P11A-2061
The Composition of the Lunar Crust as Revealed by the Study of Impact Basin Rings using the Kaguya Multiband Imager
Monday, 14 December 2015
Poster Hall (Moscone South)
Myriam Lemelin, University of Hawaii at Manoa, Honolulu, HI, United States, Paul G Lucey, Hawaii Inst Geophys & Planetol, Honolulu, HI, United States, Lisa R Gaddis, USGS Astrogeology Science Center, Flagstaff, AZ, United States and Katarina Miljkovic, Massachusetts Institute of Technology, Earth, Atmospheric, and Planetary Sciences, Cambridge, MA, United States
Abstract:
Impact basins excavate material from below the lunar surface and expose it on their peak rings. Peak rings can thus be used as probes to study the composition of the lunar crust with depth, which can in turn be compared to models of the formation of the lunar crust. Global surveys conducted to find exposures of nearly pure minerals have found rare lithologies such as norites, troctolites, and anorthosites associated with many basins rings [Yamamoto et al., 2010; 2012, Nakamura et al., 2012], but the abundance of these lithologies relative to the rings as a whole was not determined. Taking a comprehensive approach, Cheek et al. [2013] found that every immature exposure in the inner rook ring of the Orientale basin consists of anorthosite, suggesting that a massive layer of anorthosite is present at the Orientale target site. In this study, we take the approach of Cheek et al. [2013] and examine all the immature exposures in the rings of 14 impact basins. We use Multiband Imager (415-1550 nm) data and radiative transfer modeling to quantify the abundance of the four major lunar minerals in the inner ring of these basins, and determine the dominant lithologies exposed by the rings. We identify the inner ring of these basins using GRAIL crustal thickness data, and derived the mineralogy at a spatial resolution of 80 meters per pixel. Our preliminary results indicate that the dominant lithology in the inner ring of 12 of the 14 basins is anorthosite, with modal plagioclase content ranging between 92-94 wt%, suggesting that a massive layer of anorthosite is widespread under the lunar surface. The dominant lithologies in the other two basins are noritic and gabbroic anorthosites. The other lithologies present in the 14 basins will be investigated next, and the depth of excavation of each of these basin rings as well as the crustal thickness at these sites will be used to determine the composition of the crust with depth.
