Search

We examined the global distribution and geological context of lunar sites where olivine‐ and plagioclase‐rich materials co‐exist. These sites are areas showing plagioclase‐rich spectra adjacent to areas showing olivine‐rich spectra, and they extend over several hundreds of meters on the lunar surface. From an analysis of the high‐spatial‐resolution data obtained from the SELENE (Kaguya) multiband imager, we identified 14 co‐existing occurrences among 49 olivine‐rich sites located around large impact basins. We found that the co‐existing occurrences are limited to a few sites among the olivine‐rich sites in the Moscoviense, Crisium, and Imbrium basins, while six of seven olivine‐rich sites in the Schrödinger basin show co‐existing occurrence. The geological features between the co‐existing occurrences and the olivine‐rich sites without plagioclase‐rich materials showed no clear difference, but both types of site are found at fresh geological features located around the peak rings of impact basins. These results may suggest that the co‐existing occurrences are closely related to the material heterogeneity of the peak ring regions. The heterogeneity could be formed by mixing of the olivine‐rich mantle and the anorthosite‐rich crust during impact basin formation, or it might be a reflection of the compositional heterogeneity of the lunar lower crust. For future sample return missions, the detailed information on the co‐existing occurrences presented here might be useful for a sampling strategy to select a "one‐stop" site that provides important information for the overall characterization of lunar mantle and crustal materials. Plain Language Summary: The surroundings of several impact basins on the lunar surface are known to contain olivine‐rich sites that are dominated by olivine‐rich spectra. Some of these olivine‐rich sites co‐exist with plagioclase‐rich (purest anorthosite) materials, which are adjacent to the olivine‐rich materials. The detailed study of these co‐existing occurrences would provide critical constraints on the structure, composition, and evolution of the lunar crust and upper mantle. In this study, we examined the global distribution and geological context of co‐existing occurrences based on the analysis of the high‐spatial‐resolution data obtained from the SELENE (Kaguya) multiband imager. Our results showed that the locations of co‐existing occurrences are limited to fresh geological features around the peak rings of impact basins, and their spatial distributions are sporadic along the peak rings, suggesting material heterogeneity in these regions. The heterogeneity could be due to mixing of the olivine‐rich mantle and anorthositic crust during the formation of the impact basins, or it may reflect a compositional heterogeneity of deep‐seated materials in the lower crust. For future sample return missions, the detailed information on co‐existing occurrences given here will be useful for a selecting a "one‐stop" sampling site to better characterize the lunar mantle and crustal materials. Key Points: We examined the global distribution and geological context of sites where olivine‐ and plagioclase‐rich materials co‐existWe identified 14 co‐existing occurrences among 49 olivine‐rich sites located around large impact basinsThe presence of co‐existing occurrences may indicate material heterogeneity in the peak rings of impact basins [ABSTRACT FROM AUTHOR]

Abstract: Cathodoluminescence (CL) analyses were carried out on maskelynite and lingunite in L6 chondrites of Tenham and Yamato‐790729. Under CL microscopy, bright blue emission was observed in Na‐lingunite in the shock veins. Dull blue‐emitting maskelynite is adjacent to the shock veins, and aqua blue luminescent plagioclase lies farther away. CL spectroscopy of the Na‐lingunite showed emission bands centered at ~330, 360–380, and ~590 nm. CL spectra of maskelynite consisted of emission bands at ~330 and ~380 nm. Only an emission band at 420 nm was recognized in crystalline plagioclase. Deconvolution of CL spectra from maskelynite successfully separated the UV–blue emission bands into Gaussian components at 3.88, 3.26, and 2.95 eV. For comparison, we prepared K‐lingunite and experimentally shock‐recovered feldspars at the known shock pressures of 11.1–41.2 GPa to measure CL spectra. Synthetic K‐lingunite has similar UV–blue and characteristic yellow bands at ~550, ~660, ~720, ~750, and ~770 nm. The UV–blue emissions of shock‐recovered feldspars and the diaplectic feldspar glasses show a good correlation between intensity and shock pressure after deconvolution. They may be assigned to pressure‐induced defects in Si and Al octahedra and tetrahedra. The components at 3.88 and 3.26 eV were detectable in the lingunite, both of which may be caused by the defects in Si and Al octahedra, the same as maskelynite. CL of maskelynite and lingunite may be applicable to estimate shock pressure for feldspar‐bearing meteorites, impactites, and samples returned by spacecraft mission, although we need to develop more as a reliable shock barometer. [ABSTRACT FROM AUTHOR]

Cathodoluminescence (CL) spectra of unirradiated, He ion-implanted and electron-irradiated plagioclase minerals contain the following emission bands: (1) below 300 nm due to Pb, (2) at ~320 and ~350 nm to Ce, (3) at 380-420 nm to Eu, Ti and/or Al-O-Al/Ti defects, (4) at 560-580 nm to Mn and (5) at 720-760 nm to Fe. During the implantation of He ion, much of their energy may be dissipated by partial destruction and strain of the feldspar framework, resulting in quenching of CL. Deconvolution of CL spectra acquired from albite and oligoclase reveals an emission component at 1.86 eV (666 nm) assigned to a radiation-induced defect center associated with Na atoms. As its intensity increases with radiation dose, this emission component has potential for geodosimetry and geochronometry. Electron irradiation causes Na migration in plagioclase, and then a considerable reduction in intensity of emissions assigned to impurity centers, which is responsible for an alteration in the energy state or a decrease in luminescence efficiency following the change of activation energy. Emission intensity at 1.86 eV positively correlates with electron irradiation time for unimplanted and He ion-implanted albite and oligoclase, but negatively for the implanted albite above 1.07 × 10 C/cm. It implies that radiation halo produced by α-particles should not be measured using CL spectroscopy to estimate β radiation dose on albite in the high radiation level. [ABSTRACT FROM AUTHOR]

Purest anorthosite (PAN), which consists mostly of plagioclase (≥98%), provides key information for understanding the deep crust of the Moon, because PAN observed at central peaks of large impact craters was uplifted from a deep-seated layer. For future sample return of PAN, we examined the visible and near-infrared spectra of lunar meteorites and the mineralogical and petrological studies for Apollo FAN 60015. Sample analyses for lunar meteorites and Apollo FAN 60015 showed the existence of PAN in lunar samples. However, PAN clasts in lunar meteorites were so small that not enough sampled material could be secured for multiple analyses, such as determining their crystallization ages. The lunar meteorites were also heavily brecciated by multiple impacts on the surface. The brecciation and recrystallization on the surface may have disturbed the original information (i.e., age, texture, etc). Therefore, sample return of PAN rocks that have recently fallen from the central peaks of the large craters is required for analysis to determine the parent magma composition and timing of PAN formation. We investigated the PAN distributions in Jackson crater on the lunar farside and found that PAN rocks are widely distributed over the central peak and parts of the crater wall, using SELENE (Kaguya) observational data to locate where PAN would best be collected from the lunar surface. Based on the slope that a rover can manage, we recommend two areas appropriate for collecting samples of PAN rocks that have separated from the central peak. • We examined analyses for lunar samples and SELENE data for sample return of PAN. • PAN was widely distributed over the central peak of Jackson crater. • We provided two areas appropriate for collecting PAN rocks within Jackson crater. [ABSTRACT FROM AUTHOR]