standby for tektites photo

left to right and top to bottom:
Quiongshan, Hainan, China (Guang Dong-type, 23.1 g)
Muong Nong, Thailand (Muong Nong-type, layered, 43.4 g)
Mt. Dare, S. Australia (Australite, button/lens-shaped, 2.7 g)
Dalat, Vietnam (Indochinite, 13.0 g)
Boyaca, Columbia (Calitite [formerly Colombianite], 6.9 g)
Libyan Desert Glass (Desert Glass, 26.7 g)
(see descriptions below)

It is commonly accepted that tektites, a word derived from the Greek "molten", formed from vaporized terrestrial rock following a hypervelocity impact on Earth. One could think of tektites as meteorites from Earth in the sense that they were blasted from the Earth through impact and shaped by aerodynamic forces as they plummeted back through the atmosphere to create defined strewn fields. Previous theories espousing an origin from volcanic eruptions on the Moon have been adequately disputed through comparative studies of the chemistry and mineralogy of lunar samples returned from the Moon by the Apollo astronauts. Hydrocode simulations of impacts (Artemieva, 2001) have demonstrated that high-velocity impacts (35–40 km/s) having impact angles of 30° to 50° from the horizon, and impacting dry target material, are consistent with model constraints on tektite production.

Lechatelierite, a form of fused quartz, and other relict mineral inclusions showing evidence of shock metamorphism, are found inside tektites, consistent with an impact origin rather than one based on igneous volcanism. Moreover, the high-pressure polymorph of quartz known as coesite has been identified in tektites, indicating pressures greater than 2 GPa. Elemental abundance patterns, along with size and shape characteristics of the mineral inclusions, suggest that the typical parent material for tektites was a terrestrial, fine-grained, sedimentary deposit similar to a graywacke or loess.

One revealing fact in the tektite origin debate is that no unique tektites have ever been found in Antarctica, where meteorites from most all classes have previously been recovered, including many lunar specimens. A major point of contention held by the lunar-origin theorists (Futrell and O'Keefe, 1997) has been the very low content of water in tektites compared to the terrestrial source rock. A recent study into the physics and chemistry of impact-induced melting and vaporization explains this lack of water as a natural outcome of the thermodynamics associated with shock pressures in excess of 100 GPa and temperatures in excess of 50,000°C. Under these conditions, volatile-containing bubbles would carry all of the water vapor out of the silicate droplets, along with free oxygen, leading to reduction of Fe and the formation of the dark green to black colors associated with tektites. Furthermore, lunar rocks contain even less water than tektites do.

Most tektite strewn fields have now been associated with a particular impact structure with an established age directly relating the tektite to its corresponding ejecta deposit: Moldavites with the Ries Crater in Germany, Ivory Coast tektites with the Bosumtwi crater in Ghana, and the North American tektites with the Chesapeake Bay Impact Crater. The largest known strewn field, represented by the Austalasian tektites, has yet to be identified with a particular impact structure. Geochemical data suggest that these tektites sample typical post-Archean sedimentary, upper crustal rocks. Analyses of Australasian microtektites by Folco et al. (2017, #6036), based on Co/Ni vs. Cr/Ni, revealed a chondritic signature most similar to LL chondrites with an admixture of terrestrial material. This is inconsistent with an airburst model and indicates that this was a cratering event. In a study involving tektite samples from Australia, China, Thailand, and Vietnam, Jourdan et al. (2019) incorporated data from three institutions utilizing four different mass spectrometers and obtained a high-precision Ar–Ar weighted mean formation age of 788.1 (±2.8) t.y.

standby for tektite ar-ar age diagram
Diagram credit: Jourdan et al., MAPS, vol. 54, #10, p. 2581 (2019)
'Ultraprecise age and formation temperature of the Australasian tektites constrained by 40Ar/39Ar analyses'

