The geochemistry of the Sorvik granite—a TIB-1 granite

Abstract

The Sörvik granite occurs as rounded massifs in the Revsund granite in central Sweden. The rock is medium-grained with rounded quartz crystals (‘drop quartz’) and occasional, sometimes albiterimmed megacrysts of K-feldspar. It is a faintly peraluminous I-type granite with some A-type affinities showing a limited chemical variation. The SiO2 content normally varies between 68 and 77 weight%. The rock is fairly high in Rb and rather low in Ta, Nb, Sr and Ti. REE patterns are weakly differentiated with moderate negative Eu-anomalies. Chemically, the Sörvik granite is more similar to rapakivi granite than to the neighbouring Revsund granite. εNd at the time of intrusion varies between −1.5 and −0.9. Zr-thermometry gives a minimum temperature around 800°C for the magma generation. The source rock is modelled as a granodioritic rock. Anhydrous melting due to biotite breakdown supplies insufficient amounts of water to meet a reasonable rheologically critical melt percentage. If the temperature estimate is correct, either low degrees of granitic melt might segregate from its place of origin, or some water was added during melting. A local, probably late-magmatic F-metasomatism has caused a Nb-Ta-U-Th anomaly resulting in specific Nb minerals.