Replication Data for: The H2O content of the ureilite parent body.

The fate of highly volatile elements (H, C, F, Cl and S) during planetary accretion and differentiation is debated. Recent analyses of water in non-carbonaceous chondrites (RC, OC, EC) and achondrites (angrites, eucrites) have been used to argue that inner solar system parent bodies accreted and retained their highly volatile element budgets from their primary feedstock without substantial loss during accretion, metamorphism and differentiation. An alternative model posits that differentiated inner solar system parent bodies (e.g., the angrite parent body, 4 Vesta, Earth) derived the majority of their water from a carbonaceous chondrite-like source, delivered during the final stages of accretion. In order to add new constraints to this debate, we have measured water in nominally anhydrous minerals, melt inclusions, and interstitial glass in ureilites, the largest group of primitive achondrites in the terrestrial meteorite collection. Primitive achondrites did not experience global melting and homogenization. Therefore, these meteorites capture part of the transition from chondritic to achondritic parent bodies, allowing us to constrain the fate of water during the earliest stages of differentiation. Our nano-scale secondary ion mass spectrometry (nanoSIMS) analyses allow us to assess the viability of ureilite-like material as a potential source of terrestrial water. Analyses of pigeonite in main group ureilites yield a range of 2.0 – 6.0 µg/g H2O, and analyses of high-Ca pyroxene and glass (glassy melt inclusions and interstitial glass) in the Almahata Sitta ureilitic trachyandesite yield ranges of 13 – 19 µg/g H2O and 44 – 216 µg/g H2O, respectively. Mass balance, incremental melting, and batch melting calculations yield a preferred ureilite parent body H2O content of 2 – 20 µg/g, similar to previous estimates of water in the eucrite parent body (4 Vesta), but lower than estimates of Earth’s water budget. With these data, we demonstrate that 1) the ureilite parent body is H2O-depleted relative to the Earth; 2) ureilite-like material is unlikely to be a primary source of H2O to the Earth; 3) C and H are not necessarily coupled elements during planetary accretion and thermal processing; and 4) accretion, heating, partial melting, and degassing of rocky planetesimals likely results in significant depletion of H2O.

行星吸积与分异过程中，高挥发性元素（H、C、F、Cl及S）的归宿问题尚存争议。近期针对非碳质球粒陨石（non-carbonaceous chondrites，RC、OC、EC）及无球粒陨石（achondrites，angrites、eucrites）中的水开展的分析研究表明，太阳系内侧行星母体可通过初始原料吸积并保留其高挥发性元素储量，且在吸积、变质作用与分异过程中未发生显著损耗。另有假说认为，已发生分异的太阳系内侧行星母体（如钛辉无球粒陨石母体、4号灶神星、地球）其大部分水均来自类似碳质球粒陨石的源区，并在吸积的最终阶段被输送至此。

为给这场争论提供新的约束依据，我们对橄辉无球粒陨石（ureilites）——地球陨石收藏中规模最大的原始无球粒陨石类群——中的名义上无水矿物、熔融包裹体及间隙玻璃开展了水含量测定。原始无球粒陨石未经历全球性熔融与均化作用，因此这类陨石保留了从球粒陨石母体向无球粒陨石母体转变的部分信息，使我们得以约束行星分异早期阶段的水的归宿问题。

我们采用纳米二次离子质谱（nano-scale secondary ion mass spectrometry, nanoSIMS）开展的分析，可用于评估类似橄辉无球粒陨石的物质是否可作为地球水的潜在源区。对主群橄辉无球粒陨石中的古铜辉石（pigeonite）开展的分析显示，其水含量范围为2.0~6.0 µg/g H₂O；对阿尔马哈塔西塔（Almahata Sitta）橄辉无球粒质粗安岩中的富钙辉石及玻璃（熔融包裹体玻璃与间隙玻璃）的分析则分别得到13~19 µg/g H₂O与44~216 µg/g H₂O的含量范围。

通过质量平衡、渐进熔融与批量熔融计算，我们得出橄辉无球粒陨石母体的优选水含量范围为2~20 µg/g，该结果与此前对钙长辉长无球粒陨石母体（4号灶神星）的水含量估算值相近，但低于地球水储量的估算结果。基于上述数据，我们得出以下结论：1）相较于地球，橄辉无球粒陨石母体的水含量显著贫化；2）类似橄辉无球粒陨石的物质不太可能是地球水的主要源区；3）在行星吸积与热演化过程中，碳与氢并非必然呈现耦合关系；4）岩质行星微行星的吸积、加热、部分熔融与脱气作用，大概率会导致水发生显著损耗。