The Trysil granitoids of southeast Norway constitute a relatively undeformed element in the northern part of the late Palaeoproterozoic Transscandinavian Igneous Belt (TIB) exposed southeast of the Scandinavian Caledonides. In the Trysil-Engerdal area younger granites intruded foliated granitoids (ca. 1800 Ma older Yarmland type) and lower parts of the Dala/Trysil volcanic rocks. Two main types of younger granite are distinguished. The traditional 'Tricolor' granite with pink K-feldspar, bluish quartz, greenish plagioclase and dark patches of biotite probably intruded an amphibole-bearing, mesoperthitic granite. Both varieties are I-type granites, generated in a within-plate tectonic setting. They have similar trace and major element geochemistry, and their Nd isotopes indicate a source characteristic of a depleted mantle component and a short crustal residence time. According to U-Pb dating of zircons, the 'Tricolor' granite intruded 1673 ± 8 Ma ago. A somewhat younger Rb-Sr age of 1642 ± 35 Ma has been obtained from six whole-rock sarnples of the two granites. The younger Trysil granites can be correlated in age and tectonic setting with the post-volcanic Dala (e.g. Garberg) and Ra tan granites further east in the Swedish part of the TIB. It is conceivable that this type of granitoid (e.g. the Odalen granite) extends westwards in to the South west Scandinavian Domain as far as the Mylonite Zone, with an increasing intluence from Sveconorwegian events.
Michael Heim* & Fredrik Chr. Wolff, Norges geologiske undersøkelse, Postboks 3006 Lade, N-7002 Trondheim, Norway;
Torbjörn Skiöld, Laboratoriet for isotopgeologi, Naturhistoriska riksmuseet, Box 50007, S-104 05 Stockholm, Sweden.
*Present address: Norges Landbrukshøgskole, Inst. for jord- og vannfag, Postboks 5028, N-1432 Ås, Norway.