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

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

Two-stage Development of the Lunar Farside Highlands Crustal Formation

The correlation between the spatial patterns of surface Thorium (Th) abundance measured by SELENE GRS data and the crustal thickness from the GRAIL gravity field and LRO LOLA data is investigated in the lunar highland area. Our analysis reveals that there are several areas of local minima for Th abundance exhibiting similar values but different crustal thicknesses. To explain the result, we propose a two-stage scenario for crustal formation. In the first stage, plural thin plateaus form on the surface of the lunar magma ocean (LMO), which corresponds to the observed surface Th distribution. In the second stage, a global crust with dichotomy forms by solidification of the LMO under the plateaus

Tectonic evolution of northwestern Imbrium of the Moon that lasted in the Copernican Period

The formation ages of tectonic structures and their spatial distributions were studied in the northwestern Imbrium and Sinus Iridum regions using images obtained by Terrain Camera and Multiband Imager on board the SELENE spacecraft and the images obtained by Narrow Angle Camera on board LRO. The formation ages of mare ridges are constrained by the depositional ages of mare basalts, which are either deformed or dammed by the ridges. For this purpose, we defined stratigraphic units and determined their depositional ages by crater counting. The degradation levels of craters dislocated by tectonic structures were also used to determine the youngest limits of the ages of the tectonic activities. As a result, it was found that the contractions to form mare ridges lasted long after the deposition of the majority of the mare basalts. There are mare ridges that were tectonically active even in the Copernican Period. Those young structures are inconsistent with the mascon tectonics hypothesis, which attributes tectonic deformations to the subsidence of voluminous basaltic fills. The global cooling or the cooling of the Procellarum KREEP Terrane region seems to be responsible for them. In addition, we found a graben that was active after the Eratosthenian Period. It suggests that the global or regional cooling has a stress level low enough to allow the local extensional tectonics