Single-grain zircon U–Pb age constraints of the western and eastern sanukitoid zones in the Finnish part of the Karelian Province

A single-grain zircon U–Pb secondary ion mass spectrometer (SIMS) study of nine granitoid intrusions with sanukitoid geochemistry from the Finnish part of the Karelian Province shows their time-limited emplacement. The age results indicate emplacement at ~ 2715 and 2745 Ma. We observed also a significant number of relict cores in the zircons with 207Pb/206Pb ages up to 3.2 Ga, emphasizing the importance of inheritance processes in the petrogenesis of the sanukitoids. Compiled single-grain age data of the Finnish and Russian (Bibikova et al., 2005a) parts of the Karelian Province confirm the occurrence of two temporally diverging sanukitoid zones throughout the Province. The western zone shows a younger average age (~ 2718 Ma) and the eastern zone an older average age (~ 2740 Ma), with an apparent age difference of ~ 20 Ma between the zones. Most of the sanukitoid intrusions in Finland belong to the western sanukitoid zone, but the southernmost intrusions can be regarded as a part of the eastern sanukitoid zone. The boundary between the sanukitoid zones specifies the boundary of the Western and Central Karelian terranes. Worldwide sanukitoid magmatism at ~ 2.95–2.55 Ga, as reported from several Archean blocks, followed sharply after prolonged tonalite–trondhjemite–granodiorite (TTG) magmatism indicating a short-lived tectonomagmatic phenomenon at the end of convergent accretion.