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Classification of four mesosiderites and implications for their formation

Zachén, Gabriel LU (2020) In Dissertations in Geology at Lund University GEOR02 20192
Department of Geology
Abstract
Mesosiderites are rare stony-iron meteorites with enigmatic origins. Their unusual mix of crustal and
core materials have inspired many formation theories over the last century. Some of the outstanding questions have
regarded the origin of the metal, whether it came from another celestial body or from within the parent body, and
the absence of mantle material. The role of impacts has been central to the theories, and yet the mesosiderites show
little evidence of shock. The mystery of the origin of mesosiderites is further compounded by the lack of study, as
well as scarcity of samples. This thesis was designed to rectify this with the classification of the mesosiderites
Lamont, Acfer 265, QUE 86900, and MAC 88102, together with... (More)
Mesosiderites are rare stony-iron meteorites with enigmatic origins. Their unusual mix of crustal and
core materials have inspired many formation theories over the last century. Some of the outstanding questions have
regarded the origin of the metal, whether it came from another celestial body or from within the parent body, and
the absence of mantle material. The role of impacts has been central to the theories, and yet the mesosiderites show
little evidence of shock. The mystery of the origin of mesosiderites is further compounded by the lack of study, as
well as scarcity of samples. This thesis was designed to rectify this with the classification of the mesosiderites
Lamont, Acfer 265, QUE 86900, and MAC 88102, together with petrographic analysis of their textures. The classification
and analyses are performed with the help of polarised microscopy, SEM-EDS, and Raman spectrometry.
Lamont is classified as a B4, Acfer 265 and QUE 86900 as A1, and MAC 88102 as an A4 mesosiderite. Observations
of sets of parallel lamellae in cristobalite and anorthite in Lamont, and an immiscible silicate emulsion and
pyroxene-troilite melt droplets in QUE 86900 are proposed to be shock-related features. In Lamont, these textures
are interpreted to be subsequent to the initial impact which mixed crustal and core material, and prior to deep burial.
The textures in QUE 86900 are interpreted as coeval with the initial impact. Finally, a modified theory of formation
for mesosiderites is presented, where the textural sub-groups formed as a result of variable initial burial depth and
subsequent shock- and thermal metamorphism caused by impact gardening. In this modified theory, continuous
accretion of material forms a thick and thermally insulating regolith, necessary for the slow cooling rates observed
in mesosiderites. (Less)
Abstract (Swedish)
Mesosideriter är sällsynta sten-järnmeteoriter med ett gåtfullt ursprung. Deras ovanliga blandning
av skorp- och kärnmaterial har föranlett många bildningsteorier under det senaste århundradet. Några frågor
har avsett ursprunget till metallen, huruvida den kom från en annan himlakropp, eller från moderkroppens egen
kärna, samt varför det finns så pass lite mantelmaterial. Nedslag har haft en central roll i teorierna, men mesosideriterna
visar få spår av chockmetamorfos. Brist på forskning och meteoritprover amplifierar mesosideriternas enigmatiska
natur. Detta examensarbete formulerades för att föra forskningen framåt, med klassificering av mesosideriterna
Lamont, Acfer 265, QUE 86900, och MAC 88102, tillsammans med petrografisk... (More)
Mesosideriter är sällsynta sten-järnmeteoriter med ett gåtfullt ursprung. Deras ovanliga blandning
av skorp- och kärnmaterial har föranlett många bildningsteorier under det senaste århundradet. Några frågor
har avsett ursprunget till metallen, huruvida den kom från en annan himlakropp, eller från moderkroppens egen
kärna, samt varför det finns så pass lite mantelmaterial. Nedslag har haft en central roll i teorierna, men mesosideriterna
visar få spår av chockmetamorfos. Brist på forskning och meteoritprover amplifierar mesosideriternas enigmatiska
natur. Detta examensarbete formulerades för att föra forskningen framåt, med klassificering av mesosideriterna
Lamont, Acfer 265, QUE 86900, och MAC 88102, tillsammans med petrografisk analys av deras texturer.
