Weathering and polymerization of tektites: An x‐ray photoelectron spectroscopy (XPS) investigation

Abstract

Abstract-Tektites are natural glasses formed from terrestrial material that was melted and displaced by the impact of an extraterrestrial body. The surface and near-surface compositions of tektite glass results from fractionation during impact and ejection, and/or postsolidification weathering. The first goal of this study was to characterise the surface and near-surface (in the order of tens of angstroms) chemical composition of two tektites by x-ray photoelectron spectroscopy (XPS), and to estimate the importance of weathering vs. fi-actionation during flying. In order to separate the chemical modification due to weathering from that due to fractionation during ballistic flight, we studied two samples from the Australasian tektite strewn field. One of them was collected in a hot desert area (Nullarbor Plain, Australia) and the other, in a humid climate (Thailand). Our study reveals the presence of well-developed leached layers in both tektites. In the Australian tektite, Si is depleted in the topmost layers (a few tens of angstroms). A more complex chemical zoning is defined in the tektite from Thailand. These leached layers are comparable to those observed in weathered glasses, and therefore we conclude that weathering is responsible for the chemical composition of the surface and near-surface compositions. The second goal was to investigate the chemical environment of 0, N and C in the glass. The 0 peak was resolved into two bridging 0 components (Si-0-Si and Al-0-Si) that are comparable to 0 environments in artificial glasses. The binding energy of the C I , electron is typical for C-C and C-H bonds in hydrocarbons; minor organic acid components are also present. Nitrogen is only observed on the surface of the Thailand tektite. The binding energy of NI, is comparable to that of ammonia, and the surface enrichment in N is interpreted as due to sorption related to interactions between glass and fluid buffered by the organic material in the soil.