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Titanium- and chromium-rich opaque minerals in condensed sediments : chondritic, lunar and terrestrial origins

Holm, Sanna (2008) In Examensarbeten i geologi vid Lunds universitet
Department of Geology
Abstract
Evidence from terrestrial sedimentary successions indicate that the amount of extraterrestrial material reaching Earth is not constant, but has been increased during parts of the Phanerozoic. An increase in the flux of extraterrestrial material to Earth has been proposed for the Middle Ordovician and the Late Eocene. These showers of extraterrestrial material on Earth are thought to have resulted from disruption events in the Main Asteroid Belt.

An asteroid shower affecting Earth would also have a great influence on the Moon. A projectile that impacts on the Moon can cause lunar matter to be launched into space, some of which will reach the Earth. Increased amounts of lunar impact ejecta reaching Earth has been proposed to have caused a... (More)
Evidence from terrestrial sedimentary successions indicate that the amount of extraterrestrial material reaching Earth is not constant, but has been increased during parts of the Phanerozoic. An increase in the flux of extraterrestrial material to Earth has been proposed for the Middle Ordovician and the Late Eocene. These showers of extraterrestrial material on Earth are thought to have resulted from disruption events in the Main Asteroid Belt.

An asteroid shower affecting Earth would also have a great influence on the Moon. A projectile that impacts on the Moon can cause lunar matter to be launched into space, some of which will reach the Earth. Increased amounts of lunar impact ejecta reaching Earth has been proposed to have caused a prominent 3He anomaly in Late Eocene sediments from Massignano, Italy, as the lunar regolith is extremely enriched in this rare isotope of helium derived from the solar wind. The lunar impact ejecta should not only be preserved in the form of a 3He anomaly, but minerals representing the ejected matter should also be preserved in terrestrial sediments.

Chrome spinel and ilmenite are resistant minerals that are common in both lunar and terrestrial rocks. These minerals occur in dissolved limestone samples from Kinnekulle, Sweden, eastern Yangtze Gorges area, China, and Massignano, Italy, and their provenance can be discussed based on their chemical composition. Chondritic chromite was confirmed among the grains, but due to the complex overlap in terrestrial and lunar Cr-rich spinel composition, the existence of any lunar chrome spinel could not be definitely confirmed. In order to identify lunar chrome spinel other methods, such as isotope geochemistry, need to be applied.

The study presented in this paper shows that ilmenite is less suitable than Cr-rich spinel when trying to identify lunar minerals in terrestrial sediments. Ilmenite grains are more likely to become altered, which makes provenance studies harder. When comparing the chemical composition of ilmenite grains, which have not been subjected to severe alteration, from this study with the compositions of lunar and chondritic ilmenite it was clear that the grains most likely have a terrestrial origin, even if a few grains have the potential to be of lunar or chondritic origin.

The vast majority of the ilmenite and chrome spinel grains recovered from the dissolved limestone samples come from terrestrial sources. The origin of these grains is discussed in this paper, and the most likely origin for them is erosion of igneous rocks and transportation to the depositional environment by currents. (Less)
Abstract (Swedish)
Bevis från terrestriska sedimentära lagerföljder indikerar att inflödet av extraterrestriskt material till Jorden inte är konstant, utan har varit förhöjt under perioder av Jordens historia. Ett ökat flöde av extraterrestriskt material till Jorden har föreslagits för perioderna mellanordovicium och sen eocen. Orsaken tros vara asteroidskurar orsakade av uppbrytningar av asteroider i asteroidbältet mellan Mars och Jupiter.

En asteroidskur som påverkat Jorden skulle också ha stor påverkan på Månen. En kropp som träffar Månen kan få material att slungas ut i rymden, en del av vilket kommer att nå Jorden. Ökade mängder utslungat material från Månen har föreslagits vara orsaken till en tydlig 3He-anomali i sediment från Massignano, Italien,... (More)
Bevis från terrestriska sedimentära lagerföljder indikerar att inflödet av extraterrestriskt material till Jorden inte är konstant, utan har varit förhöjt under perioder av Jordens historia. Ett ökat flöde av extraterrestriskt material till Jorden har föreslagits för perioderna mellanordovicium och sen eocen. Orsaken tros vara asteroidskurar orsakade av uppbrytningar av asteroider i asteroidbältet mellan Mars och Jupiter.

En asteroidskur som påverkat Jorden skulle också ha stor påverkan på Månen. En kropp som träffar Månen kan få material att slungas ut i rymden, en del av vilket kommer att nå Jorden. Ökade mängder utslungat material från Månen har föreslagits vara orsaken till en tydlig 3He-anomali i sediment från Massignano, Italien, avsatta under sen eocen. Månens regolit är extremt berikad på den här ovanliga heliumisotopen som kommer från solvinden. Spår av utslungat material från Månen i terrestriska sediment bör inte bara vara bevarade i form av en 3He-anomali, utan också i form av bevarade månmineral.