Gravity and topography data from Seasat and Geosat shows an ~100-km circular feature off the coast of Vietnam in the South China Sea centered at 13.6° N., 110.5° E., which could prove to be the elusive crater. Other searches have been conducted in Guangdong and Guangxi provinces in South China utilizing satellite imagery. By this method, a complex structure measuring 25–30 km in diameter has been identified which may be associated with the Australasian tektites (Kenkmann et al., 2014). Designated "Zaotang", the structure is centered at 25° 56' 16" N., 111° 36' 30" E.; in Hunan province. Based on the spatial variation in microtektite concentrations determined from deep-sea drilling sediment cores, as well as the variation in size and in the microimpact features along a North–South transect covering a distance of 1,300 km in the Central Indian Ocean, a possible location for the source crater is thought to be in eastern Cambodia (12° N., 106° E.), in agreement with previous predictions (Prasad et al., 2007, 2010). Conversely, Whymark (2013) reviewed the current state of the evidence for this event, including macro- and micro-tektite distribution, crater ray alignment, and chronological/isotopic data, and it was concluded that the fall likely occurred in the Gulf of Tonkin, possibly within the Song Hong-Yinggehai (SHY) Basin. The diameter of the source crater was previously estimated to be 17–114 km, and after further refinement, ~40 km. Consistent with this, an ~43 km circular feature having rings extending to ~90 km has been detected in the SHY Basin (17°45'20" N, 107°50'30" E). Still another proposed location for the impact crater is the Badain Jaran Desert in the Alxa Plateau of Northwest China covering an expanse of 49,000 km² (Mizera et al., 2016).

Recoveries of some Indochinite tektites with signs of stretching during flight provide more evidence for an impact origin rather than an extraterrestrial origin. If these features had been the result of etching by soil acids, as some have argued, the stretch areas would have been etched to a similar degree as the rest of the tektite, which is not the case. This leads to the conclusion that these features were formed by aerodynamic sculpting instead. The internal heating demonstrated by the plastic stretching is also further evidence that the tektites did not arrive on Earth as individuals, in which case the only heating effects would be those on the exterior caused by heating during entry. Instead, these features were the result of spallation on a large, rapidly rotating body within the atmosphere.

The photo above shows four members of the ~788 t.y.-old Australasian strewn field, which covers about 20% of the Earth's surface. Transantarctic Mountain microtektites, in the form of microscopic, pale-yellow to pale-green, transparent glassy spherules, likely represent the southern-most extent of the Australasian tektite strewn field (Folco et al., 2009). Other tektite sources likely represented by this strewn field include those from Tibet, the Philippines (Rizalite, Bikolite, Anda) and Java.

An issue that remains unresolved concerns the origin of the kinetic energy required to produce the flange flattening of australite button-form tektites. An atmospheric reentry speed of ~10 km/s was experimentally calculated by Chapman and Larson (1962) to reproduce this particular tektite morphology. However, after considering the loss of energy due to shock vaporization during ejection, about half of this value (or ¾ of the launch kinetic energy) remains unaccounted for. Furthermore, given the ~10 km/s australite reentry speed, a minimum suborbital flight duration (Time Of Flight) of ~3.25 hours was calculated by Thomas H. S. Harris (archived publications, which would necessarily result in a landing point ~32,000 km from the source due to Earth's rotation; this is inconsistent with the known geographic distribution of ejecta and rules out a launch site in Indochina, or even from within the same hemisphere. Notably, calculations for microtektites indicate significantly longer loft times, which makes Earth's rotation an even greater factor in the longitudinal aspect.

