Dateringsmetoder för terrestriska nedslagskratrar med fokus på Siljan
(2024) In Examensarbeten i geologi vid Lunds universitet GEOL02 20241Department of Geology
- Abstract (Swedish)
- I detta arbete diskuterar jag problematiken kring olika radiometriska dateringsmetoder samt möjligheten att generera noggranna och precisa dateringar. Goda dateringar av nedslagskratrar är en förutsättning för att undersöka intensiteten av nedslag på vår planet, korrelationen till massutdöende eller de hydrotermala system som uppstår efter ett nedslag och pågår i tusentals år. Problem relaterade till såväl analytiska som geologiska orsaker kan resultera i åldrar som saknar signifikans. De senaste årtionden har däremot utvecklingen av analytiska tekniker förbättrat dateringsmetodernas precision och noggrannhet.
Dateringen av kratrar bygger på radioaktivt sönderfall där förhållandet mellan isotoper mäts för att bestämma en ålder. Kratern... (More) - I detta arbete diskuterar jag problematiken kring olika radiometriska dateringsmetoder samt möjligheten att generera noggranna och precisa dateringar. Goda dateringar av nedslagskratrar är en förutsättning för att undersöka intensiteten av nedslag på vår planet, korrelationen till massutdöende eller de hydrotermala system som uppstår efter ett nedslag och pågår i tusentals år. Problem relaterade till såväl analytiska som geologiska orsaker kan resultera i åldrar som saknar signifikans. De senaste årtionden har däremot utvecklingen av analytiska tekniker förbättrat dateringsmetodernas precision och noggrannhet.
Dateringen av kratrar bygger på radioaktivt sönderfall där förhållandet mellan isotoper mäts för att bestämma en ålder. Kratern Siljan, belägen i mellersta Sverige, har en nuvarande allmänt accepterad ålder på 380,9 ± 4,6 Ma. På grund av osäkerheter i dateringen fortgår dateringsförsöken än idag och med denna anledning ligger studiens fokus på att vidare undersöka Siljan. Eventuell korrelation mellan Siljan och massutdöendet Frasnian-Famennian är inte möjlig till följd av osäkerheter i båda dateringarna. Ytterligare noggrannhet och precision krävs.
Med polarisationsmikroskop, svepelektronmikroskop (SEM) och energidispersiv spektrometer (EDS) analyserades två tunnslip av ett bergartsprov från Siljan. Provet består av smältbreccia med syenitiska inklusioner vilka till stor del innehåller kalifältspat. Både kvarts och kalifältspat uppvisade planar deformations features (PDFs) som bildas genom chockmetamorfos. Dessutom observerades granulär zirkon vilket återspeglar höga temperaturer och tryck som berggrunden blivit utsatt för under nedslaget. Förslag på möjliga dateringsmetoder för detta bergartsprov visade sig vara U-Pb på granulära zirkonkristaller och Ar-Ar på den mest homogena smältan. Andra dateringsmetoder, såsom Rb-Sr och (U,Th)-He har inte förutsättningarna att generera lika precisa dateringar och prioriteras därför inte i samma utsträckning. (Less) - Abstract
- In this study, I discuss the issues related to radiometric dating methods and the possibility of generating accurate and precise ages. Such dating of impact craters is crucial for investigating impact intensity, correlation with mass extinctions, or the hydrothermal systems that form after an impact and last for thousands of years. Problems related to both analytical and geological causes can result in ages that lack significance. However, in recent decades, the development of analytical techniques has improved both the precision and accuracy of dating methods.
The dating of impact craters is based on radioactive decay where the ratio of isotopes is measured to determine an age. The Siljan impact structure, located in central Sweden,... (More) - In this study, I discuss the issues related to radiometric dating methods and the possibility of generating accurate and precise ages. Such dating of impact craters is crucial for investigating impact intensity, correlation with mass extinctions, or the hydrothermal systems that form after an impact and last for thousands of years. Problems related to both analytical and geological causes can result in ages that lack significance. However, in recent decades, the development of analytical techniques has improved both the precision and accuracy of dating methods.
