| Summary: | Introduction: : A variety of processes have been considered possibly contributing volatiles, including the noble gases, to the terrestrial planets (e.g., [1-3]). Special consideration has been given to the concept of accretion of volatilerich materials by the forming planets. This might include infalling extraterrestrial material of various sizes, i.e. from planetesimals down to dust, and could include material from the outer asteroid belt, as well as material of cometary origin. Currently, the dominant source of extraterrestrial material accreted by the Earth is represented by micrometeorites (MMs) with sizes mostly in the 100-400 μm range [3, 4]), and according to [3] accretion of early micrometeorites may have played a major role in the formation of the terrestrial atmosphere and oceans. We have therefore set out to investigate in more detail the complete inventory of noble gases in MMs. Here we summarize some of the results we obtained on MMs collected in micrometeorite traps on the tops of the Transantarctic Mountains [5]. Trapped noble gases: Concentrations in “unmelted” MMs, in the size range ~400-1000 μm, are compared to those in CM meteorites (exemplified by CM2 Maribo) in Figure 1. While He has been largely lost, the abundance of Ne often exceeds that in CMs, because of higher abundances of trapped solar wind Ne. Ar, Kr, Xe are somewhat lower and quite variable. This is in line with our mineralogical observations on separate pieces of the analyzed MMs that mostly show similarities to ordinary chondrites of various types rather than CMs - contrary to the situation for recently fallen MMs recovered from ice and snow of Central Antarctica [6, 7]. Note, though, that uncertainty is induced by a) the fact that the MMs are often not homogeneous in composition and b) the complex interaction during passage through the terrestrial atmosphere. Among others, we found in several cases (two scoriaceous, one unmelted) Kr and Xe showing the signature of isotopically fractionated air with the heavier isotopes enriched ...
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