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Den geologiska utvecklingen av Hamrångesynklinalens suprakrustalbergarter, centrala Sverige

Erlandsson, Maria (2007) In Examensarbeten i geologi vid Lunds universitet
Department of Geology
Abstract (Swedish)
Området som undersöktes i denna studie ligger i västra delen av Hamrångesynklinalen. I studien
har bergarter, bergartsgränser och strukturer karterats i fält. Tunnslip undersöktes med optisk mikroskopi i avseende
på petrografi och förekomst av mikrostrukturer. Flera av tunnslipen har punkträknats för bergartsklassificering.
Några bergarter har Rietveldanalyserats för närmare bestämning av mineralsammansättning. Mineral både utanför
och från Hamrångesynklinalen har 40Ar/39Ar-daterats.
Hamrångesynklinalen ligger ca 30 km norr om Gävle och består framför allt av välbevarade suprakrustala bergarter.
Ytbergarterna tillhör den Svekofenniska domänen och utgörs av både sedimentära och vulkaniska bergarter. De
senare sprider i sammansättning... (More)
Området som undersöktes i denna studie ligger i västra delen av Hamrångesynklinalen. I studien
har bergarter, bergartsgränser och strukturer karterats i fält. Tunnslip undersöktes med optisk mikroskopi i avseende
på petrografi och förekomst av mikrostrukturer. Flera av tunnslipen har punkträknats för bergartsklassificering.
Några bergarter har Rietveldanalyserats för närmare bestämning av mineralsammansättning. Mineral både utanför
och från Hamrångesynklinalen har 40Ar/39Ar-daterats.
Hamrångesynklinalen ligger ca 30 km norr om Gävle och består framför allt av välbevarade suprakrustala bergarter.
Ytbergarterna tillhör den Svekofenniska domänen och utgörs av både sedimentära och vulkaniska bergarter. De
senare sprider i sammansättning från mafisk till felsisk. I området som undersöktes i denna studie förekommer endast
vulkaniter. De stratigrafiskt lägsta delarna utgörs av felsisk vulkanit som övergår till en mindre vanligt förekommande
felsisk-intermediär vulkanit överlagrad av mafiska vulkaniter vilka till övervägande del utgörs av lavor.
Stratigrafiskt överst ligger mafisk-intermediära vulkaniter. Troligen överlagras även de mafisk-intermediära vulkaniterna
av en felsisk-intermediär vulkanit. Mellan den mafiska vulkaniten och den mafisk-intermediära vulkaniten
och i den undre felsisk-intermediära vulkaniten förekommer mineraliserade enheter. Vulkaniterna är delvis omlagrade
och närvaron av kuddlavor tyder på att de avsattes i en marin miljö. Framför allt de mafiska vulkaniterna är
kraftigt kalksilikatomvandlade.
Den strukturella utvecklingen av östra centrala Svekofennium präglas av minst två veckfaser och skjuvning, relaterade
till D2 och D3. En första deformation D1 har identifierats i metasedimentära bergarter norr om Hamrångesynklinalen.
Senare spröda skjuvzoner förekommer även i området.
På en lokal i det karterade området finns spår av en tidig deformation, D1. Denna deformation kan vara relaterad till
kompaktion eller tektonisk deformation. En intensiv D2 deformation finns i området och syns som en penetrativ
foliation och en tydlig lineation. Isoklinala F2 veck har identifierats liksom D2 skjuvzoner. D2 skjuvzonerna visar att
de är relaterade till överskjutningar. F3 veck uppträder förutom som ett storskaligt veck i hela området som små
öppna parasitveck. F3 har ett brant O-V-ligt axialplan och en veckaxel som stupar med ca 23º åt öst.
Avkylningshistorian visar att Hamrångesynklinalen och bergarterna utanför passerade 350ºC isograden vid ca 1.74
Ga. Tidpunkten och temperaturen när avkylningskurvorna möts visar att rörelsen berodde på spröda till semispröda
deformationszoner. En möjlig kandidat är en spröd till semispröd deformationszon som förekommer söder om
Hamrångesynklinalen. (Less)
Abstract
The studied area is located in the western part of the Hamrånge syncline. In this area, the rocks, contacts
and structures were mapped . Thinsections were investigated regarding petrography and microstructures, and representative
thinsections were pointcounted. Three samples were selected for Rietveld analysis to receive the chemical
compositions. Minerals from both the syncline and the area outside has been dated by the 40Ar/39Ar method.
The Hamrånge area is located in the central part of Sweden, 30 km north of Gävle, near the Baltic coast. The Hamrånge
syncline is mainly composed of well preserved supracrustal rocks belonging to the Svecofennian Domain.
The supracrustal rocks are of both sedimentary and volcanic orgins. The later... (More)
The studied area is located in the western part of the Hamrånge syncline. In this area, the rocks, contacts
and structures were mapped . Thinsections were investigated regarding petrography and microstructures, and representative
thinsections were pointcounted. Three samples were selected for Rietveld analysis to receive the chemical
compositions. Minerals from both the syncline and the area outside has been dated by the 40Ar/39Ar method.
The Hamrånge area is located in the central part of Sweden, 30 km north of Gävle, near the Baltic coast. The Hamrånge
syncline is mainly composed of well preserved supracrustal rocks belonging to the Svecofennian Domain.
