NEW ISOTOPIC DATA ON THE PROTOLITH AGE AND EVOLUTIONARY STAGES OF THE CHUPA FORMATION, BELOMORIAN BELT

Abstract

New isotopic-geochemical data were obtained in order to date the distinct evolutionary stages of the Chupa Formation in the Belomorian Mobile Belt. Reference U-Pb and Sm-Nd isotopic data are reported for relict rock volumes, which were the least altered during several migmatization stages. Our results indicate that the initial volcanism processes took place at 2850 ± 30 Ma, and high-grade metamorphism is dated at 2820 ± 20 and 2720 ± 20 Ma. The age of the protolith of the metasediments, determined using the cores of detrital zircon grains on a secondary-ion mass spectrometer, lies within the range of 2900-3000 Ma and is consistent with the whole-rock Sm-Nd age values.