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Petrological study of the metamafic rocks across the Småland-Blekinge Deformation Zone

Rimša, Andrius (2002) In Dissertations in Geology at Lund University
Department of Geology
Abstract (Swedish)
Den viktigaste tektoniska strukturen i Blekinge-Bornholm Provinsen (BBP), i sydost Blekinge, är den s.k. Småland-Blekinge Deformationszonen (SBDZ). Denna zon har en ungefärlig ost-västlig orientering och separerar Smålandsgranitoiderna, tillhörande TIB i norr från Tvingsgranitoider (graniter, granodioriter, tonaliter) i söder. Detta arbete en petrologisk och geokemisk jämnförelse av små mafiska massiv som förekommer i granitoiderna på båda sidor av SBDZ.

Huvuddelen av de finkorniga, metamorfoserade, mafiska bergarterna (i fortsättningen kallade för metamafiska bergarter) norr om SBDZ är strikt kalk-alkalina, vars sammansättning varierar från basalt-andesiter till andesiter. Samtidigt uppvisar de finkristallina metamafiska bergarterna... (More)
Den viktigaste tektoniska strukturen i Blekinge-Bornholm Provinsen (BBP), i sydost Blekinge, är den s.k. Småland-Blekinge Deformationszonen (SBDZ). Denna zon har en ungefärlig ost-västlig orientering och separerar Smålandsgranitoiderna, tillhörande TIB i norr från Tvingsgranitoider (graniter, granodioriter, tonaliter) i söder. Detta arbete en petrologisk och geokemisk jämnförelse av små mafiska massiv som förekommer i granitoiderna på båda sidor av SBDZ.

Huvuddelen av de finkorniga, metamorfoserade, mafiska bergarterna (i fortsättningen kallade för metamafiska bergarter) norr om SBDZ är strikt kalk-alkalina, vars sammansättning varierar från basalt-andesiter till andesiter. Samtidigt uppvisar de finkristallina metamafiska bergarterna söder om SBDZ en basaltisk sammansättning kan vidare indelas i två grupper: den ena uppvisar en basaltisk sammansättning och tillhör en kalk-alkalin serie, medan den andra tillhör en tholeiitisk serien. Geokemi och isotopdata indikerar att samtliga finkorniga metamafiska bergarter på bägge sidor om SBDZ tillhör samma bergartssvit. Förutom de två förstnämnda grupperna uppträder olivingabbro och metagabbro tillsammans i Rödebymassivet. Olivingabbron i Rödebymassivet är ometamorfoserad och odeformerad, medan metagabbron antas vara en starkt deformerade och retrogradmetamorfoserade delen av intrusionen. Massivets förhållande till de finkorniga, metamafiska bergarterna är inte utrett.

Mingling och lokaliserad mixing mellan granitoiderna och mafiska bergarter på ömse sidor av SBDZ indikerar en liknande ålder för de metamafiska bergarterna som för Smålands- och Tvingsgranitoiderna, nämligen 1770-1800 Ma. Geokemi och isotopdata antyder en enhetligt utarmad mantel som källa för de mafiska bergarterna på ömse sidor av SBDZ och stödjer därmed Kornfälts (2000) hypotes om en sammanhängande terräng vid tiden för av den mafiska magmatismen. Dessutom antyder skillnader i huvudelementkoncentrationen kontaminering av den mafiska smältan med äldre jordskorpematerial av olikartad sammansättning på ömse sidor av SBDZ.

Spårelementfördelningen för de metamafiska bergarterna liknar den för destruktiva plattgränser och ger stöd för tolkningen att TIB bildades längs en konvergerande plattgräns liknande den för Anderna idag. (Less)
Abstract
The Blekinge-Bornholm province (BBP), in the south-eastern part of Blekinge, consists of foliated granite, granodiorite and tonalite, collectively called the Tving granitoids. The most important tectonic feature in the area is the Småland-Blekinge Deformation Zone (SBDZ). This approximately E-W trending zone separates the TIB Småland-type granitoids in the north from the Tving granitoids in the south. This work focuses on petrological and geochemical comparison of the minor mafic rock bodies occurring mostly within the granitoids on both sides of the SBDZ.