Klassificering och petrografisk analys utfördes med hjälp av polarisationsmikroskopi, SEM-EDS, och Ramanspektrometri.
Lamont klassificeras som B4, Acfer 265 och QUE 86900 som A1, och MAC 88102 som en A4
mesosiderit. Observerade parallella set av lameller i kristobalit och anortit i Lamont, samt oblandbara silikatemulsioner
och smältdroppar av pyroxen och troilite i QUE 86900, föreslås vara chock-relaterade. Texturerna i Lamont
tolkas som efterföljande och separat från det tidiga nedslaget som blandade metall- och skorpmaterial, men tidigare
än den påföljande djupa begravningen. Texturerna i QUE 86900 tolkas som samtidiga med det tidiga nedslaget.
Slutligen presenteras en modifierad teori för mesosideriternas bildning, där de texturella undergrupperna bildats på
grund av varierande begravningsdjup efter det tidiga nedslaget, samt chock- och termal metamorfos orsakat av upprepade
nedslag. I denna modifierade teori ackreteras material kontinuerligt och bildar en mäktig och isolerande regolit
som är nödvändig för de långsamma avkylningshastigheter som observerats i mesosideriter. (Less)
Please use this url to cite or link to this publication:
author
Zachén, Gabriel LU
supervisor
organization
alternative title
Klassifiering av fyra mesosideriter och konsekvenser för deras bildning
course
GEOR02 20192
year
type
H2 - Master's Degree (Two Years)
subject
keywords
mesosiderites, meteorites, stony-irons, classification, textures shock, emulsion, melt droplet, Lamont Acfer 265, QUE 86900, MAC 88102
publication/series
Dissertations in Geology at Lund University
report number
604
language
English
id
9024472
date added to LUP
2020-07-07 15:23:30
date last changed
2020-07-07 15:23:30
@misc{9024472,
  abstract     = {Mesosiderites are rare stony-iron meteorites with enigmatic origins. Their unusual mix of crustal and
core materials have inspired many formation theories over the last century. Some of the outstanding questions have
regarded the origin of the metal, whether it came from another celestial body or from within the parent body, and
the absence of mantle material. The role of impacts has been central to the theories, and yet the mesosiderites show
little evidence of shock. The mystery of the origin of mesosiderites is further compounded by the lack of study, as
well as scarcity of samples. This thesis was designed to rectify this with the classification of the mesosiderites
Lamont, Acfer 265, QUE 86900, and MAC 88102, together with petrographic analysis of their textures. The classification
and analyses are performed with the help of polarised microscopy, SEM-EDS, and Raman spectrometry.
Lamont is classified as a B4, Acfer 265 and QUE 86900 as A1, and MAC 88102 as an A4 mesosiderite. Observations
of sets of parallel lamellae in cristobalite and anorthite in Lamont, and an immiscible silicate emulsion and
pyroxene-troilite melt droplets in QUE 86900 are proposed to be shock-related features. In Lamont, these textures
are interpreted to be subsequent to the initial impact which mixed crustal and core material, and prior to deep burial.
The textures in QUE 86900 are interpreted as coeval with the initial impact. Finally, a modified theory of formation
for mesosiderites is presented, where the textural sub-groups formed as a result of variable initial burial depth and
subsequent shock- and thermal metamorphism caused by impact gardening. In this modified theory, continuous
accretion of material forms a thick and thermally insulating regolith, necessary for the slow cooling rates observed
in mesosiderites.},
  author       = {Zachén, Gabriel},
  keyword      = {mesosiderites,meteorites,stony-irons,classification,textures shock,emulsion,melt droplet,Lamont Acfer 265,QUE 86900,MAC 88102},
  language     = {eng},
  note         = {Student Paper},
  series       = {Dissertations in Geology at Lund University},
  title        = {Classification of four mesosiderites and implications for their formation},
  year         = {2020},
}