Mineralogical Characteristics of the Lorentz and Coulomb-Sarton Basins Reveal Early Magmatic Activity on the Lunar Farside

Abstract

Mg# (molar Mg/(Mg+Fe)) is a critical geochemical indicator for quantifying the evolution of the lunar crust, providing essential insights into regional compositional variability, crustal differentiation processes, and the crystallization history of the early lunar magma ocean (LMO). The Lorentz and Coulomb-Sarton (LCS) basins on the lunar farside exhibit significant magnesium anomalies in global surface chemistry maps that challenge traditional models of lunar crustal development. By integrating multisource lunar remote sensing data, we applied spectral parameter techniques and the Hapke radiative transfer model to assess the mineralogical characteristics of the LCS region and produce an updated geological map. The results reveal that the LCS region is predominantly dominated by plagioclase (>72.1 wt%), primarily in the form of ferroan anorthosites (FANs) with low-Mg# (<70) lithologies. Regions of elevated Mg# (>70) are concentrated in the western and northern portions of the Coulomb-Sarton basin and the central ring of the Lorentz basin. These localized anomalies correspond to Mg-rich lithologies that are interpreted as magnesian anorthosites derived from deeper crustal levels and subsequently exposed by impact excavation. This spatial pattern is consistent with a vertically stratified crustal structure, in which the upper crust consists predominantly of primordial FANs formed during the early LMO solidification. While deeper crustal materials may be related to magmatic intrusion from mantle-derived melts, they are intermittently exposed by large impact events and basin-scale modification processes. These findings provide new insights into the mineralogy and composition of the lunar farside highlands and constraints on the complex crustal evolution of the LCS region.