Kromspinell och ilmenit är resistenta mineral som är vanliga i både terrestriska bergarter och på Månen. De här mineralen förekommer i upplösta kalkstensprover från Kinnekulle, Sverige, östra Yangtze Gorges-området i Kina och Massignano, Italien, och deras ursprung kan diskuteras baserat på deras kemiska sammansättningar. Förekomst av kromspinell från primitiva stenmeteoriter, kallade kondriter, i proverna kunde bekräftas, men på grund av att sammansättningen hos kromspinell från Månen och terrestrisk kromspinell överlappar varandra, så kunde inte förekomst av kromspinell från Månen i proverna definitivt bekräftas. För att kunna identifiera kromspinell från Månen måste andra metoder, till exempel isotopgeokemi appliceras.

Studien som presenteras i det här arbetet visar att ilmenit är mindre lämplig att använda än kromspinell när man ska identifiera månmineral i terrestriska sediment. Ilmenitkorn löper större risk att bli omvandlade, vilket försvårar studier av kornens ursprung. När den kemiska sammansättningen hos ilmenitkorn från den här studien, som inte blivit kraftigt omvandlade, jämfördes med sammansättningen hos månilmenit och kondritisk ilmenit blev det klart att kornen sannolikt har ett terrestriskt ursprung, även om några få korn hade potential att vara från Månen eller en kondritisk källa.

Majoriteten av ilmenit- och kromspinellkornen som hittats i de upplösta kalkstensproverna kommer från terrestriska källor. Ursprunget för dessa korn diskuteras i det här arbetet, och det mest sannolika scenariot är att de utgör erosionsrester som förts till depositionsmiljön av strömmar. (Less)
Please use this url to cite or link to this publication:
author
Holm, Sanna
supervisor
organization
alternative title
Titan- och kromrika opaka mineral i kondenserade sediment : extraterrestriska och terrestriska ursprung
year
type
H1 - Master's Degree (One Year)
subject
keywords
Ilmenite, chrome spinel, 3He, lunar impact ejecta, source rock, Middle Ordovician, Late Eocene, ilmenit, kromspinell, impakt ejekta, källbergart, mellanordovicium, sen eocen
publication/series
Examensarbeten i geologi vid Lunds universitet
report number
235
language
English
id
2303189
date added to LUP
2012-01-27 16:40:43
date last changed
2013-02-06 15:48:25
@misc{2303189,
  abstract     = {Evidence from terrestrial sedimentary successions indicate that the amount of extraterrestrial material reaching Earth is not constant, but has been increased during parts of the Phanerozoic. An increase in the flux of extraterrestrial material to Earth has been proposed for the Middle Ordovician and the Late Eocene. These showers of extraterrestrial material on Earth are thought to have resulted from disruption events in the Main Asteroid Belt.

An asteroid shower affecting Earth would also have a great influence on the Moon. A projectile that impacts on the Moon can cause lunar matter to be launched into space, some of which will reach the Earth. Increased amounts of lunar impact ejecta reaching Earth has been proposed to have caused a prominent 3He anomaly in Late Eocene sediments from Massignano, Italy, as the lunar regolith is extremely enriched in this rare isotope of helium derived from the solar wind. The lunar impact ejecta should not only be preserved in the form of a 3He anomaly, but minerals representing the ejected matter should also be preserved in terrestrial sediments.

Chrome spinel and ilmenite are resistant minerals that are common in both lunar and terrestrial rocks. These minerals occur in dissolved limestone samples from Kinnekulle, Sweden, eastern Yangtze Gorges area, China, and Massignano, Italy, and their provenance can be discussed based on their chemical composition. Chondritic chromite was confirmed among the grains, but due to the complex overlap in terrestrial and lunar Cr-rich spinel composition, the existence of any lunar chrome spinel could not be definitely confirmed. In order to identify lunar chrome spinel other methods, such as isotope geochemistry, need to be applied.

The study presented in this paper shows that ilmenite is less suitable than Cr-rich spinel when trying to identify lunar minerals in terrestrial sediments. Ilmenite grains are more likely to become altered, which makes provenance studies harder. When comparing the chemical composition of ilmenite grains, which have not been subjected to severe alteration, from this study with the compositions of lunar and chondritic ilmenite it was clear that the grains most likely have a terrestrial origin, even if a few grains have the potential to be of lunar or chondritic origin.

The vast majority of the ilmenite and chrome spinel grains recovered from the dissolved limestone samples come from terrestrial sources. The origin of these grains is discussed in this paper, and the most likely origin for them is erosion of igneous rocks and transportation to the depositional environment by currents.},
  author       = {Holm, Sanna},
  keyword      = {Ilmenite,chrome spinel,3He,lunar impact ejecta,source rock,Middle Ordovician,Late Eocene,ilmenit,kromspinell,impakt ejekta,källbergart,mellanordovicium,sen eocen},
  language     = {eng},
  note         = {Student Paper},
  series       = {Examensarbeten i geologi vid Lunds universitet},
  title        = {Titanium- and chromium-rich opaque minerals in condensed sediments : chondritic, lunar and terrestrial origins},
  year         = {2008},
}