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Petrography of impactites from the Dellen impact structure, Sweden

Mroczek, Robert LU (2023) In Dissertations in Geology at Lund University GEOR02 20202
Department of Geology
Abstract
Identification and characterization of shock-metamorphic features in hypervelocity impact craters is important for our understanding of how shock waves interact with geologic materials and how impact craters form, which in turn is essential to our understanding of what role impact cratering played in the development of our solar system. Of particular interest are accessory minerals like apatite, which contains various volatiles that can affect the atmosphere of a body, or magnetite whose magnetic properties constitute a remote sensing indicator which allows us to study and understand the internal structures of distant bodies. Understanding how these magnetic properties are affected by shock waves in impacts allows for better modelling and... (More)
Identification and characterization of shock-metamorphic features in hypervelocity impact craters is important for our understanding of how shock waves interact with geologic materials and how impact craters form, which in turn is essential to our understanding of what role impact cratering played in the development of our solar system. Of particular interest are accessory minerals like apatite, which contains various volatiles that can affect the atmosphere of a body, or magnetite whose magnetic properties constitute a remote sensing indicator which allows us to study and understand the internal structures of distant bodies. Understanding how these magnetic properties are affected by shock waves in impacts allows for better modelling and interpretation of data retrieved by remote sensing. This study reports on multiple examples of shock-metamorphic features from allochthonous samples retrieved from the Dellen impact structure, Sweden. Shock-metamorphic features chiefly in apatite and magnetite, but also zircon, titanite, biotite, quartz and feldspar are reported on. Apatite and magnetite grains were both found to show signs of dynamic recrystallization, and apatite also displays tentative micro-vesicles. Other shock-metamorphic features identified include ‘ballen quartz’ and baddeleyite formation in zircon. Some features were also found which may have been induced by the shock waves, but whose origins are unclear, such as exsolution textures in titanite. (Less)
Abstract (Swedish)
Identifiering och karaktärisering av chock-metamorfa strukturer i nedslagskratrar är viktigt för vår förståelse av hur chockvågor interagerar med geologiska material och hur nedslagskratrar bildas, vilket i sin tur är essentiellt för att förstå rollen meteoritnedslag har spelat under vårt solsystems utveckling. Accessoriska mineral är av speciellt intresse. Två av dessa är Apatit, vilket innehåller volatiler som kan påverka atmosfären på en kropp, och magnetit, vars magnetiska egenskaper är viktiga för fjärranalys. Att förstå hur dessa magnetiska egenskaper i magnetiska mineral förändras efter att ha utsatts för chockvågor tillåter bättre modellering och tolkning av fjärranalys-data. Denna studie rapporterar flera exempel på... (More)
Identifiering och karaktärisering av chock-metamorfa strukturer i nedslagskratrar är viktigt för vår förståelse av hur chockvågor interagerar med geologiska material och hur nedslagskratrar bildas, vilket i sin tur är essentiellt för att förstå rollen meteoritnedslag har spelat under vårt solsystems utveckling. Accessoriska mineral är av speciellt intresse. Två av dessa är Apatit, vilket innehåller volatiler som kan påverka atmosfären på en kropp, och magnetit, vars magnetiska egenskaper är viktiga för fjärranalys. Att förstå hur dessa magnetiska egenskaper i magnetiska mineral förändras efter att ha utsatts för chockvågor tillåter bättre modellering och tolkning av fjärranalys-data. Denna studie rapporterar flera exempel på chock-metamorfa strukturer i alloktona prover insamlade från nedslagskratern Dellen i Sverige. Chock-metamorfa strukturer rapporteras framför allt i apatit och magnetit, men även zircon, titanit, biotit, kvarts och fältspat. Både apatit och magnetit har blivit granulära, medan apatit även innehåller mikro-vesikler och potentiella tecken på att avgasning har orsakat frakturering av apatitkorn. Andra chock-metamorfa strukturer som hittats inkluderar ’ballen kvarts’ och baddeleyit-formation i zircon. Andra strukturer som också kan ha orsakats av chock-vågorna men som är osäkra inkluderar utfällningstexturer i titanit. (Less)
Popular Abstract
140 Million years ago, a meteorite traveling at tens of kilometers per second struck ground in what
is today central Sweden. The impact formed an impact structure measuring at least 20 km across.
Powerful shock waves caused by the impact excavated a crater and gave rise to microscopic effects
in the constituent minerals of the impacted area. Understanding these features advances our
ability to read the planetary evolution of our solar system and beyond.
