Svecofennian crustal deformation of the Baltic Shield and UPb age of late-kinematic tonalitic intrusions in the Burträsk Shear Zone, northern Sweden

Abstract

Post-collisional crustal deformation of the Svecofennian region involved (1) lateral escape movements along crustal-scale dominantly dextral shear zones that roughly correspond to boundaries between volcanic and sedimentary terranes, and (2) crustal thickening eventually resulting in regional migmatite-formation and granitic magmatism. UPb dating of titanite from skarnified limestone in the contact-metamorphic aureole of late-kinematic tonalites in the Burträsk Shear Zone, one of these major dextral shear zones in northern Sweden, yields 1825 +4 −3 Ma (2σ). This age corresponds to the end of ductile deformation along the Burträsk Shear Zone, but it also coincides with important migmatite formation and granite emplacement in the southern part of the Svecofennian region. The available geochronologic data from the Svecofennian region illustrate that as migmatites and granites become regionally important in the interior of sediment-dominated terranes, movements along shear zones at the margin of terranes become subordinate and compressional deformation is concentrated into the interior of the terranes.