Coated impact melt lapilli and bombs from the Wabar crater field, Saudi Arabia

Abstract We report on a petrographic and geochemical study of coated impact melt lapilli and bombs from the ejecta blanket of the Wabar crater field (Saudi Arabia), which formed ~300 years ago by the hypervelocity impact of an iron asteroid against sand dunes. These objects, up to 15 cm across and with aerodynamic shapes, characteristically consist of a thin coat of vesicular Fe‐Ni‐rich siliceous black glass enveloping a core of pumiceous silica‐rich white glass. Both glasses are geochemically indistinguishable from the white or black glass masses found earlier in the ejecta blanket and interpreted as the product of impact melting of the target material and of the mixing of target and impactor impact melts, respectively. The black glass coating studied here contains high concentrations of Fe (8.7 wt%), Ni (4770 μg g −1 ), and Co (463 μg g −1 ), indicating high impactor contamination (4–17 wt%) typical of impactor–target interface melts. We propose a qualitative model for the formation of the coated lapilli and bombs within the context of the contact and excavation stages of a crater‐forming event, thereby contributing to the understanding of the physical–chemical interactions between impactor and target impact melts during the formation of impact craters in rocky planetary surfaces.