Multi-element constraints on the sources of volatiles to Earth
Multi-element constraints on the sources of volatiles to Earth
复制标题
地球挥发物来源的多元素限制
DOI：
10.1016/j.gca.2022.07.007
复制
发表时间：
2022
影响因子：
5
通讯作者：
Olson, P.L.
中科院分区：
文献类型：
--
作者：
Sharp, Z.D.;Olson, P.L.
许多研究使用一种或几种同位素系统来估计地球挥发物的来源。在这些模型中通常考虑几个挥发源和随后的挥发损失。在本文中，我们使用了一个基于假定的地球形成历史的正演模型，同时约束了七种挥发性元素（H，He，N，Ne，Ar，Kr和Ar）的来源。我们考虑三个潜在的挥发性来源：星云吸入，彗星和彗星。汇包括早期流体动力逃逸损失和电离态的长期损失。10，000次蒙特卡罗模拟产生了数百个解决方案，这些解决方案将所有这些元素的丰度与当今地球值的1/12倍以及临界同位素比率（δ 15 N，20 Ne/22 Ne，36 Ar/38 Ar，Kr和Ar）相匹配。不同元素的挥发分来源明显不同。我们的研究结果表明，有大量过量的H，He和Ne由星云吸入提供，随后的大量损失（>99%的He和Ne）由早期的流体动力逃逸。Kr和Kr主要由彗星提供，N几乎全部（>98%）由彗星提供。Ar的来源是混合的，其中50-90%为碳酸氢盐，其余来自气体的进入。与地球值相匹配的氮同位素比的溶液需要> 92%的E球粒陨石源。使用C球粒陨石源的δ 15 N值太高（>20‰ vs AIR）。我们的结果表明，晚加入的彗星为7.5 ± 0.7 × 1021 g，C为8.3 ± 5.6 × 1024 g，E为1.2 ± 0.5 × 1026 g，Kr同位素模式应符合彗星输入的模式，因为90%以上的Kr来自彗星源。我们的结果与67 P/C-G彗星的测量值在误差范围内吻合。如果我们假设在电离氦向空间损失期间有一个大的依赖于质量的富集因子，那么利用太阳同位素值作为假设的彗星源，氦同位素数据可以与地球值相匹配。67 P/C-G彗星的轻、重氢同位素比值与地球大气数据不匹配，表明该彗星在我们的模型中不是地球彗星氢源的代表。氢的摄入量与氧逸度密切相关，早期岩浆海洋的氧逸度为现今海洋总量的11 ~ 22倍。即使在低f（O2）值下，大部分水也以H2O而不是H的形式溶解。流体动力逃逸过程中氢同位素分馏（α = 1.6 ~ 1.7）较大，是解释现今D/H值的必要条件。该α值对应于在1300 °C时H2和H2O之间的平衡或原子H向空间的损失。地球历史早期氢的损失很容易解释现今地球地幔中相对较高的氧含量。
A number of studies have used one or several isotopic systems to estimate the origin of Earth’s volatiles. Several volatile sources and subsequent volatile loss are generally considered in these models. In this communication, we use a forward model based on the presumed formation history of Earth to simultaneously constrain the sources for seven volatile elements (H, He, N, Ne, Ar, Kr and Xe). We consider the three potential volatile sources: nebular ingassing, chondrites, and comets. Sinks include loss by early hydrodynamic escape and long-term loss of ionized Xe. 10,000 Monte Carlo simulations generate several hundred solutions that match the abundance of all these elements to within a factor of ∼2 of the present-day Earth values, as well as critical isotope ratios (δ15N,20Ne/22Ne,36Ar/38Ar, Kr and Xe). The source of volatiles is distinctly different for different elements. Our results indicate that there was a large excess of H, He and Ne supplied by nebular ingassing, with subsequent massive loss (>99% He and Ne) by early hydrodynamic escape. Kr and Xe were supplied primarily by comets, and N was supplied almost entirely (>98%) by chondrites. The source of Ar is mixed, with 50–90% chondrites and the remainder from ingassing. Solutions with nitrogen isotope ratios that match Earth values require a > 92% E chondrite source. δ15N values are far too high using a C chondrite source (>20‰ vs AIR). Our results suggest late addition of 7.5 ± 0.7 × 1021g comets, 8.3 ± 5.6 × 1024g C chondrites and 1.2 ± 0.5 × 1026g E chondrites.The Kr isotope pattern should follow that of cometary input, given that > 90% of all Kr comes from a comet source. Our results fit the measured values of Comet 67P/C-G within error. Xe isotope data can be matched to Earth values using solar isotope values as an assumed cometary source if we assume a large mass-dependent enrichment factor during loss of ionized Xe to space. The measured isotope data for Comet 67P/C-G have both light and heavy Xe isotope ratios that do not match the Earth atmosphere data, suggesting that this comet is not, in our model, representative of the Earth cometary Xe source.The amount of ingassed H is critically dependent on oxygen fugacity, ranging from 11 to 22 times the present day ocean amount for presumed lowf(O2) of the early magma ocean. Even at lowf(O2) values, most of the water is dissolved as H2O rather than H. A large hydrogen isotope fractionation during hydrodynamic escape (α = 1.6 to 1.7) is required to explain the present-day D/H values. This α value corresponds to equilibrium between H2and H2O at ∼300 °C or loss of atomic H to space. Loss of hydrogen early in Earth’s history easily accounts the relatively highf(O2) of Earth’s present-day mantle.
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地球吸积期间捕获的星云气体被保存在深地幔氖中
影响因子：
64.8
作者：
C. Williams;S. Mukhopadhyay
通讯作者：
S. Mukhopadhyay
流体动力学逃逸中的质量分馏
DOI：
--
发表时间：
1987
期刊：
影响因子：
--
作者：
D. Hunten;R. Pepin;James C. G. Walker
通讯作者：
James C. G. Walker
影响因子：
56.9
作者：
Mario Trieloff;J. Kunz;D. Clague;Darrell Harrison;C. Allègre
通讯作者：
Mario Trieloff;J. Kunz;D. Clague;Darrell Harrison;C. Allègre
影响因子：
10.3
作者：
R. Pepin
通讯作者：
R. Pepin
无阴极辉光放电中的 Xe 同位素分馏。
DOI：
10.1016/0016-7037(86)90197-3
发表时间：
1986
期刊：
--
影响因子：
--
作者：
T. Bernatowicz;A. Fahey
通讯作者：
A. Fahey