Geochronology of high-grade metamorphism in the Sveconorwegian belt, S. Norway: U-Pb, Th-Pb and Re-Os data

Abstract

The Mesoproterozoic crust in the southwest part of the Fennoscandian Shield was reworked during the Sveconorwegian orogeny (Pasteels & Michot 1975; Berthelsen 1980; Demaiffe & Michot 1985; Falkum 1985). Though this idea has been well established in the literature for decades, it is not until recently that the Sveconorwegian age of high-grade metamorphism was established in all lithotectonic units of the Sveconorwegian orogenic belt. Especially controversial was the timing of granulitefacies metamorphism in the Bamble Terrane in south Norway (Kullerud & Dahlgren 1993) and the Eastern Segment in southwestern Sweden (Johansson et al. 1991). Today, the objective is to improve the chronologic and tectonic model for the Sveconorwegian orogenic event itself. In this paper, monazite, zircon and titanite U-Pb data and molybdenite Re-Os data are reported from metamorphic rocks to date high-grade metamorphism in the four main lithotectonic units in south Norway. A pressure-temperature estimate is reported for one critical sample. These data were derived from material collected over several years, in the course of regional geologic investigations, and analysed using different analytical methods. Together, they provide a significantly enlarged field coverage, and point to important differences in the metamorphic evolution of the four lithotectonic units. These data are integrated in an orogen-scale tectonometamorphic model in a companion paper (Bingen et al. 2008).