The diversity of CM carbonaceous chondrite parent bodies explored using Lewis Cliff 85311

Lee, M. R. , Cohen, B. E. , King, A. J. and Greenwood, R. C. (2019) The diversity of CM carbonaceous chondrite parent bodies explored using Lewis Cliff 85311. Geochimica et Cosmochimica Acta, 264, pp. 224-244. (doi: 10.1016/j.gca.2019.07.027)

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Lewis Cliff (LEW) 85311 is classified as a Mighei-like (CM) carbonaceous chondrite, yet it has some unusual properties that highlight an unrealised diversity within the CMs, and also questions how many parent bodies are sampled by the group. This meteorite is composed of rimmed chondrules, chondrule fragments and refractory inclusions that are set in a fine-grained phyllosilicate-rich matrix. The chondrules are of a similar size to those in the CMs, and have narrow fine-grained rims. LEW 85311 has been mildly aqueously altered, as evidenced by the preservation of melilite and kamacite, and X-ray diffraction results showing a low phyllosilicate fraction and a high ratio of cronstedtite to Fe,Mg serpentine. The chemical composition of LEW 85311 matrix, fine-grained rims, tochilinite and P-rich sulphides is similar to mildly aqueously altered CMs. LEW 85311 is enriched in refractory elements and REEs such that its CI-normalised profile falls between the CMs and CVs, and its oxygen isotopic composition plots in the CV-CK-CO field. Other distinctive properties of this meteorite include the presence of abundant refractory inclusions, and hundreds of micrometer size objects composed of needle-fibre calcite. LEW 85311 could come from part of a single CM parent body that was unusually rich in refractory inclusions, but more likely samples a different parent body to most other members of the group that accreted a subtly different mixture of materials. The mineralogical and geochemical evolution of LEW 85311 during subsequent aqueous alteration was similar to other CMs and was arrested at an early stage, corresponding to a petrologic subtype of CM2.7, probably due to an unusually low proportion of accreted ice. The CM carbonaceous chondrites sample multiple parent bodies whose similar size and inventory of accreted materials, including radiogenic isotopes, led to a comparable post-accretionary evolution.

Item Type:Articles
Glasgow Author(s) Enlighten ID:Cohen, Dr Benjamin and Lee, Professor Martin
Authors: Lee, M. R., Cohen, B. E., King, A. J., and Greenwood, R. C.
College/School:College of Science and Engineering > School of Geographical and Earth Sciences
Journal Name:Geochimica et Cosmochimica Acta
ISSN (Online):1872-9533
Published Online:23 July 2019
Copyright Holders:Copyright © 2019 The Authors
First Published:First published in Geochimica et Cosmochimica Acta 264: 224-244
Publisher Policy:Reproduced under a Creative Commons License

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
697411A journey from the solar nebula to planetary bodies: cycling of heat, water and organicsMartin LeeScience & Technology Facilities Council (STFC)ST/N000846/1GES - GES ADMINISTRATION