Evidence for Flow and Gravity Settling in the Parent Lavas of the Nakhlite (Martian) Meteorites from Crystal Textures and Fabrics

Daly, L., Piazolo, S., Trimby, P.W., Lee, M.R. , Baumgartner, R.J., Cohen, B.E. and Forman, L.V. (2017) Evidence for Flow and Gravity Settling in the Parent Lavas of the Nakhlite (Martian) Meteorites from Crystal Textures and Fabrics. 1st British Planetary Science Congress, Glasgow, UK, 3-5 Dec 2017.

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Abstract

The nakhlite meteorites are Martian igneous rocks that sample at least four lava flows erupted between ~1,416 and 1,332 Ma1 . They contain phenocrysts of augite and olivine, between which is a finely crystalline mesostasis. The augite phenocrysts are coarse and prismatic, and so may be ideal for recording processes that operated during emplacement. Here we evaluated the evidence for flow and gravitational settling by quantifying the crystallographic preferred orientations of phenocrysts via large area electron backscatter diffraction (LA-EBSD) mapping of thin sections of three nakhlites: Nakhla, Governador Valadares and Miller Range (MIL) 03346. LA-EBSD analyses reveal a moderate alignment of the long axis (<c>) of augite phenocrysts in a plane forming a magmatic foliation in all samples, as well as a moderate linear alignment with maxima of the <a>, <b> and <c> axes in the general foliation plane. The linear alignment is most pronounced in those meteorites with a low ratio of mesostasis to phenocrysts: alignment increases from MIL 03346 to Grosvenor Valadares to Nakhla. Lineations defined by elongate minerals in lavas can be generated by shear stresses associated with flow2 , while foliations are attributed to gravity settling3 and compaction. Here we have observed good evidence for both processes, thus confirming that the nakhlites do represent lava flows, with an associated gravitational component.

Item Type:Conference or Workshop Item
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Daly, Dr Luke and Cohen, Dr Ben and Lee, Professor Martin
Authors: Daly, L., Piazolo, S., Trimby, P.W., Lee, M.R., Baumgartner, R.J., Cohen, B.E., and Forman, L.V.
College/School:College of Science and Engineering > School of Geographical and Earth Sciences
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