Paper Number: 1602
Polymetallic and Nitrogen Carbide Debris in Ferruginous Palaeosol from the Libyan Desert Glass Area, SW Egypt: Further Evidence of a Cometary Origin for the Diamond-bearing Hypatia Stone
Andreoli, M.A.G.1, Belyanin, G.2, Block, D.3, de Kock, D.4, Di Martino, M.5, Gibson, R.L.1, Huotari, S.6, Jinnah, Z.1, Kramers, J.2, Mouri, H.2, Ntsoane, T. 3, Pischedda, V.7, Serra, R.8, Sigalas, I.9, Stengel, I.10, van der Merwe3, R., Ziegler, A.11, Zinner, E.12
1 School of Geosciences, Witwatersrand University, Johannesburg, South Africa, Marco.Andreoli@wits.ac.za
2 Dept. of Geology, University of Johannesburg, Johannesburg, South Africa
3 South African Nuclear Energy Corporations, Pretoria, South Africa
4Deaprtment of Applied Mathematics, Witwatersrand University, Johannesburg, South Africa
5 INAF – Osservatorio Astrofisico di Torino, Pino Torinese, Italy
6 University of Helsinki, Helsinki, Finland
7 ILM, Université de Lyon 1, Villeurbanne, France
8 Dipartimento di Fisica e Astronomia, Universita’ di Bologna, Italy
9 Polytechnic of Namibia, Windhoek, Namibia
10Department of Metallurgy, Witwatersrand University, Johannesburg, South Africa
11 Microscopy and Microanalysis Unit, Witwatersrand University, Johannesburg, South Africa
12 Deceased
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Following the discovery of a diamond-bearing carbonaceous pebble in the Libyan Desert Glass (LDG) area of SW Egypt [1], subsequent investigations accounted for the extraterrestrial origin of this stone, nicknamed Hypatia, either as a shocked comet relic [1, 2] or an unusual meteorite [3]. Our expedition to the find area failed to recover similar material, but returned samples of goethite-cemented, Cenozoic pebbly sandstone with pedogenic characteristics widely represented in the region. One of these samples, less than 1 kg in weight, was crushed and digested in acids (aqua regia ± HF) followed by bromoform separation to test for nanodiamonds in the heavy minerals fraction. This investigation is on-going and involves several micro-analytical techniques, including synchrotron tomography and Raman spectroscopy. In addition to aluminosilicates, pyrite, ilmenite, zircon and rutile, a large number of unusual metallic and carbonaceous particles have been recovered. These may be divided into three main groups: I) mainly spherical to ovoid metallic particles either single or clustered (size range: ~1 mm to < 1 μm); II) flakes of partly oxidized Al>Si (±Bi, Fe) metal (size: ~50 x ~80 μm); and III) carbonaceous mineraloids, including the first occurrence of a natural carbon nitride. With regard to (I) new work on two mm-sized Ti-metal clusters shows that they are alloyed to ~1.0 atomic % Al and locally host quenched gas bubbles, blebs of titanium aluminide, N-α-Ti, aluminum oxycarbonitride, and monometallic particles of Zr, Ag, and Zn. In places, the Ti-metal clusters are also coated by films and filaments of graphitized carbonaceous matter. Metal spherules of Ag and/or Ti (in varying proportions with Si, Al, Ca, O and minor Na, Mg, S), and grains of SnPb and Si>Al, Ti, Ca are common in the finer, <30 μm, size fraction of the sample. In order to explain the groups above, we considered various models: anthropogenic or geological products, fulgurites, cosmic spherules, metal-rich meteorites, or impact-related melts and carbonaceous matter. No example was found in the literature to support any of these interpretations; however, grains of metallic silver, aluminium and titanium occur in the Hypatia stone [4, 5]. In conclusion, our finds suggest that the LDG area may be underlain by a strewn field derived from a comet with an unusual chemistry and constituents never seen before in nature.
References:
[1] Barakat A. 2012. The Precious Gift of Meteorites and Meteorite Impact Processes. Nova Science Publishers
[2] Kramers J et al. (2013) Earth and Planetary Science Letters 382: 21-31
[3] Avice G et al. (2015) Earth and Planetary Science Letters 432: 243-253
[4] Andreoli MAG et al. (2015) Nuclear Instruments and Methods B 363: 79-85
[5] Belyanin G et al., submitted