Interpretation of Nd, Sr and Pb isotope data from Archean migmatites in Lofoten-Vesterålen, Norway

Sm-Nd data for the Archean granulite and amphibolite facies migmatites of Langøy and Hinnøy in Vesterålen are presented which indicate that their protoliths formed ∼2.6 AE ago. Rubidium and U loss during a granulite facies metamorphism at ∼1.8 AE caused serious disturbance of total-rock U-Pb and Rb-Sr systems. Therefore these systems do not provide any precise age information for the granulite facies migmatites. For the amphibolite facies migmatites of Vesterålen both Sm-Nd, Rb-Sr and Pb-Pb total-rock systems give model ages of ∼2.6 AE. The results on both granulite and amphibolite facies rocks are thus in agreement. Previous interpretations based on Pb-Pb data, which indicated an age of 3.41 AE for the Archean terrane of Vesterålen, are not valid. One Sm-Nd model age from the granulite facies migmatites at Moskenesøy in Lofoten indicates that the protoliths of these migmatites formed ∼2.0 AE ago and are thus not related to the Vesterålen migmatites