Meteoritic Matter and Spherules in a Presumed Impact Crater at Emmerting, Germany

Abstract

Bulk composition, mineralogy and microchemistry of various fractions of the filling of the Crater No. 4 at Emmerting were investigated. Here we present mainly the fine fractions, which, in contrast to pebbles larger than ca. 4 cm, are relatively poor in material affected by melting. A 0.1 mm long meteorite fragment without ablation features was found, and remelted fragments of the same body have been identified. The projectile was dominated by enstatite, also containing forsterite, basic plagioclase, Ni-rich pyrrhotite and troilite, kamacite, silica, and probably merrillite. The molten fragments contain porous Mg-rich glass (indicating temperature > 1500 °C), minor Fe oxides, and occasionally uncommon Ni-rich minerals. The bulk composition and electron microprobe show that the amount of meteoritic material is low (<< 1 %), and it is not unequivocally manifested even in platinum-group elements abundances and osmium isotope ratios (the latter, however, were only measured in two samples). This can be explained by dilution of the filling by particles brought after the crater formation, and by probably achondritic composition of the projectile. Relatively large hollow spheroid Fe oxide particles were observed in thin sections from the magnetic fraction. A Mn oxide hollow spherule has also been found. In magnetically separated filling from the nearby Crater No. 5, bulk chemical composition points to contamination with several metals and metalloids probably due to influence of recent alluvial sediments. Therefore, the extent of meteoritic contamination in this crater may be even smaller.