SM-ND GEOCHRONOLOGY OF SVECONORWEGIAN GRANULITE-FACIES MINERAL ASSEMBLAGES IN THE BAMBLE SHEAR BELT, SOUTH NORWAY

The age of the granulite facies metamorphism in the Bamble Belt has long been a matter of debate. Samples from four localities in the coastal section of the belt have, therefore, been used to obtain Sm-Nd mineral ages. All gave dates within the range 1070-1100 Ma. Earlier Rb-Sr data of Field et al, had placed the maximum metamorphism of the region at 1540 Ma. These authors deduced that any subsequent metamorphism in the Sveconorwegian (similar to 1100 Ma) was low grade since the Rb-Sr system had not been completely reset at this time. New U-Pb data, published elsewhere, indicate two periods of deformation and metamorphism; a pre-Sveconorwegian metamorphism at 1437 +/- 8 Ma and a Sveconorwegian period at 1100 Ma. Our Sm-Nd data indicate that the Sveconorwegian period lasted for at least 50 Ma, and included granulite facies metamorphism ending at 1095 Ma, We further deduce that Rb-Sr whole-rock systems were not necessarily totally reset during the granulite facies metamorphic event. Our conclusions represent a return to older interpretations concerning the significance of the Sveconorwegian event.