SmNd geochronology of Sveconorwegian granulite facies mineral assemblages in the Bamble Shear Belt, South Norway

Abstract

Abstract 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 (∼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.