Lunar Anorthosite: Identification and Distribution of Remnants of the Primordial Crust

Evidence strongly suggests that Earth's moon was once covered by a magma ocean which differentiated as it cooled. In the later stages of crystallization, plagioclase feldspar formed a cumulate flotation crust composed primarily of anorthosite many kilometers thick. The concurrent and subsequent heavy bombardment experienced by the moon has disrupted or obscured much of this original crust, but portions of it appear to have remained intact, especially on the northern lunar farside and globally at depth. While some other mechanisms for the production of anorthosite, such as the differentiation of plutons, have been suggested, the great majority of anorthosite outcrops present at the surface of the moon today may be portions of the original crust. Several spectral techniques are available for remotely identifying anorthosite on the moon. They utilize multispectral data sets obtained from Earth-based telescopes or from spacecraft orbiting or flying by the moon. While the techniques are related, they differ in their strengths and weaknesses. By comparing and combining the results from the various techniques, we can increase our confidence in our understanding of the global distribution of anorthosite.