U-Pb datering av zirkon i metasediment tillhörande Stora Le-Marstrand, SV Sverige
(2023) In Examensarbeten i geologi vid Lunds universitet GEOL02 20231Department of Geology
- Abstract (Swedish)
- Under den cirka en miljard år gamla Svekonorvegiska orogenesen deformerades den västra randzonen av Fennoskandiska urbergsskölden. Denna händelse ligger till grund för hur sydvästra Skandinaviens berggrund ser ut idag, men det är ännu omdiskuterat hur orogenesen skedde i detalj. Idefjordenterrängen som avgränsas till Östra Segmentet av Mylonitzonen, innehåller sekvenser av metasediment tillhörande Stora-Le Marstrandformationen. Detrital zirkon från denna formation har i denna studie åldersbestämts för att undersöka varifrån sedimentet har sitt ursprung. Dessa resultat har betydelse för om Idefjorden ska betraktas som en ”exotisk” terräng relativt Fennoskandia och därmed om Mylonitzonen representerar en kollisionssutur eller en intrakrustal... (More)
- Under den cirka en miljard år gamla Svekonorvegiska orogenesen deformerades den västra randzonen av Fennoskandiska urbergsskölden. Denna händelse ligger till grund för hur sydvästra Skandinaviens berggrund ser ut idag, men det är ännu omdiskuterat hur orogenesen skedde i detalj. Idefjordenterrängen som avgränsas till Östra Segmentet av Mylonitzonen, innehåller sekvenser av metasediment tillhörande Stora-Le Marstrandformationen. Detrital zirkon från denna formation har i denna studie åldersbestämts för att undersöka varifrån sedimentet har sitt ursprung. Dessa resultat har betydelse för om Idefjorden ska betraktas som en ”exotisk” terräng relativt Fennoskandia och därmed om Mylonitzonen representerar en kollisionssutur eller en intrakrustal deformationszon. U-Pb datering av zirkon utfördes med Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). Skottpunkter bestämdes i förväg med svepelektronmikroskopi (SEM). Åldersdata som betraktas geologiskt signifikanta (≤ 10% diskordanta) avslöjar två distinkta ålderspopulationer, där den yngre har ett viktat medelvärde vid 1611±4 Ma (n = 69/72; MSWD = 2), vilket sammanfaller med Idefjordens protolitåldrar, och framför allt med granitoider tillhörande Göteborg-Åmål bältet. Den äldre ålderspopulationen utgör ett intervall av åldrar mellan 1972 och 1654 Ma, vilket sammanfaller med protolitåldrar för gnejser i Östra Segmentet, det vill säga Transskandinaviska Magmatiska Bältet (TIB) och bergarter tillhörande den Svekofenniska orogenen. En enstaka zirkon har en arkeisk ålder på cirka 2703 Ma. Th/U för zirkonerna är mellan 0,21 och 1,68, vilket är typiskt för primärt magmatiskt bildade zirkon. Resultaten påvisar att metasedimentet som idag utgör Stora Le-Marstrand har flera ursprung och att Idefjorden sannolikt befann sig i ungefär samma position relativt Östra Segmentet som det gör idag. Är denna tolkning korrekt ska Mylonitzonen betraktas som en intrakrustal deformationszon. (Less)
- Abstract
- The approximately 1 Ga old Sveconorwegian orogen occupies the western margin of the Fennoscandian shield and comprise tectonically reworked and metamorphosed rocks. This event accounts for the characteristics of the bedrock in southwest Scandinavia today, but it is still debated how this development took place in detail, and especially if it was a collisional or non-collisional orogeny. The Idefjorden terrane, which is delimited to the Eastern Segment by the Mylonite Zone, contains sequences of metasediments belonging to the Stora Le-Marstrand Formation. In this study, detrital zircon from this formation have been dated to investigate the origin of the sediment. These results have implications for whether the Idefjorden terrane was... (More)
- The approximately 1 Ga old Sveconorwegian orogen occupies the western margin of the Fennoscandian shield and comprise tectonically reworked and metamorphosed rocks. This event accounts for the characteristics of the bedrock in southwest Scandinavia today, but it is still debated how this development took place in detail, and especially if it was a collisional or non-collisional orogeny. The Idefjorden terrane, which is delimited to the Eastern Segment by the Mylonite Zone, contains sequences of metasediments belonging to the Stora Le-Marstrand Formation. In this study, detrital zircon from this formation have been dated to investigate the origin of the sediment. These results have implications for whether the Idefjorden terrane was “exotic” relative to Fennoscandia before the