40Ar/39Ar hornblende geochronology from the Forsmark area in central Sweden: Constraints on late Svecofennian cooling, ductile deformation and exhumation

Brittle tectonic evolution and paleostress field reconstruction in the southwestern part of the Fennoscandian Shield, Forsmark, Sweden

“…Summary of radiometric age data and the bedrock geological evolution in the Forsmark area (data from Hermansson et al [2007, 2008a, 2008b], Sandström et al [2008, 2009], and Söderlund et al [2008, 2009]). Only a selection of (U‐Th)/He data from drill core KFM01A, as discussed by Stephens and Wahlgren [2008], is shown.…”

“…Around 1.8 Ga, the area slowly cooled beneath the 500°C geotherm (Figure 3 [ Hermansson et al , 2008b]) and ductile deformation under lower amphibolite‐ to upper greenschist‐facies conditions was spatially constrained along deformation zones within the subvertical, high‐strain belts that strike WNW‐ESE or NW‐SE (Figure 2 [ Stephens et al , 2008b]). A deformation zone refers to an essentially 2‐D structure, along which there is a concentration of brittle, ductile or combined brittle and ductile deformation, without any specification whether there has or has not been shear movement along the zone [ Stephens et al , 2007].…”

“…Determination of the relative chronology between the different paleostress fields and of their relationships to the overall tectonic evolution in southeastern Sweden is a formidable challenge, due to the Paleoproterozoic age of the rocks and the limited control on the timing of the different phases of brittle deformation. Despite these limitations, an attempt is made to relate the reconstructed paleostress fields to the already identified main tectonic phases in this part of the Fennoscandian Shield, with the help of available absolute dating of the ductile deformation, the regional cooling history and the fracture mineralogy [ Hermansson et al , 2007, 2008a, 2008b; Sandström et al , 2008, 2009; Söderlund et al , 2008, 2009]. This contribution also takes account of a similar study that was completed earlier at the Laxemar‐Simpevarp site [ Viola et al , 2009].…”

Review of the deterministic modelling of deformation zones and fracture domains at the site proposed for a spent nuclear fuel repository, Sweden, and consequences of structural anisotropy

“…Ductile deformation continued to around 1.8 Ga along discrete deformation zones with WNW-ESE or NW-SE strike under lower amphiboliteor greenschist-facies metamorphic conditions (Hermansson et al, 2008b). These zones are spatially constrained within the earlier, higher-temperature ductile shear belts (Fig.…”

Magmatism during Gondwana break-up: new geochronological data from Westland, New Zealand

“…Details of the analytical methods used at UNLV have been reported in the Appendix to Scott et al (2011b), and analytical procedures of 40 Ar/ 39 Ar dating at Universität Potsdam are summarized in Wiederkehr et al (2009). Sample KST-2 was analysed at Lund University, Sweden following the methods described by Hermansson et al (2008). Data from UNLV and from Universität Potsdam were standardized against FC-2, Fish Canyon tuff sanidine (with an assumed age of 28.02 ± 0.28 Ma after Renne et al (1998)) at UNLV, whereas an age of 27.5 Ma (after Uto et al 1997) was assumed for analyses carried out at Universität Potsdam, the reported data are corrected for this minor Table 1 Recalculation of K/Ar ages of lamprophyre dikes and a basalt sill reported by Adams & Nathan (1978) to decay constants of Steiger & Jäger (1977 Renne et al 1998).…”