Effects of shock and Martian alteration on Tissint hydrogen isotope ratios and water content

L.J Hallis,G.R Huss,K Nagashima,G.J Taylor,D Stöffler,C.L Smith,M.R Lee

doi:10.1016/j.gca.2016.12.035

Abstract

The Tissint meteorite, a picritic shergottite, fell to Earth in Morocco on the 18th of July 2011, and is only the fifth Martian meteorite witnessed to fall. Hydrogen isotope ratios and water contents are variable within different minerals in Tissint. Ringwoodite and shock melt pockets contain elevated D/H ratios relative to terrestrial values (δD=761–4224‰). These high ratios in recrystallized phases indicate significant implantation of hydrogen from the D-rich Martian atmosphere during shock. In contrast, although olivine has detectable water abundances (230–485ppm), it exhibits much lower D/H ratios (δD=+88 to −150‰), suggesting this water was not implanted from the Martian atmosphere. The minimal terrestrial weathering experienced by Tissint gives confidence that the olivine-hosted water has a Martian origin, but its high concentration indicates direct inheritance from the parental melt is improbable, especially given the low pressure of olivine crystallisation. Incorporation of a low δD crustal fluid, or deuteric alteration during crystallisation, could explain the relatively high water contents and low D/H ratios in Tissint olivine.

Highlights

IntroductionTissint fell to Earth in Morocco on the 18th of July 2011, and is only the fifth Martian meteorite witnessed to fall
The primary igneous texture of the coarse-grained Tissint olivine basalt is essentially preserved in most parts of thin-sections MfN S1 and MfN S2, plagioclase has been completely transformed to diaplectic glass (Supplementary materials 1)
Olivine-hosted fractures are filled with deposits of sulphide and metal – a process known as shock blackening

Summary

Introduction

Tissint fell to Earth in Morocco on the 18th of July 2011, and is only the fifth Martian meteorite witnessed to fall. Mineralogical and petrological investigations indicate that Tissint is a picritic shergottite, with a composition. The interior of the meteorite consists of olivine macrocrysts set in a finegrained matrix of pyroxene, diaplectic plagioclase glass (maskelynite) and smaller olivine phenocrysts (Irving et al, 2012). The matrix is highly fractured and contains numerous dark shock veins and patches filled with a black glassy material that encloses bubbles (e.g., Chennaoui Aoudjehane et al, 2012; Smith and Ahmed, 2012; Baziotis et al, 2013; Chen et al, 2015).

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Conclusion