NGT 60 3 175-188.Pdf
Geochronological investigations in the Oppdal area, central Norway STEINAR SOLHEIM Solheim, S.: Geochronological investigations in the Oppdal area, central Norway. Norsk Geologisk Tidsskrift, Vol. 60, pp. 175-188. Oslo 1980. ISSN 0029-196X. The isochron ages obtained have been grouped in four geological time periods: 1700-1750 m.y. (dioritic gneisses, GråhØ/TronfjeU Complexes), 1450-1500 m.y. (augen gneisses and intrusives, GråhØ/TronfjeU Complexes), -1050 m.y. (Basement Complex and Flagstone Group), and -400 m.y. (minerals). The Caledonian influence in the area seems to be smaller than previously assumed since it has on! y caused a resetting of the isotopic system between minerals. The isochron ages of- 1050 m.y. are thought to reflect secondary events during the Sveconorwegian Cycle. The time of deposition/intrusion of the rocks of the Basement Complex and the Flagstone Group is thought to be earlier than 1450-1500 m.y. One extensive metamorphism has been recognized, and 1450-1500 m.y. is considered to be a minimum age for this event. S. Solheim, Mineralogisk-geologisk museum, Sars gt. l, Oslo 5. Present address: Norsk Hydro, Oljedivisjonen, Kjørboko/len, 1300 Sandvika, Norway. The Oppdal area is situated in southern ses, granitic gneisses and augen gneisses. Eggen TrØndelag (Fig. l). Geologically the area is (1977) interprets the banded gneisses as bordered by Caledonian rocks of the Trondheim metavolcanics. In the southern part of the area Region in the east and Precambrian rocks of the the zone of outcrops of the banded gneisses Gneiss Region in the west. The aim of this work becomes narrower and it ends just south of the has been to date the various rock units in this area mapped by Eggen (1977), Evensen (1977) area and in this way to contribute to a hetter and Sjulsen (1977).
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