Lunar surface chemistry observed by the KAGUYA multiband imager

Abstract

The abundance and distribution of oxides and Mg# (Mg/(Mg ​+ ​Fe) in mole percent) values are important for revealing the petrologic characteristics and evolutionary history of the Moon. In this work, new lunar surface chemistry maps, including Al2O3, CaO, FeO, MgO, TiO2, and Mg# maps, are generated from KAGUYA multiband imager (MI) spectra. These new maps are produced by the machine learning algorithm of the particle swarm optimization-support vector machine (PSO-SVM), and are characterized by relatively high accuracies and a high spatial resolution of 59 ​m/pixel, which are free to some degree from the topographic shadow effect. Moreover, Mg# values across the Moon exhibit an obvious chemical trichotomy. According to this Mg# feature, a new geological partition is suggested, and the lunar surface is divided into three geological units: the PM, SPAM, and FH units. The PM unit features low Mg# values, with an average of 0.55. The PM unit consists of Oceanus Procellarum, Grimaldi Crater, Tsiolkovskiy Crater, and some maria on the nearside and farside (e.g., the Frigoris, Imbrium, Tranquillitatis, Smythii, Crisium, Marginis, Orientale, and Moscoviense Maria). The FH unit possesses the highest Mg# values across the Moon, with an average of 0.70. The FH unit is composed of the Feldspathic Highlands Terrane (FHT), except for some maria (e.g., Orientale, Moscoviense, Australe, Marginis, and Smythii) and some craters (e.g., Tsiolkovskiy and Schickard). The SPAM unit is typical of medium Mg# values with an average of 0.65, and is constituted by the South Pole-Aitken Terrane (SPAT), Mare Australe, and some craters (e.g., the Schickard, Phocylides, Nasmyth, Schiller, and Inghirami Craters). The significant difference in Mg# values among the three geological units highlights the asymmetric magmatic evolution, crustal growth, and mare volcanism in the three units.