Shock metamorphic effects in the Luna 16 soil sample from Mare Fecunditatis

Abstract

Shock metamorphic effects characteristic of meteorite impact and virtually identical to those observed in Apollo samples are common in fragments of the Luna 16 soil sample from Mare Fecunditatis. Two types of shock effects are present: (1) deformation and partial melting features in rock and mineral fragments (1–2 per cent of fragments); (2) heterogeneous glasses and glassy breccias produced by shock melting (70–80 per cent of fragments). Shock effects were observed in pyroxene (deformation twin lamellae; multiple planar shock lamellae; extreme mosaicism; partial isotropization); in plagioclase (planar shock lamellae; complete isotropization to form maskelynite); and in basalt fragments (plagioclase isotropization; selective partial melting). The glasses and glassy aggregates exhibit several characteristics of shock melting, especially: (1) diversity in chemical composition; (2) association with shocked mineral fragments and Ni-Fe spherules; (3) heterogeneous schlieren and incipient fusion of mineral inclusions. The shock metamorphic effects in Luna 16 soil and its similarity to Apollo material indicate that regolith formation by meteorite impact has occurred in Mare Fecunditatis and is a general process over the entire moon.