Experimental serpentinization of iron-rich olivine (hortonolite): Implications for hydrogen generation and secondary mineralization on Mars and icy moons
Experimental serpentinization of iron-rich olivine (hortonolite): Implications for hydrogen generation and secondary mineralization on Mars and icy moons
复制标题
富铁橄榄石（hortonolite）的实验性蛇纹石化：对火星和冰卫星上的氢生成和二次矿化的影响
DOI：
10.1016/j.gca.2022.08.025
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发表时间：
2022
影响因子：
5
通讯作者：
Solheid, Peter
中科院分区：
文献类型：
--
作者：
McCollom, Thomas M.;Klein, Frieder;Moskowitz, Bruce;Solheid, Peter
富含橄榄石的超镁铁质岩石的蛇纹石化作用被认为在整个太阳系的历史中广泛存在，对行星岩石圈的化学和物理性质、大气成分和天体生物学具有重要意义。蛇纹石化的一个特别重要的产物是分子氢（H2），它的产生与蛇纹石化过程中铁的氧化密切相关。虽然多年来进行了许多蛇纹岩化的实验模拟，但这些研究几乎完全是使用含有相对高Mg和低Fe含量的反应矿物进行的，这些反应矿物代表了陆地地幔岩石。相比之下，很少有研究对可能在太阳系其他天体上占主导地位的更富铁的矿物成分进行了研究。在这项研究中，研究了富铁橄榄石（hortonolite; Fo ~ 62）在230°C和35 MPa下蛇纹石化过程中的矿物蚀变和H2generation。经过3500小时的反应，~ 55%的石沸石反应成由蛇纹石（温石棉）和磁铁矿组成的次生矿物。温石棉中铁含量比原石中少，反映了部分铁分块成磁铁矿；然而，在相同的反应条件下，它的铁含量远高于富镁、贫铁的陆相地幔橄榄石（Fo ~ 90）蚀变沉淀的蛇纹石。与富镁橄榄石反应产生的磁铁矿也是富镁橄榄石的4倍以上。在整个实验过程中，h2的生成都是稳定的，在相同条件下，每摩尔钙石的h2生成量是贫铁橄榄石的5倍以上。结果表明，火星和其他行星上富铁超镁铁质岩石的蛇纹石化可能比地球上的贫铁超镁铁质岩石产生h2和沉淀磁铁矿的能力要大得多，这将增强它们支持基于h2的生物群落的潜力，有助于大气变暖，并增强行星岩石圈的局部磁特征。
Serpentinization of olivine-rich ultramafic rocks is recognized to have been widespread across the solar system throughout its history, with substantial implications for the chemical and physical properties of planetary lithospheres, atmospheric compositions, and astrobiology. One especially significant product of serpentinization is molecular hydrogen (H2), whose generation is closely linked to the oxidation of Fe as serpentinization proceeds. While numerous experimental simulations of serpentinization have been conducted over the years, these studies have been performed almost exclusively using reactant minerals that contain relatively high Mg and low Fe contents representative of terrestrial mantle rocks. In contrast, very few studies have been conducted with the more Fe-enriched mineral compositions that may predominate on other solar system bodies. In this study, an experiment was conducted to investigate mineral alteration and H2generation during serpentinization of Fe-rich olivine (hortonolite; Fo∼62) at 230 °C and 35 MPa. After 3500 h of reaction, ∼55 % of the hortonolite reacted to secondary minerals composed of serpentine (chrysotile) and magnetite. Chrysotile contained proportionally less Fe than the original hortonolite, reflecting the partitioning of some Fe into magnetite; however, it contained substantially more Fe than serpentine precipitated from alteration of Mg-rich, Fe-poor terrestrial mantle olivine (Fo∼90) under the same reaction conditions. Reaction of hortonolite also produced more than four times as much magnetite as Mg-rich olivine. Generation of H2occurred steadily throughout the experiment, with more than five times as much H2generated per mole of hortonolite reacted than observed for Fe-poor olivine at the same conditions. The results suggest that serpentinization of Fe-rich ultramafic rocks on Mars and other planetary bodies may have a substantially greater capacity to generate H2and to precipitate magnetite than their Fe-poor terrestrial counterparts, which would enhance their potential to support H2-based biological communities, contribute to atmospheric warming, and augment local magnetic signatures in planetary lithospheres.