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NOGAT

Noble Gas tracing of volatile elements in the Atmosphere

PI : Bernard Marty

CRPG participants : Pete Burnard

This proposal has the objective to enhance our understanding of sources, sinks and processes fixing the composition of the atmosphere at different time periods of time, from 3.8 Gyr ago to Present. The core of the proposal is : (i) the development of multi-collector mass spectrometry analysis of noble gas isotopes coupled with standard bracketing, aimed at reaching the per mil or better precision level, (ii) the analysis of unique cometary samples, of ancient sediments, and of present-day air sampled at different geographical and altitudinal scales, (iii) the quantification of sources and sinks of atmospheric volatiles through the study of the fluxes of noble gas isotopes.

Fig 1 : fluid inclusions in quartz filling vacuoles in 3.5 Ga komatiites, Dresser Formation. Top : vacuoles filled by quartz ; the preservation of the vacuole shape indicates that Qz cristallised soon after komatiite emplacement, which is confirmed by Ar-Ar study of fluids trapped in fluid inclusions. The size of the vacuole is approximately 1 cm.

Fig 2 Detail of a 10 micron-sized fluid inclusion in quartz. The shape and distribution, and fluid composition of inclusions strongly suggest that they are primary. This type of sample yielded an initial 40Ar/36Ar ratio of 133±34 attributed to the occurrence of 3.5 Gyr old air (Pujol et al. submitted).