The majority of the metamorphosed, fine-grained mafic rocks (hereafter called “metamafic rocks”) to the north of the SBDZ is strictly calc-alkaline, having basalt-andesitic or... (More)
The Blekinge-Bornholm province (BBP), in the south-eastern part of Blekinge, consists of foliated granite, granodiorite and tonalite, collectively called the Tving granitoids. The most important tectonic feature in the area is the Småland-Blekinge Deformation Zone (SBDZ). This approximately E-W trending zone separates the TIB Småland-type granitoids in the north from the Tving granitoids in the south. This work focuses on petrological and geochemical comparison of the minor mafic rock bodies occurring mostly within the granitoids on both sides of the SBDZ.

The majority of the metamorphosed, fine-grained mafic rocks (hereafter called “metamafic rocks”) to the north of the SBDZ is strictly calc-alkaline, having basalt-andesitic or andesitic compositions. To the south of the SBDZ, however, the fine-grained metamafic rocks have a basaltic composition but splits into two subgroups: one belonging to the calc-alkaline series, the other one to the tholeiitic series. The geochemical and isotopic data suggest that all the fine-grained metamafic rocks across the SBDZ belong to the same rock suite. In addition to the fine-grained metamafic rocks, olivine gabbro and metagabbro compose the Rödeby massif. Here, the olivine gabbro is essentially not metamorphosed and not deformed, whereas the metagabbro probably represents intensely deformed and retrograde metamorphosed parts of the olivine-gabbro intrusion. The relationships of these gabbros with the fine-grained metamafic rocks have not been established.

Mingling and localized mixing between the granitoids and the mafic rocks across the SBDZ evidence for identical ages for the metamafic rocks and the Småland and Tving granitoids, i.e. 1770-1800 Ma. Chemical and isotopic data suggest a uniform depleted mantle source for the mafic rocks and support the hypothesis of Kornfält (2000) of a coherent terrane of the mafic magmatism subsequently cut by the SBDZ. However, the major element variation pattern suggests contamination of the mafic melts by a pre-existing crust that was compositionally different on either side of the SBDZ.

