Metamorphic zones in SW Finland: monazite and zircon U-Pb dating of leucosomes in paragneisses

Abstract

<p>The Central Svecofennian Arc Complex (CSAC) and the Southern Svecofennian Arc Complex (SSAC) show<br />different ages of peak metamorphism: ~1.88 Ga in the CSAC and ~1.83 Ga in the SSAC. In the present project we study the age of the metamorphism in SW Finland. We have collected two samples. Of these the Eurajoki leucosome zircons were > 1.92 Ga, i.e.,inherited, but monazites show two populations: ~1.83 Ga and ~1.7 Ga. The zircons from the Rauma leucosome yielded two populations: ~1.86 Ga and ~1.83 Ga. The monazites show ages of ~1.83 Ga and ~1.7 Ga. We interpret that the ~1.86 Ga zircons represent the older metamorphism and the 1.83 Ga zircon and monazite group to represent the younger metamorphism. The 1.7 Ga group is unusual and needs further investigation.<br /></p>