Petrology and reflectance spectroscopy of lunar meteorite Yamato 981031: Implications for the source region of the meteorite and remote-sensing spectroscopy

摘要

Combined mineralogy and reflectance spectroscopy of lunar meteorite Yamato (Y) 981031 were investigated to determine its possible source region. Mineralogical observations indicate that Y981031 is a mixture of mafic mare and feldspathic highland components. Y981031 has abundant mineral fragments and lithic clasts in a comminuted matrix. Although the most of the lithic clasts are pyroxene-dominant basaltic clasts, some plagioclase-rich lithic fragments are also present. High- and low-Ca pyroxene grains with wide compositional variations are included in the breccia. Since high-Ca pyroxene (Wo43En40Fs17 to Wo29En23Fs48) and a part of Fe-rich low-Ca pyroxene are found in pyroxene-dominant basaltic clasts, they were derived from mare materials. In contrast, abundant Mg-rich low-Ca pyroxene (approximately Wo10En63Fs27) is of highland origin because their chemical compositions resemble highland low-Ca pyroxene. Fusion crust glass compositions (TiO2=0.50-0.77wt and FeO=11.7-15.4wt) suggest that source mafic components of Y981031 have very low-Ti (VLT) affinity. In comparison with global remote-sensing data, the above TiO2 and FeO concentrations resemble those of the VLT affinity in Mare Frigoris and adjacent maria. Thus, we propose that Y981031 was launched from this area. Modified gaussian model analysis of reflectance spectrum shows absorption features of high-Ca pyroxene (mare-origin) and Mg-rich low-Ca pyroxene (highland-origin), and enables us to observe separately mineralogical characteristics of each end member of Y981031 as the soil mixture.