| Summary: | P(論文) Six Muong Nong-type tektites from Laos and Thailand and one indochinite from Viet Nam were studied petrologically, and their fission-track age was determined. Under the microscope the tektites have conspicuous flow structures, formed by alternating bands of glass of slightly different refractive index. In one sample B, pale brown parts are present sporadically in the colorless matrix, and both of them show some difference in chemical composition. Major elements were determined by a Hitachi scanning electron probe microanalyzer. It is remarkable that there is a wide range in chemical composition of Muong Nong-type tektites, ranging from 71 to 82% SiO_2,which almost covers the whole range of tektites in general. For determination of water content, a finely powdered sample was melted in a high-frequency induction furnace in vacuum, and evolved water was converted to hydrogen. Water content was determined by measuring the volume of the hydrogen, and the isotopic composition of the hydrogen was determined by a mass spectrometer MAT 250. H_2O content ranges from 0.08 to 0.10%, and δD from -56.4 to -79.2‰. These values preclude the possibility that the water was derived from the lunar rocks, but may support the terrestrial origin of these tektites. Fission-track age dating gives values from 0.65 to 0.70 Ma, which agree with the ages obtained by other workers using fission-track and other methods on the indochinites in general. departmental bulletin paper
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