Australasian impact crater buried under the Bolaven volcanic field, Southern LaosOPEN ACCESS
Kerry Sieh, Jason Herrin, Brian Jicha, Dayana Schonwalder Angel, James D. P. Moore, Paramesh Banerjee, Weerachat Wiwegwin, Vanpheng Sihavong, Brad Singer, Tawachai Chualaowanich, and Punya Charusiri
PNAS first published December 30, 2019
“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.”
The Australasian tektite source crater: Found at last?
H. J. Melosh
PNAS first published January 6, 2020
“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. While this proposal does not fully prove the case, it offers strong evidence implicating a ∼15-km-diameter impact crater in Laos that has been hiding in plain sight beneath a mass of younger volcanic rocks. From here, it is clear that the next step in proving its parentage must be drilling through the volcanic rocks into the putative impact rocks below.
Tektites are centimeter-scale black or green blobs of glass that have long fascinated humans (2). Moldavites, an Eastern European variety, were found interred with the much more famous Venus of Willendorf, dating back to 30,000 BCE, possibly reflecting our ancestors’ interest in unusual rocks as well as female deities. Individual tektites occur in widely strewn fields of which about 4 are currently known (there are other candidate strewn fields). Each of these fields, which extend over hundreds to thousands of kilometers, is associated with a meteorite impact crater—except one, the biggest of them all, the Australasian strewn field. It ranges south from Southeast Asia, across Australia then south of Tasmania to East Antarctica, with a western extension that crosses over Madagascar and an eastern extension into the western Pacific Ocean, covering about 10% of Earth’s surface. The tektites in this enormous field have been intensively studied using modern analytical methods. They are divided into a number of distinct types, ranging from meter-scale irregular masses of black glass called Muong … “