orogeny or if it was a part of the shield. This has also implications on what type of tectonic structure the Mylonite Zone represents, whether it constitutes a true collisional suture or represents an intracrustal deformation zone. U-Pb dating of zircon was done using Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). Specific spots where selected using a scanning electron microscope (SEM). Age data considered geologically significant (≤ 10% discordant) reveal two distinct age populations, with the younger having a weighted mean of 1611±4 Ma (n=69/72; MSWD = 2), which coincides with Idefjorden protolith ages, in particular with granitoids belonging to the Göteborg-Åmål Belt. The older population comprise a range of ages from 1972 Ma to 1654 Ma, which coincides with protolith ages of the Transscandinavian Igneous Belt (TIB) in the Eastern Segment, and the Svecofennian Orogen further to the northeast. A single zircon yields an Archean age of about 2703 Ma. Th/U ratios of the zircons are between 0,21 and 1,68, which is typical for magmatic zircon. These results indicate that the metasediment of Stora Le-Marstrand have two main, relatively proximate, sources and that Idefjorden prior to the Sveconorwegian orogeny was in approximately the same position relative to the Eastern Segment as today. If this is correct the Mylonite zone represents an intracrustal deformation zone and not a collisional suture. (Less)
Please use this url to cite or link to this publication:
http://lup.lub.lu.se/student-papers/record/9133243
- author
- Lindow, Wilma LU
- supervisor
- organization
- course
- GEOL02 20231
- year
- 2023
- type
- M2 - Bachelor Degree
- subject
- keywords
- Sveconorwegian orogeny, Stora Le-Marstrand, Mylonite Zone, Zircon, U-Pb, LA-ICP-MS
- publication/series
- Examensarbeten i geologi vid Lunds universitet
- report number
- 663
- language
- Swedish
- id
- 9133243
- date added to LUP
- 2023-08-03 09:48:54
- date last changed
- 2023-08-03 09:48:54
@misc{9133243,
abstract = {{The approximately 1 Ga old Sveconorwegian orogen occupies the western margin of the Fennoscandian shield and comprise tectonically reworked and metamorphosed rocks. This event accounts for the characteristics of the bedrock in southwest Scandinavia today, but it is still debated how this development took place in detail, and especially if it was a collisional or non-collisional orogeny. The Idefjorden terrane, which is delimited to the Eastern Segment by the Mylonite Zone, contains sequences of metasediments belonging to the Stora Le-Marstrand Formation. In this study, detrital zircon from this formation have been dated to investigate the origin of the sediment. These results have implications for whether the Idefjorden terrane was “exotic” relative to Fennoscandia before the orogeny or if it was a part of the shield. This has also implications on what type of tectonic structure the Mylonite Zone represents, whether it constitutes a true collisional suture or represents an intracrustal deformation zone. U-Pb dating of zircon was done using Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). Specific spots where selected using a scanning electron microscope (SEM). Age data considered geologically significant (≤ 10% discordant) reveal two distinct age populations, with the younger having a weighted mean of 1611±4 Ma (n=69/72; MSWD = 2), which coincides with Idefjorden protolith ages, in particular with granitoids belonging to the Göteborg-Åmål Belt. The older population comprise a range of ages from 1972 Ma to 1654 Ma, which coincides with protolith ages of the Transscandinavian Igneous Belt (TIB) in the Eastern Segment, and the Svecofennian Orogen further to the northeast. A single zircon yields an Archean age of about 2703 Ma. Th/U ratios of the zircons are between 0,21 and 1,68, which is typical for magmatic zircon. These results indicate that the metasediment of Stora Le-Marstrand have two main, relatively proximate, sources and that Idefjorden prior to the Sveconorwegian orogeny was in approximately the same position relative to the Eastern Segment as today. If this is correct the Mylonite zone represents an intracrustal deformation zone and not a collisional suture.}},
author = {{Lindow, Wilma}},
language = {{swe}},
note = {{Student Paper}},
series = {{Examensarbeten i geologi vid Lunds universitet}},
title = {{U-Pb datering av zirkon i metasediment tillhörande Stora Le-Marstrand, SV Sverige}},
year = {{2023}},
}