Petrographic and compositional indicators of formation and alteration conditions from LL chondrite sulfides

Devin L. Schrader, Thomas Zega

Research output: Contribution to journalArticle

Abstract

Sulfide minerals occur in many types of extraterrestrial samples and are sensitive indicators of the conditions under which they formed or were subsequently altered. Here we report that chemical and petrographic analyses of Fe,Ni sulfides can be used to determine the metamorphic type of the host LL chondrite, and constrain their alteration conditions. Our data show that the major- and minor-element compositions of the pyrrhotite-group sulfides (dominantly troilite) and pentlandite vary with degree of thermal metamorphism experienced by their host chondrite. We find that Fe,Ni sulfides in LL3 chondrites formed during chondrule cooling prior to accretion, whereas those in LL4 to LL6 chondrites formed during cooling after thermal metamorphism in the parent body, in agreement with previous work. High degrees of shock (i.e., ≥S5) caused distinct textural, structural, and compositional changes that can be used to identify highly shocked samples. Distinct pyrrhotite-pentlandite textures and minerals present in Appley Bridge (LL6) suggest that they cooled more slowly and therefore occurred at greater depth(s) in the host parent body than those of the other metamorphosed LL chondrites studied here. Sulfides in all LL chondrites studied formed under similar sulfur fugacities, and the metamorphosed LL chondrites formed under similar oxygen fugacities. The data reported here can be applied to the study of other LL chondrites and to sulfides in samples of asteroid Itokawa returned by the Hayabusa mission in order to learn more about the formation and alteration history of the LL chondrite parent body.

Original languageEnglish (US)
Pages (from-to)165-179
Number of pages15
JournalGeochimica et Cosmochimica Acta
Volume264
DOIs
StatePublished - Nov 1 2019

Fingerprint

Sulfides
chondrite
sulfide
parent body
pentlandite
Cooling
Sulfide minerals
Asteroids
pyrrhotite
fugacity
Sulfur
sulfide group
Minerals
metamorphism
Textures
cooling
indicator
troilite
Oxygen
chondrule

Keywords

  • LL chondrite
  • Pentlandite
  • Pyrrhotite
  • Shock
  • Sulfide
  • Thermal metamorphism

ASJC Scopus subject areas

  • Geochemistry and Petrology

Cite this

Petrographic and compositional indicators of formation and alteration conditions from LL chondrite sulfides. / Schrader, Devin L.; Zega, Thomas.

In: Geochimica et Cosmochimica Acta, Vol. 264, 01.11.2019, p. 165-179.

Research output: Contribution to journalArticle

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