U-Pb zircon determinations from the Keikyä Breccia and other sites in the Svecofennides: indications of a Svecokarelian protocrust

Heterogeneous zircon populations from four different localities within the Svecofennian area in Finland demonstrate that the ca. 1890 Ma old syntectonic granitoids contain older material, probably belonging to the ca. 1950 Ma Svecofennian protocrust, the influence of which is also evident in metaturbidites deformed by the Svecokarelian orogeny