TEKTITE

TEKTITE

by: Charles O’Dale

The name tektite comes from the Greek word ‘tektos’, meaning ‘molten’. Tektites do not contain any water. They can be mistaken for obsidian or pitchstone (black volcanic glasses), but these will emit some water on strong heating. Their density is similar to, or a little lighter than, quartz beach sand.

Tektites are small, glassy pebble-like objects that form during meteorite impact. They represent droplets of molten target rock that are ejected up into the Earth’s atmosphere, which then fall back to the surface up to several hundred kilometers from where their source impact crater. They often acquire aerodynamic shapes as they fly through the atmosphere.


Natural, silica-rich, homogeneous glasses produced by complete melting and dispersed as aerodynamically shaped droplets during terrestrial impact events. The process of tektite formation is disputed, but many researchers believe that they are formed in the early contact and compression stage of impact cratering. They range in color from black or dark brown to gray or green. Tektites have been found in  “strewn fields” on the Earth’s surface.

TEKTITE STREWN FIELDS

Tektites often occur in so-called strewn fields, areas over which tektites with similar chemical and physical properties are found.
Tektite Strewn Field Age (Ma) Crater Source Notes
Aouellou 3.1 ± 0.3 Aouellou Mauritania
Australasian 0.7881 ± .002.8 Bolaven volcanic field Southern Laos
Darwin Glass 0.816 ± .007 Darwin Crater Tasmania/td>
Libyan Desert Glass ~29 North Africa Possible Air Burst
Ivory Coast 1.07 Bosumtwi Ghana
Moldavite 14.808 ± .038 Ries Germany
North American 35.5 Chesapeake Virginia
K-Pg (KT) Boundary 66.043 Chicxulub Yucatan Peninsula
Irghizite 0.9 ± 0.1 Zhamanshin Kazakhstan

AOUELLOUL

Aouelloul tektites are associated with a nearby impact crater in Mauritania – tektite collected by Robert F. Fudali of the Smithsonian Institution.  (Scientific American 1978)

Aouelloul crater from the space / NASA/JPL, public domain

Aouelloul impact crater, Mauritania, is located in the Akchar Desert, approximately 50 km southeast of Atar. The crater is 390 metres wide and roughly circular. The rim rises up to 53 metres above the bottom of the crater. Sediments in the crater are approximately 23 metres thick. Its age is estimated to be 3.1 ± 0.3 million years (Pliocene).

Tektite is found around the crater, although very few meteorites have been found. Zerga meteorite was found in 1973 at the bottom of the crater, but scientists are unsure if it is the same meteorite (or even a part of it) that formed the crater.

AUSTRALASIAN

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

Kerry Sieha, Jason Herrina, Brian Jichab, Dayana Schonwalder Angela, James D. P. Moorea, Paramesh Banerjeea, Weerachat Wiwegwinc, Vanpheng Sihavongd, Brad Singerb, Tawachai Chualaowanichc, and Punya Charusirie

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 Bolaven Plateau volcanic field likely buries the impact crater that produced the tektites of the Australasian strewn field. It is the only adequately large and thick postimpact deposit on the Khorat Plateau, the largest region of plausible target rocks. It is also the only thick, postimpact deposit within the inner Muong Nong strewn field, the region containing exclusively nonaerodynamically shaped Muong-Nong–type tektites (circumscribed by the blue ellipse). Tektite find locations data from ref. 52 and this study. Basalt fields adapted with permission of ref. 53 and ref. 54; permission conveyed through Copyright Clearance Center, Inc. Outline of the Khorat Plateau data from ref. 55. Inset, finds of Australasian tektites and microtektites data from ref. 56 (white dots) define an asymmetric strewn field (blue). Credit: Proceedings of the National Academy of Sciences – 2020

