TY - JOUR
T1 - Unique chemistry of a diamond-bearing pebble from the Libyan Desert Glass strewnfield, SW Egypt
T2 - Evidence for a shocked comet fragment
AU - Kramers, Jan D.
AU - Andreoli, Marco A.G.
AU - Atanasova, Maria
AU - Belyanin, Georgy A.
AU - Block, David L.
AU - Franklyn, Chris
AU - Harris, Chris
AU - Lekgoathi, Mpho
AU - Montross, Charles S.
AU - Ntsoane, Tshepo
AU - Pischedda, Vittoria
AU - Segonyane, Patience
AU - Viljoen, K. S.(Fanus)
AU - Westraadt, Johan E.
PY - 2013/11/15
Y1 - 2013/11/15
N2 - 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.
AB - 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.
KW - Carbon isotopes
KW - Comet nucleus
KW - Extraterrestrial carbonaceous matter
KW - Libyan Desert Glass
KW - Noble gas isotopes
KW - Shock diamonds
UR - http://www.scopus.com/inward/record.url?scp=84884582362&partnerID=8YFLogxK
U2 - 10.1016/j.epsl.2013.09.003
DO - 10.1016/j.epsl.2013.09.003
M3 - Article
AN - SCOPUS:84884582362
SN - 0012-821X
VL - 382
SP - 21
EP - 31
JO - Earth and Planetary Science Letters
JF - Earth and Planetary Science Letters
ER -