Precambrian geochronology of south-eastern Sweden

Abstract

Geochronological investigations in south-eastern Sweden, based on U–Pb, Rb-Sr and K–Ar determinations, yield ages between 2465 Ma and 900 Ma. The oldest age, 2465 Ma, is obtained on zircons from the Västervik quartzite. Intrusion of synkinematic Svecokarelian granites occurred between 1970 Ma and 1840 Ma ago. Intrusion of late-kinematic Svecokarelian granites then followed, accompanied by wide-spread migmatization, deformation and folding affecting the older rocks. Between 1730 Ma and 1655 Ma, different generations of the Småland porphyries and Småland granites were emplaced. The last dated activity in postorogenic time was the intrusion of the Småland dyke porphyries 1655 Ma ago. The effect of the intrusion of the Småland granites was intense in the Västervik area and caused a resetting of the Rb-Sr ages of the older granites to 1665–1655 Ma. The lowering of the K–Ar ages to approximately 1400 Ma is probably due to anorogenic intrusions, like the Götemar granite at 1380 Ma, and metamorphic events in southern and south-western Sweden. The K–Ar results also confirm that the Sveconorwegian orogeny had no influence in south-eastern Sweden.