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U-Pb datering av zirkon från migmatitisk gnejs i Delsjöområdet, Idefjordenterrängen

Ingered, Mimmi LU (2017) In Examensarbeten i geologi vid Lunds universitet GEOL01 20171
Department of Geology
Abstract (Swedish)
Under den Svekonorvegiska orogenesen omkristalliserade stora delar av sydvästra Sverige och bildade metamorfa migmatitiska gnejser. I Idefjordenterrängen, väster om Mylonitzonen, har migmatiterna inte daterats och då kunskapen om de metamorfa processerna i området brister kan migmatiterna ge en bättre bild av när metamorfosen skedde. En migmatitisk gnejs från Delsjöområdet i östra Göteborg har daterats för att undersöka om migmatitbildningen i Idefjordenterrängen är av Svekonorvegisk ålder. U-Pb datering på zirkon från migmatiten har utförts med Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) och skottpunkter bestämdes i förhand i svepelektronmikroskop (SEM) med katodluminiscens (CL) och backscattered electron... (More)
Under den Svekonorvegiska orogenesen omkristalliserade stora delar av sydvästra Sverige och bildade metamorfa migmatitiska gnejser. I Idefjordenterrängen, väster om Mylonitzonen, har migmatiterna inte daterats och då kunskapen om de metamorfa processerna i området brister kan migmatiterna ge en bättre bild av när metamorfosen skedde. En migmatitisk gnejs från Delsjöområdet i östra Göteborg har daterats för att undersöka om migmatitbildningen i Idefjordenterrängen är av Svekonorvegisk ålder. U-Pb datering på zirkon från migmatiten har utförts med Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) och skottpunkter bestämdes i förhand i svepelektronmikroskop (SEM) med katodluminiscens (CL) och backscattered electron imaging (BSE). I CL kunde komplexa kärnor och tydliga tillväxtzoner urskiljas i zirkonkristallerna som har olika dateringar och Th/U. Viktade medelvärden för konkordanta data ger 207Pb/ 206Pb = 1598 ± 6,6 Ma (MSWD = 0,89) för magmatiskt zonerade kärnor med Th/U > 0,2 respektive 1002 ± 9 Ma (MSWD = 0,09) för tillväxtzoner och enskilda korn från leucosom. Den yngre populationen har Th/U < 0,01 och antas ha ett metamorft ursprung. Den äldre populationen tolkas som protolitens magmatiska kristallisationsålder och den yngre populationen som åldern på migmatitbildning i samband med den Svekonorvegiska orogenesen. Ett par zirkoner ger dateringar upp mot 1700 Ma, vilket kan utgöra ärvda komponenter. (Less)
Abstract
During the Sveconorwegian orogenesis, parts of southwestern Sweden was recrystallized and formed metamorphic migmatites. In the Idefjorden terrane, west of the Mylonite zone, the migmatites have not been dated and since knowledge of the metamorphic processes in the area is lacking, the migmatites can provide better constraints of when metamorphosis occurred. A migmatitic gneiss from the Delsjö area in eastern Gothenburg has been dated to investigate whether migmatite formation in the Idefjorden terrane is of Sveconorwegian age. U-Pb dating of zircon from the migmatite has been done with Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) after selecting points for analyses in scanning electron microscopy (SEM) with... (More)
During the Sveconorwegian orogenesis, parts of southwestern Sweden was recrystallized and formed metamorphic migmatites. In the Idefjorden terrane, west of the Mylonite zone, the migmatites have not been dated and since knowledge of the metamorphic processes in the area is lacking, the migmatites can provide better constraints of when metamorphosis occurred. A migmatitic gneiss from the Delsjö area in eastern Gothenburg has been dated to investigate whether migmatite formation in the Idefjorden terrane is of Sveconorwegian age. U-Pb dating of zircon from the migmatite has been done with Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) after selecting points for analyses in scanning electron microscopy (SEM) with cathodoluminescence (CL) and backscattered electron imaging (BSE). In CL, complex cores and clear growths zones could be distinguished in the zircon crystals, which have different dates and Th/U ratios. Weighted mean values for concordant data yield 207Pb/ 206Pb = 1598 ± 6.6 Ma (MSWD = 0.89) for magmatically zoned cores with Th/U > 0.2 and 1002 ± 9 Ma (MSWD = 0.09) for rims as well as for individual grains from leucosome. The younger population zircon has Th/U < 0.01 and is interpreted to have a metamorphic origin. The old population is interpreted as the magmatic crystallization age of the protolith and the younger populations as the age of migmatization in conjunction with the Sveconorwegian orogenesis. A few zircons yielded 207Pb/ 206Pb dates of 1700 Ma and may represent inherited cores. (Less)
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author
Ingered, Mimmi LU
supervisor
organization
course
GEOL01 20171
year
type
M2 - Bachelor Degree
subject
keywords
Svekonorvegiska orogenesen, Idefjordenterrängen, U-Pb, Migmatit, Zirkon, LA-ICP-MS
publication/series
Examensarbeten i geologi vid Lunds universitet
report number
512
language
Swedish
id
8918456
date added to LUP
2017-06-26 15:16:34
date last changed
2017-06-26 15:16:34
@misc{8918456,
  abstract     = {During the Sveconorwegian orogenesis, parts of southwestern Sweden was recrystallized and formed metamorphic migmatites. In the Idefjorden terrane, west of the Mylonite zone, the migmatites have not been dated and since knowledge of the metamorphic processes in the area is lacking, the migmatites can provide better constraints of when metamorphosis occurred. A migmatitic gneiss from the Delsjö area in eastern Gothenburg has been dated to investigate whether migmatite formation in the Idefjorden terrane is of Sveconorwegian age. U-Pb dating of zircon from the migmatite has been done with Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) after selecting points for analyses in scanning electron microscopy (SEM) with cathodoluminescence (CL) and backscattered electron imaging (BSE). In CL, complex cores and clear growths zones could be distinguished in the zircon crystals, which have different dates and Th/U ratios. Weighted mean values for concordant data yield 207Pb/ 206Pb = 1598 ± 6.6 Ma (MSWD = 0.89) for magmatically zoned cores with Th/U > 0.2 and 1002 ± 9 Ma (MSWD = 0.09) for rims as well as for individual grains from leucosome. The younger population zircon has Th/U < 0.01 and is interpreted to have a metamorphic origin. The old population is interpreted as the magmatic crystallization age of the protolith and the younger populations as the age of migmatization in conjunction with the Sveconorwegian orogenesis. A few zircons yielded 207Pb/ 206Pb dates of 1700 Ma and may represent inherited cores.},
  author       = {Ingered, Mimmi},
  keyword      = {Svekonorvegiska orogenesen,Idefjordenterrängen,U-Pb,Migmatit,Zirkon,LA-ICP-MS},
  language     = {swe},
  note         = {Student Paper},
  series       = {Examensarbeten i geologi vid Lunds universitet},
  title        = {U-Pb datering av zirkon från migmatitisk gnejs i Delsjöområdet, Idefjordenterrängen},
  year         = {2017},
}