In the 2015 paper 'Suborbital Imprint Matching', Thomas H. S. Harris proposes an alternative origin for the Austalasian tektites in North America. He demonstrates that an oblique impact during the Quaternary/Pleistocene Ice Age (2.58 m.y. ago to the present) onto the North American Laurentide ice sheet covering quartz sediments is more consistent with orbital analyses and other data related to these tektites. He further argues that adiabatic water vapor expansion in the form of steam or plasma arising from such an impact can account for the remaining energy contributing to tektite suborbital flight, and can also explain the uniform iron oxidation state of the tektites. It was posited by Harris (2016) that an impact onto an extensive ice sheet resulted in the shock-melting of quartz substrate and the disassociation of water under electromagnetic conditions which supported the prolonged availability of oxygen ions, thus promoting the uniform Fe oxidation observed in the tektites. In addition, Harris observed that the ~1,600 km³ Carolina Bays sand unit, which covers ~5% of the continental U.S., shows depositional features (e.g., ovoid shape with latitude-dependent axes possibly associated with Coriolis force) consistent with suborbital transport and density impedance processes. The age of the Carolina Bays have been calculated to be between 140 t.y. and 1.6 m.y., which encompasses the age of the Australasian tektites.

A suspect ejecta blanket imaged with LIDAR, showing a portion of 45,000+ co-aligned sand bed voids scaling from 100 meters to several kilometers,
aligned systematically by latitude, with robust adherence to only 6 different archetype ovoid shapes, which are now referred to as 'Davias archetypes' by investigators.
Image credit: M. Davias—Cintos Research; Caption credit: Thomas H. S. Harris (2015), 'Suborbital Deconvolution Of Ejecta And Strewn'

An experimental model was employed by A. Zamora (2017) to demonstrate the Glacier Ice Impact Hypothesis for the formation of the shallow elliptical Carolina Bays and Nebraska Rainwater Basins. This hypothesis explains how a meteorite impact on the Laurentide Ice Sheet created secondary oblique (~35°) impact features by glacier ice boulders striking shock-liquefied ground. The total kinetic energy needed to create the ~500,000 Carolina Bays was estimated by Zamora (2017), which corresponds to a primary impactor measuring ~3 km in size and traveling at a speed of 17 km/s. The GIF below shows the following sequence of events:
  1. Impacts by ice projectiles create conical cavities on a viscous surface.
  2. Viscous relaxation converts conical cavities into shallow bays with raised rims.
  3. New impacts make conical cavities without disturbing adjacent bays.
  4. Viscous relaxation of adjacent conical cavities creates overlapping bays.

GIF images credit: Antonio Zamora, Geomorphology, vol. 282, pp. 209–216 (2017)
'A model for the geomorphology of the Carolina Bays'

Obtaining Soil Samples at Arabia Bay

See more videos by Antonio Zamora about the Carolina Bays and associated research at his YouTube channel.

A correlated cosmic impact origin for the Australasian tektites (and certain other tektites), the Carolina Bays, and an elongated, oval "thumb-like" depression in Saginaw Bay, Michigan (historically attributed to glacial erosion), has been conjectured by Davias and Harris (2015) in 'A Tale Of Two Craters: Coriolis-Aware Trajectory Analysis Correlates Two Pleistocene Impact Strewn Fields And Gives Michigan A Thumb'. Their hypothesis is supported by forensic evidence (e.g., target rock composition, zircon age, combed gravity aspect) and sub-orbital calculations.

An example martian oblique impact crater with a butterfly-shaped ejecta blanket overlain on a Google image of Saginaw Bay
GIF images credit: Michael E. Davias—'Correlating the Orientation of Carolina bays to a Cosmic Impact'

Home Page
mouseover the time machine set to 788 t.y. before present

A consistency in variability with respect to distance has been demonstrated for multiple parameters in recent Australasian tektite studies. Each of these independent studies below (most are open access) constrain the origin of the Australasian tektites and demonstrate that they should originate from a location in southeast Asia. A highly oblique impact is generally considered the most probable scenario.

10Be isotopes
Ma et al., 2001
Ma et al., 2004
Rochette et al., 2018
M. Trnka, 2020"Considering the arguments above, it is unlikely that the geographical variability in 10Be contents of tektites and microtektites is related to the original depth of deposition of their source material."

