Noble Gases and Nitrogen in the Kle98300 Eh3 Chondrite

Introduction: The KLE98300 meteorite is an Antarctic meteorite and is classified as an EH3 chondrite [1]. In this meteorite, we found large numbers of graphite grains associated with Fe-Ni metal. Such graphite grains are considered to be products of parent body metamorphism [2, 3]. Isotopic compositions of carbon and nitrogen in graphite and in bulk meteorites give important clues to the parent body processes [e.g., 3-5]. We have initiated a mineralogical, Cand N-isotopic, and chemical study of graphite in KLE98300 and the bulk meteorite. This study should provide information on parent body processes of enstatite chondrite parent bodies. Here we report the results of noble gas and nitrogen analyses of the bulk meteorite as the beginning of our comprehensive study. Experimental: We measured noble gases and nitrogen in two ways: stepped pyrolysis and total extraction. A 66.22mg sample was used for stepped pyrolysis at 500, 900, 1200, and 1700°C. A 27.79mg sample was used for total extraction at 1700°C. Concentrations and isotopic ratios of noble gases and nitrogen were measured with a MAP215-50 mass spectrometer [6]. Results and Discussion: Ne is mostly cosmogenic except for some atmospheric-Ne released at 500°C. Elemental ratios in this fraction also show the presence of atmospheric gases (Fig. 1; [7]), indicative of terrestrial contamination. With increasing temperatures, elemental ratios decrease towards the origin (Fig. 1). In the 1200 and 1700°C fractions, data plot below subsolar, characteristic for E4-6 chondrites [8, 9] and even below Q [10]. The low Artrapped/Xe ratios suggest the presence of sub-Q gases (Ar/Xe=37±18; [9]). Sub-Q gases are characteristic for solar-gas-free E3 chondrites and are believed to originate from fractionation of Q-gases [9]. Xe isotopic ratios in the 500 and 900°C fractions plot between Xe-Q [10] and -Air [11] (Fig. 2). In the 1200 and 1700°C fractions, Xe isotopic ratios are close to those of Xe-Q, but not to those of Xe in E4-6 chondrites with subsolar gases [8, 9] (Fig. 2). Small contributions of cosmogenic-Xe are seen in these fractions (not shown in Fig. 2) and of Xe produced by fission of Pu [7] in the 1700°C fraction (Fig. 2). The low Artrapped/Xe ratios in the 1200 and 1700°C fractions and Xe-Q like isotopic ratios in these fractions support the conclusion that sub-Q gases are fractionated Q-gases [9].