Martian Igneous Activity and Fluid-Based Alteration: Chronological Constraints from 40Ar/39Ar Analyses of the Nakhlites

Cohen, B.E., Mark, D.F., Tomkinson, T., Lee, M.R. and Smith, C.L. (2015) Martian Igneous Activity and Fluid-Based Alteration: Chronological Constraints from 40Ar/39Ar Analyses of the Nakhlites. In: 46th Lunar and Planetary Science Conference, The Woodlands, TX, USA, 16-20 Mar 2015,

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Abstract

The nakhlites are a group of mafic igneous rocks that crystallized on Mars at ca. 1.3-1.4 Ga [1-5]. They are amongst the least shocked Martian meteorites, with cumulate igneous textures (Fig. 1) and thus provide a crucial record of igneous activity and fluid-rock interaction on the red planet. Crystallization of the nakhlites. Understanding the original structure of the nakhlite source is crucial for using these stones to explore Martian igneous processes. In particular, are the different nakhlites from a single thick and differentiated lava flow/sill [6; 7], or do they instead represent magmatically related – but distinct – flows/intrusions? If the various meteorites are derived from separate units, then there will be differences in crystallization ages within the nakhlite suite – which may be identified if these differences are sufficiently large relative to the attainable precision of radioisotopic dating techniques. Some studies [e.g., 5] appear to resolve age differences between different stones, and we aim to test the single vs. multiple unit hypotheses via application of detailed 40Ar/39Ar stepheating of six nakhlites.

Alteration of the nakhlites, and the timing of waterrock interaction. In addition to primary magmatic minerals and glasses, the nakhlites contain secondary minerals including clays and carbonates that were precipitated by Martian aqueous fluids prior to impact ejection (Fig. 2) [8-10]. When did this alteration occur? As the clays contain potassium, they are amenable to K-Ar and 40Ar/39Ar dating. K-Ar data from Lafayette suggests the alteration phases formed between 0 to 670 Ma [11]. We consider further the timing of alteration using our 40Ar/39Ar data.

Item Type:Conference Proceedings
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Mark, Dr Darren and Tomkinson, Dr Tim and Cohen, Dr Benjamin and Smith, Dr Caroline and Lee, Professor Martin
Authors: Cohen, B.E., Mark, D.F., Tomkinson, T., Lee, M.R., and Smith, C.L.
College/School:College of Science and Engineering > School of Geographical and Earth Sciences
College of Medical Veterinary and Life Sciences > School of Medicine, Dentistry & Nursing > Dental School
Copyright Holders:Copyright © 2015 The Authors
Publisher Policy:Reproduced in accordance with the copyright policy of the publisher
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