Spectral reflectance properties of magnetites: Implications for remote sensing
Spectral reflectance properties of magnetites: Implications for remote sensing
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DOI：
10.1016/j.icarus.2018.10.002
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发表时间：
2019-02-01
期刊：
影响因子：
3.2
通讯作者：
Sherman, David M.
中科院分区：
文献类型：
--
作者：
Izawa, Matthew R. M.;Cloutis, Edward A.;Sherman, David M.
磁铁矿 (Fe3+(Fe2+Fe3+)(2)O-4) 在地球和行星物质中普遍存在，形成于火成岩、变质岩和沉积岩环境中，有时会受到微生物的影响。磁铁矿可用于研究许多不同的行星过程，例如岩浆的氧化态、古地磁、水-岩石相互作用（例如陨石母体上发生的蛇纹石化、蚀变和变质作用）以及天体生物学。与常见的行星材料相比，磁铁矿在紫外、可见和近红外区域的光谱反射特征有些不寻常，这表明磁铁矿的远程检测和表征应该是可能的。在这里，我们使用天然和合成样品对磁铁矿的反射光谱特性进行了系统研究。我们研究化学替代、晶粒尺寸变化以及与其他相的混合物的影响，以便更好地限制对含磁铁矿岩性的远程光谱搜索和解释。磁铁矿的特点是在此处考虑的整个波长范围内具有高消光度，因此表面散射比体积散射占主导地位。磁铁矿反射光谱受到高于 Verwey 转变温度（类似于 120 K）的离域电子的强烈影响，导致类似金属的散射行为，即高消光、表面散射占主导地位，并且反射率随着波长的增加而普遍增加，即“红斜且无特征”。叠加在类金属反射率上的是局部反射率最大值，我们将其归因于对应于 Fe-O 氧金属电荷转移过程（类似于 0.27 和类似于 0.39 μm）和 Fe 相关场 d 轨道跃迁（类似于 0.65 μm）的菲涅尔反射峰。我们还发现，随着磁铁矿中化学杂质的增加，0.65 μm 菲涅耳峰的波长位置发生系统性移动。磁铁矿的反射光谱与钛磁铁矿和方锰矿的反射光谱最相似，而与其他 Fe-(Ti) 氧化物的反射光谱不同，例如钛铁矿、水铁矿、钙镁尖晶石、磁赤铁矿、铁板钛矿和铝铁矿。
Magnetite (Fe3+(Fe2+Fe3+)(2)O-4) is ubiquitous in Earth and planetary materials, forming in igneous, meta-morphic, and sedimentary settings, sometimes influenced by microbiology. Magnetite can be used to study many and varied planetary processes, such as the oxidation state of magmas, paleomagnetism, water-rock interactions such as serpentinization, alteration and metamorphism occurring on meteorite parent bodies, and for astro-biology. The spectral reflectance signature of magnetite in the ultraviolet, visible, and near-infrared is somewhat unusual compared to common planetary materials, suggesting that remote detection and characterization of magnetite should be possible. Here we present a systematic investigation of the reflectance spectral properties of magnetite using natural and synthetic samples. We investigate the effects of chemical substitutions, grain size variations, and mixtures with other phases in order to better constrain remote spectral searches for, and interpretation of, magnetite-bearing lithologies. Magnetite is characterized by high extinction over the entire wavelength range considered here, and therefore surface scattering dominates over volume scattering. Magnetite reflectance spectra are strongly influenced by the presence of delocalized electrons above the Verwey transition temperature (similar to 120 K), leading to metal-like scattering behavior, that is, high extinction, surface scattering dominant, and a general increase in reflectance with increasing wavelength, i.e. "red-sloped and featureless". Superimposed upon the metal-like reflectance are local reflectance maxima which we ascribe to Fresnel reflectance peaks corresponding to Fe-O oxygen metal charge transfer processes (similar to 0.27 and similar to 0.39 mu m) and Fe-related field-d orbital transitions (similar to 0.65 mu m). We also find a systematic shift in the wavelength position of the 0.65 mu m Fresnel peak with increasing chemical impurity in magnetite. Magnetite reflectance spectra are most similar to those of titanomagnetite and wiistite, and unlike those of other Fe-(Ti) oxides, such as ilmenite, hwmatite, ulvospinel, maghemite, pseudobrookite, and armalcolite.