Mineralogical constraints on the thermal history of martian regolith breccia Northwest Africa 8114
Mineralogical constraints on the thermal history of martian regolith breccia Northwest Africa 8114
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西北非洲 8114 火星风化角砾岩热史的矿物学限制
DOI：
10.1016/j.gca.2018.11.026
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发表时间：
2019
影响因子：
5
通讯作者：
MacArthur J
中科院分区：
文献类型：
--
作者：
MacArthur J
火星陨石西北非洲（NWA）8114 -NWA 7034的配对石头-提供了一个机会来研究火星风化层的热历史，并研究火星撞击坑附近的近地表过程和古代环境条件。我们的研究报告岩相和蚀变纹理，并侧重于辉石和氧化铁颗粒。部分辉石碎屑显示出溶纹层，表明高温岩浆成因和缓慢冷却。然而，透射电子显微镜显示，其他主要的辉石碎屑是多孔的，并已部分重结晶形成磁铁矿和含钾的菱晶玻璃质材料，连同残余辉石。这种击穿事件与氧化有关，使用Fe-K XANES测量的残留辉石中的Fe 3 +/Fe 3Fe高达25%。与以往的研究相比，辉石的分解和氧化很可能是在氧化性风化层环境中，在700 °C以上的温度下，至少保持7天的冲击加热的结果，我们报告了一个单独的、分离的普通辉石碎屑的~（40）Ar-~（39）Ar最大年龄为1.13-1.25 Ga。光谱的扰动性质妨碍了精确的年龄测定。在剖面上，这种碎屑是多孔的，含有氧化铁颗粒。这表明它经历了在其他残留辉石碎屑中所见的高温部分分解，并且具有高达25%Fe 3 +/Fe 3 + Fe。我们推断，这一年龄对应于撞击冲击加热事件，该事件导致许多辉石在撞击喷出物覆盖层固结后发生高温分解。700 °C以上的高温可能维持了足够长的时间，使一些碱性长石碎屑重新活动并一致地部分熔融，从而产生长石脉和晕，这些脉和晕横切，在某些情况下包围，氧化辉石然而，矿脉也可能是撞击风化层中热液事件的结果。一个简单的傅立叶冷却模型表明，至少5米深的风化层将足以保持温度与辉石分解超过7 day.Low温度含水蚀变发生形成针铁矿，通过XRD，XANES和FTIR鉴定。与前人研究结果相比，针铁矿可能是火星黄铁矿的陆地蚀变假成。
Martian meteorite Northwest Africa (NWA) 8114 – a paired stone to NWA 7034 – provides an opportunity to examine the thermal history of a martian regolith and study near-surface processes and ancient environmental conditions near an impact crater on Mars. Our study reports petrographic and alteration textures and focuses on pyroxene and iron oxide grains. Some of the pyroxene clasts show exsolution lamellae, indicating a high temperature magmatic origin and slow cooling. However, transmission electron microscopy reveals that other predominantly pyroxene clasts are porous and have partially re-crystallised to form magnetite and a K-bearing feldspathic glassy material, together with relict pyroxene. This breakdown event was associated with oxidation, with up to 25% Fe3+/ΣFe in the relict pyroxene measured using Fe-K XANES. By comparison with previous studies, this breakdown and oxidation of pyroxene is most likely to be a result of impact shock heating, being held at a temperature above 700 °C for at least 7 days in an oxidising regolith environment.We report an approximate40Ar-39Ar maximum age of 1.13–1.25 Ga for an individual, separated, augite clast. The disturbed nature of the spectra precludes precise age determination. In section, this clast is porous and contains iron oxide grains. This shows that it has undergone the high temperature partial breakdown seen in other relict pyroxene clasts, and has up to 25% Fe3+/ΣFe. We infer that the age corresponds to the impact shock heating event that led to the high temperature breakdown of many of the pyroxenes, after consolidation of the impact ejecta blanket.High temperatures, above 700 °C, may have been maintained for long enough to remobilise and congruently partially melt some of the alkali feldspar clasts to produce the feldspar veins and aureoles that crosscut, and in some cases surround, the oxidised pyroxene. However, the veins could alternatively be the result of a hydrothermal event in the impact regolith. A simple Fourier cooling model suggests that a regolith of at least five metres depth would be sufficient to maintain temperatures associated with the pyroxene breakdown for over seven days.Low temperature hydrous alteration took place forming goethite, identified via XRD, XANES and FTIR. Comparing with previous studies, the goethite is likely to be terrestrial alteration pseudomorphing martian pyrite.
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DOI：
10.1002/2015je004989
发表时间：
2016
期刊：
Journal of Geophysical Research: Planets
影响因子：
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影响因子：
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DOI：
--
发表时间：
2018
期刊：
影响因子：
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作者：
M. Schmieder;T. Kennedy;F. Jourdan;E. Buchner;W. Reimold
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