Terrestrial exposure of a fresh Martian meteorite causes rapid changes in hydrogen isotopes and water concentrations

Alice Stephant,Laurence A J Garvie,Richard Hervig,Prajkta Mane,Meenakshi Wadhwa

doi:10.1038/s41598-018-30807-w

Alice Stephant, Laurence A J Garvie + Show 3 more

Open Access

https://doi.org/10.1038/s41598-018-30807-w

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Abstract

Determining the hydrogen isotopic compositions and H2O contents of meteorites and their components is important for addressing key cosmochemical questions about the abundance and source(s) of water in planetary bodies. However, deconvolving the effects of terrestrial contamination from the indigenous hydrogen isotopic compositions of these extraterrestrial materials is not trivial, because chondrites and some achondrites show only small deviations from terrestrial values such that even minor contamination can mask the indigenous values. Here we assess the effects of terrestrial weathering and contamination on the hydrogen isotope ratios and H2O contents of meteoritic minerals through monitored terrestrial weathering of Tissint, a recent Martian fall. Our findings reveal the rapidity with which this weathering affects nominally anhydrous phases in extraterrestrial materials, which illustrates the necessity of sampling the interiors of even relatively fresh meteorite falls and underlines the importance of sample return missions.

Highlights

Hydrogen isotope compositions and H2O contents of extraterrestrial samples, including meteorites, can provide insights into the abundance, origin and source(s) of water on planetary and asteroidal bodies[1]
In the case of hydrogen isotope compositions, some previous studies have suggested that the effects of terrestrial contamination are negligible for extraterrestrial samples that exhibit δD values far from the terrestrial value
The ranges in H2O contents and δD values of olivines in the polished surface of the T3 sample exposed for 3 years (T3′) are similar to those in olivines of T1 (Fig. 2)

Summary

Introduction

Hydrogen isotope compositions and H2O contents of extraterrestrial samples, including meteorites, can provide insights into the abundance, origin and source(s) of water on planetary and asteroidal bodies[1]. The somewhat lower δD values recently reported in some terrestrial basalts thought to originate from the deep mantle compared to typical mid-ocean ridge basalts has reignited a long-standing controversy about the origin of water on Earth[2,3] As another example, multiple hydrogen isotope investigations of the Martian meteorites have shown δD values ranging from ~−200‰ to ~ + 6000‰ in primary igneous phases in these samples[4,5,6,7,8,9]. Robert and Deloule[25] studied the hydrogen isotope composition of the Semarkona ordinary chondrite and concluded that “...in light of the large D/H variations observed in Semarkona, the problem of the terrestrial contamination can be ignored.” These interpretations have typically been based on analyses of bulk samples or minerals with relatively high H2O concentrations (>0.2 wt.% H2O). It is important to characterize the rate at, and degree to which, the δD-H2O systematics in such phases are altered by terrestrial exposure

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