon ages and Sm-Nd data are presented for layered basic-ultrabasic intrusions of the Kola Peninsula and northern Karelia in the northeastern part of the Baltic Shield. All ages are in the range between 2.5 and 2.4 Ga, but there appear to exist three phases of intrusion. Thus the Monchegorsk Intrusion and the Fedorovy-Pansky Massif have ages between 2493 and 2470 Ma, the Kivakka and Lukkulaisvaara massifs of the Olanga group of intrusions between 2445 and 2435 Ma, while the Imandra Lopolith is 2396 +/- 7 Ma old. A narrow range of negative epsilon(Nd)(T) values between -2.3 and -1.2 suggests formation by partial melting of a semi-homogeneous enriched mantle source.