Isotopic age determinations in Bergslagen, Sweden: IV granites of the Grängen area, east of Hjulsjö

Abstract

Rb-Sr whole-rock isotope analyses of ten samples of Grängen granite yield a best-fit line corresponding to an age of 1663 ± 51 Ma with an initial 87Sr/86Sr ratio of 0.70844 ± 0.00578. Four samples of Tallåsberget granite give a best-fit line corresponding to an age of 1639 ± 185 Ma with an initial 87Sr/86Sr ratio of 0.70191 ± 0.04241. Isochron relationships appear disturbed by the low-grade retrograde metamorphism which has affected the granites. Taking account of the limits of error it is suggested that the Grängen and Tallåsberget granites in the Hjulsjö region, Bergslagen, Central Sweden, are coeval with the 1.7-1.6 Ga granites of the Småland and Värmland Groups in S and SW Sweden.