Petrology and metallogeny associated with the Tryvann Granite Complex, Oslo Region.

Abstract

The Tryvann Granite Complex (TGC) comprises four separate intrusive bodies within the Oslo Graben. It constitutes a differentiated suite of young (240- 245 Ma) alkaline quartz syenites and granites derived from a strongly fractionated, hydrous residual melt which was emplaced during the collapse of the Bærum Cauldron. The emplacement occurred contemporaneously with the formation of the ring-dyke complex. Intramagmatic vein-type molybdenite, pyrite and Fe-oxide mineralizations occur associated with a wisdespread albitic hydrothermal lteration confined chiefly to fracture zones within the TGC complex. On a regional scale, the geological pattern, as revealed by gravimetric anomalies, and the spatial metamorphic and metasomatic alteration patterns adjacent to the southern part of the Bærum Cauldron, indicate the existence of a (partly) hidden, NE-SW trending, elongated plutonic complex to which the TGC may be related. This complex apparently follows a central volcanic axis which constitutes a possible plutonic link between the Bærum and Nittedal Cauldrons of the Oslo Graben.