Transpressive shear related to arc magmatism: The Paleoproterozoic Storsjon-Edsbyn Deformation Zone, central Sweden

The polyphase, 15-30 km wide and >200 km long Storsjon-Edsbyn Deformation Zone (SEDZ) apparently separates two major Paleoproterozoic provinces in central Sweden. Four main phases of deformation have been recognized along the zone; associated high-strain rocks are characterized by their mineralogy, microstructures, kinematic patterns, magnetic signatures, and relative ages. The mineral and stretching lineations are consistently steeply to moderately plunging. Analysis of mesoscopic shear zone populations of different generations suggests that most displacements are compatible with north-south to northeastsouthwest bulk regional shortening. The structural analysis suggests that the main ductile deformation along the SEDZ was due to dextral transpression with a steep coaxial component. Field evidence combined with published age data constrain the main deformation to the time interval circa 1.7-1.3 Ga. Synkinematic titanite from a ductile protomylonite in the SEDZ yields an U-Pb age of 1674(plus-minus)6 Ma. The combined results imply transpressive deformation broadly synchronous with, and spatially related to, volcanism and plutonism in a continental margin magmatic arc setting.