52. P. S. Fiske et al., Layered tektites of southeast Asia: Field studies in central Laos and Vietnam. Meteorite. Planet. Sci. 34, 757–761 (1999).
53. S. M. Barr, A. S. Macdonald, Geochemistry and geochronology of late Cenozoic basalts of southeast Asia. Geol. Soc. Am. Bull. 92, 1069–1142 (1981)
54. J. L. Whitford-Stark, A Survey of Cenozoic Volcanism on Mainland Asia (Geological Society of America Special Papers, 1987), vol. 213, pp. 1–74, 10.1130/SPE1213-p1131.
55. J.-S. Ren et al., 1:5 million international geological map of Asia. Acta Geoscientica Sinica 34, 24–30 (2013).
56. L. Folco, M. D’Orazio, M. Gemelli, P. Rochette, Stretching out the Australasian microtektite strewn field in Victoria Land Transantarctic Mountains. Polar Sci. 2, 147–159 (2016).

 

Ultraprecise age and formation temperature of the Australasian tektites constrained by 40Ar/39Ar analyses

Fred Jourdan, Sebastien Nomade, Michael T. D. Wingate, Ela Eroglu, Al Deino

Abstract

The Australasian tektites are quench melt glass ejecta particles distributed over the Asian, Australian, and Antarctic regions, the source crater of which is currently elusive. New 40Ar/39Ar age data from four tektites: one each from Thailand, China, Vietnam, and Australia measured using three different instruments from two different laboratories and combined with published 40Ar/39Ar data yield a weighted mean age of 788.1 ± 2.8 ka (±3.0 ka, including all sources of uncertainties) (P = 0.54). This age is five times more precise compared to previous results thanks, in part, to the multicollection capabilities of the ARGUS VI noble gas mass spectrometer, which allows an improvement of almost fourfold on a single plateau age measurement. Diffusion experiments on tektites combined with synthetic age spectra and Monte Carlo diffusion models suggest that the minimum temperature of formation of the Thai tektite is between 2350 °C and 3950 °C, hence a strict minimum value of 2350 °C

Several Australasian tektites (from Thailand), showing the variety in shapes and forms. Tektites are distal impact ejecta, which formed by total melting of continental crustal target rocks (source crater still unknown, although a large crater in Western Cambodia, Lake Tonle Sap, has been proposed).
A multiring circular to oval structure is now clearly evident on the latest Google Earth updates – South China Sea.

Australasian microtektites: Impactor identification using Cr, Co and Ni ratios

CHICXULUB

Chicxulub Impact structure spherules (microtektites) are abundant components of the K-T boundary that encircles the Earth. They are less than 0.5mm in diameter and consist mostly of Ni-bearing magnesioferrite spinel crystals (at the Canadian Museum of Nature in Ottawa).

Dating K-T Tektites
One of the most exciting and important scientific findings in decades was the 1980 discovery that a large asteroid, about 10 kilometers diameter, struck the earth at the end of the Cretaceous Period. The collision threw many tons of debris into the atmosphere and possibly led to the extinction of the dinosaurs and many other life forms. The fallout from this enormous impact, including shocked quartz and high concentrations of the element iridium, has been found in sedimentary rocks at more than 100 locations worldwide at the precise stratigraphic location of the Cretaceous-Tertiary (K-T) boundary (Alvarez and Asaro 1990; Alvarez 1998). We now know that the impact site is located on the Yucatan Peninsula. Measuring the age of this impact event independently of the stratigraphic evidence is an obvious test for radiometric methods, and a number of scientists in laboratories around the world set to work.

In addition to shocked quartz grains and high concentrations of iridium, the K-T impact produced tektites, which are small glass spherules that form from rock that is instantaneously melted by a large impact. The K-T tektites were ejected into the atmosphere and deposited some distance away. Tektites are easily recognizable and form in no other way, so the discovery of a sedimentary bed (the Beloc Formation) in Haiti that contained tektites and that, from fossil evidence, coincided with the K-T boundary provided an obvious candidate for dating. Scientists from the US Geological Survey were the first to obtain radiometric ages for the tektites and laboratories in Berkeley, Stanford, Canada, and France soon followed suit. The results from all of the laboratories were remarkably consistent with the measured ages ranging only from 64.4 to 65.1 Ma (Table 2). Similar tektites were also found in Mexico, and the Berkeley lab found that they were the same age as the Haiti tektites. But the story doesn’t end there.

