Transpressive shear related to arc magmatism: The Paleoproterozoic Storsjön‐Edsbyn Deformation Zone, central Sweden

Abstract

The polyphase, 15–30 km wide and >200 km long Storsjön‐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 northeast‐southwest 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 ± 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.

Relationships among magnetic fabrics, microfractures and shock pressures at an impact crater: A case study from Lockne crater, Sweden

“…5, 6c, d). In agreement to the regional flat-lying, dip b30°, trend of the dolerite sills and dykes (Bergman et al, 2006), the magnetic fabrics represent magmatic emplacement and simultaneous plastic deformation, which is also manifested by curved and deformed plagioclase crystals (Fig. 2f).…”

“…The granites are cut by vertical faults, some running tangentially to the periphery of the crater, and are intruded by Mesoproterozoic, c. 1.2 Ga ago, dykes and sills known as Åsby dolerite (Fig. 1;Bergman et al, 2006;Gorbatschev and Gaál, 1987;Lindström and Sturkell, 1992;Söderlund et al, 2005).…”

Migmatization related to mafic underplating and intra- or back-arc spreading above a subduction boundary in a 2.0–1.8 Ga accretionary orogen, Sweden

“…This boundary continued to be active but in more outboard positions to the south-west around 1.7 Ga (Nyström, 2004;Bergman et al, 2006b) and later during the Mesoproterozoic (Åhäll and Connelly, 2008), in what Åhäll and Connelly (2008) described as a remarkably persistent convergent-margin system. However, further evaluation of the degree of allochthoneity of the 1.7-1.5 Ga accretionary orogenic event(s) relative to the older continental margin to the east is required, due to crustal reworking during the 1.1-0.9 Ga Sveconorwegian orogeny.…”

“…The northern boundaries of the Ljusdal, Bergslagen and Små-land lithotectonic units are located along the Hassela Shear Zone (Högdahl and Sjöström, 2001;Högdahl et al, 2012); the Hagsta Gneiss Zone (Högdahl et al, 2009) and Storsjön-Edsbyn Deformation Zone (Bergman et al, 2006b); and the Loftahammar-Linköping Deformation Zone (Stephens et al, 1997;Beunk and Page, 2001;Wik et al, 2005), respectively ( Fig. 2A).…”

Danopolonian migmatization of Mesoproterozoic sedimentary rocks in southernmost Sweden: a SIMS zircon study

“…There, an array of various terranes was accreted at c. 1.73 -1.55 Ga during the Gothian orogeny, and several depositional basins were developed (Gaál & Gorbatschev 1987;Bergman et al 2006;Å häll & Connelly 2008). Also later, between c. 1.55 and 1.40 Ga, Fennoscandia was involved in intense intracontinental extensional to compressional deformation and magmatism.…”