Gebel Kamil: The iron meteorite that formed the Kamil crater (Egypt)

摘要

The 45m in diameter Kamil impact crater was formed <5000yr ago in the eastern Sahara, close to the southern border of modern Egypt. The original features of this structure, including thousands of fragments of the meteorite impactor, are extremely well preserved. With the exception of a single 83kg regmaglypted individual, all specimens of Gebel Kamil (the iron meteorite that formed the Kamil crater) are explosion fragments weighing from <1g to 34kg. Gebel Kamil is an ungrouped Ni-rich (about 20wt% Ni) ataxite characterized by high Ge and Ga contents (approximately 120μgg~-1 and approximately 50μgg~-1, respectively) and by a very fine-grained duplex plessite metal matrix. Accessory mineral phases in Gebel Kamil are schreibersite, troilite, daubréelite, and native copper. Meteorite fragments are cross-cut by curvilinear shear bands formed during the explosive terrestrial impact. A systematic search around the crater revealed that meteorite fragments have a highly asymmetric distribution, with greater concentrations in the southeast sector and a broad maximum in meteorite concentration in the 125-160°N sector at about 200m from the crater rim. The total mass of shrapnel specimens >10g, inferred from the density map compiled in this study is 3400kg. Field data indicate that the iron bolide approached the Earth's crust from the northwest (305-340°N), travelling along a moderately oblique trajectory. Upon hypervelocity impact, the projectile was disrupted into thousands of fragments. Shattering was accompanied by some melting of the projectile and of the quartz-arenite target rocks, which also suffered shock metamorphism.