Samples of impactites (rock-and sediment types created
by the impact) have been retrieved from the shores of
the Dellen lakes and examined with scanning electron
and polarizing microscopes in hopes of furthering our
knowledge of how accessory minerals react to the shock
... (More)
140 Million years ago, a meteorite traveling at tens of kilometers per second struck ground in what
is today central Sweden. The impact formed an impact structure measuring at least 20 km across.
Powerful shock waves caused by the impact excavated a crater and gave rise to microscopic effects
in the constituent minerals of the impacted area. Understanding these features advances our
ability to read the planetary evolution of our solar system and beyond.
Samples of impactites (rock-and sediment types created
by the impact) have been retrieved from the shores of
the Dellen lakes and examined with scanning electron
and polarizing microscopes in hopes of furthering our
knowledge of how accessory minerals react to the shock
waves of hypervelocity impact. Minerals such as apatite,
magnetite, quartz, feldspars, zircon, biotite and titanite
among others have all been affected by the event,
showing unique crystallization and deformation which
can tell us what the conditions at the time of impact
were and how they could affect earth and other bodies
were impacts to occur there.
Minerals are the constituents of rocks, and when a
mineral such as apatite undergoes metamorphism due
to changes in temperature or pressure, it can release
water and other molecules which can form
atmospheres or oceans.
Magnetic minerals can help us in other ways to understand. measuring magnetic parameters can teach us
about surface changes of other planets such as Mars. Magnetite is by far the most important magnetic
mineral in such measurements because of its abundance and ability to be magnetized.
The magnetite grains from Dellen shows clear signs of having recrystallized into tiny subgrains
measuring 1 micrometre across in the most shocked samples. Such recrystallization into smaller
crystals negatively affects the magnetic properties of magnetite and may be the cause of a
widespread grading -7 mGal magnetic anomaly in the Dellen area.
The apatite on the other hand, aside from recrystallizing, shows signs of having possibly released
part of its volatile contents, displaying what is thought to be vesicles created following the passage
of the shock wave and that may have played a part in shattering its host crystal. There is also
opposing signs, however. EDS analysis of apatite grains showed no clear sign that degassing had
occurred. Whether shock-metamorphism can cause the degassing of apatite remains unanswered
yet, but there are some signs that it may be the case. Further research into the microscopic features
found in apatite such as those found in Dellen could soon reveal an answer (Less)
Please use this url to cite or link to this publication:
author
Mroczek, Robert LU
supervisor
organization
alternative title
Petrografi av impaktiter från impact strukturen i Dellen, Sverige
course
GEOR02 20202
year
type
H2 - Master's Degree (Two Years)
subject
keywords
Dellen, Impact, structure, magnetite, apatite, shock waves, shock-metamorphic, features, Impactite, petrography, scanning electron microscope, SEM, geology
publication/series
Dissertations in Geology at Lund University
report number
648
language
English
id
9111216
date added to LUP
2023-02-21 11:56:10
date last changed
2023-02-21 11:56:10
@misc{9111216,
  abstract     = {{Identification and characterization of shock-metamorphic features in hypervelocity impact craters is important for our understanding of how shock waves interact with geologic materials and how impact craters form, which in turn is essential to our understanding of what role impact cratering played in the development of our solar system. Of particular interest are accessory minerals like apatite, which contains various volatiles that can affect the atmosphere of a body, or magnetite whose magnetic properties constitute a remote sensing indicator which allows us to study and understand the internal structures of distant bodies. Understanding how these magnetic properties are affected by shock waves in impacts allows for better modelling and interpretation of data retrieved by remote sensing. This study reports on multiple examples of shock-metamorphic features from allochthonous samples retrieved from the Dellen impact structure, Sweden. Shock-metamorphic features chiefly in apatite and magnetite, but also zircon, titanite, biotite, quartz and feldspar are reported on. Apatite and magnetite grains were both found to show signs of dynamic recrystallization, and apatite also displays tentative micro-vesicles. Other shock-metamorphic features identified include ‘ballen quartz’ and baddeleyite formation in zircon. Some features were also found which may have been induced by the shock waves, but whose origins are unclear, such as exsolution textures in titanite.}},
  author       = {{Mroczek, Robert}},
  language     = {{eng}},
  note         = {{Student Paper}},
  series       = {{Dissertations in Geology at Lund University}},
  title        = {{Petrography of impactites from the Dellen impact structure, Sweden}},
  year         = {{2023}},
}