New Insights into the Compositional Variability of the Lunar Crust

Image credit: ISRO/NASA/JPL-Caltech/Brown University/USGS

The composition and mineralogy of the lunar surface provides important clues to the formation and evolution of the Moon through geologic time. A group of scientists led by Mรฉlissa Martinot from Vrije Universiteit Amsterdam, The Netherlands, performed a mineralogical survey of the anorthositic Feldspathic Highlands Terrane (FHT), a region comprising much of the lunar farside and defined by its high abundance of anorthosite rock having low FeO and thorium contents. Using spectroscopic data from the Moon Mineralogy Mapper instrument onboard Chandrayaan-1 orbital spacecraft, the group examined the central peak or peak rings of 75 craters to investigate the lateral and vertical heterogeneity of the FHT. Although the authors find the FHT to be laterally homogeneous in composition, a possible heterogeneous vertical gradation is observed in the composition of the mineral pyroxene. The study concludes that the upper lunar crust contains high-Ca pyroxene with pyroxene compositions becoming less calcic with increasing depth and proximity to the crust-mantle boundary. These results are consistent with recent interpretations suggesting that the upper lunar mantle may be dominated by low-Ca pyroxene, contrary to models of an olivine-dominated upper mantle. Further investigation of craters hypothesized to expose or sample material near the crust-mantle boundary will help to assess this finding. READ MORE