Effects of oxidation on pyroxene visible-near infrared and mid-infrared spectra
Effects of oxidation on pyroxene visible-near infrared and mid-infrared spectra
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DOI：
10.1016/j.icarus.2020.113978
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发表时间：
2020-07
期刊：
影响因子：
3.2
通讯作者：
M. McCanta;M. Dyar
中科院分区：
文献类型：
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作者：
M. McCanta;M. Dyar
辉石在可见光近红外(VNIR)和中红外(MIR)波段的光谱特征受到传统变质作用和冲击变质作用氧化的影响。观察到的效应是由于结晶温度或压力的变化或用Fe3+取代Fe2+而引起的晶体结构的改变。来自地幔包体的高氧化辉石和冲击实验表明，单斜辉石的氧化光谱效应比斜方辉石更大，因为单斜辉石在结构上可以容纳更多的Fe3+。与氧化增加相关的单斜辉石极低频红外光谱的变化包括0.8Gμm吸收带向更短波长的移动和Fe~(2+)↔Fe~(3+)价间电荷转移(IVCT)带的加强，这使得1.0Gμm特征的带深减少了约20%。尽管震荡的单斜辉石被氧化到与地幔包体相似的水平，但震荡的影响叠加了VNIR中的氧化作用。其中包括2.35亿μm特征的强度降低约76%，1.0亿μm特征的强度降低约70%。在MIR中，氧化和冲击的影响微乎其微，导致能带深度总体下降5%。这些位移和变化可以解释为Fe离子周围多面体的变化，从而减少了晶场分裂和晶体结构的有序性。通过极低频红外遥感方法确定行星表面成分需要仔细考虑冲击和/或氧化过程引起的潜在变化。
Pyroxene spectral features in the visible near-infrared (VNIR) and mid-infrared (MIR) wavelengths are affected by oxidation resulting from traditional metamorphic processes as well as impact metamorphism. The observed effects are due to modifications in the crystal arising from changes in crystallization temperature or pressure or from substituting Fe3+for Fe2+. Highly oxidized pyroxenes from terrestrial mantle xenoliths and shock experiments indicate that the spectral effects of oxidation are greater in clinopyroxene than orthopyroxene because clinopyroxene can accommodate more Fe3+structurally. Changes in clinopyroxene VNIR related to increasing oxidation include a shift in the 0.8 μm absorption band to shorter wavelengths and a strengthening of the Fe2+↔Fe3+intervalence charge transfer (IVCT) band, which reduces the band depth of the 1.0 μm feature by ~20%. Although shocked clinopyroxenes are oxidized to similar levels to that seen in the mantle xenoliths, the effects of shock overprint those of oxidation in the VNIR. These include a decrease of ~76% intensity of the 2.35 μm feature and a decrease of ~70% intensity of the 1.0 μm feature. In the MIR, the effects of oxidation and shock are minimal, resulting in a 5% overall decrease in band depth. These shifts and changes can be interpreted as a result of changes in the polyhedra surrounding the Fe cations which reduce crystal field splitting and the order of the crystal structure. Determination of planetary surface composition through VNIR remote sensing methods requires careful consideration of potential changes induced via shock and/or oxidation processes.