The K-T boundary is recorded in numerous sedimentary beds around the world. The Z-coal, the Ferris coal, and the Nevis coal in Montana and Saskatchewan all occur immediately above the K-T boundary. Numerous thin beds of volcanic ash occur within these coals just centimeters above the K-T boundary, and some of these ash beds contain minerals that can be dated radiometrically. Ash beds from each of these coals have been dated by 40Ar/39Ar, K-Ar, Rb-Sr, and U-Pb methods in several laboratories in the US and Canada. Since both the ash beds and the tektites occur either at or very near the K-T boundary, as determined by diagnostic fossils, the tektites and the ash beds should be very nearly the same age, and they are (Table 2).

There are several important things to note about these results. First, the Cretaceous and Tertiary periods were defined by geologists in the early 1800s. The boundary between these periods (the K-T boundary) is marked by an abrupt change in fossils found in sedimentary rocks worldwide. Its exact location in the stratigraphic column at any locality has nothing to do with radiometric dating — it is located by careful study of the fossils and the rocks that contain them, and nothing more. Second, the radiometric age measurements, 187 of them, were made on 3 different minerals and on glass by 3 distinctly different dating methods (K-Ar and 40Ar/39Ar are technical variations that use the same parent-daughter decay scheme), each involving different elements with different half-lives. Furthermore, the dating was done in 6 different laboratories and the materials were collected from 5 different locations in the Western Hemisphere.

DAKHLA GLASS

Fragments of so-called Dakhla glass appear in clumps of ancient lake sediment excavated in Egypt’s Western Desert. Scientists have concluded that the glass is the product of a meteorite slamming into Earth between 100,000 and 200,000 years ago

Mysterious Egyptian Glass Formed by Meteorite Strike, Study Says

Stefan Lovgren
for National Geographic News

December 21, 2006

Strange specimens of natural glass found in the Egyptian desert are products of a meteorite slamming into Earth between 100,000 and 200,000 years ago, scientists have concluded.

The glass—known locally as Dakhla glass—represents the first clear evidence of a meteorite striking an area populated by humans.

At the time of the impact, the Dakhla Oasis, located in the western part of modern-day Egypt, resembled the African savanna and was inhabited by early humans, according to archaeological evidence.

“This meteorite event would have been catastrophic for all living things,” said Maxine Kleindienst, an anthropologist at the University of Toronto in Canada.

“Even a relatively small impact would have exterminated all life for [several] miles.”

Crater Mystery

The origin of the glass had puzzled scientists since Kleindienst discovered it in 1987.

Some researchers had suggested the Stone Age glass may have been produced by burning vegetation or lightning strikes.

But a chemical analysis showed that the glass was created in temperatures so high that they could only have been the result of a meteorite impact.

Gordon Osinski, a geologist at the Canadian Space Agency in Saint-Hubert who conducted the analysis, found that the glass samples contain strands of molten quartz, a signature of meteorite impacts.

“We can now say for definite that they were caused by a meteorite impact,” he said.

DARWIN GLASS

Darwin glass is a natural glass found south of Queenstown in West Coast, Tasmania. It takes its name from Mount Darwin in the West Coast Range, where it was first reported, and later gave its name to Darwin Crater, a probable impact crater, and the inferred source of the glass.

Scientific drilling of lake sediments at Darwin Crater in Tasmania

Darwin Crater (42°18.39′S, 145°39.41′E), is the assumed source crater for the glass.

 

 

Drone picture during drilling operations at Darwin Crater. The drill site and camp near the crater center is visible in white.
Darwin Crater Tasmania, indicated by the red dot.

