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About LDG
How LDG was formed in the first place is a mystery. Why did it form here and nowhere else? The composition and structure of the glass is consistent with the scenario that is was formed from melted dune sand, and then cooled over a period greater than 24 hours in an earth atmosphere. LDG has been dated at about 28.5 million years using fission-track dating. Fission-track dating is one type of radioactive dating method used by archaeologists to determine the age of artifacts containing uranium-bearing minerals. Small fission tracks through the glass left by decay products are created at a constant rate throughout time. So from the density of tracks present it is possible to determine the amount of time that has past since the track accumulation began."Libyan Desert Glass (LDG) represents 1.4 x 109 g of natural glass fragments scattered over about 6500 km2 of the western Desert of Egypt. We made a systematic study (employing INAA, microprobe and mass spectrometry techniques) of several varieties of LDG and locally associated sand and sandstone to provide insight into the nature and formation of these enigmatic glass fragments. These studies indicate that:
1. Although the LDG has restricted major element compositions (97.98 wt% SiO2 ; 1-2 wt % Al2 O3 ) their trace element contents (ppm) (Fe, 490-5200; Co, 0.2-1.2; Cr, 1.2-29 and Sc. 0.462.5) vary by as much as a factor of 5 to 30.
2. The LDG fragments exhibit a factor of three variation in the REE abundances (La, 5.4-15.3 ppm). They all show parallel and steep LREE enriched patterns ([La/Sm]N , 3.8-4.2) and flat HREE ([Tb/Lu]N , 1.1- 1.2) and distinct negative europium anomalies (Eu/Eu*, about 0.5).
3. The gases in the vesicles of LDG (N2 , Ar, O2 , CO2 , H2 O and their dissociation products) are present in proportions consistent with derivation from the terrestrial atmosphere.
4. Dark streaks present in some samples of LDG contain significantly higher siderophile element abundances (Ir, about 0.5 ppb), possibly representing a meteoritic residue.
"Our studies suggest that LDG is the product of meteorite impact into quartz-rich surficial eolion and alluvial sand, and perhaps also into quartz-rich sandstone, of the western Desert of Egypt."
info more : www.thaicosmic.comMonday, July 21, 2008
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