Late Palaeoproterozoic monazite and titanite U–Pb ages in the Archaean Suomujärvi Complex, N-Finland

The paper documents a late Palaeoproterozoic episode of metamorphism and anatexis in the Suomujärvi Complex, an Archaean enclave in the Palaeoproterozoic Central Lapland Granitoid Complex of northern Finland. U–Pb ages were obtained from monazite and titanite in four Archaean granitoid rocks, one quartzite and a massive granite. The results show that growth of monazite and titanite in these rocks spanned a period of about 15 million years between 1780 and 1765 Ma, presumably reflecting complex processes of metamorphic (re-) crystallisation, invasion by granitic dykes, veins and fluids and post-peak-metamorphic retrogression. The timing of this activity corresponds to post-orogenic granitoid magmatism throughout the Baltic Shield. In this region, between the Lapland-Kola and that of Svecofennian orogens, it may represent a retarded response to their coeval, ca. 1.9 Ga convergent collision. The results support a proposed affinity of the Suomujärvi Complex with the Belomorian rather than the Archaean Karelian Province.