Occurrence and Provenance of KREEP Components in Glassy Agglutinates From Chang'e-5 Lunar Regolith

Abstract

This study investigates the petrogenesis of glassy agglutinates in a polished section of the Chang'e-5 lunar regolith sample CE5C0800YJYX018GP through integrated petrographic, mineralogical, and geochemical analyses of four representative particles (18GP-01 to 18GP-04). The agglutinates contain diverse lithic clasts, including basaltic fragments, anorthositic fragments, and a barred olivine-rich fragment, together with glass fragments. Mineral clasts are dominated by plagioclase, pyroxene, olivine, and ilmenite, with minor apatite, troilite, and silica phases. The glassy matrix formed primarily through impact melting of basaltic materials and shows compositions comparable to those of low-Ti mare basalts from Oceanus Procellarum. In contrast, some glass domains exhibit strong enrichment in K (K₂O up to 1.37 wt.%), P (P₂O₅ up to 4.84 wt.%), and rare earth elements (ΣREE up to 3,196.1 ppm). These enriched domains display pronounced LREE enrichment, relatively flat HREEs, and negative Eu anomalies, similar to the KREEP-rich lunar regolith from Oceanus Procellarum. Given the KREEP-poor geochemical background of the Chang'e-5 landing site, these features are most consistent with an exotic origin rather than in situ evolution of local basalts, and are best explained as material derived from the Procellarum KREEP Terrane and transported by large impact events. The micrometer-scale, heterogeneous distribution of KREEP-rich domains, together with agglutinated melt glass, and cristobalite, provides clear evidence for impact-driven transport and mixing. These observations place new constraints on lunar material redistribution, the preservation of late-stage magmatic residues, and the thermal evolution of the Moon.