Mineralogy and crystallization history of the Ilafegh 009 EL‐chondritic impact melt rock: An ATEM investigation

Abstract— The Ilafegh 009 meteorite is an impact melt rock from an EL‐chondritic parent body. Its mineralogic assemblage is the result of rapid crystallization after shock‐induced melting. We report here an analytical transmission electron microscopy (ATEM) study of the major minerals of this meteorite (enstatite, plagioclase, Fe‐Ni metal and sulfides). Based on this study, we discuss the crystallization sequence and the further evolution of the rock in the solid state. Microstructure and microanalyses confirm that the mineralogy of Ilafegh 009 results from the crystallization of an EL‐chondritic melt. The high compositional variability of plagioclases and the presence of silica‐rich glass pockets indicate fast cooling. During crystallization, the large enstatite grains trapped a large number of phases (plagioclase, silica‐rich glass and enstatite nuclei). Sulfides (troilite, alabandite and daubreelite) form finely polycrystalline areas and reveal a complex crystallization sequence. Although Fe‐Ni metal grains formed during rapid cooling, their microstructures show that some postsolidification process occurred in Ilafegh 009. A large number of tiny Ni‐P‐Si‐rich precipitates were detected that formed as a result of exsolution of elements that become insoluble in kamacite at low temperature. Finally, the microstructure (dislocation arrangements and phase transformations) observed in enstatite and Fe‐Ni metal attests that Ilafegh 009 also experienced a moderate postsolidification shock event.