Petrologic Insights Into the South Pole-Aitken Basin From Raman Spectroscopy of Returned Chang'e-6 Coarse Clasts

Abstract

As the largest and oldest impact basin on the Moon, the South Pole-Aitken (SPA) basin preserves critical information about the composition and evolution of the deep lunar crust and may even expose materials from the lunar mantle. China's Chang'e-6 mission returned the first farside samples from the southern mare unit of the Apollo basin within the SPA basin, where the regolith records a complex geological history and diverse non-mare lithologies. In this study, Raman spectroscopy was applied to 50 coarse-grained clasts (average diameter of ∼950 μm) from the Chang'e-6 samples to investigate their mineral composition and reveal the lithological diversity of the farside crust within the SPA basin. Based on modal mineralogy, these clasts are classified into breccias (n = 34), basalts (n = 8), and non-mare lithologies (n = 8). The non-mare clasts are dominated by norite (n = 5), anorthosite (n = 2), and troctolite (n = 1), exhibiting Mg# values (molar [Mg/(Mg + Fe)] × 100) of olivine and/or pyroxene ranging from 53 to 73. Notably, noritic clasts provide direct sample-based evidence that the Mg-rich pyroxene annulus of the SPA basin is predominantly composed of ferroan norite, with an average Mg# of ∼64 and model abundances of ∼61 vol% plagioclase and ∼29 vol% orthopyroxene. These results provide new insights into the crustal composition and evolution of the lunar farside within the SPA basin. This study demonstrates the capability of Raman-based lithologic classification and highlights its potential for future in situ mineralogical investigations in forthcoming lunar exploration by Chang'e-7 Lunar Raman Spectrometer.