The supracrustal rocks are of both sedimentary and volcanic orgins. The later ranges from mafic to felsic in composition.
In the studied area only volcanic rocks compose the bedrock. The volcanic sequence is a felsic volcanic rock occurring
in the stratigrafically lowest parts, which are overlain by minor amounts of felsic-intermediate volcanic rock.
Overlaying these rocks are mafic volcanics, dominated by mafic lavas, which is in turn overlain by maficintermediate
volcanics. Between these rocktypes and in the felsic-intermediate volcanics are minor units of mineralised
rocks. It is likely that felsic-intermediate volcanic rocks are stratigrafically on top of the mafic-intermediate
volcanic rocks. The occurrence of redeposition of some volcanics and pillow lavas indicate a marine environment.
Mainly the mafic lavas are occasionally altered to skarn.
The central part of Svecofennium has been deformed by at least two major fold and thrust episodes related to D2
and D3. A previous deformation event, D1, has been recognised in metasedimentary rocks north of the Hamrånge
syncline. The area has also been affected by later brittle deformation.
Indications of an early deformation, D1, have been found at one locality in the Hamrånge area. This fabric can be
related to either compaction or to tectonic deformation. Intense D2 deformation appears as a penetrative foliation
and a strong stretching lineation. Both isoclinal F2 folds and D2 thrusts have been identified. F3 folds have been
identified both as a regional fold and as minor open parasite folds. The F3 fold has a steep axial plane striking E-W
and a fold axis plunging c. 23° to the east.
The cooling history shows that the Hamrånge syncline and the highgrade area outside passed through the 350º isograde
at about 1.74 Ga. Both the timing and the temperature when the two curves meet suggest that deformation
occurred under semi-brittle conditions. One candidate is a deformation zone located south of the Hamrånge syncline. (Less)
Please use this url to cite or link to this publication:
author
Erlandsson, Maria
supervisor
organization
alternative title
The geological evolution for the supracrustals in the western part of the Hamrånge syncline, central Sweden
year
type
H1 - Master's Degree (One Year)
subject
keywords
Svekofennium, Hamrångesynklinalen, 40Ar/39Ar, Rietveldanalys, strukturell anlys, petrografi, Svecofennium, Hamrånge syncline, Rietveldanalysis, structural analysis, petrography
publication/series
Examensarbeten i geologi vid Lunds universitet
report number
210
language
Swedish
id
2338053
date added to LUP
2012-02-02 15:04:27
date last changed
2012-02-02 15:04:27
@misc{2338053,
  abstract     = {{The studied area is located in the western part of the Hamrånge syncline. In this area, the rocks, contacts
and structures were mapped . Thinsections were investigated regarding petrography and microstructures, and representative
thinsections were pointcounted. Three samples were selected for Rietveld analysis to receive the chemical
compositions. Minerals from both the syncline and the area outside has been dated by the 40Ar/39Ar method.
The Hamrånge area is located in the central part of Sweden, 30 km north of Gävle, near the Baltic coast. The Hamrånge
syncline is mainly composed of well preserved supracrustal rocks belonging to the Svecofennian Domain.
The supracrustal rocks are of both sedimentary and volcanic orgins. The later ranges from mafic to felsic in composition.
In the studied area only volcanic rocks compose the bedrock. The volcanic sequence is a felsic volcanic rock occurring
in the stratigrafically lowest parts, which are overlain by minor amounts of felsic-intermediate volcanic rock.
Overlaying these rocks are mafic volcanics, dominated by mafic lavas, which is in turn overlain by maficintermediate
volcanics. Between these rocktypes and in the felsic-intermediate volcanics are minor units of mineralised
rocks. It is likely that felsic-intermediate volcanic rocks are stratigrafically on top of the mafic-intermediate
volcanic rocks. The occurrence of redeposition of some volcanics and pillow lavas indicate a marine environment.
Mainly the mafic lavas are occasionally altered to skarn.
The central part of Svecofennium has been deformed by at least two major fold and thrust episodes related to D2
and D3. A previous deformation event, D1, has been recognised in metasedimentary rocks north of the Hamrånge
syncline. The area has also been affected by later brittle deformation.
Indications of an early deformation, D1, have been found at one locality in the Hamrånge area. This fabric can be
related to either compaction or to tectonic deformation. Intense D2 deformation appears as a penetrative foliation
and a strong stretching lineation. Both isoclinal F2 folds and D2 thrusts have been identified. F3 folds have been
identified both as a regional fold and as minor open parasite folds. The F3 fold has a steep axial plane striking E-W
and a fold axis plunging c. 23° to the east.
The cooling history shows that the Hamrånge syncline and the highgrade area outside passed through the 350º isograde
at about 1.74 Ga. Both the timing and the temperature when the two curves meet suggest that deformation
occurred under semi-brittle conditions. One candidate is a deformation zone located south of the Hamrånge syncline.}},
  author       = {{Erlandsson, Maria}},
  language     = {{swe}},
  note         = {{Student Paper}},
  series       = {{Examensarbeten i geologi vid Lunds universitet}},
  title        = {{Den geologiska utvecklingen av Hamrångesynklinalens suprakrustalbergarter, centrala Sverige}},
  year         = {{2007}},
}