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Zircon geochronology in polymetamorphic gneisses in the Sveconorwegian orogen, SW Sweden: ion microprobe evidence for 1.46-1.42 and 0.98-0.96 Ga reworking

Söderlund, Ulf LU ; Möller, Charlotte LU ; Andersson, Jenny LU ; Johansson, Leif LU and Whitehouse, M (2002) In Precambrian Research 113(3-4). p.193-225
Abstract
Ion microprobe U-Th-Pb analyses of zircons in variably metamorphosed and veined orthogneisses in the southern part of the parautochthonous Eastern Segment of the Sveconorwegian (1.20-0.90 Ga) orogen, SW Sweden, broadly define two age groups, oscillatory and sector zoned magmatic zircon cores yield 1.70-1.68 Ga while overgrowths, homogeneous crystals, and recrystallized domains in primary zircon yield 1.46-1.42 Ga. In addition, a late-kinematic pegmatite was dated at 0.96 Ga, while a penetratively deformed granite dyke contains both 1444 +/- 8 Ma magmatic and 982 +/- 15 Ma metamorphic zircons. The 1.70-1.68 Ga ages date the orthogneiss protoliths and fall in the same age range as well-preserved rocks of the Transscandinavian Igneous Belt... (More)
Ion microprobe U-Th-Pb analyses of zircons in variably metamorphosed and veined orthogneisses in the southern part of the parautochthonous Eastern Segment of the Sveconorwegian (1.20-0.90 Ga) orogen, SW Sweden, broadly define two age groups, oscillatory and sector zoned magmatic zircon cores yield 1.70-1.68 Ga while overgrowths, homogeneous crystals, and recrystallized domains in primary zircon yield 1.46-1.42 Ga. In addition, a late-kinematic pegmatite was dated at 0.96 Ga, while a penetratively deformed granite dyke contains both 1444 +/- 8 Ma magmatic and 982 +/- 15 Ma metamorphic zircons. The 1.70-1.68 Ga ages date the orthogneiss protoliths and fall in the same age range as well-preserved rocks of the Transscandinavian Igneous Belt that forms a major part of the crust east of the Sveconorwegian orogen. Despite Sveconorwegian penetrative deformation under granulite to upper amphibolite conditions, secondary zircons yielding Sveconorwegian ages are virtually absent in the 1.70-1.68 Ga orthogneisses but are abundant in rocks younger than ca. 1.45 Ga. It is suggested that Zr hosted in magmatic phases was redistributed to form new zircon during the 1.46-1.42 Ga event, resulting in a mineralogy in which the main minerals were depleted in Zr. These data, therefore, imply that high-grade metamorphism may occur without associated growth of new zircon. Furthermore, the absence of secondary zircons with ages > ca. 1.46 Ga suggests a re-assessment of models calling for extensive Gothian deformation and metamorphism in the Eastern Segment. (C) 2002 Elsevier Science B.V. All rights reserved. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
zircon, Sveconorwegian, 1.4 Ga, Hallandian, Gothian, metamorphic, ion probe, Sweden
in
Precambrian Research
volume
113
issue
3-4
pages
193 - 225
publisher
Elsevier
external identifiers
  • wos:000173268900002
  • scopus:0037204161
ISSN
0301-9268
DOI
10.1016/S0301-9268(01)00206-6
language
English
LU publication?
yes
id
24e182db-704b-43a6-8900-66de6b172a43 (old id 344703)
date added to LUP
2007-11-14 13:12:29
date last changed
2017-07-30 03:51:04
@article{24e182db-704b-43a6-8900-66de6b172a43,
  abstract     = {Ion microprobe U-Th-Pb analyses of zircons in variably metamorphosed and veined orthogneisses in the southern part of the parautochthonous Eastern Segment of the Sveconorwegian (1.20-0.90 Ga) orogen, SW Sweden, broadly define two age groups, oscillatory and sector zoned magmatic zircon cores yield 1.70-1.68 Ga while overgrowths, homogeneous crystals, and recrystallized domains in primary zircon yield 1.46-1.42 Ga. In addition, a late-kinematic pegmatite was dated at 0.96 Ga, while a penetratively deformed granite dyke contains both 1444 +/- 8 Ma magmatic and 982 +/- 15 Ma metamorphic zircons. The 1.70-1.68 Ga ages date the orthogneiss protoliths and fall in the same age range as well-preserved rocks of the Transscandinavian Igneous Belt that forms a major part of the crust east of the Sveconorwegian orogen. Despite Sveconorwegian penetrative deformation under granulite to upper amphibolite conditions, secondary zircons yielding Sveconorwegian ages are virtually absent in the 1.70-1.68 Ga orthogneisses but are abundant in rocks younger than ca. 1.45 Ga. It is suggested that Zr hosted in magmatic phases was redistributed to form new zircon during the 1.46-1.42 Ga event, resulting in a mineralogy in which the main minerals were depleted in Zr. These data, therefore, imply that high-grade metamorphism may occur without associated growth of new zircon. Furthermore, the absence of secondary zircons with ages > ca. 1.46 Ga suggests a re-assessment of models calling for extensive Gothian deformation and metamorphism in the Eastern Segment. (C) 2002 Elsevier Science B.V. All rights reserved.},
  author       = {Söderlund, Ulf and Möller, Charlotte and Andersson, Jenny and Johansson, Leif and Whitehouse, M},
  issn         = {0301-9268},
  keyword      = {zircon,Sveconorwegian,1.4 Ga,Hallandian,Gothian,metamorphic,ion probe,Sweden},
  language     = {eng},
  number       = {3-4},
  pages        = {193--225},
  publisher    = {Elsevier},
  series       = {Precambrian Research},
  title        = {Zircon geochronology in polymetamorphic gneisses in the Sveconorwegian orogen, SW Sweden: ion microprobe evidence for 1.46-1.42 and 0.98-0.96 Ga reworking},
  url          = {http://dx.doi.org/10.1016/S0301-9268(01)00206-6},
  volume       = {113},
  year         = {2002},
}