Signatures of the post-hydration heating of highly aqueously altered CM carbonaceous chondrites and implications for interpreting asteroid sample returns

Lindgren, P. et al. (2020) Signatures of the post-hydration heating of highly aqueously altered CM carbonaceous chondrites and implications for interpreting asteroid sample returns. Geochimica et Cosmochimica Acta, 289, pp. 69-92. (doi: 10.1016/j.gca.2020.08.021)

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Abstract

The CM carbonaceous chondrites have all been aqueously altered, and some of them were subsequently heated in a parent body environment. Here we have sought to understand the impact of short duration heating on a highly aqueously altered CM through laboratory experiments on Allan Hills (ALH) 83100. Unheated ALH 83100 contains 83 volume per cent serpentine within the fine-grained matrix and altered chondrules. The matrix also hosts grains of calcite and dolomite, which are often intergrown with tochilinite, Fe(Ni) sulphides (pyrrhotite, pentlandite), magnetite and organic matter. Some of the magnetite formed by replacement of Fe(Ni) sulphides that were accreted from the nebula. Laboratory heating to 400 °C has caused partial dehydroxylation of serpentine and loss of isotopically light oxygen leading to an increase in bulk δ18O and fall in Δ17O. Tochilinite has decomposed to magnetite, whereas carbonates have remained unaltered. With regards to infrared spectroscopy (4000–400 cm−1; 2.5–25 µm), heating to 400 °C has resulted in decreased emissivity (increased reflectance), a sharper and more symmetric OH band at 3684 cm−1 (2.71 µm), a broadening of the Sisingle bondO stretching band together with movement of its minimum to longer wavenumbers, and a decreasing depth of the Mgsingle bondOH band (625 cm−1; 16 µm). The Sisingle bondO bending band is unmodified by mild heating. With heating to 800 °C the serpentine has fully dehydroxylated and recrystallized to ∼Fo60/70 olivine. Bulk δ18O has further increased and Δ17O decreased. Troilite and pyrrhotite have formed, and recrystallization of pentlandite has produced Fe,Ni metal. Calcite and dolomite were calcined at ∼700 °C and in their place is an un-named Ca-Fe oxysulphide. Heating changes the structural order of organic matter so that Raman spectroscopy of carbon in the 800 °C sample shows an increased (D1 + D4) proportional area parameter. The infrared spectrum of the 800 °C sample confirms the abundance of Fe-bearing olivine and is very similar to the spectrum of naturally heated stage IV CM Pecora Escarpment 02010. The temperature-related mineralogical, chemical, isotopic and spectroscopic signatures defined in ALH 83100 will help to track the post-hydration thermal histories of carbonaceous chondrite meteorites, and samples returned from the primitive asteroids Ryugu and Bennu.

Item Type:Articles
Additional Information:We are grateful to ANSMET for the loan of ALH 83100. US Antarctic meteorite samples are recovered by the Antarctic Search for Meteorites (ANSMET) program, which has been funded by NSF and NASA, and characterized and curated by the Department of Mineral Sciences of the Smithsonian Institution and Astromaterials Acquisition and Curation Office at NASA Johnson Space Center. Terry Donnelly at SUERC helped with the experimental heating procedure. Peter Chung and Anita Andreassen at the University of Glasgow helped with the SEM analyses. This work was funded by the UK Science and Technology Facilities Council through grants ST/K000942/1, ST/N000846/1, ST/R000727/1, ST/T002328/1 and ST/T506096/1, and the Swedish Research Council grant number 2015-04084. R.D.H. was supported by the OSIRIS-REx Participating Scientist Program – Grant 80NSSC18K0229. V.E.H. was partially supported by the OSIRIS-REx project, under NASA Contract NN-M10AA11C issued through the New Frontiers Program. We are grateful to Kieren Howard, Eric Quirico and an anonymous reviewer for their detailed and careful reviews that have significantly improved the manuscript.
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Lindgren, Dr Paula and Floyd, Mr Cameron and Martin, Pierre-Etienne and Lee, Professor Martin
Authors: Lindgren, P., Lee, M., Sparkes, R., Greenwood, R. C., Hanna, R. D., Franchi, I. A., King, A. J., Floyd, C., Martin, P.-E., Hamilton, V. E., and Haberle, C.
College/School:College of Science and Engineering
College of Science and Engineering > School of Geographical and Earth Sciences
College of Science and Engineering > Scottish Universities Environmental Research Centre
Journal Name:Geochimica et Cosmochimica Acta
Publisher:Elsevier
ISSN:0016-7037
ISSN (Online):1872-9533
Published Online:25 August 2020
Copyright Holders:Copyright © 2020 The Authors
First Published:First published in Geochimica et Cosmochimica Acta 289:69-92
Publisher Policy:Reproduced under a Creative Commons License

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
167657Reconstructing thermal and fluid alteration histories of planetary materials.Martin LeeScience and Technology Facilities Council (STFC)ST/K000942/1GES - Earth Sciences
172314A journey from the solar nebula to planetary bodies: cycling of heat, water and organicsMartin LeeScience and Technology Facilities Council (STFC)ST/N000846/1GES - Earth Sciences
308251UK leadership in extraterrestrial sample returnMartin LeeScience and Technology Facilities Council (STFC)ST/T002328/1P&S - Physics & Astronomy
309276STFC Glasgow Earth 2019 DTPMartin LeeScience and Technology Facilities Council (STFC)ST/T506096/1GES - Geography