Plate tectonic settings of the Svecofennian Palaeoproterozoic volcanic rocks at Hamrånge and Loos, south central Sweden, based on geochemical data

Mafic plutonic rocks in a continental‐arc setting: geochemistry of 1.87–1.78 Ga rocks from south‐central Sweden and models of their palaeotectonic setting

“…According to Bergman et al (2008) the youngest detrital zircons found in metasedimentary rocks indicate that sedimentary basin formation occurred at 1.85-1.82 Ga in this general area, which after the cessation of the Ljusdal magmatism was stabilized to a continental back-arc region. The juvenile character of the Loos sediments ) and basalts (Ogenhall 2007), as well as the short time of formation (1.87-1.86 Ga), suggest an oceanic setting, shortly before microcontinent docking.…”

“…This setting is supported by the geochemistry that indicates continental-arc character, transitional to oceanic. Contemporaneously, in the area immediately to the north of Bergslagen, little continental crust appears to have been present; for example early volcanic sequences of the Hamrånge area (1.89 Ga; Bergman et al 2008) show oceanic-arc type compositions, while a transitional arc-MORB affinity characterizes the volcanic sequence at Loos somewhat later (at c. 1.86 Ga; Delin and Persson 1999), indicating a transition from oceanic-arc to back-arc environments (Ogenhall 2007). Subduction both towards the north beneath the Bothnia microcontinent and towards the south below the Bergslagen microcontinent have been proposed for the period 1.89-1.87 Ga (Nironen 1997;Lahtinen et al 2005) and this oceanic segment is inferred to have been consumed by 1.86 Ga.…”

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

“…It has been proposed that the rocks in all units formed by subduction-related processes along a convergent, active continental plate margin (e.g. Andersson et al, 2004;Mansfeld et al, 2005;Ogenhall, 2007;Hermansson et al, 2008a;Åhäll and Connelly, 2008;Högdahl et al, 2008;Stephens et al, 2009;Johansson et al, 2012;Johansson and Hålenius, 2013). The differences between the lithotectonic units are presented in more detail in Sections 2.3 and 2.4, with focus on the Bergslagen and Småland lithotectonic units where new data have been acquired.…”

Deep drilling in a Palaeoproterozoic hot orogen – potential for deciphering the orogenic accretion and physical properties of a tectonically layered crust

“…Several E-dipping thrusts have been recorded in the metasupracrustal rocks but also in the 1.86 Ga Ljusdal granitoids in the footwall to the west. Geochemical studies define the metavolcanic rocks as formed in an oceanic island arc setting (Ogenhall 2007) while the Ljusdal granitoids formed in a continental margin setting . Consequently the thrusts may reflect a terrane accretion of the outboard Hamrånge group to the continental margin.…”