Thermochronology of eclogitic rocks of the Kola peninsula

According to the results of U-Pb, Sm-Nd and Rb-Sr dating of metamorphic minerals the chronology of metamorphic events and thermal history of eclogitic rocks of the Wide and Narrow Salma and eclogites of the Chalmozero area (Yona district of the Belomorian Mobile Belt, the Kola Peninsula) have been reconstructed. The conclusion has been made that the studied rocks for more than 700 Ma have been located at depth at high temperature, which lead to a disturbance of U-Pb and Sm-Nd system in minerals at temperature below the closure temperatures, obtained experimentally. Closure temperatures for U-Pb and Sm-Nd isotopic systems in rutile are largely dependent on the grain size and cooling rate of rocks. Closure temperature for U-Pb system in 0.3 mm rutile grains can be 600 C, higher than usually accepted 400-450 °C. Closure temperature for Sm-Nd system in rutile is about 350 C, significantly lower than that for U-Pb system. Duration of metamorphic processes and cooling rate of rocks provide constrains on geodynamic models.