¹Jiawei Zhao et al. (>10)
American Mineralogist 111, 376-393 Link to Article [https://doi.org/10.2138/am-2025-9877]
¹State Key Laboratory of Geological Processes and Mineral Resources, Planetary Science Institute, School of Earth Sciences, China University of Geosciences, Wuhan 430074,
China
Copyright: The Mineralogical Society of America

Pyroxene is a primary constituent mineral in basaltic lunar regolith. These minerals form through the cooling and crystallization of lunar basaltic magma and are subsequently altered by impact events. Thus, pyroxene can serve as a significant indicator for interpreting lunar magmatic processes and impact phenomena. For lunar samples that are mostly mafic and frequently shocked to various degrees, deciphering the effect of shock on pyroxene is necessary for a better understanding of the primary magmatic processes. However, previous studies have neglected to investigate the impact metamorphism of pyroxene in lunar regolith and the potential compositional changes that may result from such impacts. Lunar regolith samples returned by the Chang’E-5 (CE-5) mission are reworked from a monolithic mafic protolith with well-constrained compositions and record strong to mild shock effects that are widespread in the samples. The returned samples provide an excellent chance to distinguish the signatures of impact processes from magmatic activities. Here we report microstructural and compositional variations in a shocked pyroxene within a basaltic clast from CE-5 lunar regolith, which were analyzed by Raman spectroscopy, analytical scanning electron microscopy, electron probe microanalysis, and scanning transmission electron microscopy. The shock microstructures are characterized by the glide system of dislocation [001](100), pigeonite formation induced by shock-related deformations, and solid-melt partitioning and localized frictional melting at grain boundaries or within pyroxene. Combined with the occurrence of shock twins in ilmenite adjacent to the shock melt vein, these shock phenomena are approximately indicative of low-to-moderate shock pressure (9–17 GPa). Most parts of the pyroxene have abnormal Raman peaks at ∼822 cm−1, suggesting the substitution of Si4+ by Al3+ in the tetrahedral site of this shocked pyroxene structure, and this characteristic is recognized as a shock indicator. Evidence from the morphology and elemental distribution of pigeonite within host augite suggests that the Si-Al substitution is consistent with the pigeonite formation, which is triggered or modified by shock-induced deformations and local frictional melting under the fast shear stress. The multiple trends of composition evolution in this single shocked pyroxene reflect sequential processes of magma crystallization, shock-related exsolution, and frictional melting. Our findings indicate that shock effects in pyroxene under low-to-moderate shock conditions can induce changes in composition and structure, and may obscure the evidence of magmatic evolution in pyroxene.

^1,2Xinxin Yan, ³Xinzhuan Guo, ³Yun Zhou, ^1,2Yuping Song, ⁴Qingshan Zhang, ^1,2Meng Lv
Earth and Planetary Science Letters 684, 120009 Link to Article [https://doi.org/10.1016/j.epsl.2026.120009]
¹Key Laboratory of High-Temperature and High-Pressure Study of the Earth’s Interior, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, Guizhou 550081, China
²University of Chinese Academy of Sciences, Beijing 100049, China
³State Key Laboratory of Critical Mineral Research and Exploration, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, Guizhou 550081, China
⁴China University of Mining and Technology, Xuzhou 221116, China
Copyright Elsevier

The thermal conductivity and diffusivity of mantle minerals fundamentally control planetary cooling rates. Orthopyroxene is a major constituent of the lunar mantle, yet the influence of trace water on its thermophysical properties under high-pressure and high-temperature conditions relevant to the lunar interior has remained unquantified. Here, we present high P–T measurements of these properties for synthetic enstatite containing 0–427 ppm H2O using an enhanced transient plane source method. Our results demonstrate that even trace water drastically reduces thermal transport efficiency by enhancing phonon scattering. Incorporating these data into lunar thermal evolution models reveals that a hydrated mantle maintains significantly higher internal temperatures than an anhydrous system over geologic time. By reconciling our model geotherms with the solidus of various lunar mantle constituents and with seismic constraints on the largely solid modern mantle, we constrain the bulk water content of the lunar mantle to around 300 ppm. This work redefines the thermal state of the Moon and provides a critical mechanism for explaining its prolonged magmatic evolution.