IRGHIZITES

IRGHIZITES, from Kazakhstan in the U.S.S.R., are the most recently discovered tektites. These specimens, which range from about .8 inch to 1.1 inches long (portions were removed from two of them for analysis), were made available to U.S. investigators by Institute of Geology in U.S.S.R. Academy of Sciences through P. V. Florensky, who first reported on them.

Zhamanshin 14 km crater N 48° 24′ E 60° 58′

Landsat

IVORY COAST

Ivory Coast (linked to the Bosumtwi crater in Ghana, West Africa)

Bosumtwi Crater – Space Shuttle Photograph Courtesy NASA Latitude N 6° 30′ Longitude W 1° 25′ – Diameter 10.5 km
The Bosumtwi crater in Ghana is a ~1.05 million year old, very well-preserved complex meteorite impact structure of approximately 10.5 km rim-to-rim diameter. The interior of the structure is largely filled by Lake Bosumtwi, and the crater rim and the environs of the crater are covered by dense tropical rainforest.

 

LIBYAN DESERT GLASS

The origin of Libyan Desert glass is uncertain. Meteoritic origins have long been considered possible, and recent research links the glass to impact features, such as zircon-breakdown, vaporized quartz and meteoritic metals, and to an impact crater. Some geologists associate the glass with radiative melting from meteoric large aerial bursts, making it analogous to trinitite created from sand exposed to the thermal radiation of a nuclear explosion. Libyan Desert glass has been dated as having formed about 26 million years ago.

High-pressure evidence from zircon in Libyan Desert Glass
Aaron J. Cavosie, Christian Koeberl
Geology (2019)
Enigmatic natural glasses have been cited as geologic evidence of the threat posed by large airbursts. Libyan Desert Glass (LDG) is a natural glass found in western Egypt that formed ~29 m.y. ago, however its origin is disputed; the two main formation hypotheses include melting by meteorite impact or melting by a large, 100 Mt–class airburst. High-temperature fusion occurs during both processes, however airbursts do not produce shocked minerals; airbursts generate overpressures at the level of thousands of pascals in the atmosphere, whereas crater-forming impacts generate shockwaves at the level of billions of pascals on the ground. Here we report the presence in LDG of granular zircon grains that are comprised of neoblasts that preserve systematic crystallographic orientation relations that uniquely form during reversion from reidite, a 30 GPa high-pressure ZrSiO4 polymorph, back to zircon. Evidence of former reidite provides the first unequivocal substantiation that LDG was generated during an event that produced high-pressure shock waves; these results thus preclude an origin of LDG by airburst alone.

MIAMI STRUCTURE: Ethereal ‘Pearls’ in Fossil Clams Are Evidence of an Ancient Meteorite Hitting Earth

MOLDAVITE

Moldavite is an unusual type of tektite with a beautiful translucent green clarity. The moldavites are tektites derived from the Ries impact structure, German. Moldavite is a special term coming from German and means ‘Vltava River Stone’. The moldavites are found in adjacent “strewn fields” in Bohemia and Moravia; they are named for the Moldau River.

Hillshaded Elevation Model (DEM) of the Ries crater (lat = 48°530N, long = 10°370E, ∅ = 24 km) using TanDEM-X data (a) and DGM10 based on LiDAR scanning (b).  (Color figure can be viewed at wileyonlinelibrary.com.)

Nördlinger Ries’s status as an impact crater did not become apparent until the 1960s. Prior to that time, many geologists suspected the crater had been formed by volcanic activity. One line of evidence supporting the impact theory included shocked quartz grains, which are formed by meteorite impacts. Another was the building material used for the church of St. George.

NORTH AMERICAN

The age of the 85-kilometer-diameter Chesapeake Bay impact structure (35 million years old)  and the composition of some of its breccia clasts are consistent with the structure being the source of the North American tektites.
The differential subsidence in the geology at the rim of the Chesapeake impact structure diverting the James and York Rivers – circled. (Poag, 1999). The abrupt diversions of the lower courses of the James and York Rivers (indicated by the small circles in the map above) coincide with the Chesapeake crater rim. (see side-note #4 [St Martin] below).

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