Isotopic age determinations in Bergslagen, Sweden: VI. acid metavolcanics of the Bergslagen Supracrustal Series, Grythyttan-Hjulsjo area

Abstract

Metavolcanic rocks of the Bergslagen Supracrustal Series in the Grythyttan-Hjulsjö area, central Sweden, are 1.9-1.8 Ga old according to published zircon U-Pb data. Rhyolitic rocks from Gillershöjden-Kullberget and Norr-Algen and metatuffites from Salbosjön and Kranktorp give Rb-Sr whole-rock ages of 1.6 ± 0. 1 Ga and 1.8 ± 0.1 Ga, respectively. The rhyolitic rocks show reset Rb-Sr whole-rock ages due to a thermal event related to the intrusion of 1.7-1.6 Ga old granites,whereas the Rb-Sr whole-rock ages of the metatuffites still approximate the age of emplacement and earliest metamorphism of the supracrustals.