Continental margin magmatism and migmatisation in the west-central Fennoscandian Shield

1.8 Ga magmatism in southern Finland: strongly enriched mantle and juvenile crustal sources in a post-collisional setting

“…Chapter 8), results in initial 87 Sr/ 86 Sr(t) values between the unrealistically low 0.6977 (sample #5) and 0.7062. All except two samples (#2a and #5) have values higher than that estimated for the uniform reservoir at 1.80 Ga (0.7024;McCulloch and Chappell 1982;Faure 2001; Figure 15), resulting in positive e Sr (t) values (Table 2) The reference data are collected from Martin et al (1983), Wilson et al (1986), Valbracht (1991), O'Brien et al (1993), Valbracht et al (1994), Claesson and Lundqvist (1995), Billström and Weihed (1996), Andersson (1997), Kononova et al (1999Kononova et al ( , 2000, , Andersson et al (2002Andersson et al ( , 2006aAndersson et al ( , 2007, Högdahl et al (2008), Rutanen and Andersson (2009 and references therein), Woodard and Huhma (in review …”

Geochronology of the Palaeoproterozoic Kautokeino Greenstone Belt, Finnmark, Norway: Tectonic implications in a Fennoscandia context

“…This interpretation was already suggested by Olesen & Sandstad (1993). (2) The Ráiseatnu Complex represents a reworked Svecofennian sedimentary-volcanic succession deposited in the c. 1960-1850 Ma time interval, akin to the widespread basins exposed southwestwards in Finland and Sweden in the Svecokarelian orogen (Lahtinen et al, 2005;Korja et al, 2006;Högdahl et al, 2008). This basin is possibly far travelled and unrelated to the Kautokeino Greenstone Belt.…”

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.…”

“…12). The older metamorphic event was accompanied by synmigmatite ductile shearing while the stromatic migmatite formed at 1.83-1.82 Ga was affected by folding and later ductile shearing (Högdahl and Sjöström, 2001;Högdahl et al, 2008Högdahl et al, , 2012Wik et al, 2009).…”

“…This change involved a shift from a short period of crustal shortening with transpressive ductile strain around 1.87-1.86 Ga (Hermansson et al, 2008a;Högdahl et al, 2009;Stephens et al, 2009) to a longer period of extension or transtension inside the time interval 1.86-1.83 Ga (Stephens et al, 2009), the latter resulting in the development of a so-called intraorogenic sedimentary basin (Bergman et al, 2008). The time period between 1.87 and 1.84 Ga also involved considerable igneous activity related to subduction processes along an active continental margin (TIB-0; Andersson et al, 2004;Högdahl et al, 2008;Stephens et al, 2009;Kleinhanns et al, 2015). The data presented here suggest that ductile strain related to the crustal shortening event possibly occurred a little later around 1.86-1.85 Ga in the Småland lithotectonic unit.…”