We present the results of a combined study of shocked labradorite from the Lonar crater, India, using optical microscopy, micro-Raman spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, high-energy X-ray total scattering experiments, and micro-Fourier transform infrared (micro-FTIR) spectroscopy. We show that maskelynite of shock class 2 is structurally more similar to fused glass than to crystalline plagioclase. However, there are slight but significant differences-preservation of original preimpact igneous zoning, anisotropy at infrared wavelengths, X-ray anisotropy, and preservation of some intermediate range order-which are all consistent with a solid-state transformation from plagioclase to maskelynite.

Plagioclase feldspars are common on the surfaces of planetary objects in the solar system such as the Moon and Mars, and in meteorites. Understanding their response to shock deformation is important for interpretations of data from remote sensing, returned samples, and naturally shocked samples from impact craters. We used optical petrography, micro‐Raman, and micro–Fourier transform infrared spectroscopy to systematically document vibrational spectral differences related to structural changes in experimentally shocked (0–56 GPa) albite‐, andesine‐, and bytownite‐rich rocks as a function of pressure and composition. Across all techniques, the specific composition of feldspars was confirmed to affect shock deformation, where more Ca‐rich feldspars transform to an amorphous phase at lower shock conditions than more Na‐rich feldspars. Onset of amorphization occurs at ~50 GPa for albite, between 28 and 30 GPa for andesine, and between 25 and 27 GPa for bytownite. Complete amorphization occurred at pressures greater than ~55 GPa for albite, ~47 GPa for andesine, and ~38 GPa for bytownite. Petrographically, these experimentally shocked samples do not exhibit the planar microstructures common in naturally shocked plagioclase, despite showing the expected trends of internal disordering and deformation as seen in the micro‐Raman and infrared spectra. Average spectra of hyperspectral images of these samples mimic macroscale measurements acquired previously. However, we see micro‐scale heterogeneity in the shock response, resulting from variations in either composition, crystal orientation, or the inherent heterogeneity of the shock wave topology. This is an important factor to consider when deducing shock pressures in naturally shocked samples.

Nanophase iron (oxyhydr)oxides are ubiquitous on Earth, globally distributed on Mars, and likely present on numerous other rocky solar system bodies. They are often structurally and, therefore, spectrally distinct from iron (oxyhydr)oxide bulk phases. Because their spectra vary with grain size, they can be difficult to identify or distinguish unless multiple analysis techniques are used in tandem. Yet, most literature reports fail to use multiple techniques or adequately parameterize sample morphology, making it difficult to understand how morphology affects spectral characteristics across techniques. Here, we present transmission electron microscopy, Raman, visible and near-infrared, and mid-infrared attenuated total reflectance data on synthetic, nanophase akaganéite, lepidocrocite, goethite, hematite, ferrihydrite, magnetite, and maghemite. Feature positions are tabulated and compared to those for bulk (oxyhydr)oxides and other nanophase iron (oxyhydr)oxides from the literature. The utility and limitations of each technique in analyzing nanophase iron (oxyhydr)oxides are discussed. Raman, mid-infrared, and visible near-infrared spectra show broadening, loss of some spectral features, and shifted positions compared to bulk phases. Raman and mid-infrared spectroscopies are useful in identifying and distinguishing akaganéite, lepidocrocite, goethite, and hematite, though ferrihydrite, magnetite, and maghemite have overlapped band positions. Visible near-infrared spectroscopy can identify and distinguish among ferrihydrite, magnetite, and maghemite in pure spectra, though akaganéite, lepidocrocite, and goethite can have overlapping bands. It is clear from this work that further understanding of variable spectral features in nanophase iron (oxyhydr)oxides must await additional studies to robustly assess effects of morphology. This study establishes a template for future work.

Abstract-The Tenoumer impact structure is a small, well-preserved crater within Archean to Paleoproterozoic amphibolite, gneiss, and granite of the Reguibat Shield, north-central Mauritania. The structure is surrounded by a thin ejecta blanket of crystalline blocks (granitic gneiss, granite, and amphibolite) and impact-melt rocks. Evidence of shock metamorphism of quartz, most notably planar deformation features (PDFs), occurs exclusively in granitic clasts entrained within small bodies of polymict, glass-rich breccia. Impact-related deformation features in oligoclase and microcline grains, on the other hand, occur both within clasts in melt-breccia deposits, where they co-occur with quartz PDFs, and also within melt-free crystalline ejecta, in the absence of co-occurring quartz PDFs. Feldspar deformation features include multiple orientations of PDFs, enhanced optical relief of grain components, selective disordering of alternate twins, inclined lamellae within alternate twins, and combinations of these individual textures. The distribution of shock features in quartz and feldspar suggests that deformation textures within feldspar can record a wide range of average pressures, starting below that required for shock deformation of quartz. We suggest that experimental analysis of feldspar behavior, combined with detailed mapping of shock metamorphism of feldspar in natural systems, may provide critical data to constrain energy dissipation within impact regimes that experienced low average shock pressures.