Geochemistry and U–Pb age of zircons from the Vurechuaivench massif, Monchegorsk complex, Kola region

Abstract

The paper presents data on the geochemical and geochronological characteristics of zircons from mafic rocks of part of the Monchegorsk layered complex represented by the Vurechuaivench massif. Ages of zircons (SHRIMP-II) from samples V-l-09 (anorthosite) and V-2-09 (gabbronorite) are dated back to 2508 ± 7 and 2504 ± 8 Ma, respectively. The chondrite-normalized REE patterns confirm the magmatic nature of zircons. The data unequivocally indicate that the U–Pb age of zircon from both gabbronorite and anorthosite corresponds to the age of melt crystallization in a magmatic chamber. The mantle origin of gabbroic rocks of the Vurechuaivench massif is confirmed by the REE patterns of three zircon generations with different crystallization sequences. The wide range of the Ce/Ce* ratio (9.96–105.24) established for zircons from gabbroic rocks of the Vurechuaivench massif indicates sharply oxidative conditions of zircon crystallization. For deepseated mantle rocks, these data can only be explained by significant contamination of the melt with country rock material.