¹A. Sedaghat, ¹C. McLeod, ²M. Loocke, ³B. Shaulis
Icarus (in Press) Open Access Link to Article [DOI: 10.1016/j.icarus.2026.117331]
¹Department of Geology and Environmental Earth Science, Miami University, Oxford, OH 45056, USA
²Department of Geology and Geophysics, Louisiana State University, Baton Rouge, LA 70803, USA
³Trace Element and Radiogenic Isotope Laboratory (TRAIL), University of Arkansas, Fayetteville, AR 72701, USA
Copyright Elsevier

Through integrated textural, mineralogical, and geochemical studies, symplectites provide fundamental constraints on the evolution and stability of geological systems. The returned 2018–2019 Antarctic Search for Meteorites Dominion (DOM) Range lunar meteorites contain ubiquitous three-phase symplectites consisting of fayalitic olivine (Fa), Ca-Fe-rich pyroxene (Px), and a silica phase (Si). Here, the textures and compositions of two textural symplectite types in DOM 18509 and DOM 18543 are investigated. Typical symplectites are characterized by a relatively uniform distribution of Fa-Px-Si and fine grain sizes (≤5 μm). Fayalite is Fe-rich (Fa_91–96) with associated pyroxene at Wo_31–40En_6–11Fs_51–61. Bulk compositions determined via reconstruction and broad beam analyses yielded lunar pyroxferroite compositions. The preservation of rare pyroxferroite in lunar materials is reported for DOM 18509: Wo_12-13En_9-10Fs_77–78. In contrast, non-typical symplectites exhibit variable grain sizes and consist of a Ca-rich host pyroxene (Wo_23–40En_8-18Fs_49–68) containing blebs of olivine (Fa_86–95) and silica. Reconstruction for the bulk precursor material yields a metastable pyroxene (Wo_24-26En_12-16Fs_58–64). While both symplectite types are interpreted as subsolidus breakdown products during slow cooling, their formation is associated with different breakdown pathways from distinct precursor phases. During late-stage crystallization in highly evolved lunar basaltic systems, pyroxene compositions enter the forbidden zone. At this stage, metastable Ca-rich pyroxene forms, followed by crystallization of metastable pyroxferroite during extreme Fe-enrichment. Subsequently, non-typical symplectites form through the subsolidus multistep breakdown of metastable Ca-rich pyroxene, whereas typical symplectites form through the direct subsolidus breakdown of pyroxferroite. These two symplectite textures record the evolution of metastable phases within reduced magmatic conditions in extraterrestrial environments.

¹Adriana Pisarčíková, ¹Jiří Borovička, ²Pavol Matlovič
Icarus (in Press)
Open Access Link to Article [DOI: 10.1016/j.icarus.2026.117327]
¹Astronomical Institute of the Czech Academy of Sciences, Fričova 298, Ondřejov, 25165, Czech Republic
²Faculty of Mathematics, Physics and Informatics, Comenius University Bratislava, Mlynská dolina, 84248 Bratislava, Slovakia
Copyright Elsevier

Laboratory simulations of meteor ablation provide a critical quantitative link between the chemical composition of meteoroids and their observed spectral features. In this work, we analyzed high-resolution Echelle spectra (wavelength range 380–780 nm) of 22 diverse meteorites from the dataset presented in our previous work (Matlovič et al., 2024), representing the largest collection of laboratory meteor analogs to date. Using a radiative transfer model assuming local thermodynamic equilibrium (LTE) and accounting for self-absorption in optically thick plasma, we derived plasma parameters and elemental abundances for both major (Fe, Mg, Cr, Mn, Si, Na, Ni, Li, and K) and minor (Co, Cu, and V) species. Comparison with known bulk meteorite compositions allowed us to validate the modeling approach and assess chemical biases resulting from laboratory-induced ablation. Our analysis suggested plasma temperatures between 5220 and 5810 K and revealed systematic discrepancies in the elemental abundances compared to the original chemical composition. Specifically, we observed a significant enhancement of volatile species (Na, K) relative to Fe, accompanied by a depletion of the moderately volatile element Mg, while refractory elements (Al, Ca, Ti) remained undetected in the plasma radiation. These trends are consistent with the equilibrium vaporization model and demonstrate that under the simulated entry conditions ($\sim$12 km s⁻¹ at $\sim$80 km altitude), the ablation process is dominated by incomplete and fractional vaporization. We conclude that while laboratory spectra of plasma from ablated meteorites do not fully reflect the original bulk composition, radiative transfer modeling effectively characterizes the state of the radiating plasma, offering a more robust approach for interpreting compositional properties from meteor observations.