Geochemistry and origin of Libyan Desert glasses

We analysed ten Libyan Desert glasses (LDGs) for chemical composition by ICP-AES and ICP-MS and four samples for their Sr and Nd isotopic compositions. Our results confirm the close compositional relationship of LDGs to mature sandstones. The glasses are LREE enriched (La-n/Sm-n = 4.2-4.5), and display significant negative Eu anomalies (Eu/Eu* = 0.6-0.75) similar to post-Archaean sediments. In addition, most element abundances are correlated with REE contents. The correlations are interpreted as mixing lines and strongly suggest that the parent material was composed of quartz grains coated with a mixture of kaolinite, Fe-Ti oxides, and accessory phases. Significant PGE concentrations were measured in the dark coloured part of an LDG sample. Its normalized-pattern is chondritic, demonstrating the presence of a meteoritic component in the glass. Several hypotheses have been proposed for the origin of LDGs. However, our results confirm that LDGs are impact-derived glasses and have some petrographical and chemical features similar to those of Muong Nong-type tektites. Neodymium and Sr isotopic signatures of LDGs are consistent with their derivation by melting of mature sandstones derived from Proterozoic materials such as the East Saharan basement rocks. The most likely target rocks are the quartz arenites of the Jurassic-Cretaceous Nubia Group. Copyright (C) 1997 Elsevier Science Ltd.