Microimpact features
Prasad et al., 2010

Size distribution
Ginneken et al., 2018

Geochemical data
Lee et al., 2004

Re–Os isotope systematics
Ackerman et al., 2019

Catastroloess source
Bunopas et al., 1999

Chemical composition
Goderis et al., 2017
A. Hildebrand, 2019
A. Hildebrand, 2019 (see diagram below)

Composition of Australite Tektites vs. Champasak A Melt Sheet
standby for nwa 10503 o-isotope diagram
click on image for a magnified view

Diagram credit: A. Hildebrand, 82nd MetSoc, #6489 (2019)

Schwarz et al. (2013) obtained Ar–Ar ages for the Australasian tektites and the tektite-like melt glass samples recently discovered in Western Canada and Belize. Their results indicated that all of these objects formed at the same time within uncertainties 785 (±7) t.y. ago, but that the chemical composition of the Belize tektite-like glass was distinct from tektites/melt glass from the other two locations. Thereafter, Schwarz et al. (2016) conducted more precise Ar–Ar measurements of these various objects and determined that the Australasian tektites and the compositionally similar Western Canadian tektite-like glass have indistinguishable ages of 785 (±7) t.y., indicating that they formed during the same impact event. By comparison, they found that the compositionally different tektite-like glass samples from Belize have a younger age of 769 (±16) t.y., indicating that these objects formed during an earlier, separate impact event.

The button/lens-shaped Australite above, which was the first type of tektite described in the literature by naturalist Charles Darwin, exhibits typical concentric ring-wave flow ridges on the forward face emanating from the stagnation point, consistent with aerodynamically stable hypervelocity ablation during descent. The Muong Nong-type layered tektites are generally thought to have formed close to the source crater, consistent with their lack of ablation features and a recovery location very near that predicted for the source crater.

The last photo shown above is a mass of Libyan desert glass (LDG), melted silica glass thought to have been formed by an asteroid impact in the Great Sand Sea region of western Egypt ~28.5 m.y. ago. In contrast to the commonly accepted scenario of a near-surface airburst, the occurrence of an asteroid impact with consequent heating to temperatures of ~1550°C and the simultaneous formation of lechatelierite and cristobalite is supported by the presence of brownish inclusions of a molten low-Ca, Al-rich orthopyroxene target rock, as well as by the incorporation of deep-seated terrestrial material (Greshake et al., 2010). Shock metamorphosed sandstones are also consistent with this impact scenario, although O-isotopic analysis found that the target rocks consisted of quartz sands derived from intrusives of Pan-African age (Longinelli et al., 2011).

Another study of C and Cl in Libyan desert glass reveals quenching upon impact of a carbon-rich projectile with silica-rich crustal rocks and sea-water rather than an impact on dry land (Miura, 2009). It has been estimated that at least 10 million tons of LDG were created in a layer up to a few mm thick extending over an area of 6,500 km², from which 20 tons has been collected (Pratesi et al., 2002; Greshake et al., 2010). A small, extensively weathered fragment of oxidized iron showing remnants of an octahedral structure (named Great Sand Sea 003) is possibly associated with this event. Although a meteoritic component of ~0.5% has been previously identified in LDG, dark streaks with nonchondritic elemental ratios represent terrestrial material. The energy released during this explosion is calculated to have been equivalent to that of the Tunguska event.

Resulting high-temperature melt-products identified in LDG glass include lechatelierite and cristobalite from quartz, and baddeleyite from zircon. Cathodoluminescence imaging has identified previously unrecognized quenched flow textures in this glass, potentially useful for characterizing the temperature of formation (Gucsik et al., 2003); temperatures in the 1700–2100°C range have now been calculated (Pratesi et al., 2002). These rare brown to bluish (from Rayleigh scattering by 60 nm-sized or smaller particles) streaks have been resolved into discrete rounded glass spherules which constitute an immiscible liquid within the silica-glass matrix. These spherules are enriched in Al, Fe, and Mg, as well as Ir, Os, Cr, Co, and Ni, elements which may reflect a significant meteoritic component. Graphite ribbons, possibly derived from the impactor, have also been identified.

