Maximum age of the synmetamorphic Svecokarelian fold phases in south central Sweden

Abstract

At St. Vika in south central Sweden, a pegmatite has conformably intruded an early Proterozoic, Svecokarelian limestone. Isoclinal folds F1 along N-S axes and subsequent crossfolds F₂ caused the present structures. Zircons separated from the pegmatite have an age of 1854 ± 5 Ma (2sd), which is considered to reflect the time of intrusion of the pegmatite and consequently the maximum age of the deformation. The Rb-Sr whole rock age of the pegmatite is 1777 ± 24 Ma (2 sd). The closure of the Rb-Sr whole rock system reflects the cessation of the Svecokarelian late-kinematic actitvity and a time when the bedrock had cooled below the threshold for ⁸⁷Sr migration.