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Elephant Moraine 96029, a very mildly aqueously altered and heated CM carbonaceous chondrite : Implications for the drivers of parent body processing

Lee, Martin R.; Lindgren, Paula LU ; King, Ashley J.; Greenwood, Richard C.; Franchi, Ian A. and Sparkes, Robert (2016) In Geochimica et Cosmochimica Acta 187. p.237-259
Abstract

Elephant Moraine (EET) 96029 is a CM carbonaceous chondrite regolith breccia with evidence for unusually mild aqueous alteration, a later phase of heating and terrestrial weathering. The presence of phyllosilicates and carbonates within chondrules and the fine-grained matrix indicates that this meteorite was aqueously altered in its parent body. Features showing that water-mediated processing was arrested at a very early stage include a matrix with a low magnesium/iron ratio, chondrules whose mesostasis contains glass and/or quench crystallites, and a gehlenite-bearing calcium- and aluminium-rich inclusion. EET 96029 is also rich in Fe,Ni metal relative to other CM chondrites, and more was present prior to its partial replacement by... (More)

Elephant Moraine (EET) 96029 is a CM carbonaceous chondrite regolith breccia with evidence for unusually mild aqueous alteration, a later phase of heating and terrestrial weathering. The presence of phyllosilicates and carbonates within chondrules and the fine-grained matrix indicates that this meteorite was aqueously altered in its parent body. Features showing that water-mediated processing was arrested at a very early stage include a matrix with a low magnesium/iron ratio, chondrules whose mesostasis contains glass and/or quench crystallites, and a gehlenite-bearing calcium- and aluminium-rich inclusion. EET 96029 is also rich in Fe,Ni metal relative to other CM chondrites, and more was present prior to its partial replacement by goethite during Antarctic weathering. In combination, these properties indicate that EET 96029 is one of the least aqueously altered CMs yet described (CM2.7) and so provides new insights into the original composition of its parent body. Following aqueous alteration, and whilst still in the parent body regolith, the meteorite was heated to ~400-600 °C by impacts or solar radiation. Heating led to the amorphisation and dehydroxylation of serpentine, replacement of tochilinite by magnetite, loss of sulphur from the matrix, and modification to the structure of organic matter that includes organic nanoglobules. Significant differences between samples in oxygen isotope compositions, and water/hydroxyl contents, suggests that the meteorite contains lithologies that have undergone different intensities of heating. EET 96029 may be more representative of the true nature of parent body regoliths than many other CM meteorites, and as such can help interpret results from the forthcoming missions to study and return samples from C-complex asteroids.

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author
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Aqueous alteration, CM carbonaceous chondrites, Thermal processing
in
Geochimica et Cosmochimica Acta
volume
187
pages
23 pages
publisher
Elsevier
external identifiers
  • scopus:84973094058
ISSN
0016-7037
DOI
10.1016/j.gca.2016.05.008
language
English
LU publication?
no
id
67d0efc5-087f-4697-8b08-c4266dbd0e11
date added to LUP
2017-06-16 15:43:37
date last changed
2017-10-22 05:32:10
@article{67d0efc5-087f-4697-8b08-c4266dbd0e11,
  abstract     = {<p>Elephant Moraine (EET) 96029 is a CM carbonaceous chondrite regolith breccia with evidence for unusually mild aqueous alteration, a later phase of heating and terrestrial weathering. The presence of phyllosilicates and carbonates within chondrules and the fine-grained matrix indicates that this meteorite was aqueously altered in its parent body. Features showing that water-mediated processing was arrested at a very early stage include a matrix with a low magnesium/iron ratio, chondrules whose mesostasis contains glass and/or quench crystallites, and a gehlenite-bearing calcium- and aluminium-rich inclusion. EET 96029 is also rich in Fe,Ni metal relative to other CM chondrites, and more was present prior to its partial replacement by goethite during Antarctic weathering. In combination, these properties indicate that EET 96029 is one of the least aqueously altered CMs yet described (CM2.7) and so provides new insights into the original composition of its parent body. Following aqueous alteration, and whilst still in the parent body regolith, the meteorite was heated to ~400-600 °C by impacts or solar radiation. Heating led to the amorphisation and dehydroxylation of serpentine, replacement of tochilinite by magnetite, loss of sulphur from the matrix, and modification to the structure of organic matter that includes organic nanoglobules. Significant differences between samples in oxygen isotope compositions, and water/hydroxyl contents, suggests that the meteorite contains lithologies that have undergone different intensities of heating. EET 96029 may be more representative of the true nature of parent body regoliths than many other CM meteorites, and as such can help interpret results from the forthcoming missions to study and return samples from C-complex asteroids.</p>},
  author       = {Lee, Martin R. and Lindgren, Paula and King, Ashley J. and Greenwood, Richard C. and Franchi, Ian A. and Sparkes, Robert},
  issn         = {0016-7037},
  keyword      = {Aqueous alteration,CM carbonaceous chondrites,Thermal processing},
  language     = {eng},
  month        = {08},
  pages        = {237--259},
  publisher    = {Elsevier},
  series       = {Geochimica et Cosmochimica Acta},
  title        = {Elephant Moraine 96029, a very mildly aqueously altered and heated CM carbonaceous chondrite : Implications for the drivers of parent body processing},
  url          = {http://dx.doi.org/10.1016/j.gca.2016.05.008},
  volume       = {187},
  year         = {2016},
}