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P–T evolution of Precambrian eclogite in the Sveconorwegian orogen, SW Sweden

Tual, Lorraine LU ; Pitra, Pavel and Möller, Charlotte LU (2016) In Journal of Metamorphic Geology
Abstract
Conditions of the prograde, peak-pressure and part of the decompressional P–T path of two Precambrian eclogites in the eastern Sveconorwegian orogen have been determined using the pseudosection approach. Cores of garnet from a Fe–Ti-rich eclogite record a first prograde and syn-deformational stage along a Barrovian gradient from ~670 °C and 7 kbar to 710 °C and 8.5 kbar. Garnet rims grew during further burial to 16.5–19 kbar at ~850–900 °C, along a steep dP/dT gradient. The pseudosection model of a kyanite-bearing eclogite sample of more magnesian bulk composition confirms the peak conditions. Matrix reequilibration associated with subsequent near-isothermal decompression and partial exhumation produced plagioclase-bearing symplectites... (More)
Conditions of the prograde, peak-pressure and part of the decompressional P–T path of two Precambrian eclogites in the eastern Sveconorwegian orogen have been determined using the pseudosection approach. Cores of garnet from a Fe–Ti-rich eclogite record a first prograde and syn-deformational stage along a Barrovian gradient from ~670 °C and 7 kbar to 710 °C and 8.5 kbar. Garnet rims grew during further burial to 16.5–19 kbar at ~850–900 °C, along a steep dP/dT gradient. The pseudosection model of a kyanite-bearing eclogite sample of more magnesian bulk composition confirms the peak conditions. Matrix reequilibration associated with subsequent near-isothermal decompression and partial exhumation produced plagioclase-bearing symplectites replacing kyanite and clinopyroxene at an estimated 850–870 °C and 10–11 kbar. The validity of the pseudosections is discussed in detail. It is shown that in pseudosection modelling the fractionation of FeO in accessory sulphides may cause a significant shift of field boundaries (here displaced by up to 1.5 kbar and 70 °C) and must not be neglected. Fast burial, exhumation and subsequent cooling are supported by the steepness of both the prograde and the decompressional P–T paths as well as the preservation of garnet growth zoning and the symplectitic reaction textures. These features are compatible with deep tectonic burial of the eclogite-bearing continental crust as part of the underthrusting plate (Eastern Segment, continent Baltica) in a collisional setting that led to an effectively doubled crustal thickness and subsequent exhumation of the eclogites through tectonic extrusion. Our results are in accordance with regional structural and petrological relationships, which demonstrate foreland-vergent partial exhumation of the eclogite-bearing nappe along a basal thrust zone and support a major collisional stage at c. 1 Ga. We argue that the similarities between Sveconorwegian and Himalayan eclogite occurrences emphasize the modern style of Grenvillian-aged tectonics. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
epub
subject
keywords
P–T path, Sveconorwegian, Eclogite, Precambrian, pseudosection, Metamorphic petrology
in
Journal of Metamorphic Geology
publisher
Wiley-Blackwell
external identifiers
  • scopus:8501307797
  • wos:000402647600002
ISSN
0263-4929
DOI
10.1111/jmg.12242
language
English
LU publication?
yes
id
41897904-e245-4c0f-88e9-c5bf84c90eb6
date added to LUP
2017-01-06 10:44:41
date last changed
2017-09-18 11:35:21
@article{41897904-e245-4c0f-88e9-c5bf84c90eb6,
  abstract     = {Conditions of the prograde, peak-pressure and part of the decompressional P–T path of two Precambrian eclogites in the eastern Sveconorwegian orogen have been determined using the pseudosection approach. Cores of garnet from a Fe–Ti-rich eclogite record a first prograde and syn-deformational stage along a Barrovian gradient from ~670 °C and 7 kbar to 710 °C and 8.5 kbar. Garnet rims grew during further burial to 16.5–19 kbar at ~850–900 °C, along a steep dP/dT gradient. The pseudosection model of a kyanite-bearing eclogite sample of more magnesian bulk composition confirms the peak conditions. Matrix reequilibration associated with subsequent near-isothermal decompression and partial exhumation produced plagioclase-bearing symplectites replacing kyanite and clinopyroxene at an estimated 850–870 °C and 10–11 kbar. The validity of the pseudosections is discussed in detail. It is shown that in pseudosection modelling the fractionation of FeO in accessory sulphides may cause a significant shift of field boundaries (here displaced by up to 1.5 kbar and 70 °C) and must not be neglected. Fast burial, exhumation and subsequent cooling are supported by the steepness of both the prograde and the decompressional P–T paths as well as the preservation of garnet growth zoning and the symplectitic reaction textures. These features are compatible with deep tectonic burial of the eclogite-bearing continental crust as part of the underthrusting plate (Eastern Segment, continent Baltica) in a collisional setting that led to an effectively doubled crustal thickness and subsequent exhumation of the eclogites through tectonic extrusion. Our results are in accordance with regional structural and petrological relationships, which demonstrate foreland-vergent partial exhumation of the eclogite-bearing nappe along a basal thrust zone and support a major collisional stage at c. 1 Ga. We argue that the similarities between Sveconorwegian and Himalayan eclogite occurrences emphasize the modern style of Grenvillian-aged tectonics.},
  author       = {Tual, Lorraine and Pitra, Pavel and Möller, Charlotte},
  issn         = {0263-4929},
  keyword      = {P–T path,Sveconorwegian,Eclogite,Precambrian,pseudosection,Metamorphic petrology},
  language     = {eng},
  month        = {12},
  publisher    = {Wiley-Blackwell},
  series       = {Journal of Metamorphic Geology},
  title        = {P–T evolution of Precambrian eclogite in the Sveconorwegian orogen, SW Sweden},
  url          = {http://dx.doi.org/10.1111/jmg.12242},
  year         = {2016},
}