Titanite-rutile thermochronometry across the boundary between the ArchaeanCraton in Karelia and the Belomorian Mobile Belt, eastern Baltic Shield

U-Pb isotopic dating has been carried out on titanites and rutiles from the Karelian Protocraton, the Belomorian Mobile Belt and the intervening junct ion zone. These are some of the principal Archaean crustal units in the Bal tic Shield which have undergone regeneration to various degrees during the Palaeoproterozoic. Palaeoproterozoic resetting of U-Pb titanite ages was co mplete in the Belomorian Belt and almost complete in the junction zone. whi le it hardly affected the Karelian Protocraton. In the latter, major crusta l cooling occurred at 2.71-2.69 Ga after a major igneous event at 2.74-2.72 Ga, but a tectonothermal event at 2.65-2.64 Ga was less comprehensive. In the Belomorian Belt, a northeastern marginal zone immediately underlying th e collisional-thrusting suture of the Lapland-Kola orogen has somewhat high er titanite ages of ca. 1.94-1.87 Ca than the central zone where these ages range between 1.87 and 1.82 Ga. Comparison between the titanite and rutile U-Pb ages suggests a postorogenic cooling rate between 2 and 4 degrees /Ma in these parts of the Belt. The Neoarchaean junction zone between the Kare lian and Belomorian provinces was a zone of particularly intense tectonic, magmatic and hydrothermal activity during or after the Palaeoproterozoic La pland-Kola orogeny. Dominant, newly grown titanites in that zone have ages as young as 1.78-1.75 Ca. and the age differences between the titanite and rutile U-Pb ages are substantially smaller than elsewhere. (C) 2001 Elsevie r Science B.V. All rights reserved.