Opal-A in the Nakhla meteorite: a tracer of ephemeral liquid water in the Amazonian crust of Mars

Lee, M. , MacLaren, I. , Andersson, S., Kovacs, A., Tomkinson, T., Mark, D. and Smith, C. (2015) Opal-A in the Nakhla meteorite: a tracer of ephemeral liquid water in the Amazonian crust of Mars. Meteoritics and Planetary Science, 50(8), pp. 1362-1377. (doi:10.1111/maps.12471)

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Abstract

The nakhlite meteorites are clinopyroxenites that are derived from a ~1300 million year old sill or lava flow on Mars. Most members of the group contain veins of iddingsite whose main component is a fine-grained and hydrous Fe- and Mg-rich silicate. Siderite is present in the majority of veins, where it straddles or cross-cuts the Fe-Mg silicate. This carbonate also contains patches of ferric (oxy)hydroxide. Despite 40 years of investigation, the mineralogy and origins of the Fe-Mg silicate is poorly understood, as is the paragenesis of the iddingsite veins. Nanometer-scale analysis of Fe-Mg silicate in the Nakhla meteorite by electron and X-ray imaging and spectroscopy reveals that its principal constituents are nanoparticles of opal-A. This hydrous and amorphous phase precipitated from acidic solutions that had become supersaturated with respect to silica by dissolution of olivine. Each opal-A nanoparticle is enclosed within a ferrihydrite shell that formed by oxidation of iron that had also been liberated from the olivine. Siderite crystallized subsequently and from solutions that were alkaline and reducing, and replaced both the nanoparticles and olivine. The fluids that formed both the opal-A/ferrihydrite and the siderite were sourced from one or more reservoirs in contact with the Martian atmosphere. The last event recorded by the veins was alteration of the carbonate to a ferric (oxy)hydroxide that probably took place on Mars, although a terrestrial origin remains possible. These results support findings from orbiter- and rover-based spectroscopy that opaline silica was a common product of aqueous alteration of the Martian crust.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Mark, Professor Darren and Tomkinson, Dr Tim and Lee, Professor Martin and MacLaren, Dr Ian and Smith, Dr Caroline
Authors: Lee, M., MacLaren, I., Andersson, S., Kovacs, A., Tomkinson, T., Mark, D., and Smith, C.
College/School:College of Medical Veterinary and Life Sciences > School of Medicine, Dentistry & Nursing > Dental School
College of Science and Engineering > School of Geographical and Earth Sciences
College of Science and Engineering > School of Physics and Astronomy
College of Science and Engineering > Scottish Universities Environmental Research Centre
Journal Name:Meteoritics and Planetary Science
Publisher:Wiley
ISSN:1086-9379
ISSN (Online):1945-5100
Copyright Holders:Copyright © 2015 The Authors
First Published:First published in Meteoritics and Planetary Science 50(8):1362-1377
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