Major and trace element compositions of georgiaites: Clues to the source of North American tektites

Electron microprobe and laser ablation, inductively-coupled plasma mass spe ctrometer analyses of 24 georgiaites show that these tektites are all Si-ri ch (79-83 wt% SiO2) glasses with variable major and trace element abundance s (e.g., FeO varies from 2.1 to 3.7 wt%). Glass compositions are similar to but not identical with average upper continental crust. For example, georg iaites are light rare earth element enriched with small negative Eu anomali es (Eu/Eu* = 0.73-0.86) and La-Th-Sc systematics are intermediate between t hat of Archean and post-Archean continental crust. When the georgiaite data are placed in the context of data for all North American tektites, triangu lar arrays appear on some oxide-oxide plots (e.g., FeO-MgO). Large variatio ns in refractory element abundances and ratios compared to the variation in SiO2 favors mixing over volatilization as a cause of the compositional var iation. If all the tektites formed as a result of a single impact, then tri angular arrays in oxide-oxide variation diagrams require at least three sou rce components. These components include a Si-rich material, probably a qua rtz-rich sand that was predominant in the formation of georgiaites. Two rel atively silica-poor and Fe-rich components have compositional characteristi cs similar to shales and greywackes. The La-Th-Sc systematics of the georgi aites and most other North American tektites are distinctive and could pote ntially be used to link the tektites to Eocene sediments at the Chesapeake Bay impact structure.