Investigating Local Variations of Lunar Rock Types at Sites of "Purest Anorthosite" Detection
Abstract
"Purest anorthosite" (PAN) are rocks of the lunar primary crust with over 98 vol% plagioclase. Understanding the distribution and purity of PAN on a local scale can help put constraints on the efficiency of plagioclase separation from the lunar magma ocean and help to illuminate the makeup of the Moon's primary crust. Here we use Lunar Reconnaissance Orbiter Camera (LROC) Narrow Angle Camera (NAC) photometry to investigate sites where PAN has been identified spectrally. We determine Hapke photometric parameters and minimize the effects of topography on local albedo variations using NAC images and photometric processing with local incidence and emission angles derived from NAC DTMs. The areas investigated are two sites in the Orientale Basin Inner Rook Ring (IRR) and one site at the central peaks of Jackson Crater (JKSN). Recent impact craters and the steepest slopes on the massifs have the highest single scattering albedo values (w) at the IRR sites, but areas interpreted to be mature PAN regolith have values of w=0.52-0.64. Variations in w not associated with maturity indicate differences in composition. PAN on both shallow and steep slopes at JKSN have values of w=0.75-0.84. Jackson Crater, however, is only a few hundred Myr old, compared to Orientale structures, which are 3.75 Byr old, and the JKSN central peaks are fresh and immature. To investigate mineralogy, spectra from the Moon Mineralogy Mapper (M3) were examined. JKSN has strong pyroxene absorptions on the central peak and clear plagioclase absorptions (1250 nm) on steep central-peak slopes. Spectra from a PAN massif of the IRR range from featureless, in some locations, to variable depths of the 1250 nm absorption feature. Several factors cause variations in absorption strength (e.g., grain size, differences in maturity, or mixtures of crystalline and amorphous plagioclase). We examine these data in detail to assess the purity of PAN and composition of coexisting rock types at these two sites. In areas of mature regolith, we find an inverse correlation between w and Clementine-derived wt.% FeO (i.e., high w is associated with low wt.% FeO), similar to that observed from lunar soils at the Apollo landing sites.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.P12A..07S
- Keywords:
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- 0933 Remote sensing;
- EXPLORATION GEOPHYSICSDE: 5460 Physical properties of materials;
- PLANETARY SCIENCES: SOLID SURFACE PLANETSDE: 5464 Remote sensing;
- PLANETARY SCIENCES: SOLID SURFACE PLANETSDE: 5470 Surface materials and properties;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS