The HO concentration and HO/Ce ratio in olivine-hosted melt inclusions are high in lunar pyroclastic sample 74220 (HO up to 1410 ppmw; HO/Ce up to 77) but lower (HO 10 to 430 ppmw; HO/Ce 0.3 to 9.4) in all other lunar samples studied before this work. The difference in HO concentration and in HO/Ce ratio is absent for other volatile elements (F, S, and Cl) in melt inclusions in 74220 and other lunar samples. Because HO (or H) is a critical volatile component with significant ramifications on the origin and evolution of the Moon, it is important to understand what causes such a large gap in HO/Ce ratio between 74220 and other lunar samples. Two explanations have been advanced. One is that volcanic product in sample 74220 has the highest cooling rate and thus best preserved HO in melt inclusions compared to melt inclusions in other samples. The other explanation is that sample 74220 comes from a localized heterogeneity enriched in some volatiles. To distinguish these two possibilities, here we present new data from two rapidly cooled lunar samples with glassy melt inclusions: olivine-hosted melt inclusions (OHMIs) in 79135 regolith breccia (unknown cooling rate but with glassy MIs similar in texture with those in 74220), and pyroxene-hosted melt inclusions (PHMIs) in 15597 pigeonite basalts (known high cooling rate, second only to 74220 and 15421). In addition, we also investigated new OHMIs in sample 74220. If the gap is due to the difference in cooling rates, samples with cooling rates between those of 74220 and other studied lunar samples should have preserved intermediate HO concentrations and HO/Ce ratios. Our results show that melt inclusions in 79135 and 15597 contain high HO concentrations (up to 969 ppmw in 79135 and up to 793 ppmw in 15597) and high HO/Ce ratios (up to 21 in 79135 and up to 13 in 15997), bridging the big gap in HO/Ce ratio among 74220 and other lunar samples. Combined with literature data, we confirm that HO/Ce ratios of different lunar samples are positively correlated to the cooling rates and independent of the type of mare basalts. We hence reinforce the interpretation that the lunar sample with the highest cooling rate best represents pre-eruptive volatiles in lunar basalts due to the least degassing. Based on Ce concentration in the primitive lunar mantle, we estimate that HO concentration in the primitive lunar mantle (meaning bulk silicate Moon) is 121 ± 15 ppmw. Our new data also further constrain F/P, S/Dy and Cl/Ba ratios in lunar basalts and the lunar mantle. Estimated F, P, and S concentrations in the lunar primitive mantle are 4.4 ± 1.1 ppmw, 22 ± 8 ppmw, and ppmw, respectively.

中文翻译：

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月海玄武岩熔体包裹体中的挥发物：弥补月火山碎屑样品 74220 和其他月海样品中熔体包裹体之间 H2O/Ce 比率的差距

月球火山碎屑样品 74220 中橄榄石熔融包裹体的 H2O 浓度和 H2O/Ce 比率较高（H2O 高达 1410 ppmw；H2O/Ce 高达 77），但较低（H2O 10 至 430 ppmw；H2O/Ce 0.3 至 9.4） ）在这项工作之前研究的所有其他月球样本中。 74220 和其他月球样品中熔体包裹体中的其他挥发性元素（F、S 和 Cl）不存在 H2O 浓度和 H2O/Ce 比率差异。由于 H2O（或 H）是一种关键的挥发性成分，对月球的起源和演化具有重大影响，因此了解导致 74220 与其他月球样本之间 H2O/Ce 比率如此大差距的原因非常重要。提出了两种解释。一是样品 74220 中的火山产物具有最高的冷却速率，因此与其他样品中的熔体包裹体相比，熔体包裹体中的 H2O 保存得最好。另一种解释是样品 74220 来自富含某些挥发物的局部异质性。为了区分这两种可能性，我们在这里提供了来自两个具有玻璃状熔融包裹体的快速冷却月球样本的新数据：79135风化角砾岩中的橄榄石熔融包裹体（OHMI）（冷却速率未知，但玻璃状MI的质地与74220中的相似） ，以及 15597 紫云母玄武岩中的辉石主熔体包裹体（PHMI）（已知冷却速率高，仅次于 74220 和 15421）。此外，我们还研究了样品 74220 中的新 OHMI。如果差异是由于冷却速率差异造成的，则冷却速率介于 74220 和其他研究的月球样品之间的样品应该保留中间的 H2O 浓度和 H2O/Ce 比率。我们的结果表明，79135 和 15597 中的熔体包裹体含有高 H2O 浓度（79135 中高达 969 ppmw，15597 中高达 793 ppmw）和高 H2O/Ce 比率（79135 中高达 21，15997 中高达 13），桥接74220与其他月球样品的H2O/Ce比值差距较大。结合文献数据，我们证实不同月球样品的 H2O/Ce 比值与冷却速率呈正相关，且与月海玄武岩类型无关。因此，我们强化了这样的解释：由于脱气最少，冷却速率最高的月球样本最能代表月球玄武岩中喷发前的挥发物。根据原始月幔中的 Ce 浓度，我们估计原始月幔（即块状硅酸盐月球）中 H2O 浓度为 121 ± 15 ppmw。我们的新数据还进一步限制了月球玄武岩和月幔中的 F/P、S/Dy 和 Cl/Ba 比率。月球原始地幔中 F、P 和 S 的估计浓度分别为 4.4 ± 1.1 ppmw、22 ± 8 ppmw 和 ppmw。