Zircon ages of metavolcanic and synorogenic granitic rocks from the Svärdsjö and Yxsjöberg areas, south central Sweden

Radiometric dating of Svecokarelian metarhyolites and prekinematic granitoids from Bergslagen, south central Sweden

“…U-Pb zircon datings of a leptite and a prekinematie granite at Svardsjo gave upper intercepts of 1900f 19 Ma and 1873:;; Ma, respectively (Aberg et al 1983). A dating of the prekinematic Horrsjo granite gave a U-Pb zircon age of 1850Z; Ma (Aberg et al 1984) and a lower intercept of 304 Ma, similar to that of the prekinematic granite (76319) dated in this study.…”

“…The Ludvika area was intruded by latekinematic granites around 1755 Ma (Aberg, unpublished results) and postkinematic granites around 1700 Ma (Aberg & Fredrikson 1984). Both events as well as post-Svecokarelian episode(s) of lowgrade metamorphism (Nystrom & Levi 1980) might have affected the older rocks.…”

“…A uranium loss related to zircon size would also permit greater loss for smaller grains due to larger surfacelvolume ratio. Such cases have been described for the IlorrsjB granite (Aberg et al 1983) and leptites and granites in the Svirdsjii-Yxsjoberg areas (Aberg et al 1984).…”

“…The contact between granitic and tonalitic varieties is gradual in locality 76319. The metavolcanics are of rhyolitic composition and very similar to those dated with the U-Pb method (zircon) in the Svardsjii-Yxsjoberg areas (Aberg et al 1984), i.e. they are fine-grained rocks with quartz and feldspar phenocrysts in a quartz-feldspar-biotite(-chlorite) groundmass.…”

Radiometric dating of the Horrsjö granite, south central Sweden

“…The reversed position of the Horrsjii granite zircon size fractions on discordia and the nearness to the upper intercept with concordia sug- Aberg et al (1983) where zircons even showed reversed discordance due to uranium loss. However, the uranium loss in the Horrsjii zircons must have been accompanied by lead loss in order to maintain the zircons positions on discordia.…”