Apatite Fission-Track Ages from the Archean Karelian Craton: First Results

The first apatite fission-track ages (AFTA) from surface samples of geological objects within the Archean Karelian Craton–the Kivakka massif (901 ± 95 Ma (±2σ)), the Pirttiguba dyke (957 ± 87 and 1024.3 ± 91 Ma) and the Ropruchey sill (990 ± 101 Ma) have been obtained. The results indicate the absence of regional thermal events above 120°C within the Karelian Craton over the past billion years. This suggestion is consistent with fission-track data from conjugate sites located in the Karelian Craton and the Svecofennian orogen within Finland. Models of the thermal evolution of the studied magmatic bodies indicate monotonic cooling of rocks of the Karelian Craton during the Phanerozoic at a rate of 0.12–0.31°C/Myr. This corresponds to a denudation rate of 6–16 m/Myr (assuming a geothermal gradient value of 20°C/km).