Geochronology of eclogite facies metamorphism in the Sveconorwegian Province of SW Sweden

Decompressed eclogites in the Sveconorwegian Province, SW Sweden, have been dated using U-Pb geochronology. Zircons are common as inclusions ill garne t and kyanite, and other minerals in the decompressed eclogites. Titanite i nclusions are found exclusively in the core of garnets. The mineral inclusi ons and the chemical zoning of the garnets suggest inital growth under prog rade amphibolite facies conditions followed by eclogite facies metamorphism and subsequent decompression through the high-pressure granulite and upper amphibolite facies. The zircon and titanite thus formed prior to the eclog ite stage of the P-T path. The age of the eclogite forming event was determ ined by ion probe dating of zircon inclusions in garnets. The obtained age of 972 +/- 14 Ma is the maximum age of the eclogitisation. The age of the t itanite inclusions in garnet is 945 +/- 4 Ma. This age is similar to other U-Pb ages of titanite in the region which suggest that the titanite has bee n isotopically reset and that the age reflects cooling. The mode of occurrence. textural relationships and the chemical homogeneity suggest that the zircons formed from Zr released from magmatitic Fe-Ti oxi des and possibly amphiboles during breakdown of magmatic minerals at the on set of the Sveconowegian metamorphism. Spot analyses of complex zircons from a granitic dyke in the eclogite yield ed an age of 1403 +/- 15 Ma for magmatic cores and an age of 963 +/- 22 Ma for metamorphic rims. The older age is a minimum age of the eclogite protol ith and correspond to the age of a generation of granites in the region. Th e rim age is within error identical to the age of eclogite metamorphism. Th e eclogite metamorphism in SW Sweden is younger than its Grenvillian counte rparts in Scotland, Canada and USA. (C) 2001 Elsevier Science B.V. All righ ts reserved.