Hidenori Kumagai

<jats:p>The peak height comparison K-Ar dating method was applied to very young (younger than ca. 35 ka) vesiculated bombs from three pyroclastic units (Komakusadaira Pyroclastics, Kattadake Pyroclastics, and Umanose Agglutinate) from Zao Volcano in northeast Japan. Because the 38Ar/36Ar ratios differed from 0.187, the mass fractionation was corrected for all measurement data. The obtained K-Ar ages are 30.0 ± 32.2 ka (no. 1-1, weakly vesiculated), 37.4 ± 64.8 ka, and 33.0 ± 58.0 ka (nos. 2-1, 2-2, weakly vesiculated) for the samples from Komakusadaira Pyroclastics; 12.6 ± 46.7 ka (no. 3-1, highly vesiculated) for a sample from Kattadake Pyroclastics; and 5.3 ± 44.9 ka, 5.7 ± 14.3 ka (no. 4-1, 4-2, weakly vesiculated), and 17.3 ± 79.3 ka (no. 5-1, moderately vesiculated) for the samples from Umanose Agglutinate on a 1σ error basis. For all cases, the obtained ages’ errors exceed 100%, with none involved within the error range. Therefore, the following age value upper limits are considered statistically significant: no. 1-1 is ≤94.4 ka, 2-1 is ≤167.0 ka, 2-2 is ≤149.0 ka, 3-1 is ≤106.0 ka, 4-1 is ≤95.1 ka, 4-2 is ≤34.3 ka, and 5-1 is ≤175.9 ka, considering 2σ errors. The obtained ages are generally consistent with those previously estimated using 14C dating.</jats:p>

Abstract The Martian atmospheric Ne may reflect recent gas supply from its mantle via volcanic degassing, due to its short (∼100 Myr) escape timescale. The isotopic ratio of the Martian atmospheric Ne would therefore provide insights into that of the Martian mantle, further suggesting the origin of Mars volatiles during planetary formation. Mass spectrometric analysis of the Martian atmospheric Ne, however, has faced challenges from interference between ²⁰Ne⁺ and ⁴⁰Ar⁺⁺. Previous studies using a polyimide membrane for ²⁰Ne/⁴⁰Ar separation were limited by the drawbacks of elastomeric O-rings to support the membrane, such as low-temperature intolerance, outgassing, and the need to endure environmental conditions during the launch and before/after landing on Mars. This study proposes a new method employing a metal C-ring to secure a 100 μm polyimide sheet within vacuum flanges. Environmental tests, including vibration, shock, extreme temperatures, and radiation exposure, were conducted on the gas separation flanges. Pre- and post-test analyses for He, Ne, and Ar demonstrated the membrane-flange system’s resilience. Gas permeation measurements using terrestrial air effectively permeated ⁴He and ²⁰Ne, while reducing ⁴⁰Ar by more than six orders of magnitude. This study achieved a &lt;3% accuracy in determining the ²⁰Ne/²²Ne ratio, sufficient for assessing the origins of Ne in the Martian mantle. Furthermore, experiments with a 590 Pa gas mixture simulating the Martian atmosphere achieved a 10% accuracy for the ²⁰Ne/²²Ne isotope ratio, with gas abundances consistent with numerical predictions based on individual partial pressures. These results validate the suitability of the developed polyimide membrane assembly for in situ Martian Ne analyses.