1,2K. A. Cone et al. (>10)
Journal of Geophysical Research: Planets, 131, e2026JE009701
Open Access Link to Article [DOI: 10.1029/2026JE009701]
1Department of Earth and Environmental Sciences, University of Rochester, Rochester, NY, USA
2Earth, Environmental and Planetary Sciences, Rice University, Houston, TX, USA
Published by arrangement with John Wiley & Sons
Hypervelocity impacts modify planetary crusts and can alter the microstructures of key minerals used to reconstruct planetary histories. We investigated the potential effects of impacts on three common accessory minerals found in terrestrial crusts by experimentally shocking zircon, apatite, and whitlockite at 5, 10, 20, and 40 GPa. The internally consistent suite of shock-metamorphosed microstructures was characterized using scanning electron microscopy, Raman spectroscopy, electron backscatter diffraction, and in situ U-Pb isotope analysis. Crystal orientation mapping reveals patchy reidite formation near zircon grain exteriors at 20 GPa and pervasive reidite domains at 40 GPa. Annealing sharpens the characteristic ∼1,006 cm−1 zircon Raman peak at ≤20 GPa but does not restore this peak in the reidite formed at 40 GPa. Apatite retains crystalline domains through 40 GPa despite broadening of some Raman bands at ∼1,051 and ∼1,145 cm−1, with annealing restoring spectra to pre-shock patterns. Whitlockite develops merrillite-like Raman spectra with pressure, but the data cannot resolve dehydrogenation or transformation to merrillite. Shocked zircon exhibits U-Pb discordance, whereas annealing at 950°C improves concordance, suggesting that shock-induced microstructural modification may produce matrix effects and apparent age offsets, complicating reconstruction of events such as a lunar bombardment. Collectively, these experiments also demonstrate heterogeneity in mineral responses—both among and within grains—to a single shock pressure. Thus, the absence of a diagnostic microstructure within analyzed domains does not necessarily preclude exposure to an associated shock pressure, emphasizing the importance of whole-grain micro- to nanoscale characterization and consideration of grain size in shocked planetary materials.
