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The Säm fold structure : characterization of folding and metamorphism in a part of the eclogite–granulite region, Sveconorwegian orogen

Michalchuk, Stephen LU (2013) In Dissertations in Geology at Lund University GEOR02 20131
Department of Geology
Abstract
Structural and petrological studies on complexly folded mafic and felsic layered sequences have been mapped in the parautochthonous basement of the Sveconorwegian Province, Sweden. Three deformation phases (D1, D2, D3)involving at least two fold phases (F2, F3) and two lineation phases (L2, L3) characterize a polyphase fold, which is primarily defined by a migmatized and highly competent garnet amphibolite. This unit was folded and boudinaged into map-scale tectonic lenses during upper amphibolite to granulite facies metamorphism.

Penetrative deformation during D3 and D2 created strong, composite fabrics. The oldest, D1 event is interpreted as simply a deformation phase forming a gneissic S1. D2 folded the S1 into similar-shaped,... (More)
Structural and petrological studies on complexly folded mafic and felsic layered sequences have been mapped in the parautochthonous basement of the Sveconorwegian Province, Sweden. Three deformation phases (D1, D2, D3)involving at least two fold phases (F2, F3) and two lineation phases (L2, L3) characterize a polyphase fold, which is primarily defined by a migmatized and highly competent garnet amphibolite. This unit was folded and boudinaged into map-scale tectonic lenses during upper amphibolite to granulite facies metamorphism.

Penetrative deformation during D3 and D2 created strong, composite fabrics. The oldest, D1 event is interpreted as simply a deformation phase forming a gneissic S1. D2 folded the S1 into similar-shaped, upright to inclined, closed to isoclinal folds (F2). L2 lineations have a bimodal distribution with two distinct clusters trending 37/318 and 26/160. The F2 folds were subsequently refolded into a NE-plunging, open, Class 1C, Type 3 interference pattern folds (F3) during D3. The majority of L3 lineations align parallel with the F3 fold axis. L3 has shallow to moderate plunges all trending NE (mean vectors: 19/052, 29/039 & 08/060). Syn-kinematic shear-sense indicators are consistently top-to-the-east.

Upper amphibolite to granulite facies was achieved in the garnet amphibolite gneiss. The earliest assemblages preserved plagioclase inclusions in clinopyroxene, and orthopyroxene forming coronas around clinopyroxene and Fe-Ti oxides, indicative of high temperatures ~800-850 °C at ~10 kbar. The texturally equilibrated mineral assemblage consists of garnet + clinopyroxene + plagioclase + quartz + hornblende + Fe-Ti oxide + biotite, and is found stable at P-T conditions of ~700-800 °C and ~9-14 kbar.

Mineral assemblages studied in the sillimanite-bearing quartz-feldspar gneiss showed a clockwise P-T-t evolution. A single grain of kyanite is believed to have been found. Tentatively, the paragneiss travelled through the relatively higher pressure, kyanite stability field; possibly during D2. A stable mineral assemblage containing quartz + K-feldspar + plagioclase + biotite + sillimanite + garnet + Fe-Ti oxide, suggests P-T conditions of ~650-850 °C and ~3-10 kbar. Cordierite was found reacting with garnet in the presence of K-feldspar, which suggested D3 decompression of ≤5 kbar occurred at high temperatures (≥650 °C).

Tectonic implications relating this structure with deformation observed elsewhere in the Eastern Segment is discussed. (Less)
Abstract (Swedish)
Strukturella och petrologiska studier av komplext veckade mafiskt- och felsiskt varvade sekvenser har genomförts i den paraautoktona delen av Svekonorvegiska provinsen i sydvästra Sverige. Tre deformationsfaser (D1, D2, D3) innefattande minst två veckfaser (F2, F3) och två lineationsfaser (L2, L3) karakteriserar ett flerfasigt veck i migmatiserad och mycket kompetent granatamfibolit. Denna enhet veckades och boudinerades till tektoniska linser under metamorfos i övre amfibolit- till granulitfacies.

Penetrativ deformation under D3 och D2 skapade sammansatta strukturer. Den äldsta, D1 tolkas som en deformationsfas vilken endast bildar en gnejsig S1 struktur. D2 veckade S1 till likformade, upprätta till lutande, slutna till isoclinala veck... (More)
Strukturella och petrologiska studier av komplext veckade mafiskt- och felsiskt varvade sekvenser har genomförts i den paraautoktona delen av Svekonorvegiska provinsen i sydvästra Sverige. Tre deformationsfaser (D1, D2, D3) innefattande minst två veckfaser (F2, F3) och två lineationsfaser (L2, L3) karakteriserar ett flerfasigt veck i migmatiserad och mycket kompetent granatamfibolit. Denna enhet veckades och boudinerades till tektoniska linser under metamorfos i övre amfibolit- till granulitfacies.

Penetrativ deformation under D3 och D2 skapade sammansatta strukturer. Den äldsta, D1 tolkas som en deformationsfas vilken endast bildar en gnejsig S1 struktur. D2 veckade S1 till likformade, upprätta till lutande, slutna till isoclinala veck (F2). L2 lineationen har en bimodal fördelning med två distinkta poler, 37/318 och 26/160. F2 vecken omveckades därefter till ett NÖ-stupande, öppen, klass 1C, typ 3 interferensmönsterveck (F3) under D3. Majoriteten av L3 lineationerna är parallella med F3-veckaxeln. L3 stupar svagt till måttligt i riktning NÖ (medelvärde för vektorerna: 19/052, 29/039 och 08/060). Synkinematiska skjuvindikatorer är genomgående topp-mot-öst.

