Geology, geochemistry and age of the 'Tricolor' granite and some other Proterozoic (TIB) granitoids at Trysil, southeast Norway MICHAEL HEIM, TORBJORN SKIOLD & FREDRIK CHR. WOLFF Heim, M., Skiiild, T. & Wolff, F. C.: Geology, geochemistry and age of the 'Tricolor' granite and some other Proterozoic (TIB) granitoids at Trysil, southeast Norway. Norsk Geologisk Tidsskrift. Vol. 76, pp. 45-54. Oslo 1996. lSSN 0029-196X. The Trysil granitoids of southeast Norway constitute a relatively undeformed element in the northem 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. 1800Ma 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 Ratan 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 Southwest 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; Torbjorn Skiold, 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. Introduction with associated pre-, syn- and post-volcanic syenitoid to granitoid intrusions. Recent age datings indicate that Most of southwest Fennoscandia was accreted to the oldest rocks within the TIB may represent xenolithic Baltic Shield during Palaeo- and Mesoproterozoic times. complexes with Svecofennian affinity (Patchett et al. Tectonically, and with respect to age, the region is subdi­ 1987; Jarl & Johansson 1988; Persson & Lundqvist 1993; vided into several domains (inset map in Fig. 1). Accord­ Welin 1992; Lindstrom et al. 1991). A general pattern of ing to Gaal & Gorbatschev ( 1987) these include, from westward younging events of crust formation across the northeast to southwest, the Svecofennian Domain, the TIB has been suggested by Larson & Berglund ( 1992) Transscandinavian lgneous Belt (TIB) and the South­ and Lindh (1987). west Scandinavian Domain (SSD). The last domain The granitoid rocks described here are located in the shows extensive overprint by both the Gothian/Kongs­ western, Norwegian part of the TIB. The investigation is bergian (1.75-1.5 Ga) and Sveconorwegian (1.25- focused on the geological setting, chemistry and age of 0.9 Ga) orogenies (Lindh 1987; Starmer 1993). To the the younger Trysil granites in the eastemmost Protero­ east, the SSD terminates in an eastemmost belt of zoic basement of southern Norway. One of the granites, polyphase Palaeo- to Mesoproterozoic shearing and the traditional 'Tricolor' granite, has been known since faulting, traditionally known as the 'Protogine Zone' the earliest 'geognostic' survey of Norway (see be1ow). (e.g. Larson et al. 1990), or in the somewhat further The investigation is part of a regional mapping pro­ eastward-extending Sveconorwegian Frontal Deforma­ gramme carried out by the Geological Survey of Norway tion Zone of Wahlgren et al. ( 1994). In contrast to the (NGU) including two of the authors (M. H. and F. W.). SSD, the major part of the TIB ( 1.8-1.6 Ga) and the The results of detailed fieldwork have been presented by Svecofennian Domain (2.0- 1.8 Ga) are only weakly, or Nystuen ( 1975 and 1976) and Heim ( 1989) and the not at all affected by the Sveconorwegian orogeny. Pri­ regional aspects by Wolff et al. (1995). mary relationships with respect to Gothian and Sve­ cofennian events are therefore well preserved. Geology and age relations within the TIB are well established in the Swedish areas of Dalarna, Varmland Regional setting and Småland (for a summary, see Lindstrom et al. 199 1). The volcanic rocks have traditionally been divided into The Trysil-Engerdal area is situated in the easternmost the Lower and Upper Dala 'Series' (Hjelmqvist 1966) part of southern Norway, geographically forming a lobe 46 M. Heim et al. NORSK GEOLOGISK TIDSSKRIFT 76 (1996) V • • l ~·~ • • • • • • • • • • Enger en • • • . x~· ~)(\~ . • ~)((9~ . ~)(· X. o i o o o o o o Fig. l. Geological sketch map of the Trysil-Engerdal area with sample o o localities ( modified after Siedlecka et al. o 1987 and Wolff et al. 1995). Caledonian o o o units: l. Kvitvola Nappe; 2. Osen-Røa Nappe; 3. Cambro-Ordovician cover (autochthon). Jotnian units: 4. basic dyke/ o sill; 5. basalt (6je Basalt); 6. Trysil and Dala sandstone with basal conglomerate. Transscandinavian lgneous Belt: 7. Trysil granitoids (younger Dala/Vårmland granitoids); 8. quartz syenite; 9. Trysil/ Dala porphyry; 10. greenstone/metabasalt; + + + +, 11. Older Dala/Vårmland granitoids. , Symbols; 12. Caledonian thrust fault; 13. + + +,l Post-Caledonian normal fault (Permian in , part); 14. sample site with number (4: ~, U-Pb sample); 