月表镁尖晶石矿物的光谱特征与遥感探测:以第谷撞击坑为例

The spectral characteristics and remote detection of lunar Mg-spinel: A case study of Tycho Crater

月球镁尖晶石矿物隶属于深成岩,可以通过撞击作用被带到月表,它蕴含月壳深部甚至月幔的成分信息,对于研究月壳岩石成因与岩浆演化具有重要意义.本文分别从实验室和遥感研究两方面系统回顾月球镁尖晶石矿物的研究进展,以辐射传输模型为基础,作出了镁尖晶石与辉石、橄榄石和斜长石等矿物的一系列定量混合光谱.我们发现辉石与镁尖晶石矿物的相对含量与光谱波段比值之间存在对数关系,由此利用二次方程来拟合这种关系,建立了镁尖晶石矿物定量反演模型.以第谷(Tycho)撞击坑为例,我们利用遥感成像光谱数据(M^3)发现其中央峰主要矿物有辉石、斜长石和镁尖晶石等,尤其是发现了辉石与镁尖晶石的混合分布,但并未发现橄榄石矿物.利用上述矿物反演模型获得的混合矿物中镁尖晶石比例约为5.4vol%–6.4vol%,这与实验室月球样品的研究结果相符.我们推测这种辉石与镁尖晶石的混合矿物可能属于深成岩,被撞击作用抬升到月表,其中橄榄石只在坑壁附近发现有小范围的分布,可能属于浅层侵入岩.

Mg-spinel is often regarded as a specific deep-seated lunar mineral excavated onto the surface by giant impacts. The investigations of spinel would provide key compositional information of lunar lower crust or even mantle, thus is meaningful for the study of lunar petrogenesis and crustal evolution. This work overviews the recent progresses of lunar Mg-spinels studies by both remote Sensing and laboratory methods, Based on radiative transfer model, a series of mixtures of spinel and other mafic minerals are built, from which we find a quadratic correlation between logarithm spinel content and band ratio parameters. A spinel-pyroxene mixture model is established to quantify the spinel content based on this correlation. We apply this model to the spinel-pyroxene spectra detected by Moon Mineralogy Mapper （M3） data for Tycho Crater, yielding a result that the spinel content only takes up 5.4vol%- 6.4vo1% out of the spinel-pyroxene mixture. This result is consistent with those from lunar sample studies. We also find that these kinds of spinel-pyroxene mixtures occur originated from the lower crust, while the olivine mineral from shallow plutonic magma intrusion. without any olivine observed, indicating that they may be detected around the wall of Tycho Crater may be originated