Metamorfos i övre amfibolit- till granulitfacies kännetecknar granat-amfibolitgnejsen. De tidigaste mineralsällskapen består av plagioklasinneslutningar i klinopyroxen, ortopyroxen med coronabildning runt klinopyroxen samt Fe-Ti-oxider. De indikerar höga temperaturer, ~800-850 °C vid ~10 kbar. Mineralsällskapet i texturell jämvikt, bestående av granat + klinopyroxen + plagioklas + kvarts + hornblände + Fe-Ti-oxid + biotit, är stabilt vid P-T förhållanderna ~700-800 °C och ~9-14 kbar.

Mineralsällskapen i den sillimanitförande kvarts-fältspatgnejsen visar en medurs P-T-t utveckling. Endast ett korn av kyanit tros ha identifierats. Detta indikerar att paragnejsen har utsatts för högre tryck inom kyanitens stabilitetsområde, eventuellt under D2. Ett stabilt mineralsällskap bestående av kvarts + K-fältspat + plagioklas + biotit + sillimanit + granat + Fe-Ti-oxider ger tryck och temperaturer kring ~650-850 °C och ~3-10 kbar. Reaktion mellan kordierit och granat i närvaro av K-fältspat, antyder att D3 dekompressionen till ≤5 kbar skedde vid höga temperaturer (≥650 °C).

De tektoniska konsekvenserna av tolkningen av veckstrukturen i Säm diskuteras i relation till andra deformationsstrukturer i Östra segmentet. (Less)
Please use this url to cite or link to this publication:
author
Michalchuk, Stephen LU
supervisor
organization
alternative title
Veckstruckturen i Säm : karakterisering av veckning och metamorfos i en del av eklogit–granulit regionen, Svekonorvegiska orogenesen
course
GEOR02 20131
year
type
H2 - Master's Degree (Two Years)
subject
keywords
anatexis, high-T granulite, interference folds, polydeformation, Sveconorwegian orogen, SW Sweden
publication/series
Dissertations in Geology at Lund University
report number
367
language
English
id
4023150
date added to LUP
2013-09-13 09:46:46
date last changed
2015-09-13 04:12:49
@misc{4023150,
  abstract     = {Structural and petrological studies on complexly folded mafic and felsic layered sequences have been mapped in the parautochthonous basement of the Sveconorwegian Province, Sweden. Three deformation phases (D1, D2, D3)involving at least two fold phases (F2, F3) and two lineation phases (L2, L3) characterize a polyphase fold, which is primarily defined by a migmatized and highly competent garnet amphibolite. This unit was folded and boudinaged into map-scale tectonic lenses during upper amphibolite to granulite facies metamorphism.

Penetrative deformation during D3 and D2 created strong, composite fabrics. The oldest, D1 event is interpreted as simply a deformation phase forming a gneissic S1. D2 folded the S1 into similar-shaped, upright to inclined, closed to isoclinal folds (F2). L2 lineations have a bimodal distribution with two distinct clusters trending 37/318 and 26/160. The F2 folds were subsequently refolded into a NE-plunging, open, Class 1C, Type 3 interference pattern folds (F3) during D3. The majority of L3 lineations align parallel with the F3 fold axis. L3 has shallow to moderate plunges all trending NE (mean vectors: 19/052, 29/039 & 08/060). Syn-kinematic shear-sense indicators are consistently top-to-the-east.

Upper amphibolite to granulite facies was achieved in the garnet amphibolite gneiss. The earliest assemblages preserved plagioclase inclusions in clinopyroxene, and orthopyroxene forming coronas around clinopyroxene and Fe-Ti oxides, indicative of high temperatures ~800-850 °C at ~10 kbar. The texturally equilibrated mineral assemblage consists of garnet + clinopyroxene + plagioclase + quartz + hornblende + Fe-Ti oxide + biotite, and is found stable at P-T conditions of ~700-800 °C and ~9-14 kbar.

Mineral assemblages studied in the sillimanite-bearing quartz-feldspar gneiss showed a clockwise P-T-t evolution. A single grain of kyanite is believed to have been found. Tentatively, the paragneiss travelled through the relatively higher pressure, kyanite stability field; possibly during D2. A stable mineral assemblage containing quartz + K-feldspar + plagioclase + biotite + sillimanite + garnet + Fe-Ti oxide, suggests P-T conditions of ~650-850 °C and ~3-10 kbar. Cordierite was found reacting with garnet in the presence of K-feldspar, which suggested D3 decompression of ≤5 kbar occurred at high temperatures (≥650 °C).

Tectonic implications relating this structure with deformation observed elsewhere in the Eastern Segment is discussed.},
  author       = {Michalchuk, Stephen},
  keyword      = {anatexis,high-T granulite,interference folds,polydeformation,Sveconorwegian orogen,SW Sweden},
  language     = {eng},
  note         = {Student Paper},
  series       = {Dissertations in Geology at Lund University},
  title        = {The Säm fold structure : characterization of folding and metamorphism in a part of the eclogite–granulite region, Sveconorwegian orogen},
  year         = {2013},
}