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

Lee, M. R., Lindgren, P., King, A. J., Greenwood, R. C., Franchi, I. A. and Sparkes, R. (2016) Elephant Moraine 96029, a very mildly aqueously altered and heated CM carbonaceous chondrite: implications for the drivers of parent body processing. Geochimica et Cosmochimica Acta, 187, pp. 237-259. (doi: 10.1016/j.gca.2016.05.008)

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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 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.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Lee, Martin R and Lindgren, Dr Paula
Authors: Lee, M. R., Lindgren, P., King, A. J., Greenwood, R. C., Franchi, I. A., and Sparkes, R.
College/School:College of Science and Engineering > School of Geographical and Earth Sciences
Journal Name:Geochimica et Cosmochimica Acta
Publisher:Elsevier
ISSN:0016-7037
ISSN (Online):1872-9533
Published Online:10 May 2016
Copyright Holders:Copyright © 2016 The Authors
First Published:First published in Geochimica et Cosmochimica Acta 187:237-259
Publisher Policy:Reproduced under a Creative Commons License

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
519741Follow the water: insights into the martian hydrosphere from nakhlitesMartin LeeScience & Technologies Facilities Council (STFC)ST/H002960/1SCHOOL OF GEOGRAPHICAL & EARTH SCIENCES
602461Reconstructing thermal and fluid alteration histories of planetary materials.Martin LeeScience & Technologies Facilities Council (STFC)ST/K000942/1SCHOOL OF GEOGRAPHICAL & EARTH SCIENCES
630461Atmosphere-crust coupling and carbon sequestration on the young MarsMartin LeeUK Space Agency (UK-SPACE)ST/L002167/1SCHOOL OF GEOGRAPHICAL & EARTH SCIENCES