Orthopyroxene-dominated upper mantle melting on building early crust on the Moon

Understanding lunar crust building is important for investigating fundamentals of planetary evolution, but its nature remains enigmatic. Here we report non-Apollo-like highland clasts in the Chang’e-5 samples and find high-alumina melts enclosed in a noritic anorthosite. Geochemistry and phase equilibria modeling suggest that the melt is compositionally parental to lunar magnesian-suite rocks, and was sourced from a plagioclase-bearing, orthopyroxene-dominated upper mantle (~4.5 kbar and 1225℃). It was formed as a direct consequence of upper mantle melting at the onset of gravitational instability. We propose that early crust formation on the Moon started from multiple anorthositic cumulate flotations, to upper mantle melting caused by small-scale in-situ overturn, and eventually ended up by decompression melting of lower mantle cumulates following large-scale (global) overturn.