¹Justin I. Simon, ²Rosalind M. G. Armytage
Earth and Planetary Science Letters, 695, 120293
Open Access Link to Article [DOI: 10.1016/j.epsl.2026.120293]
¹Astromaterial Research & Exploration Science, NASA Johnson Space Center, Houston, TX, 77058, USA
²Amentum, NASA Johnson Space Center, 2101 NASA Parkway, Houston, TX, 77058, USA
Copyright Elsevier

Thermal ionization mass spectrometry measurements of non-mass-dependent calcium isotope effects in calcium-aluminum-rich refractory inclusions show resolvable anomalies, both ⁴⁸Ca isotope excesses and deficits, when compared to measured reference materials used to define the normal terrestrial planet composition (ε⁴⁸Ca = 0$\pm$3.52SD ε-unit, part in 10,000, for the ⁴⁸Ca/⁴⁴Ca ratio). For two of the studied inclusions resolvable intra ε⁴⁸Ca heterogeneity also exists. The measured range and heterogeneity of calcium isotope effects represent a vestige of presolar stellar nucleosynthetically distinct carriers contributed to the Solar protoplanetary disk at the time refractory inclusions were forming, representing the earliest record of infall events since molecular cloud collapse. When directly compared to mass-dependent calcium isotope fractionation effects, as well as mass-dependent and non-mass-dependent titanium isotope effects, and moderately refractory element isotopic signatures, a more complete view of how inclusions, and through their compositions, the early Solar System formed. Additionally, the long-debated nature of several common inclusion types, e.g., melilite-mantled coarse-grained Type B’s, can be more clearly understood when evidence from both refractory elements, for a primordial record, and the moderately refractory elements, for late nebular formation events are considered. Collectively, cosmochemical and chronological records contained in refractory inclusions are important because they formed during the early period of Solar System evolution in which the protoplanetary disk began to dissect into distinct radial reservoirs, likely caused by the formation of giant gaseous planets, directly recording reservoirs, processes, and timescales from which building blocks of terrestrial planets emerged.

¹M. A. Ivanova, ^2,3S. N. Britvin, ⁴A. N. Krot, ⁴K. Nagashima, ⁵N. G. Zinovieva
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.70234]
¹Vernadsky Institute of Geochemistry of the Russian Academy of Sciences, Moscow, Russia
²Saint-Petersburg State University, St. Petersburg, Russia
³Kola Science Center, Russian Academy of Sciences, Apatity, Russia
⁴Hawai‘i Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawai‘i at Mānoa, Honolulu, Hawaii, USA
⁵M. V. Lomonosov Moscow State University, Moscow, Russia
Published by arrangement with John Wiley & Sons

We describe here zeolites and zeolite-like phases in Ca,Al-inclusions (CAIs) from Kaidun microbreccia and Northwest Africa (NWA) 3118 (CV3) chondrite studied using scanning electron microscopy (SEM), electron probe microanalysis (EPMA), secondary ion mass spectrometry (SIMS), Fourier transform infrared (FT-IR) spectroscopy, and single-crystal X-ray diffraction (SCXRD). Large (~4–8 μm in size) fragments of a coarse-grained igneous type B CAI from Kaidun consist of melilite (Åk_35–75), anorthite, magnesian spinel (<1 wt% FeO), and Al,Ti-diopside (in wt%, TiO₂ 4–18, Al₂O₃ 16–22); perovskite, hibonite, and Fe,Ni-metal are minor. The CAI experienced aqueous alteration that resulted in replacement of melilite by the calcite + apophyllite [KCa₄ (Si₈O₂₀) (OH,F)·8H₂O] + zeolites [natrolite (Na₂Al₂Si₃O₁₀·2H₂O)] and phillipsite-Na [(Na,K,Ca_0.5)_4–7 (Al_4–7Si₁₂₋₉O₃₂)·12H₂O] assemblage previously unreported in meteorites. Oxygen isotopic composition of calcite is similar to that in CR chondrites (Δ¹⁷O ~2‰, δ¹⁸O ~41‰). Phillipsite and natrolite have Δ¹⁷O close to that of calcite; the lack of proper SIMS standards for these minerals does not allow us to constrain their δ¹⁸O values. These data and textural observations suggest co-precipitation of calcite and zeolites. Calcite–zeolite assemblages are commonly observed in terrestrial rocks that experienced aqueous alteration in the presence of low-temperature alkaline- and carbonate-rich solutions. We suggest that aqueous alteration and formation of calcite–zeolite–apophyllite assemblage in Kaidun CAI occurred in fractures, cracks, and veins from volatile-rich, alkaline hydrothermal fluids (pH = 8–10) at ~20–150°C. This alteration has little effect on oxygen and aluminum–magnesium isotope systematics of primary minerals in the Kaidun CAI: melilite, spinel, pyroxene, and anorthite have solar-like oxygen isotope compositions: Δ¹⁷O = −22 to −25‰ and show resolvable excess of radiogenic ²⁶Mg corresponding to the inferred initial ²⁶Al/²⁷Al ratio [(²⁶Al/²⁷Al)₀] of (4.97 ± 0.11) × 10⁻⁵ (MSWD = 0.57; δ²⁶Mg*₀ = 0.04 ± 0.05‰). Type C CAI from NWA 3118 consists of melilite (Åk_18–56, 0.1–0.3 wt% Na₂O), anorthite, Al,Ti-diopside (in wt%, TiO₂ 3–5, Al₂O₃ 16–24), and spinel (up to 3.3 wt% FeO). Melilite and anorthite in the peripheral part of the CAI are replaced by nepheline, sodalite, Na-bearing plagioclase, and hedenbergite. Melilite in the CAI core is replaced by a hydrated silica-rich amorphous phase, which may have been originally a zeolite that subsequently experienced structural and compositional changes during thermal metamorphism in the CV parent asteroid.