Physics
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufm.p52b0584s&link_type=abstract
American Geophysical Union, Fall Meeting 2001, abstract #P52B-0584
Physics
1035 Geochronology, 1040 Isotopic Composition/Chemistry, 3662 Meteorites, 5420 Impact Phenomena (Includes Cratering), 6240 Meteorites And Tektites
Scientific paper
Libyan Desert Glass (LDG) is an impact-related, light yellow to greenish, natural silica glass of still unknown target material. It is irregularly distributed in an area of approximately 6,500 km2 between N-S striking dunes of the Great Sand Sea in western Egypt. The estimated quantity of exposed LDG exceeds 1,400 tons, with fragments ranging from sand-sized grains to pieces heavier than 25 kg. We have determined Rb-Sr and Sm-Nd isotopic ratios from seven LDG samples and five associated sandstones from the LDG strewn field in the Great Sand Sea, Western Egypt. Planar deformation features were recently detected in quartz from these sandstones. 87Sr/86Sr ratios, epsilon-Nd values for LDG are between 0.71219 and 0.71344, -16.6 and -17.8, respectively, and hence distinct from the less radiogenic 87Sr/86Sr ratios of 0.70910 - 0.71053 and epsilon-Nd values from -6.9 to -9.6 for the local sandstones from the LDG strewn field. Previously published isotopic ratios from the Libyan BP and Oasis crater sandstones are generally incompatible to our LDG values. LDG formation undoubtedly occurred at 29 Ma (fission-track data), but neither the Rb-Sr nor the Sm-Nd isotopic system were rehomogenised during the impact event, as we can deduce from Pan-African ages of 560 ± 130 Ma and 520 ± 130 Ma, defined by regression lines from a total of 14 LDG samples from this work and the literature. Together with similar Sr and Nd isotopic values for LDG and granitoid rocks from NE Africa west of Nile, these findings point to a sandy matrix target material for the LDG derived from a Precambrian Pan-African crystalline basement, ruling out the Cretaceous sandstones of the former "Nubian Group" as possible precursors for LDG.
Mueller-Sohnius D.
Schaaf P.
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