T-t EVOLUTION OF THE EARLY PROTEROZOIC ROCKS IN THE NORTHERN LADOGA REGION FROM THE DATA ON U-Pb, Rb-Sr AND Sm-Nd SYSTEMS IN MINERALS

This paper presents the results of a study of isotopic systems in minerals and rocks in southern margin of the epi-Archean Karelian craton in the zone of its junction with the Svecofennian mobile belt. U-Pb, Sm-Nd and Rb-Sr mineral ages of metamorphic rocks allowed reconstructing a T-t trend during similar to 1.88-1.61 Ga, which reflects a wide-ranging cooling history of metamorphic rocks from the peak values of about 650-700 degrees C at 1.88-1.79 Ga (U-Pb age of monazites and apparent oldest Sm-Nd age of amphiboles) to 300-400 degrees C at 1.61 Ga (model Rb-Sr age of biotites) in zones of low- and medium-temperature metamorphism. The specificity of removal of deep-seated rocks to the present-day erosion surface and the reconstructed T-t trend comply with the development of thrust-nappe structures during the exhumation of the Svecofennids. It is also assumed that differential vertical block movements played a significant role during the post-orogenic extensional collapse and neorifting.