The age of the granulite facies metamorphism in the Bamble Belt has long been a matter of debate. Samples from fourlocalities 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 metamorphis mending 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.

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Tags: Norway