The dating of impact craters is based on radioactive decay where the ratio of isotopes is measured to determine an age. The Siljan impact structure, located in central Sweden, has a currently widely accepted age of 380.9 ± 4.6 Ma. Due to uncertainties in the dating of Siljan, ongoing efforts to establish an age persist, and thus, the focus of the study is to further investigate Siljan. Any potential correlation between Siljan and the Frasnian-Famennian extinction event is not possible due to uncertainties in both ages. Further accuracy and precision are required.
Using a polarizing microscope, scanning electron microscope (SEM), and energy dispersive spectrometer (EDS), two thin sections of a rock sample from Siljan were analyzed. The sample consists of melt breccia with syenitic inclusions which largely contain potassium feldspar. Both quartz and potassium feldspar exhibited planar deformation features (PDFs), which forms during shock metamorphism. Additionally, granular zircon was observed, reflecting the high temperatures and pressures the bedrock was subjected to during the impact. Proposed possible dating methods for this rock sample include U-Pb on granular zircon crystals and Ar-Ar on the most homogeneous melt. Other dating methods, such as Rb-Sr and (U,Th)-He, lack the capacity to generate precise ages and are therefore not prioritized to the same extent. (Less)
Please use this url to cite or link to this publication:
http://lup.lub.lu.se/student-papers/record/9169360
- author
- Fält, Smilla LU
- supervisor
-
- Carl Alwmark LU
- organization
- course
- GEOL02 20241
- year
- 2024
- type
- M2 - Bachelor Degree
- subject
- keywords
- Radiometriska dateringsmetoder, Siljan, chockmetamorfos, hydrotermal aktivitet, granulär zirkon
- publication/series
- Examensarbeten i geologi vid Lunds universitet
- report number
- 694
- language
- Swedish
- id
- 9169360
- date added to LUP
- 2024-06-28 14:49:15
- date last changed
- 2024-06-28 14:49:15
@misc{9169360,
abstract = {{In this study, I discuss the issues related to radiometric dating methods and the possibility of generating accurate and precise ages. Such dating of impact craters is crucial for investigating impact intensity, correlation with mass extinctions, or the hydrothermal systems that form after an impact and last for thousands of years. Problems related to both analytical and geological causes can result in ages that lack significance. However, in recent decades, the development of analytical techniques has improved both the precision and accuracy of dating methods.
The dating of impact craters is based on radioactive decay where the ratio of isotopes is measured to determine an age. The Siljan impact structure, located in central Sweden, has a currently widely accepted age of 380.9 ± 4.6 Ma. Due to uncertainties in the dating of Siljan, ongoing efforts to establish an age persist, and thus, the focus of the study is to further investigate Siljan. Any potential correlation between Siljan and the Frasnian-Famennian extinction event is not possible due to uncertainties in both ages. Further accuracy and precision are required.
Using a polarizing microscope, scanning electron microscope (SEM), and energy dispersive spectrometer (EDS), two thin sections of a rock sample from Siljan were analyzed. The sample consists of melt breccia with syenitic inclusions which largely contain potassium feldspar. Both quartz and potassium feldspar exhibited planar deformation features (PDFs), which forms during shock metamorphism. Additionally, granular zircon was observed, reflecting the high temperatures and pressures the bedrock was subjected to during the impact. Proposed possible dating methods for this rock sample include U-Pb on granular zircon crystals and Ar-Ar on the most homogeneous melt. Other dating methods, such as Rb-Sr and (U,Th)-He, lack the capacity to generate precise ages and are therefore not prioritized to the same extent.}},
author = {{Fält, Smilla}},
language = {{swe}},
note = {{Student Paper}},
series = {{Examensarbeten i geologi vid Lunds universitet}},
title = {{Dateringsmetoder för terrestriska nedslagskratrar med fokus på Siljan}},
year = {{2024}},
}