A four day Eurogranites 2008/IGCP 510 field trip 2008 in the Oslo rift with particular emphasis on felsic to intermediate intrusive rocks and their associated mineralization.

Andersen, T., Trønnes, R. G., Nilsen, O., Larsen, A. O. (2008) Alkaline rocks of the Oslo Rift, SE Norway: A field trip with emphasis on felsic to intermediate intrusive rocks and their associated mineralizations. August 1st to 5th, 2008. Eurogranites 2008/IGCP 510 field trip 2008. Publication of the Department of Geosciences, University of Oslo, 54 p.

Fig. 1. Simplified geological map of the Oslo Graben. From Andersen et al. (2008).

Fig. 2. Simplified geological map of the area around Oslo. From Andersen et al. (2008).

The Oslo rift can be divided into three sections - the northern Nordmarka-Hurdalen batholith composed of syenitic and granitic alkaline rocks, the central Finnemarka and Frammen batholiths largely composed of biotite granite, and the southern largely monzonitic Larvik pluton and Siljan-Mylke complex. The field trip visited outcrops of basement rocks and plutonic rocks in the central and southern part of the rift. Day 1 - basement and sedimentary rocks of the Oslo graben - the basement consists of Precambrian orthogneisses of calcalkaline compositon. Cambrian conglomerate overlies the basement followed by a package of Cambro-Silurian metasediments consisting of organic-rich black shales, limestones, and sandstone. Normal faulting (small scale basin-and-range like structures) follows deposition of the Cambro-Silurian sequence. After erosion (the sub-Perminan peneplain) Permian slates, sandstones, and conglomerates were deposited followed by the eruption of basalt and rhomb-porphyry. Day 2 - Drammen and Finnemarka biotite granites including rapakivi varieties. Also the Konnerud Pb-Zn-Cu skarn deposit. Day 3 - Siljan-Mykle plutonic complex - gabbro and nepheline syenite to biotite granite and alkali granite. The following lithologies were investigated: nordmarkite, larvikite, porphyritic syenite, microsyenite, mafic-felsic magma mingling in alkali ganite, and nepheline syenite. Day 4 - Sagåsen larvikite quarry and nepheline syenite pegmatite and the layered larvikite and moonstone pegmatites at Ula. 

Fig. 3. Geological map of the Drammen and Finnemarka batholiths. From Andersen et al. (2008).