Martian meteorites are the only available samples that can be directly measured to constrain the geological evolution of Mars. It has been suggested that the oxygen fugacity (fO₂) of martian shergottite meteorites, which have low (∼7 wt.%) to high-MgO (∼30 wt.%) compositions, correlates with incompatible trace element enrichment (i.e., La/Yb), and ⁸⁷Sr/⁸⁶Sr, ¹⁴³Nd/¹⁴⁴Nd, ¹⁸⁷Os/¹⁸⁸Os and ¹⁷⁶Hf/¹⁷⁷Hf at the time of crystallization. These relationships have been interpreted to result from early magmatic processes segregating enriched and more oxidized from depleted and more reduced reservoirs in Mars. Here we use the V-in-olivine oxybarometer to constrain the fO₂ of shergottites and the dunitic chassignites. These data, utilizing early crystallizing silicate phases, constrain the shergottite fO₂ range to between −3.72 ± 0.07 and −0.21 ± 0.55 ΔFMQ (log units relative to the fayalite-magnetite-quartz buffer), with no correlation with trace element enrichment or Nd isotope systematics. Previously employed oxybarometers that use later-formed or multiple mineral phases, and that show such correlations, likely differ from the V-in-olivine oxybarometer in that they record effects from late-stage magmatic processes. In contrast to shergottites, chassignites are relatively oxidized, at +2.1 ± 0.4 to +2.2 ± 0.5 ΔFMQ. The chassignites, along with the nakhlites, have been proposed to be sourced from metasomatized lithospheric mantle, and their high fO₂ strengthens this model. The new data implies that the martian mantle sources of shergottites have fO₂ of −2.1 ± 1.8 ΔFMQ. This estimate indicates that the mantle and core of Mars are not in redox equilibrium and therefore that oxidation of the martian mantle following core formation is required.

火星陨石是唯一可以直接测量以限制火星地质演化的样本。有人提出，火成陨石陨石的氧逸度（f O ₂）具有低（〜7 wt。％）至高MgO（〜30 wt。％）的组成，与不相容的痕量元素富集有关（即， La / Yb）和⁸⁷ Sr / ⁸⁶ Sr，¹⁴³ Nd / ¹⁴⁴ Nd，¹⁸⁷ Os / ¹⁸⁸ Os和¹⁷⁶ Hf / ¹⁷⁷结晶时的f。这些关系被解释为是由早期岩浆过程从火星的贫化和更多还原的储层中分离出富集的和更多的氧化作用所引起的。在这里，我们使用V-in-橄榄石氧饱和度计来约束斜方锰矿和辉长辉石的f O ₂。利用早期结晶的硅酸盐相，这些数据限制了斜方晶矿f O _{2的产生。}范围介于-3.72±0.07和-0.21±0.55ΔFMQ（相对于铁橄榄石-磁铁矿-石英缓冲液的对数单位）之间，与微量元素富集或Nd同位素系统无关。以前使用的气压计使用后来形成的或多个矿物相，并显示出这种相关性，这可能与V-in-橄榄石气压计不同，因为它们记录了后期岩浆过程的影响。与黑钙铁矿相反，菱镁石被相对氧化，在+2.1±0.4至+2.2±0.5ΔFMQ处。有人建议将石与纳霍石一起从交代的岩石圈地幔中获取，它们的高f O ₂加强了这一模型。新的数据意味着shergottites的火星地幔源有˚F Ø-2.1±1.8ΔFMQ中的₂ 该估计表明火星的地幔和核心未达到氧化还原平衡，因此需要在火星形成后对火星地幔进行氧化。