Abstract Hydrogen occurs at the near percent level in the most hydrated chondrites (CI and CM) attesting to the presence of water in the asteroid-forming regions. Their H abundances and isotopic signatures are powerful proxies for deciphering the distribution of H in the protoplanetary disk and the origin of Earth's water. Here, we report H contents and isotopic compositions for a set of carbonaceous and ordinary chondrites, including previously analyzed and new samples analyzed after the powdered samples were degassed under vacuum at 120 °C for 48 hours to remove adsorbed atmospheric water. By comparing our results to literature data, we reveal that the H budgets of both H-poor and H-rich carbonaceous chondrites are largely affected by atmospheric moisture, and that their precise quantification requires a specific pre-degassing procedure to correct for terrestrial contamination. Our results show that indigenous H contents of CI carbonaceous chondrites usually considered the most hydrated meteorites might be almost a factor of two lower than those previously reported, with uncontaminated D/H ratios differing significantly from that of Earth's oceans. Without pre-degassing, the H concentrations of H-poor samples (e.g., CVs chondrites) are also affected by terrestrial contamination. After correction for contamination, it appears that the amount of water in chondrites is not controlled by the matrix modal abundance, suggesting that the different chondritic parent bodies accreted variable amounts of water-ice grains. Our results also imply that (i) thermal metamorphism play an important role in determining the H content of both CV and ordinary chondrites but without affecting drastically their H isotopic composition since no clear D enrichment is observed with the increase of petrographic type and (ii) the D enrichment of ordinary chondrite organics does not result from the loss of isotopically light H2 induced by metal oxidation but is rather linked to the persistence of a thermally resistant D-rich component.

中文翻译：

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球粒陨石中的氢：母体改变和大气污染对原始成分的影响

摘要：水合度最高的球粒陨石（CI 和 CM）中的氢含量接近百分比，这证明小行星形成区域中存在水。它们的 H 丰度和同位素特征是破译原行星盘中 H 分布和地球水源的有力代理。在这里，我们报告了一组碳质球粒陨石和普通球粒陨石的 H 含量和同位素组成，包括先前分析的和在 120°C 下真空脱气 48 小时以去除吸附的大气水后对粉末样品进行分析的新样品。通过将我们的结果与文献数据进行比较，我们发现贫氢和富氢碳质球粒陨石的 H 收支在很大程度上受大气水分的影响，并且它们的精确量化需要特定的预脱气程序来纠正地面污染。我们的结果表明，通常被认为是含水量最高的陨石的 CI 碳质球粒陨石的原生 H 含量可能比之前报道的低近两倍，未受污染的 D/H 比与地球海洋的 D/H 比显着不同。如果没有预脱气，贫氢样品（例如，CV 球粒陨石）的 H 浓度也会受到陆地污染的影响。在对污染进行校正后，似乎球粒陨石中的水量不受基质模态丰度的控制，这表明不同的球粒陨石母体吸积了不同数量的水冰粒。