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.
All Science Journal Classification (ASJC) codes
- Space and Planetary Science