ESTIMATING THERMAL HISTORIES OF TEKTITES USING LECHATELIERITE INCLUSIONS
To reproduce the profiles, we undertook a series of high T melting experiments using an aerodynamic levitation laser furnace. A starting mixture of powdered natural tektite plus quartz grains was exposed to temperatures of 1800-2400˚C for 1-120 s. Direct comparison of concentration profiles between the indochinite and experiments reveals a best match at 2200˚C and 50 s. This experiment successfully reproduced all major aspects of the concentration profiles observed in the natural sample including diffusion length scale, asymmetry, order of steepness of major element profiles, and uphill diffusion of K2O.
Not enough information is available to model the full multicomponent diffusion problem, but SiO2 and Al2O3 concentration profiles from lechatelierite to surrounding felsic glass in the experiments can be fit well as a diffusion couple between silica melt and adjacent felsic melt using an effective binary diffusion approach and assuming that the effective binary SiO2 and Al2O3 diffusivities depend exponentially on SiO2 concentration. The experimentally determined diffusivities allow for estimation of possible temperature-time paths experienced by tektites, which will lead to a better understanding of impact plume dynamics.