The composition and origin of the lunar crust: Constraints from central peaks and crustal thickness modeling

Spectral-reflectance data of lunar central peaks have revealed that the Moon's crust varies both laterally and vertically in composition. We correlate the depths of origin of materials that make up central peaks with a geophysically derived dual-layered crustal thickness model and find that the peak compositions are consistent with this stratified model. Specifically, peaks composed exclusively of rocks containing more than 85% plagioclase (by volume) come from this model's upper crust, whereas peaks that contain some norite or gabbro-norite come from the model's lower crust. Extrapolating these data we find that the Moon's upper crust is composed of 88 +/- 4% plagioclase, corresponding to 29 to 32 wt.% Al2O3. The most-mafic lower portion of the crust is composed of 65 +/- 8% plagioclase, having an Al2O3 content that lies between 18 and 25 wt.%. We show that the lower portion of the crust is consistent with having formed by cumulate flotation in a lunar magma ocean.