Petrology of nattanen-type granite complexes, northern finland

Abstract

The Nattanen-type granites form a group of post-tectonic and post-metamorphic 1.77 Ga-old epizonal multiple granite intrusions in the Granulite Belt—granitic gneiss surroundings in northern Finland. The granite complexes (the Tepasto, Pomovaara and Nattanen stocks and the Riestovaara batholith in Finland and the Juvoaivi stock in the U.S.S.R.) are composed of various slightly peraluminous microcline—plagioclasebiotite granites (monzogranites) that contain sphene and magnetite as typical minor constituents. Geochemical evolution within the complexes is demonstrated by the increase of SiO 2, and Rb, and decrease of TiO 2, FeO ∗, MgO, CaO, Sr, Ba and Zr from the oldest to the youngest granite varieties. Molybdenum mineralization is associated with the latest intrusive phases of the Tepasto and Juvoaivi stocks. The isotope geochemical studies indicate a major Archaean crustal component in the source of the Nattanen stock that is situated within the early Proterozoic Granulite Belt.