Brecciated sandstone samples from the LDG area show signs of fractures, mosaicism, undulatory extinction, and cleavage. Planar deformation features and other shock features provide persuasive evidence for a hypervelocity impact origin. Koeberl and Ferrière (2019) observed shock deformation features in quartz grains obtained from bedrock at the LDG site. These features, which include planar fractures, planar deformation features, and feather features, indicate shock pressures of at least 16 GPa occurred, consistent with an impact event; however, the associated crater has since been completely eroded away. Geochronological data and isotopic ratios of Sr and Nd indicate that the target material was sand, derived from Precambrian crustal granitic rock, rather than Lower Cretaceous sandstones of the Nubia Group. In a transmission electron microscopy investigation of LDG, Kovaleva et al. (2022) not only found evidence of zircon melting at high temperatures (> 2750°C) followed by rapid quenching, but also identified the presence of the high-pressure orthorhombic phase of Zr-oxide that supports a high-pressure impact origin.

The photo shown below is an artifact recovered from King Tutankhamun's tomb. This pectoral features a yellow-green gem in the image of a scarab, carved from a piece of Libyan Desert Glass. This demonstrates the special nature of this material to the early Egyptian civilization.

Similar to LDG, the high-silica Dakhleh Glass (DG) from the Dakhleh Oasis in the Western Desert of Egypt probably derives from a low-altitude airburst ~120 (±40) t.y. ago into Pleistocene lacustrine sediments (Osinski et al., 2008). Many of the black to dark-gray DG specimens are vesiculated on the upper surface, sometimes exhibiting impressions of grass and reed vegetation on the underside, some containing burnt sediments. Dakhleh Glass is predominantly a mixture of glass and crystallites.

Pictured below is an olive-green, filigree-like moldavite, a member of the Central European strewn field associated with the 14.68 (±0.11) m.y.-old, 24-km-wide Nördlinger Ries impact crater in Germany (Laurenzi et al., 2003; Vincenzo and Skála, 2008). The 3.8-km-wide Steinheim Basin crater, located 42 km west-southwest of the Ries crater, is considered to have been formed during the same event, attesting to a binary asteroid impact. Through 3-D hydrocode simulations (Stöffler et al., 2002), it was determined that the two impact projectiles, with diameters of 1.5 km and 0.15 km, impacted at an angle of 30–50° from the horizontal at a velocity of ~20 km/s. The leading shock wave impacted the target material, consisting of both weathered and unweathered, unconsolidated, Middle Miocene silica-rich sands, with lesser amounts of clays and carbonates, generating temperatures of ~40,000°C (Skála et al., 2009). The superheated melt was distributed up to 400–500 km away in a symmetrical, ~60° fan-shaped jet, the remnant of which today is represented by the moldavite strewn fields of South Bohemia, Moravia, the Cheb Basin, northern Austria, and Lusatia. Rapid cooling and solidification of the melt ensued, leading to the formation of tektites.

Moldavites accumulated from melt particles of variable chemical composition. The ultimate shape of moldavites is a result of etching by groundwater in an acidic permeable environment. They are virtually water-free and incorporate cations that reflect differentiation based on ionic size, a result of their formation (fractional condensation) at plasma temperatures (von Engelhardt et al., 2005). Shock forces from the Ries impact created shattercones in the limestone layer below.

The four photos below represent tektites from the two remaining recognized strewn fields, along with an impact glass similar in composition to the LDGs:

standby for nakhla photo
standby for nakhla photo
click on photos for a magnified view

Still other impact glasses have been found to be associated with craters:

In addition to these, the Monturaqui glasses are associated with a ~100 t.y.-old, 370-m-wide crater located in the Atacama Desert, Chile. Since 2012, tens of thousands of small splash-form impact glasses with an age of ~7.8 m.y. have been recovered in an ~650 km² region of the central Atacama Desert and termed "Atacamaites"; however, no associated crater has yet been found (Devouard et al., 2014; Gattacceca et al., 2021). Chemical analyses indicate a probable iron impactor consistent with the IIAB group. Although many features of atacamaites are similar to those of tektites, others such as small size, distorted shape, oxidized character, and high impactor contamination provide rationale to distinguish them as impact glasses, but the authors find the term "tektoids" to be an appropriate descriptor.

