Mechanism of Muong Nong‐type tektite formation and speculation on the source of Australasian tektites

Abstract

The source crater of the youngest and largest of the tektite strewnfields, the Australasian strewnfield, has not been located. A number of lines of evidence indicate that the Muong Nong‐type tektites, primarily found in Indochina, are more primitive than the much more abundant and widespread splash‐form tektites, and are proximal to the source. In this study the spatial distribution of Muong Nong‐type tektite sites and chemical character have been used to indicate the approximate location of the source. The variation of Muong Nong‐type tektite chemical composition appears to be caused by mixing of two silicate rock end‐members and a small amount of limestone, and not by vapor fractionation. The variation in composition is not random, and does not support in‐situ melting or multiple impact theories. The distribution of both Muong Nong and splash‐form tektite sites suggest the source is in a limited area near the southern part of the Thailand‐Laos border.

Australasian microtektites and associated impact ejecta in the South China Sea and the Middle Pleistocene supereruption of Toba

“…It is much farther north (∼10°) than the location predicted by Glass and Pizzuto (1994) and supported by Lee and Wei (2000). It is even farther north and west of the region proposed by Schnetzler (1992) and Ma et al (2004) centered at 16° N and 105° E and 17° N and 107° E, respectively. However, anywhere between ∼25° N and 102° E and 19° N and 106° E explains the geographic variations in the Fig.…”

“…These sites are closer to the more recently proposed locations for the source crater of the Australasian tektite/microtektite strewn field (e.g., Schnetzler 1992;Ma et al 2004) than are previously studied Australasian microtektite-bearing core sites. Thus, we believed that the study of the microtektites and unmelted ejecta in these cores would give us a clearer understanding of the nature of the target rocks and location of the source crater for the Australasian strewn field.…”

“…Most investigators have concluded that the impact that produced the Australasian tektites took place somewhere in Indochina, but the source crater is still unknown (Stauffer 1978;Ford 1988;Schnetzler et al 1988;Schnetzler 1992;Hartung and Koeberl 1994;Glass and Pizzuto 1994;Koeberl 1994;Lee and Wei 2000;Glass 2003;Ma et al 2004).…”

Laser fusion argon‐40/argon‐39 ages of Darwin impact glass

“…During impact processes, both enrichment and losses of volatile elements by the impacting bodies or ultrabasic rocks were observed for Darwin Glass (Taylor and Solomon, 1964;Taylor and Epstein, 1969;Meisel et aI., 1990). In contrast, Australasian tektites are more uniform in composition, and very likely had post-Archean alluvial sediments such as the Jurassic alluvium deposits in Indochina as precursor material (Shaw and Wasserburg, 1982;Koeberl, 1990;Schnetzler, 1992;Blumetal., 1992). The contrast in chemical composition argues against a common origin for Darwin Glass and Australasian tektites (Taylor and Solomon, 1964;Taylor and Epstein, 1969;Meisel et al, 1990Meisel et al, , 1995.…”

Variation of chemical composition in Australasian tektites from different localities in Vietnam

“…Muong Nong-type tektites, named after a type locality in Laos (Lacroix 1935), are usually considerably larger than normal tektites and have chunky and blocky appearance. Most contain more vesicles, are more heterogeneous on a millimeter scale, and have higher volatile element contents than the splash-form tektites (e.g., Koeberl 1992;Schnetzler 1992). They are mostly found in Indochina, in the countries of Laos, Vietnam, Thailand, Cambodia, and adjacent areas of China.…”