A fission-track age for the Skaergaard intrusion and the age of the East Greenland basalts

Abstract

We report here a fission-track age of 54.6 ±1.7 m.y. for the Skaergaard intrusion, East Greenland, using zircons separated from two different rocks that give concordant results. This age is consistent with previously reported K-Ar ages for the surrounding basalts of 55 to 60 m.y. but not with the more recent K-Ar results that give ages of <50 m.y. It is also in accordance with the known age of 50.0 ± 0.4 m.y. for the neighboring alkalic intrusion known from field evidence to be younger. This date is significant because several authors have argued a key position for the East Greenland magmatic activity relative to the dating of the lower Tertiary magnetic time scale. © 1977 Geological Society..