15. main-road; 16. national + + , .;. -j,o 13 , border. Inset map after Larson & +,4 Berglund (1992) and Tucker et al. (1990): o + , 01 l"/'ls • 14 l Ruled: Transscandinavian Igneous Belt (TIB) with possible westward extension + + +,'+ + --- 15 o , jo o ol2 . ( spaced ruling). SSD: Southwest o o o + ,", + + D Scandinavian Domain. WGR = The + + 16 Western Gneiss Region. M =The Q i 1.0 15km IIVJVIVI3 Mylonite zone. P = The Protogine Zone. O = Odalen. V = Vigelen. Area of investigation marked with arrow. NORSK GEOLOGISK TIDSSKRJFf 76 (1996) Proterozoic 'Tricolor' granite, SE Norway 47 in to the Dalarna and Varmland areas of Sweden (see 'Tricolor' granite ('granit trikolor'). According to Hol­ map Fig. l). The geology of the Engerdalen area was tedahl (195 3, p. 59) this name was introduced by Kjerulf described by Holtedahl ( 1921) and essential areas around in the Vigelen area, 140 km north of Trysil, for the red-, Trysil by Heim ( 1989). The Proterozoic basement con­ blue- and green-coloured, massive granite common in the sists of predominating acid volcanic and intrusive rocks region. An early description of this granite from the of the westernmost TIB (Dala/Trysil porphyry and Dala/ Trysil area was given by Keilhau (1840), who thought it Viirmland/Trysil granitoids) with an unconformable Jot­ was older than the Caledonian cover. Because of its fresh nian (i. e. post-Gothian, 1.5-1.25 Ga) cover of as much appearance, Kjerulf (1879) and Meinich ( 1881) com­ as 1000 m sandstone (Trysil and Dala sandstone) includ­ pared the granite with the 'younger granites' in the Oslo ing a basalt flow (Oje basalt). The Jotnian rocks consti­ Region and described intrusive contacts with the Caledo­ tute the western part of an open synclinal basin. The nian arenites. Tornebohm (1896) and Reusch (1914) Sveconorwegian influence on this supracrustal cover is definitely established a pre-Caledonian age for the Trysil restricted to the formation of open large-scale folds and granites. a locally developed 'fracture cleavage' (Heim 1989). Trysil granitoids have been sampled in the narrow Primary relations are therefore well preserved within the zone between the Caledonian cover and the Trysil por­ TIB and between the TIB and the Jotnian cover phyries, close to the main valley between Trysil and (Hjelmqvist 1966; Wolff et al. 1995). TIB intrusive rocks Engerdal. Sample localities (Fig. l) are spread over a can be divided into older, weakly to moderately foliated, north-south distance of about 50 km. The sample for and younger, massive granitoids. A general correlation of the U-Pb age determination was collected at locality 4, a the Trysil granitoids with older and younger Varmland/ road-cut (national road no. 26) on the eastern shore of Dala granitoids, respectively ( Larson & Berglund 1992) Lake Engeren (sample localities are described in the is discussed below. Appendix). West and northwest of Trysil the Precambrian base­ Age relationships between different intrusions and be­ ment is nonconformably overlain by miogeoclinal Cale­ tween intrusive and volcanic rocks are not fully under­ donian sequences. Neoproterozoic arenites of the Lower stood, but a division into older, partly foliated pre- to and Middle Allochthon, thrust on a thin, autochthonous syn-vo1 canic granitoids and younger, massive, post-vol­ Cambro-Ordovician cover, are the dominating litholo­ canic granitoids has been established. All the types de­ gies (Bockelie & Nystuen 1985). Along the main valley scribed below, apart from the granodiorite, are likely to between Trysil and Engerdal, the boundary between belong to the younger granitoids. Modal compositions basement and Caledonian cover is affected by a promi­ are presented in Table l. nent fault zone with vertical offset (west-side down) locally exceeding 1000 m. In the basement around Trysil 'Trico/or' granite the fault zone appears to have a polyphase, in part Precambrian (probably Sveconorwegian) history (Heim This granite covers large parts of the investigated area 1989). Major activity, however, occurred in post-Caledo­ and corresponds to the traditional 'Tricolor' granite. The nian time, mainly during the Permian, forming the En­ samples {l , 4, liA and 14), taken from localities up to gerdalen fault (Bockelie & Nystuen 1985), characterized 25 km apart, show little variation in mineralogical com­ by cataclasites and quartz-cemented fault breccias. position and texture.