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Zircon U-Pb constraints on the timing of Sveconorwegian migmatite formation in the Western and Median Segments of the Idefjorden terrane, SW Sweden

Ingered, Mimmi LU (2019) In Dissertations in Geology at Lund University GEOR02 20191
Department of Geology
Abstract
The Western and Median Segments of the Idefjorden terrane have been metamorphosed and migmatized during the Sveconorwegian orogeny (ca. 1 Ga), but the timing of these events between the two segments remains unclear. Here I show that Sveconorwegian metamorphism and associated migmatite formation is not coeval between the Western and Median Segments and that there is a contrast between the segments in terms of strain, migmatite abundance and retrograde metamorphic overprint. Magmatic crystallization ages were determined through U-Pb spot dating on zircon using Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). Zircon cores with Th/U >0.2 yields an age of 1551±6 Ma for the Arsjön migmatite in the Western Segment, 1349±5... (More)
The Western and Median Segments of the Idefjorden terrane have been metamorphosed and migmatized during the Sveconorwegian orogeny (ca. 1 Ga), but the timing of these events between the two segments remains unclear. Here I show that Sveconorwegian metamorphism and associated migmatite formation is not coeval between the Western and Median Segments and that there is a contrast between the segments in terms of strain, migmatite abundance and retrograde metamorphic overprint. Magmatic crystallization ages were determined through U-Pb spot dating on zircon using Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). Zircon cores with Th/U >0.2 yields an age of 1551±6 Ma for the Arsjön migmatite in the Western Segment, 1349±5 Ma for the Tösslanda migmatite within the Göta Älv Shear Zone, and 1601±3 Ma and 1581±8 Ma respectively for the Hälltorp migmatites in the Median Segment. Zircon in leucosome yield dates of 1073±31 Ma for the Arsjön migmatite, 1046±21 Ma for the Tösslanda migmatite and 1019±27 Ma for the Hälltorp migmatites. The dates of the zircon rims are interpreted to be ages of metamorphism and migmatization and are supported by Th/U values around 0.02. The metamorphic ages are coeval with Sveconorwegian metamorphism in the Idefjorden terrane (1.14-0.90 Ga), but the results demonstrate that Sveconorwegian metamorphism and migmatite formation occurred earlier in the Western Segment than in the Median Segment. (Less)
Abstract (Swedish)
Det Västra segmentet och Mediansegmentet i Idefjordenterrängen omarbetades under metamorfos och migmatitbildning under den Svekonorvegiska orogenesen (ca. 1 Ga), men det råder fortfarande oklarheter kring tidpunkterna för dessa händelser inom och mellan de två segmenten. Denna studie visar att Svekonorvegisk metamorfos och associerad migmatitbildning inte är samtida i Västra segmentet och Mediansegmentet, samt att deformation, retrograd metamorf överprägling och mängden migmatiter kontrasterar mellan segmenten. Magmatiska kristallationsåldrar bestämdes med U-Pb-datering av zirkon genom laserablation och induktivt kopplad plasma masspektrometri (LA-ICP-MS). Zirkonkärnor med Th/U >0,2 ger en ålder av 1551±6 Ma för Arsjönmigmatiten i Västra... (More)
Det Västra segmentet och Mediansegmentet i Idefjordenterrängen omarbetades under metamorfos och migmatitbildning under den Svekonorvegiska orogenesen (ca. 1 Ga), men det råder fortfarande oklarheter kring tidpunkterna för dessa händelser inom och mellan de två segmenten. Denna studie visar att Svekonorvegisk metamorfos och associerad migmatitbildning inte är samtida i Västra segmentet och Mediansegmentet, samt att deformation, retrograd metamorf överprägling och mängden migmatiter kontrasterar mellan segmenten. Magmatiska kristallationsåldrar bestämdes med U-Pb-datering av zirkon genom laserablation och induktivt kopplad plasma masspektrometri (LA-ICP-MS). Zirkonkärnor med Th/U >0,2 ger en ålder av 1551±6 Ma för Arsjönmigmatiten i Västra segmentet, 1349±5 Ma för Tösslandamigmatiten i Göta Älv zonen, samt 1601±3 Ma respektive 1581±8 Ma för Hälltorpmigmatiterna i Mediansegmentet. Zirkon i leukosom ger 1073±31 Ma för Arsjönmigmatiten, 1046±21 Ma för Tösslandamigmatiten och 1019±27 Ma för Hälltorpmigmatiterna. Dateringarna av tillväxterna tolkas som åldern för metamorfos och migmatitbildning och stöds av Th/U runt 0,02. De metamorfa åldrarna är samtida med Svekonorvegisk metamorfos i Idefjordenterrängen (1.14-0.90 Ga), men resultaten visar att Svekonorvegisk metamorfos och migmatitbildning inträffade tidigare i Västra segmentet än i Mediansegmentet. (Less)
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author
Ingered, Mimmi LU
supervisor
organization
course
GEOR02 20191
year
type
H2 - Master's Degree (Two Years)
subject
keywords
Sveconorwegian orogen, U-Pb, Zircon, Migmatite, Idefjorden terrane
publication/series
Dissertations in Geology at Lund University
report number
558
language
English
id
8974649
date added to LUP
2019-04-21 08:43:07
date last changed
2021-04-18 03:40:52
@misc{8974649,
  abstract     = {{The Western and Median Segments of the Idefjorden terrane have been metamorphosed and migmatized during the Sveconorwegian orogeny (ca. 1 Ga), but the timing of these events between the two segments remains unclear. Here I show that Sveconorwegian metamorphism and associated migmatite formation is not coeval between the Western and Median Segments and that there is a contrast between the segments in terms of strain, migmatite abundance and retrograde metamorphic overprint. Magmatic crystallization ages were determined through U-Pb spot dating on zircon using Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). Zircon cores with Th/U >0.2 yields an age of 1551±6 Ma for the Arsjön migmatite in the Western Segment, 1349±5 Ma for the Tösslanda migmatite within the Göta Älv Shear Zone, and 1601±3 Ma and 1581±8 Ma respectively for the Hälltorp migmatites in the Median Segment. Zircon in leucosome yield dates of 1073±31 Ma for the Arsjön migmatite, 1046±21 Ma for the Tösslanda migmatite and 1019±27 Ma for the Hälltorp migmatites. The dates of the zircon rims are interpreted to be ages of metamorphism and migmatization and are supported by Th/U values around 0.02. The metamorphic ages are coeval with Sveconorwegian metamorphism in the Idefjorden terrane (1.14-0.90 Ga), but the results demonstrate that Sveconorwegian metamorphism and migmatite formation occurred earlier in the Western Segment than in the Median Segment.}},
  author       = {{Ingered, Mimmi}},
  language     = {{eng}},
  note         = {{Student Paper}},
  series       = {{Dissertations in Geology at Lund University}},
  title        = {{Zircon U-Pb constraints on the timing of Sveconorwegian migmatite formation in the Western and Median Segments of the Idefjorden terrane, SW Sweden}},
  year         = {{2019}},
}