The oxygen fugacity of intermediate shergottite NWA 11043: implications for Martian mantle evolution
The oxygen fugacity of intermediate shergottite NWA 11043: implications for Martian mantle evolution
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DOI：
10.1016/j.gca.2024.05.008
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发表时间：
2024-05-19
影响因子：
5
通讯作者：
Yang，Jing
中科院分区：
文献类型：
--
作者：
Chen，Jun-Feng;Zhao，Yu-Yan Sara;Yang，Jing
根据不相容的微量元素和特定的放射性同位素组成（Sr、Nd 和 Hf 同位素比），将 Shergottite 陨石分为贫化、中间或富集，它们指向多个火星地幔源区。这些地幔区域的氧逸度（fO2）是使用橄榄石-辉石-尖晶石氧气压计根据早期结晶矿物测定的，似乎与不相容的微量元素富集和同位素组成相关。然而，从橄榄石中钒氧压计得出的值对这种相关性提出了挑战，暗示了氧压计的潜在偏差或火星地幔氧化还原条件的复杂性。通过使用各种氧压计分析中间的角辉石西北非 (NWA) 11043，本研究推断其起源于还原的地幔来源，相对于铁方铁矿 (IW) 缓冲液，平均 fO2 值为 -0.77 ± 0.35。值得注意的是，这些值与代表贫化火星地幔区域的贫化谢尔哥特岩的值一致。中间型和贫化的六角辉石之间的这种氧化还原相似性与早期假设中间型六角辉石是贫化和富集的地幔衍生物的混合物的概念形成鲜明对比。此外，诸如 NWA 11043、象冰碛 (EETA) 79001A 和 Allan Hills (ALH) 77005 等中间型六角辉石显示出与贫化六角辉石类似的 176Hf/177Hf 值，这表明根据模型年龄计算，中间地幔成分可以在大约 2.2 Ga 处从贫化地幔源中分离出来。因此，自西斯皮利亚时期以来，中间和贫化的六角辉石的地幔岩浆源之间都呈现出一致的氧化还原状态，而富集的六角辉石则倾向于在源形成之后更加氧化的条件。这项研究促使人们重新评估传统理论，强调火星地幔在不同地幔源区的微妙氧化还原演化，并强调火星地幔氧化还原演化的复杂性。化学多样性地幔储层的出现可能主要源于早期岩浆海洋分化过程，尽管存在固有的氧化细微差别。在中间和贫化的shergottites之间观察到的信息差异强调需要进行更深入的研究来破译火星地幔的分化和演化。
Shergottite meteorites, classified as depleted, intermediate, or enriched based on incompatible trace elements and specific radiogenic isotope compositions (Sr, Nd, and Hf isotope ratios), point to multiple Martian mantle source regions. The oxygen fugacity (fO2) of these mantle regions, determined from early crystallizing minerals using the olivine-pyroxene-spinel oxybarometer, appears to correlate with incompatible trace element enrichment and isotope compositions. However, values derived from the vanadium-in-olivine oxybarometer challenge this correlation, hinting at potential biases in oxybarometry or complexities in the redox conditions of the Martian mantle. By analyzing the intermediate shergottite Northwest Africa (NWA) 11043 with various oxybarometers, this study deduced its origin from a reduced mantle source, with an averagefO2value of −0.77 ± 0.35 relative to the iron-wüstite (IW) buffer. Notably, these values coincide with those of depleted shergottites, which represent the depleted Martian mantle region. This redox similarity between intermediate and depleted shergottites contrasts with earlier notions that postulated intermediate shergottites as a mix of depleted and enriched mantle derivatives. Moreover, intermediate shergottites such as NWA 11043, Elephant Moraine (EETA) 79001A, and Allan Hills (ALH) 77005 display176Hf/177Hf values akin to those of depleted shergottites, suggesting that intermediate mantle components can be separated from the depleted mantle source at approximately 2.2 Ga based on model age calculations. Therefore, there presents a consistent redox state between mantle magma sources of both intermediate and depleted shergottites since the Hesperian period, while enriched shergottites lean toward more oxidized conditions past source formation.This study prompts a reassessment of conventional theories, emphasizing the nuanced redox evolution of the Martian mantle across distinct mantle source regions and underscoring the complexity of the redox evolution of the Martian mantle. The emergence of chemically diverse mantle reservoirs might predominantly arise from early magma ocean differentiation processes, albeit with inherent oxidation nuances. The differences infO2observed between intermediate and depleted shergottites underscore the need for more in-depth studies to decipher Martian mantle differentiation and evolution.