LATE SVECONORWEGIAN (GRENVILLE) HIGH-PRESSURE GRANULITE FACIES METAMORPHISM IN SOUTHWEST SWEDEN

Mafic granulite, garnet amphibolite and charnockite occur in the southwest Swedish part of the Baltic Shield. This part is generally considered to be the continuation of the Grenville collisional belt in Canada. The area with granulite facies rocks, the Southwest Swedish Granulite Region (SGR), is considerably larger than previously thought. The SGR is bounded to the east and west by two major tectonic zones. The first quantitative age data and P-T determinations for the high-grade metamorphism in the SGR are presented. Conventional geothermobarometry was applied to mafic granulites from five localities. The estimated P-T conditions for the peak of metamorphism range from 705-degrees-C and 8.1 kbar at Hallandsas in the south, to 770-degrees-C and 10.5 kbar at Ullared in the north (medium- to high-P granulite facies conditions). Sm-Nd geochronology on minerals from the mafic granulites at Hallandsas and Ullared give late Sveconorwegian (Grenville) ages of 907 +/- 12 and 916 +/- 11 Ma for the high-grade metamorphism, which is considerably younger than previously thought. Our results stress the hitherto underestimated importance of the late Sveconorwegian high-grade metamorphism in the southwestern part of the Baltic Shield.