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Petrology and ion microprobe U-Pb chronology applied to a metabasic intrusion in southern Sweden: A study on zircon formation during metamorphism and deformation

Söderlund, Pia LU ; Söderlund, Ulf LU ; Moller, C; Gorbatschev, Roland LU and Rodhe, Agnes LU (2004) In Tectonics 23(5).
Abstract
The Aker metabasite occupies a key position in a major tectonic lineament in southernmost Sweden, the Protogine Zone, which coincides closely with the eastern boundary of the late Mesoproterozoic Sveconorwegian orogen of southwest Scandinavia. Metamorphic reactions, associated with the transformation from isotropic gabbro to foliated garnet amphibolite, were identified from disequilibrium textures of which some involved release of zirconium (Zr) and growth of metamorphic zircon. Ion microprobe dating of igneous zircon gave 1562 +/- 6 Ma, whereas metamorphic zircons yielded ages of 1437 +/- 21, 1217 +/- 75, and 1006 +/- 68 Ma. The presence of baddeleyite pseudomorphs made up of saccharoidal zircon and a higher abundance of older rather than... (More)
The Aker metabasite occupies a key position in a major tectonic lineament in southernmost Sweden, the Protogine Zone, which coincides closely with the eastern boundary of the late Mesoproterozoic Sveconorwegian orogen of southwest Scandinavia. Metamorphic reactions, associated with the transformation from isotropic gabbro to foliated garnet amphibolite, were identified from disequilibrium textures of which some involved release of zirconium (Zr) and growth of metamorphic zircon. Ion microprobe dating of igneous zircon gave 1562 +/- 6 Ma, whereas metamorphic zircons yielded ages of 1437 +/- 21, 1217 +/- 75, and 1006 +/- 68 Ma. The presence of baddeleyite pseudomorphs made up of saccharoidal zircon and a higher abundance of older rather than younger metamorphic zircons suggest redistribution of Zr into new zircon, first by the breakdown of baddeleyite (ZrO2) and later by the consumption of igneous phases containing trace amounts of Zr. Several generations of metamorphic zircon and the presence of 1.56 and 1.22 Ga mafic intrusions along the Protogine Zone call for a complex tectonic history probably reaching back to at least similar to1.56 Ga. Growth of metamorphic zircon at similar to1.44 Ga may relate to a regional, compressional event. The WNW trending deformational structures on both sides of the Protogine Zone may possibly relate to that event. The similar to1.22 Ga metamorphic zircons are coeval with the emplacement of numerous granitic, syenitic, and mafic intrusions along and parallel to the Protogine Zone. The age around 1.0 Ga, finally, marks Sveconorwegian metamorphism for which thermobarometry of the Aker garnet-amphibolite suggests 1000-1200 MPa at 600degreesC-630degreesC. Thereafter, significant relative uplift of the rocks to the west of the Protogine Zone occurred on nearly vertical, north-south trending deformation zones. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
U-Pb geochronology, Protogine Zone, metamorphism
in
Tectonics
volume
23
issue
5
publisher
American Geophysical Union
external identifiers
  • wos:000223893500001
  • scopus:11944267401
ISSN
0278-7407
DOI
10.1029/2003TC001498
language
English
LU publication?
yes
id
4d96bd3d-dcc0-4563-828f-fbc8213c2690 (old id 267230)
date added to LUP
2007-11-02 08:13:54
date last changed
2017-08-06 04:35:03
@article{4d96bd3d-dcc0-4563-828f-fbc8213c2690,
  abstract     = {The Aker metabasite occupies a key position in a major tectonic lineament in southernmost Sweden, the Protogine Zone, which coincides closely with the eastern boundary of the late Mesoproterozoic Sveconorwegian orogen of southwest Scandinavia. Metamorphic reactions, associated with the transformation from isotropic gabbro to foliated garnet amphibolite, were identified from disequilibrium textures of which some involved release of zirconium (Zr) and growth of metamorphic zircon. Ion microprobe dating of igneous zircon gave 1562 +/- 6 Ma, whereas metamorphic zircons yielded ages of 1437 +/- 21, 1217 +/- 75, and 1006 +/- 68 Ma. The presence of baddeleyite pseudomorphs made up of saccharoidal zircon and a higher abundance of older rather than younger metamorphic zircons suggest redistribution of Zr into new zircon, first by the breakdown of baddeleyite (ZrO2) and later by the consumption of igneous phases containing trace amounts of Zr. Several generations of metamorphic zircon and the presence of 1.56 and 1.22 Ga mafic intrusions along the Protogine Zone call for a complex tectonic history probably reaching back to at least similar to1.56 Ga. Growth of metamorphic zircon at similar to1.44 Ga may relate to a regional, compressional event. The WNW trending deformational structures on both sides of the Protogine Zone may possibly relate to that event. The similar to1.22 Ga metamorphic zircons are coeval with the emplacement of numerous granitic, syenitic, and mafic intrusions along and parallel to the Protogine Zone. The age around 1.0 Ga, finally, marks Sveconorwegian metamorphism for which thermobarometry of the Aker garnet-amphibolite suggests 1000-1200 MPa at 600degreesC-630degreesC. Thereafter, significant relative uplift of the rocks to the west of the Protogine Zone occurred on nearly vertical, north-south trending deformation zones.},
  author       = {Söderlund, Pia and Söderlund, Ulf and Moller, C and Gorbatschev, Roland and Rodhe, Agnes},
  issn         = {0278-7407},
  keyword      = {U-Pb geochronology,Protogine Zone,metamorphism},
  language     = {eng},
  number       = {5},
  publisher    = {American Geophysical Union},
  series       = {Tectonics},
  title        = {Petrology and ion microprobe U-Pb chronology applied to a metabasic intrusion in southern Sweden: A study on zircon formation during metamorphism and deformation},
  url          = {http://dx.doi.org/10.1029/2003TC001498},
  volume       = {23},
  year         = {2004},
}