Magma oceans, iron and chromium redox, and the origin of comparatively oxidized planetary mantles
Magma oceans, iron and chromium redox, and the origin of comparatively oxidized planetary mantles
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岩浆海洋、铁和铬的氧化还原以及相对氧化的行星地幔的起源
DOI：
10.1016/j.gca.2022.04.005
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发表时间：
2022
影响因子：
5
通讯作者：
Hirschmann, M.M.
中科院分区：
文献类型：
--
作者：
Hirschmann, M.M.
地球和火星的地幔氧化程度比基于岩浆海洋阶段熔融硅酸盐和合金的低压平衡所预期的氧化程度要高。岩浆海洋中的高压硅酸盐合金平衡会在硅酸盐中产生大量的三价铁，导致近地表条件和上覆大气相对氧化。结晶后，这可能足以解释地球和火星玄武岩源区普遍存在的氧逸度。实验和第一原理研究证实 Fe3+ 在高压下稳定，但迄今为止还没有模型能够准确解释熔体成分、温度、压力和氧逸度对岩浆海 Fe3+/FeT 的综合影响。我们校准了 Fe3+/FeTa 的新模型，作为温度、压力、熔体成分和 fO2 的函数，该模型再现了实验橄榄岩液体的 Fe3+/FeT，并将 FeO 和 Fe2O3 液体热容的差异纳入了潜在的实际温度函数中。对于压力的影响，模型的两个版本是基于最近的状态方程（EOS）实现的，尽管只有 Deng 等人的 EOS。 (2020) 适用于与深部陆地岩浆海洋中金属硅酸盐平衡相关的压力。对于地球来说，在 28–53 GPa、2300–4100 K 下的金属硅酸盐平衡以及由合理的地幔和地核成分设定的 fO2 产生的 Fe3+/FeT 介于 0.034 和 0.10 之间，其变化主要是由于假设温度的差异。对于火星，不同的建议地幔成分产生的 Fe3+/FeTratios 范围从 0.026（FeO* 为 13.5 wt.%）到 0.038（FeO* 为 18.1 wt.%）不等。尽管由于与合金的高压平衡，岩浆海洋中可能存在大量 Fe3+，但结晶地幔中 Fe2O3 的预算预计将比熔融状态下的有所改变。另一个重要的附加因素是Cr的影响，Cr是与合金平衡的熔融硅酸盐中的Cr2+和陆地上地幔中的Cr3+。结晶过程中与 Cr2+ 和 Fe3+ 反应生成 Cr3+ 和 Fe2+ 可以破坏岩浆海洋阶段存在的大部分 Fe2O3。考虑到橄榄石中Cr2+的稳定性以及Cr3+在地幔硅酸盐之间的分配与温度相关，我们构建了固体尖晶石橄榄岩中Cr（即Cr2O3）分数随温度和fO2变化的经验模型。对于地球来说，至少 0.35 wt.% Fe2O3 会被岩浆海洋 CrO 的氧化破坏，而对于火星来说，超过 0.55 wt.% Fe2O3 应该被破坏。因此，无论是陆地还是火星的岩浆海中的 Fe2O3 含量都比现在的上地幔要丰富得多，或者是其他过程导致了后者的氧化。仅当陆地金属硅酸盐平衡发生在 3300 K 以上且火星地幔含有 >17 wt.% FeO* 时，岩浆海洋中 Fe2O3 过度富集才是合理的。亚铁的固相线歧化作用可能促成了当今地幔的氧化还原状态，而类球粒陨石物质的晚期吸积和氢脱气也可能影响了地球和火星的凝固地幔。
The mantles of both Earth and Mars are more oxidized than would be expected based on low pressure equilibration of molten silicate and alloy during their magma ocean stages. High pressure silicate-alloy equilibration in a magma ocean can produce appreciable ferric iron in the silicate, leading to comparatively oxidized near surface conditions and overlying atmospheres. Upon crystallization, this may feasibly be sufficient to account for oxygen fugacities prevailing in basalt source regions of Earth and Mars. Experiments and first principles studies affirm that Fe3+is stabilized at high pressure, but to date there has been no model that accounts accurately for the combined effects of melt composition, temperature, pressure, and oxygen fugacity on magma ocean Fe3+/FeT. We calibrate a new model for Fe3+/FeTas a function of temperature, pressure, melt composition, andfO2which reproduces Fe3+/FeTfor experimental peridotite liquids and which incorporates differences in FeO and Fe2O3liquid heat capacities into a potentially realistic temperature function. For the effects of pressure, two versions of the model are implemented based on recent equations of state (EOS), though only the EOS of Deng et al. (2020) is applicable to pressures relevant to metal-silicate equilibration in a deep terrestrial magma ocean. For Earth, metal-silicate equilibration at 28–53 GPa, 2300–4100 K, andfO2set by plausible mantle and core compositions produces Fe3+/FeTbetween 0.034 and 0.10, with variation mostly owing to differences in assumed temperatures. For Mars, different proposed mantle compositions produce Fe3+/FeTratios that range from 0.026 for FeO* of 13.5 wt.% up to 0.038 for FeO* of 18.1 wt.%.Although significant Fe3+may be present in magma oceans owing to high pressure equilibration with alloy, the budget of Fe2O3in crystallized mantles is expected to be modified from that in the molten state. An important additional factor is the influence of Cr, which is Cr2+in molten silicate equilibrated with alloy and Cr3+in terrestrial upper mantles. Production of Cr3+and Fe2+by reaction with Cr2+and Fe3+during crystallization can destroy much of the Fe2O3present during the magma ocean stage. Considering the stability of Cr2+in olivine and the temperature-dependent partitioning of Cr3+between mantle silicates, we construct an empirical model for the fraction of Cr that is Cr2O3in solid spinel peridotite as a function of temperature andfO2. For Earth, at least 0.35 wt.% Fe2O3is destroyed by oxidation of magma ocean CrO and for Mars, more than 0.55 wt.% Fe2O3should be destroyed. Consequently, either the terrestrial and martian magma oceans were significantly more enriched in Fe2O3than their present-day upper mantles or other processes contributed to oxidation of the latter. Over-enrichment of Fe2O3in the magma oceans is plausible only if terrestrial metal-silicate equilibration occurred above 3300 K and if the martian mantle contains >17 wt.% FeO*. Subsolidus disproportionation of ferrous iron may have contributed to the present-day redox state of the Earth’s mantle, and late accretion of chondrite-like material and hydrogen degassing also likely affected the solidified mantles of both Earth and Mars.
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Fe2+ -Mg 在过渡区的石榴石、镁方石和 (Mg,Fe)2SiO4 相之间分配
影响因子：
3.1
作者：
D. Frost
通讯作者：
D. Frost
影响因子：
16.6
作者：
Deng, Jie;Du, Zhixue;Lee, Kanani K. M.
通讯作者：
Lee, Kanani K. M.
DOI：
10.1098/rsta.2008.0147
发表时间：
2008-11-28
影响因子：
5
作者：
Frost, D. J.;Mann, U.;Rubie, D. C.
通讯作者：
Rubie, D. C.
影响因子：
5.3
作者：
Hopp, Timo;Budde, Gerrit;Kleine, Thorsten
通讯作者：
Kleine, Thorsten
影响因子：
64.8
作者：
Stagno, Vincenzo;Ojwang, Dickson O.;Frost, Daniel J.
通讯作者：
Frost, Daniel J.