The trace-element characteristics of the metamafic rocks are similar to those of mafic rocks in destructive plate margin environments, which supports the hypothesis that the TIB was formed in an Andinotype, convergent-margin environment. (Less)
Abstract
Popular science abstract: The eastern part of Blekinge consists of foliated granitic rocks, collectively called the Tving granitoids.
The most important tectonic feature in the area is the Småland-Blekinge Deformation Zone (SBDZ). This deformation zone is a result of movements in the Earth's crust along which rocks have been squeezed in.
This movement zone indicates that the part of Blekinge that is situated to the south of the SBDZ was uplifted along this zone compared to its northern side.
To the north of this approximately EW-trending zone the Småland-type granitoids appear, which are part of the Transscandinavian lgneous Belt (TIB). The TIB is a 1.85- 1.65 billion years old giant array of granitoids extending for more than 1500 km... (More)
Popular science abstract: The eastern part of Blekinge consists of foliated granitic rocks, collectively called the Tving granitoids.
The most important tectonic feature in the area is the Småland-Blekinge Deformation Zone (SBDZ). This deformation zone is a result of movements in the Earth's crust along which rocks have been squeezed in.
This movement zone indicates that the part of Blekinge that is situated to the south of the SBDZ was uplifted along this zone compared to its northern side.
To the north of this approximately EW-trending zone the Småland-type granitoids appear, which are part of the Transscandinavian lgneous Belt (TIB). The TIB is a 1.85- 1.65 billion years old giant array of granitoids extending for more than 1500 km in N-S direction across Scandinavia. The Tving granitoids appearing to the south of the SBDZ belong to a problematic geological unit, because it is unclear whether they are part of the TIB or if they belong to different geological terrane. I tried to answer this question by comparing small mafic rock massifs, which appear within the granitoids on both sides of the SBDZ. Field and microscopic observation, together with geochemical models indicate mingling and localized mixing between the granitoids and mafic rocks across the SBDZ. Mafic and granitic magmas have different physical properties, therefore they do not mix and behave like water and oil in the same pot. The mingling is an indicator that granitic and mafic magmas were intruding each other while they were still not totally crystallized, i. e. both rocks are of the same age and originated during the same magmatic event.
The metamorphosed, fine-grained mafic rocks are similar on both sides of the SBDZ. The geochemical data, which are sensitive to preserve the characteristics of the source of the melt, suggest that all the fine-grained mafic rocks across SBDZ were derived from the same source, i.e. formed during the same magmatic event.
Keeping in mind that all the metamafic rocks belong to the same rock suite and have formed during the same igneous event as the granitoids across the SBDZ it is logical to conclude that the eastern Blekinge
granitoids should be included in to the TIB.
Mafic rocks are formed during melting of the mantle. Certain chemical elements can be used to get a hint in which plate tectonic situation, they, and related granitoids, were formed.
The geochemical data of metamafic rocks across the SBDZ are similar to those in a subductian zone, where one plate is subducting under another like a floe in the ice-drift. The best recent example of such a plate tectonic situation is the western coast of South America, where the Andes mountain chain is still building up due to subduction of the Pacific oceanic plate under the South American continental plate.
If one decides to make an excursion in time and space to experience how Småland and Blekinge looked like
l,8 billion years ago - the Andes are the most recommended location! (Less)
Please use this url to cite or link to this publication:
author
Rimša, Andrius
supervisor
organization
alternative title
Petrologisk undersökning av metamafiska bergarter på bägge sidor om Småland-Blekinge Deformationszonen
year
type
H1 - Master's Degree (One Year)
subject
keywords
Småland-Blekinge Deformation Zone, petrology, geology, geography, metamafic rocks
publication/series
Dissertations in Geology at Lund University
report number
154
funder
Svenska Institutet
language
English
id
2342828
date added to LUP
2012-12-05 13:19:05
date last changed
2015-06-18 14:04:23
@misc{2342828,
  abstract     = {Popular science abstract: The eastern part of Blekinge consists of foliated granitic rocks, collectively called the Tving granitoids.
The most important tectonic feature in the area is the Småland-Blekinge Deformation Zone (SBDZ). This deformation zone is a result of movements in the Earth's crust along which rocks have been squeezed in.
This movement zone indicates that the part of Blekinge that is situated to the south of the SBDZ was uplifted along this zone compared to its northern side.
To the north of this approximately EW-trending zone the Småland-type granitoids appear, which are part of the Transscandinavian lgneous Belt (TIB). The TIB is a 1.85- 1.65 billion years old giant array of granitoids extending for more than 1500 km in N-S direction across Scandinavia. The Tving granitoids appearing to the south of the SBDZ belong to a problematic geological unit, because it is unclear whether they are part of the TIB or if they belong to different geological terrane. I tried to answer this question by comparing small mafic rock massifs, which appear within the granitoids on both sides of the SBDZ. Field and microscopic observation, together with geochemical models indicate mingling and localized mixing between the granitoids and mafic rocks across the SBDZ. Mafic and granitic magmas have different physical properties, therefore they do not mix and behave like water and oil in the same pot. The mingling is an indicator that granitic and mafic magmas were intruding each other while they were still not totally crystallized, i. e. both rocks are of the same age and originated during the same magmatic event.
The metamorphosed, fine-grained mafic rocks are similar on both sides of the SBDZ. The geochemical data, which are sensitive to preserve the characteristics of the source of the melt, suggest that all the fine-grained mafic rocks across SBDZ were derived from the same source, i.e. formed during the same magmatic event.
Keeping in mind that all the metamafic rocks belong to the same rock suite and have formed during the same igneous event as the granitoids across the SBDZ it is logical to conclude that the eastern Blekinge
granitoids should be included in to the TIB.
Mafic rocks are formed during melting of the mantle. Certain chemical elements can be used to get a hint in which plate tectonic situation, they, and related granitoids, were formed.
The geochemical data of metamafic rocks across the SBDZ are similar to those in a subductian zone, where one plate is subducting under another like a floe in the ice-drift. The best recent example of such a plate tectonic situation is the western coast of South America, where the Andes mountain chain is still building up due to subduction of the Pacific oceanic plate under the South American continental plate.
If one decides to make an excursion in time and space to experience how Småland and Blekinge looked like 
l,8 billion years ago - the Andes are the most recommended location!},
  author       = {Rimša, Andrius},
  keyword      = {Småland-Blekinge Deformation Zone,petrology,geology,geography,metamafic rocks},
  language     = {eng},
  note         = {Student Paper},
  series       = {Dissertations in Geology at Lund University},
  title        = {Petrological study of the metamafic rocks across the Småland-Blekinge Deformation Zone},
  year         = {2002},
}