Potential Source Depth of Pure Plagioclase Exposed at Peak Rings of Impact Basins on the Moon

The lunar magma ocean (LMO) hypothesis suggests that the Moon's primary crust is largely composed of pure plagioclase; however, only limited pure plagioclase outcrops on the lunar surface were detected from the remote sensing observations. The spectral observations show that most crystalline plagioclase-rich features are concentrated on the peak rings of large basins, indicating that they were likely originally buried beneath the surface and then excavated by the formation of those basins. However, the potential source depths of these exposed pure plagioclase outcrops remain unconstrained. In this work, we aim to estimate the pre-impact depth of the observed pure plagioclase via numerical simulation of peak ring basin formation, which allows tracing the pre-impact depth of peak rings in basins of various sizes. According to our systematic modeling, we propose a power-law scaling function that links the potential source depth of pure plagioclase at peak rings to the basin diameter. Our results suggest that the observed pure plagioclase on the peak-ring basins in the Feldspathic Highlands Terrane originates from depths of ∼20–30 km below the surface. This layer of pure plagioclase is thought to be part of the primary crust that was formed during LMO crystallization. Our results advance the understanding of the structure and evolution of the lunar crust, and provide a framework that can be used to investigate the crustal structure of other solid planetary bodies.