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Publication Details
AFRICAN RESEARCH NEXUS
SHINING A SPOTLIGHT ON AFRICAN RESEARCH
earth and planetary sciences
Unique chemistry of a diamond-bearing pebble from the Libyan Desert Glass strewnfield, SW Egypt: Evidence for a shocked comet fragment
Earth and Planetary Science Letters, Volume 382, Year 2013
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Description
We have studied a small, very unusual stone, here named "Hypatia", found in the area of southwest Egypt where an extreme surface heating event produced the Libyan Desert Glass 28.5 million years ago. It is angular, black, shiny, extremely hard and intensely fractured. We report on exploratory work including X-ray diffraction, Raman spectroscopy, transmission electron microscopy, scanning electron microscopy with EDS analysis, deuteron nuclear reaction analysis, C-isotope and noble gas analyses. Carbon is the dominant element in Hypatia, with heterogeneous O/C and N/C ratios ranging from 0.3 to 0.5 and from 0.007 to 0.02, respectively. The major cations of silicates add up to less than 5%. The stone consists chiefly of apparently amorphous, but very hard carbonaceous matter, in which patches of sub-μm diamonds occur. δ13C values (ca. 0‰) exclude an origin from shocked terrestrial coal or any variety of terrestrial diamond. They are also higher than the values for carbonaceous chondrites but fall within the wide range for interplanetary dust particles and comet 81P/Wild2 dust. In step heating, 40Ar/36Ar ratios vary from 40 to the air value (298), interpreted as a variable mixture of extraterrestrial and atmospheric Ar. Isotope data of Ne, Kr and Xe reveal the exotic noble gas components G and P3 that are normally hosted in presolar SiC and nanodiamonds, while the most common trapped noble gas component of chondritic meteorites, Q, appears to be absent. An origin remote from the asteroid belt can account for these features.We propose that the Hypatia stone is a remnant of a cometary nucleus fragment that impacted after incorporating gases from the atmosphere. Its co-occurrence with Libyan Desert Glass suggests that this fragment could have been part of a bolide that broke up and exploded in the airburst that formed the Glass. Its extraordinary preservation would be due to its shock-transformation into a weathering-resistant assemblage. © 2013 Elsevier B.V.
Authors & Co-Authors
Kramers, Jan Dirk
South Africa, Johannesburg
University of Johannesburg
Andreoli, Marco A.G.
South Africa, Pretoria
Necsa
South Africa, Johannesburg
University of the Witwatersrand
Atanasova, Maria T.
South Africa, Pretoria
Council for Geoscience
Belyanin, Georgy A.
South Africa, Johannesburg
University of Johannesburg
Block, David L.
South Africa, Johannesburg
University of the Witwatersrand
Franklyn, Chris B.
South Africa, Pretoria
Necsa
Harris, C.
South Africa, Cape Town
University of Cape Town
Lekgoathi, M. D.S.
South Africa, Pretoria
Necsa
Montross, Charles S.
South Africa, Springs
Element Six Pty Ltd., South Africa
Ntsoane, Tshepo P.
South Africa, Pretoria
Necsa
Pischedda, Vittoria
France, Villeurbanne
Université Claude Bernard Lyon 1
Segonyane, Patience
South Africa, Pretoria
Necsa
Viljoen, Fanus
South Africa, Johannesburg
University of Johannesburg
Westraadt, Johan Ewald
South Africa, Springs
Element Six Pty Ltd., South Africa
Statistics
Citations: 21
Authors: 14
Affiliations: 7
Identifiers
Doi:
10.1016/j.epsl.2013.09.003
ISSN:
0012821X
Research Areas
Cancer
Environmental
Study Design
Exploratory Study
Study Locations
Egypt