OXYGEN AND HYDROGEN (WATER) REGIME DURING TEKTITE FORMATION

Abstract

For five tektite glasses (moldavites, indochinites, and irgizite), oxygen fugacity (fO2) was measured within the temperature range of 800-1150°C using solid electrochemical cells, and water content was analyzed with FTIR spectroscopy. The fO2 values for moldavite and indochinite (Vietnam) at temperatures >900°C are plotted between FeO-Fe3O4 (WM) and Fe-FeO (IW) buffers. At temperatures lower than 900°C, these values are below the IW buffer. Irgizite and indochinite (Indochina) show higher fO 2, which are above fO2 (WM) at temperatures >800-1100°C. The slopes of linear dependences of log fO 2 versus 1/T K for tektite glasses, except for irgizite, are close to that for the WM buffer. The water contents in moldavite and indochinite glasses are 0.004-0.011 wt %, while those in irgizites are significantly higher reaching 0.035 wt %. Electrochemical determinations of fO2 in moldavites and indochinites indicate their significantly more reduced state as compared to crustal and mantle melts. However, their fO2 values are significantly higher than those typical of carbonaceous, ordinary, and enstatite chondrites. Irgizites have the highest iron oxidation state as compared to moldavites and indochinites, as well as significantly higher water contents. These data are consistent with a general tendency: the more oxidized state and higher water contents of impactite glasses as compared to those of tektites. However, no certain data are available that would indicate the correlation between water content and oxidation state in tektite glasses. It is suggested that the reduced character of tektite glasses and the low water contents in them are related to chemical and dynamic processes in the formation of vapor and melt phases during impact events under extremely high-energy conditions. The iron disproportionation and behavior of water and other components during tektite formation are presumably most affected by the condensation of silicate liquids from high-temperature vapor.