High-titanium mare basalts: From petrogenesis to lunar evolution

High-Ti mare basalts, characterized by their unique titanium-rich compositions (TiO2 contents up to 16 wt.%), provide critical insights into lunar magma ocean (LMO) differentiation, the structure and composition of the lunar mantle, and lunar internal dynamics. Here we systematically synthesize the spatiotemporal distribution, petrology, mineralogy, and geochemistry of high-Ti mare basalts. By integrating these compiled data with thermodynamic modeling, we present a comprehensive evaluation of the four prevailing petrogenetic models: (1) ilmenite-bearing cumulate (IBC) remelting, (2) IBC assimilation, (3) reaction of IBC-derived melts with early LMO cumulates, and (4) mantle source hybridization. Our analyses confirm that the distinct compositional characteristics of high-Ti mare basalts were inherited from late-stage, ilmenite-bearing LMO cumulates. However, we find that the IBC direct remelting, assimilation, and melt-rock reaction models (Models 1–3) each face significant limitations, failing to reconcile observed cumulate components, reproduce the full spectrum of melt compositions, or satisfy thermodynamic viability. In contrast, the mantle hybridization model (Model 4) emerges as the most promising mechanism, successfully satisfying multiple experimental and observational constraints for lunar high-Ti magmatism. We suggest that high-Ti mare basalts are not simple melting products of a single cumulate source. Instead, they represent the combined products of lunar mantle overturn, cumulate hybridization, and partial melting during the Moon’s long-term evolution. This scenario underscores a lunar interior with a far more complex physicochemical state than traditionally envisioned. Future research should prioritize constraining high-Ti mare basalts’ specific source composition and depth of origin, the mechanisms driving their distinct two-stage eruptive history (3.5–3.9 Ga and ​ and their spatial distribution patterns. Resolving these questions is paramount for understanding LMO differentiation, mantle overturn, the Moon’s thermal evolution, and the origin of the lunar hemispheric dichotomy.