A U–Pb dating of the Askersund granite and its marginal augen gneiss

Abstract

U–Pb zircon ages of 1848±15 and 1842⁺²³ _-13 Ma have been obtained for the coarse porphyritic Askersund granite (‘Filipstad type’) and for its marginal augen gneiss, respectively. The results indicate that the onset of magmatism in the Transscandinavian Igneous Belt (TIB) took place in connection with the late Svecofennian orogenic development. They also support a structural model implying that regionally deformed and folded marginal parts of older granitoid intrusions in the TIB have similar ages as the isotropic and discordant central parts. The deformation is reflected in the morphology of the zircons but does not affect the isotopic ages.

Key Words:

• U–Pb dating
• zircon
• Transscandinavian Igneous Belt
• Småland–Värmland granitoids
• late Svecofennian
• tectonic regime
• augen gneiss
• deformation