Emplacement ages and metamorphic overprinting of granitoids in the Sveconorwegian Province in V rmland, Sweden - an ion probe study

Abstract

Emplacement ages and metamorphic overprinting of granitoids in the Sveconorwegian Province in Värmland, Sweden -an ion probe study.North of Lake Vänern in the Sveconorwegian province of Sweden, veined and banded grey to red granitoids characterize the Western Segment in western Värmland. Two gneiss samples from Rackstad, north of Arvika, yielded concordant U-Pb emplacement ages of 1596 AE 11 Ma and 1590 AE 14 Ma, respectively from zircon cores, while metamorphic zircon rims in one of the samples gave a weighted mean Pb-Pb age of 971 AE 8 Ma. Patches of metamorphic zircon overgrowth pre-dating the metamorphic rims indicate that an even older metamorphic event influenced this rock. East of the Mylonite Zone, a N-S-trending Sveconorwegian shear zone, more massive reddish granitoids occupy the segment between this zone and another N-S-trending Sveconorwegian shear zone, the Protogine Zone. A sample from Hänsjön, north of Torsby, yielded concordant ages with a weighted mean of 1689 AE 12 Ma. One grain has a Pb-Pb age of 1770 AE 29 Ma, which is inherited from the source of the granite, and is similar to the age of early magmatism in the Transscandinavian Igneous Belt, east of the Torsby Segment. These results confirm that north of Lake Vänern, the Torsby Segment was formed ca. 100 Ma earlier than the adjoining segment to the west, in accordance with previous results from further south.

Mesoproterozoic continental growth: U–Pb–Hf–O zircon record in the Idefjorden Terrane, Sveconorwegian Orogen

“…3). Assigning an igneous crystallisation age to this sample is hampered by the apparent Sveconorwegian Pb-loss (not seen by Larson et al, 1999), which causes excess 207 Pb/ 206 Pbspread along the concordia (c.f. Whitehouse and Kemp, 2010).…”

“…2a). Larson et al (1999) dated a similar sample (DC94-13, grey Racken) from this area, just north of Lake Racken, which they described as a quartz monzodiorite yielding a 207 Pb/ 206 Pb weighted mean age of 1596 ± 11 Ma.…”

“…(For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) Larson et al (1999), and we interpret our upper intercept date as the best estimate of the igneous crystallisation age of this rock.…”

Character and origin of variably deformed granitoids in central southern Sweden: implications from geochemistry and Nd isotopes

“…The Eastern Segment is dominated by granitoids ranging between 1.71 and 1.65 Ga in age (e.g. Johansson, 1990;Johansson et al, 1993;Connelly et al, 1996;Christoffel et al, 1999;Larson et al, 1999;Söderlund et al, 1999Söderlund et al, , 2002Scherstén et al, 2000;Alm et al, 2002;Andersson et al, 2002a;Austin Hegardt et al, 2005;Möller et al, 2007;Rimša et al, 2007;Bingen et al, 2008;Brander et al, 2011a). Based on differences in metamorphic ages and structural characteristics, the Eastern Segment can roughly be subdivided into a northern and a southern part, with the border between the two approximately coinciding with Lake Vänern.…”

Geochronology of high‐pressure mafic granulite dykes in SW Sweden: tracking the P–T–t path of metamorphism using Hf isotopes in zircon and baddeleyite

“…The Idefjorden terrane comprises tholeiitic to calcalkaline arc‐related granitoid and volcanic rocks, the protolith ages of which range from 1.64 to 1.52 Ga (Connelly & Åhäll, 1996; Åhäll et al. , 1998, 2000; Larson et al. , 1999; Andersen et al.…”