New evidence of meteoritic origin of the Tunguska cosmic body

Abstract

Diamond–lonsdaleite–graphite micro-samples collected from peat after the 1908 catastrophic blast in the Tunguska area were studied with scanning (SEM) and transmission electron (TEM) microscopy, NanoSecondary Ion Mass Spectrometry (NanoSIMS) and Х-ray synchrotron technique. The high-pressure carbon allotropes in the Tunguska samples are being described for the first time and contain inclusions of FeS (troilite), Fe–Ni (taenite), γ-Fe and (FeNi)3P (schreibersite). The samples are nodule-like in shape and consist of 99.5% carbon minerals, e.g. diamond>lonsdaleite>graphite. Micro- and nanoinclusions of troilite (up to 0.5vol%), taenite, γ-iron and schreibersite fill cracks, cleavages and pores in the carbon matrix. Carbon isotope studies from the two analyses of the Tunguska foil showed δ13C=−16.0±1.9‰ and δ13C=−15.2±2.1‰, suggesting δ13C=−15.6±2‰ as an average characteristic of the carbon reservoir. That value is close to δ13C of some extraterrestrial samples. A negligible concentration of Ir and Os in the carbonaceous matrix promotes some controversial interpretation of the origin of the studied materials. Attributing this fact to the primary inhomogeneity, and considering the micro-structural features such as cracks, deformation of the crystal lattices, etc. coupled with high-pressure carbon allotropes association with metals, sulfides and phosphides, and the high ratio of Fe:Ni=22:1 suggest that the studied samples are meteorite micro-remnants.