Australasian impact crater buried under the Bolaven volcanic field, Southern Laos

Abstract

The crater and proximal effects of the largest known young meteorite impact on Earth have eluded discovery for nearly a century. We present 4 lines of evidence that the 0.79-Ma impact crater of the Australasian tektites lies buried beneath lavas of a long-lived, 910-km3 volcanic field in Southern Laos: 1) Tektite geochemistry implies the presence of young, weathered basalts at the site at the time of the impact. 2) Geologic mapping and 40Ar-39Ar dates confirm that both pre- and postimpact basaltic lavas exist at the proposed impact site and that postimpact basalts wholly cover it. 3) A gravity anomaly there may also reflect the presence of a buried ∼17 × 13-km crater. 4) The nature of an outcrop of thick, crudely layered, bouldery sandstone and mudstone breccia 10–20 km from the center of the impact and fractured quartz grains within its boulder clasts support its being part of the proximal ejecta blanket.

Microtektites and glassy cosmic spherules from new sites in the Transantarctic Mountains, Antarctica

“…7). The LK and RY sites are close to each other and at essentially the same distance (~12,000 km) from the presumed source region in Laos (located near 17°N, 107°E [Sieh et al 2020]), and as expected show virtually identical low ranges for Na 2 O and K 2 O (0.02-0.4 and 0.08-1.6, respectively) consistent with very high levels of volatile depletion (Fig. 7).…”

“…Microtektites are distal impact melt droplets produced by hypervelocity impacts and are widely distributed up to thousands of kilometers from their impact site (Glass 1990;Koeberl 1994). The Australasian microtektites and tektites are the most puzzling (Cavosie 2018) and intensely studied, as the location of the source crater has not been positively identified although a new candidate has been proposed recently in southern Laos (Sieh et al 2020), in agreement with previous deductions (Glass and Pizzuto 1994;Ma et al 2004;Glass and Koeberl 2006;Prasad et al 2007;Folco et al 2010;Rochette et al 2018). The elusive Australasian impact crater has been long-sought-after as the strewn field is the youngest (788.1 AE 2.8 kyr [Jourdan et al 2019]) and most extensive (Glass and Simonson 2013), covering more than 10% of the Earth's surface.…”

“…To facilitate spherule recovery, subsamples of each sediment were ultrasonically agitated in filtered water to remove fine-grained materials. After washing, the sediment was sieved using filtered water into six size The black dot shows the most recently proposed crater location (Sieh et al 2020). Also identified is a recent find in East Antarctica, Sor Rondane Mountains (SR; Soens et al 2021).…”

3D X-ray tomographic analysis reveals how coesite is preserved in Muong Nong-type tektites

“…These geochemical and isotopic data indicate a deeper origin in the target rock of MN tektites and a consequently lower ejection velocity, which suggests that they are closer to the source crater than tektites from the rest of the strewn field outside of Indochina 18 . An impact location in Indochina is actually consistent with the geographic distribution and other petrographic and geochemical trends in both tektites and microtektites [19][20][21][22][23][24] and, recently, a gravity anomaly observed in Laos was proposed as geophysical evidence of a crater buried under younger volcanic rocks of the Bolaven volcanic field 25 .…”

The Australasian tektite source crater: Found at last?

“…In PNAS, Sieh et al (1) present the best candidate yet for the long-sought source crater of the Australasian tektite strewn field. Unlike the other 4 or so tektite strewn fields, each of which can be traced back to a large impact crater, the Australasian field's source has yet to be definitively located.…”