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 |
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| 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 Martin, Pierre-Etienne and Floyd, Cameron 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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