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Microtextures in the Chelyabinsk impact breccia reveal the history of Phosphorus‐Olivine‐Assemblages in chondrites

Walton, Craig R. and Baziotis, Ioannis and Černok, Ana and Ferrière, Ludovic and Asimow, Paul D. and Shorttle, Oliver and Anand, Mahesh (2021) Microtextures in the Chelyabinsk impact breccia reveal the history of Phosphorus‐Olivine‐Assemblages in chondrites. Meteoritics and Planetary Science . ISSN 1086-9379. doi:10.1111/maps.13648. (In Press)

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The geochemistry and textures of phosphate minerals can provide insights into the geological histories of parental asteroids, but the processes governing their formation and deformation remain poorly constrained. We assessed phosphorus‐bearing minerals in the three lithologies (light, dark, and melt) of the Chelyabinsk (LL5) ordinary chondrite using scanning electron microscope, electron microprobe, cathodoluminescence, and electron backscatter diffraction techniques. The majority of studied phosphate grains appear intergrown with olivine. However, microtextures of phosphates (apatite [Ca₅ (PO₄)₃ (OH,Cl,F)] and merrillite [Ca₉NaMg(PO₄)₇]) are extremely variable within and between the differently shocked lithologies investigated. We observe continuously strained as well as recrystallized strain‐free merrillite populations. Grains with strain‐free subdomains are present only in the more intensely shocked dark lithology, indicating that phosphate growth predates the development of primary shock‐metamorphic features. Complete melting of portions of the meteorite is recorded by the shock‐melt lithology, which contains a population of phosphorus‐rich olivine grains. The response of phosphorus‐bearing minerals to shock is therefore hugely variable throughout this monomict impact breccia. We propose a paragenetic history for P‐bearing phases in Chelyabinsk involving initial phosphate growth via P‐rich olivine replacement, followed by phosphate deformation during an early impact event. This event was also responsible for the local development of shock melt that lacks phosphate grains and instead contains P‐enriched olivine. We generalize our findings to propose a new classification scheme for Phosphorus‐Olivine‐Assemblages (Type I–III POAs). We highlight how POAs can be used to trace radiogenic metamorphism and shock metamorphic events that together span the entire geological history of chondritic asteroids.

Item Type:Article
Related URLs:
URLURL TypeDescription
Walton, Craig R.0000-0003-2659-644X
Baziotis, Ioannis0000-0003-0185-5847
Černok, Ana0000-0002-9884-6535
Ferrière, Ludovic0000-0002-9082-6230
Asimow, Paul D.0000-0001-6025-8925
Shorttle, Oliver0000-0002-8713-1446
Anand, Mahesh0000-0003-4026-4476
Additional Information:© 2021 The Authors. Meteoritics & Planetary Science published by Wiley Periodicals LLC on behalf of The Meteoritical Society (MET). This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. Version of Record online: 04 April 2021; Manuscript accepted: 28 February 2021; Manuscript received: 21 July 2020. We gratefully recognize the support given by Sam Hammond and Dan Topa during EPMA work; Gordon Imlach during EBSD‐imaging; and Diane Johnson, Giulio Lampronti, and Iris Buisman for assistance with SEM and CL work. We also thank Colin H. Donaldson, Helen Williams, Sami Mikhail, Darren Mark, and Ryan Ickert for helpful scientific discussions during the course of this work. Thanks to Julia Walter‐Roszjár for providing the BSE map of one of the investigated sections. Special thanks to Richard Greenwood for initial guidance in the early stages of this work back in 2016, as well as for suggesting Chelyabinsk as a sample to work on. We thank Agata Krzesińska and an anonymous reviewer for helpful and constructive review comments, and Christian Koeberl for editorial handling. M.A. thanks the Royal Astronomical Society (RAS) for providing a Paneth Trust for Meteorites Research summer internship through which C.W. initiated this research project. C.W. acknowledges NERC and UKRI for support through a NERC DTP studentship, grant number NE/L002507/1. M.A. acknowledges support from a UK Science and Technology Facilities Council (STFC) grant (#ST/P000657/1). I.B. greatly acknowledges SYNTHESYS (—a European Union‐funded Integrated Activities grant—for support of this research. A.Č. and M.A. acknowledge funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No‐704696 RESOLVE. The authors declare no conflict of interest. Data Availability Statement: The data that supports the findings of this study are available in the supplementary material of this article. Any further details are available from the corresponding author upon request. Editorial Handling: Dr. Christian Koeberl.
Funding AgencyGrant Number
Royal Astronomical SocietyUNSPECIFIED
Natural Environment Research Council (NERC)NE/L002507/1
UK Research and InnovationUNSPECIFIED
Science and Technology Facilities Council (STFC)ST/P000657/1
European Research Council (ERC)704696 RESOLVE
Record Number:CaltechAUTHORS:20210407-125549334
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Official Citation:Walton, C.R., Baziotis, I., Černok, A., Ferrière, L., Asimow, P.D., Shorttle, O. and Anand, M. (2021), Microtextures in the Chelyabinsk impact breccia reveal the history of Phosphorus‐Olivine‐Assemblages in chondrites. Meteorit Planet Sci.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:108644
Deposited By: Tony Diaz
Deposited On:07 Apr 2021 23:27
Last Modified:07 Apr 2021 23:27

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