NJG87-3-04
2007
Silurian gabbro-diorite-trondhjemite plutons in the Trondheim Nappe Complex, Caledonides, Norway: petrology and U-Pb geochronology
87
3
pp. 329-342
978-82-92394-39-7

Large bodies of trondhjemite, up to 200 km2 in size and locally coexisting with diorite and gabbro, represent an important plutonic component of the Köli Nappes in the Trondheim Region. Zircon (and titanite) U-Pb geochronology shows that the earliest suites formed between 438.7 ± 1.5 and 437.6 ± 1.3 Ma, the ages of the Reitstøa and Gia Complexes. The same age of 437.8 ± 2.3 Ma was also obtained for a monzonite from the layered, mafic-ultramafic, Fongen-Hyllingen Complex. The bimodal Vålåsjø Complex yields ages of 435.6 ± 2.3 and 435.1 ± 2.5 Ma. The youngest trondhjemites lack mafic correlatives and formed at 432 ± 4 (Toset) and 431 ± 4 Ma (Olaberget). They also contain xenocrystic zircons with a mixed Archaean and Palaeo- to Mesoproterozoic provenance. Coeval intrusions are common throughout the Köli Nappes of the Upper Allochthon along the entire length of the Scandinavian Caledonides and represent widespread magmatism during the terminal stages of Iapetus Ocean closure, immediately prior to the peak of Scandian metamorphism and thrusting onto the Baltoscandian margin of the Baltic craton.

Odd Nilsen, Department of Geosciences, University of Oslo N-0316 Oslo, Norway (This email address is being protected from spambots. You need JavaScript enabled to view it.);
Fernando Corfu, Department of Geosciences, University of Oslo N-0316 Oslo, Norway (This email address is being protected from spambots. You need JavaScript enabled to view it.);
David Roberts, Geological Survey of Norway, N-7491 Trondheim, Norway (This email address is being protected from spambots. You need JavaScript enabled to view it.)

This email address is being protected from spambots. You need JavaScript enabled to view it.
029-196X
Print