Some basaltic eucrites and basaltic lithologies in howardites derived from the asteroid 4 Vesta exhibit unusual secondary veinlet textures consisting mostly of fayalitic olivine and Fe-enrichments within pyroxenes. Recent studies discussed the formation of these Fe-rich phases either by interaction with a vapor and/or liquid phase (metasomatism), or by a high-temperature melting process. We therefore performed a series of heating and hydrothermal experiments with liquids of different compositions on natural pyroxene crystals (augite and orthopyroxene) to evaluate these contrasting hypotheses. The results of the heating experiments show that incongruent melting of pyroxenes at about 1070 °C causes textures that are very similar to those observed in the meteorites. We conclude that a part of the natural secondary veins might be explained by heating processes at similar temperatures. The hydrothermal experiments with aqueous liquids of different Fe-enriched compositions clearly indicate ion exchange reactions resulting in partial Fe-enrichments of the pyroxene. Interestingly, these Fe-enrichments occurred independent of the Fe content of the liquid, which can be explained by an internal origin of Fe from the pyroxenes. In one hydrothermal experiment of augite with Fe-oxalate solution, deposition of fayalitic olivine was observed. From our experimental observations, we conclude that aqueous liquids are plausible candidates for explaining the deposition of Fe-enrichments and fayalitic olivine inside the fractures of pyroxene. However, we cannot rule out a high-temperature melting process slightly above the peritectic point of pyroxene to explain a fraction of observed secondary Fe-enrichments.

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玄武质晶体中的次生铁富集是如何形成的？一种实验方法

来自小行星 4 灶神星的霍华德岩中的一些玄武质 eucrits 和玄武岩岩性表现出不寻常的次生细脉结构，主要由辉石中的铁橄榄石和 Fe 富集组成。最近的研究讨论了通过与气相和/或液相（交代作用）相互作用或通过高温熔化过程形成这些富铁相。因此，我们在天然辉石晶体（辉石和斜辉石）上用不同成分的液体进行了一系列加热和水热实验，以评估这些对比假设。加热实验的结果表明，辉石在 1070°C 左右的不一致熔化会导致纹理与在陨石中观察到的纹理非常相似。我们得出的结论是，部分天然次生脉可能可以通过类似温度下的加热过程来解释。用不同富铁成分的水性液体进行的水热实验清楚地表明离子交换反应导致辉石部分富铁。有趣的是，这些 Fe 富集的发生与液体的 Fe 含量无关，这可以通过辉石中 Fe 的内部来源来解释。在使用草酸铁溶液对辉石进行的一项水热实验中，观察到铁橄榄石的沉积。根据我们的实验观察，我们得出结论，水性液体是解释辉石裂缝内富铁和铁橄榄石沉积的合理候选者。然而，