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Field relations, petrography and 40Ar/39Ar cooling ages of hornblende in a part of the eclogite-bearing domain, Sveconorwegian Orogen

Mozafari Amiri, Nasim LU (2013) In Dissertations in Geology at Lund University GEOR02 20122
Department of Geology
Abstract
High-pressure metamorphism and deformation of the Ullared Deformation Zone (UDZ) in the Eastern
segment of the Sveconorwegian Orogen, southwest Sweden is evidenced by ~ 970 Ma retro-eclogite found in
association with upper amphibolite and high-pressure granulite facies rocks. Petrographic, structural and
geochronological studies of the UDZ were carried out to better understand the regional metamorphism and
deformation history with focus on a ~N-S trending part of the zone influenced by a late stage of deformation during
Sveconorwegian orogeny, namely the Svarten Zone.
The deformational history of the investigated area can be discussed in two scenarios. In the first one, an E-W
extension component synchronized with the onset of... (More)
High-pressure metamorphism and deformation of the Ullared Deformation Zone (UDZ) in the Eastern
segment of the Sveconorwegian Orogen, southwest Sweden is evidenced by ~ 970 Ma retro-eclogite found in
association with upper amphibolite and high-pressure granulite facies rocks. Petrographic, structural and
geochronological studies of the UDZ were carried out to better understand the regional metamorphism and
deformation history with focus on a ~N-S trending part of the zone influenced by a late stage of deformation during
Sveconorwegian orogeny, namely the Svarten Zone.
The deformational history of the investigated area can be discussed in two scenarios. In the first one, an E-W
extension component synchronized with the onset of migmatization was responsible for the development of an old
upright and symmetric ESE-WNW generation of folds. The folds were later influenced by an intense phase of
shear, which formed the isoclinal folds and the parallel mineral stretching lineation. The old ESE-WNW foliation
was deflected by a later phase of NNW-SSE shear, following the isoclinal folds development. The second possible
scenario is that a NNW-SSE shear phase has taken place synchronized with E-W extension, following the regional
migmatization, resulted in E-plunging mineral stretching lineation and isoclinal folds development, which
consequently deflected ESE-WNW foliations. Regardless of which scenario is correct, the sheared limb of a young,
open and upright generation of folds indicate that a late phase of shear has taken place in association with ~N-S
structure of the Svarten Zone.
Mineral assemblages indicate the occurrence of retrograde metamorphism resulted from uplift of the Sveconorwegian
Orogen, reflected in the amphibolite mineral assemblages overprinting of the eclogite and the granulite facies.
40Ar/39Ar dating of hornblende yielded cooling ages that range from 920 Ma to 927 Ma. The cooling rates of 5.5-6.4
°C/m.y. and 4.5-5.2 °C/m.y. were obtained from the onset of partial melting and migmatization down to the hornblende
cooling age of 920 Ma to 927 Ma, respectively, upon the chosen closure temperatures of 500°C and 550°C.
The cooling rates are associated with uplift of the Sveconorwegian Orogen and cooling after peak metamorphism. (Less)
Please use this url to cite or link to this publication:
author
Mozafari Amiri, Nasim LU
supervisor
organization
course
GEOR02 20122
year
type
H2 - Master's Degree (Two Years)
subject
keywords
Sveconorwegian, retrograde metamorphism, eclogite, Svarten Zone, ductile deformation, Ar-Ar dating.
publication/series
Dissertations in Geology at Lund University
report number
329
funder
Swedish Geological Survey
language
English
id
3635945
date added to LUP
2013-04-22 10:42:24
date last changed
2015-01-31 03:57:42
@misc{3635945,
  abstract     = {High-pressure metamorphism and deformation of the Ullared Deformation Zone (UDZ) in the Eastern
segment of the Sveconorwegian Orogen, southwest Sweden is evidenced by ~ 970 Ma retro-eclogite found in
association with upper amphibolite and high-pressure granulite facies rocks. Petrographic, structural and
geochronological studies of the UDZ were carried out to better understand the regional metamorphism and
deformation history with focus on a ~N-S trending part of the zone influenced by a late stage of deformation during
Sveconorwegian orogeny, namely the Svarten Zone.
The deformational history of the investigated area can be discussed in two scenarios. In the first one, an E-W
extension component synchronized with the onset of migmatization was responsible for the development of an old
upright and symmetric ESE-WNW generation of folds. The folds were later influenced by an intense phase of
shear, which formed the isoclinal folds and the parallel mineral stretching lineation. The old ESE-WNW foliation
was deflected by a later phase of NNW-SSE shear, following the isoclinal folds development. The second possible
scenario is that a NNW-SSE shear phase has taken place synchronized with E-W extension, following the regional
migmatization, resulted in E-plunging mineral stretching lineation and isoclinal folds development, which
consequently deflected ESE-WNW foliations. Regardless of which scenario is correct, the sheared limb of a young,
open and upright generation of folds indicate that a late phase of shear has taken place in association with ~N-S
structure of the Svarten Zone.
Mineral assemblages indicate the occurrence of retrograde metamorphism resulted from uplift of the Sveconorwegian
Orogen, reflected in the amphibolite mineral assemblages overprinting of the eclogite and the granulite facies.
40Ar/39Ar dating of hornblende yielded cooling ages that range from 920 Ma to 927 Ma. The cooling rates of 5.5-6.4
°C/m.y. and 4.5-5.2 °C/m.y. were obtained from the onset of partial melting and migmatization down to the hornblende
cooling age of 920 Ma to 927 Ma, respectively, upon the chosen closure temperatures of 500°C and 550°C.
The cooling rates are associated with uplift of the Sveconorwegian Orogen and cooling after peak metamorphism.},
  author       = {Mozafari Amiri, Nasim},
  keyword      = {Sveconorwegian,retrograde metamorphism,eclogite,Svarten Zone,ductile deformation,Ar-Ar dating.},
  language     = {eng},
  note         = {Student Paper},
  series       = {Dissertations in Geology at Lund University},
  title        = {Field relations, petrography and 40Ar/39Ar cooling ages of hornblende in a part of the eclogite-bearing domain, Sveconorwegian Orogen},
  year         = {2013},
}