Noble gases in enstatite chondrites released by stepped crushing and heating

– Enstatite chondrites (ECs) were subjected to noble gas analyses using stepped crushing and pyrolysis extraction methods. ECs can be classified into subsolar gas‐carrying and subsolar gas‐free ECs based on the 36Ar/84Kr/132Xe ratios. For subsolar gas‐free ECs, elemental ratios, and Xe isotopic comp...

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Bibliographic Details
Published in:Meteoritics & planetary science 2010-03, Vol.45 (3), p.339-360
Main Authors: OKAZAKI, Ryuji, TAKAOKA, Nobuo, NAGAO, Keisuke, NAKAMURA, Tomoki
Format: Article
Language:English
Subjects:
Chondrites
Correlation
Crushing
Distillation
Enstatite
Heating
Natural gas
Stepped
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Summary:– Enstatite chondrites (ECs) were subjected to noble gas analyses using stepped crushing and pyrolysis extraction methods. ECs can be classified into subsolar gas‐carrying and subsolar gas‐free ECs based on the 36Ar/84Kr/132Xe ratios. For subsolar gas‐free ECs, elemental ratios, and Xe isotopic compositions indicate that Q gas is the dominant trapped component, the Q gas concentration can be correlated with the petrologic type, reasonably explained by gas release from a common EC parental material during subsequent heating. Atmospheric Xe with sub‐Q elemental ratios is found in Antarctic E3s at 600–800 °C and through crushing. The 132Xe released in these fractions accounts for 30–60% of the bulk concentrations. Hence, the sub‐Q signature is generally due to contamination of elementally fractionated atmosphere. Subsolar gas is mainly released (up to 78% of the bulk 36Ar) at 1300–1600 °C and through crushing, suggesting that enstatite and friable phases are the host phases. Subsolar gas is isotopically identical to solar gas, but elementally fractionated. These observations are consistent with a previous study, which suggested that subsolar gas could be fractionated solar wind having been implanted into chondrule precursors (Okazaki et al. 2001). Unlike subsolar gas‐free ECs, the primordial gas concentrations of subsolar gas‐carrying ECs are not simply correlated with the petrologic type. It is inferred that subsolar gas‐rich chondrules were heterogeneously distributed in the solar nebula and accreted to form subsolar gas‐carrying ECs. Subsequent metamorphic and impact‐shock heating events have affected noble gas compositions to various degrees.
ISSN:1086-9379
1945-5100
DOI:10.1111/j.1945-5100.2010.01025.x