Nano- and micro-structures in lunar zircon from Apollo 15 and 16 impactites: implications for age interpretations

Abstract Meteorite impact processes are ubiquitous on the surfaces of rocky and icy bodies in Solar System, including Moon. One most common accessory minerals, zircon, when shocked, produces specific micro-structures that may become indicative age shock conditions these processes. To better understand mechanisms zircon from Apollo 15 16 breccias, we applied transmission electron microscopy (TEM) studied nano-structures eight lunar zircons displaying four different morphologies breccias 15455, 67915, 67955. Our observations revealed a range shock-related features zircon: (1) planar non-planar fractures, (2) “columnar” rims around baddeleyite cores, (3) granular textured cases with sub-µm-size inclusions monoclinic ZrO 2 (baddeleyite) cubic (zirconia), (4) silica-rich glass metal FeS FeNi present at triple junctions baddeleyite, (5) rutile shocked (6) amorphous domains, (7) recrystallized domains. In many grain aggregates, overprint each other, indicating either stages single process or multiple events. During shock, some were transformed to diaplectic (6), others completely decomposed into SiO Zr-oxide, evident observed round shapes zirconia filling granules. Despite highly variable effect textures Zr phases, show no correlation relatively homogeneous U–Pb 207 Pb/ 206 Pb ages zircons. Either events occurred very soon after solidification recrystallization too brief result noticeable loss during metamorphism.