Furthermore, at least seven distinct horizons of impact glass have been identified in loess-like deposits of the Pampeano Formation of Argentina (Schultz et al., 2002, 2004):

  1. Rio Cuarto impact glass dated to the Holocene Epoch at 6 (±2) t.y. ago
  2. impact glass sites dated to the Pleistocene Epoch at 114 (±26) t.y. ago
  3. impact glass sites dated to the Pleistocene Epoch at 230 (±30) t.y. ago
  4. glass impactites dated to the Pleistocene Epoch from Centinela del Mar at 445 (±11) t.y. ago
  5. impact glass sites dated to the Pleistocene Epoch near Necochea at 445 (±21) t.y. ago
  6. impact glass near Mar del Plata dated to the Pliocene Epoch at 3.27 (±0.08) m.y. ago
  7. impact glass near Buenos Aires Province dated to the Miocene Epoch at 5.33 (±0.05) m.y. ago
  8. impact glass near Chasico dated to the Miocene Epoch at 9.23 (±0.09) m.y. ago, which is associated with a concentric structure measuring 15 km in diameter
A unique Central American tektite-like glass strewn field has been established in western Belize, but recent finds have extended the area to encompass at least 6400 km² in southern Mexico, Nicaragua, Honduras, Guatemala, San Salvador, and possibly Costa Rica (H. Povenmire et al., 2014; Koeberl and Schulz, 2016; H. Povenmire, 2016). While the first account of these tektite-like glass samples was published by A. Hildebrand et al. (1992), the first undisputed specimens to be authenticated by lab analyses were recovered by J. Cornec. Over 7,000 specimens exhibiting typical tektite-like morphologies and low water content (60–80 ppm) are estimated to have been recovered to date, in large part as a result of three hunting expeditions led by B. Burrer. These objects often occur in clusters in newly cleared agricultural lands. A precise Ar–Ar age of 769 (±16) t.y. was determined by Schwarz et al. (2016), while a subsequent analysis by Rochette et al. (2021) yielded a weighted mean Ar–Ar age of 803.7 (±8.5) t.y., which is slightly older than the age of Australasian tektites (788.1 [±2.5] t.y.; Jourdan et al., 2019). Moreover, the compositional (e.g., SiO2 contents) and isotopic differences (e.g., Sr–Nd, Os) that exist between the Australasian tektites and the Belize tektite-like glasses indicate that they represent separate impact events. Measurements of cosmogenic 10Be by Park et al. (2018) also support the assumption that Belize tektite-like glasses derive from a separate source from that of Australasian tektites (see chart below).

standby for 10be chart
Chart credit: Park et al., 49th LPSC, #1296 (2018)

The ~14-km-wide Pantasma Crater in northern Nicaragua was identified as a possible source of the tektite-like glass and the tektites, termed belizites (Povenmire et al., 2011, 2012, 2013; King et al., 2016; Rochette et al., 2017, 2019, 2021). The Rb–Sr and Sm–Nd isotopic compositions for 12 samples are more similar to terrestrial mantle values than to other tektites, and indicate that the impact source rock was either volcanic in origin or that these objects are actually volcanic glasses (Koeberl et al., 2015). Results from a combined Re–Os isotope and platinum-group element analysis conducted by Koeberl and Schulz (2016) support the hypothesis of a local (Central American arc) volcanic origin for the precursor material without incorporation of an extraterrestrial component; however, a ε54Cr analysis revealed that an impactor consistent with an ordinary chondrite has contaminated the glass (Rochette et al., 2021). With respect to their extensive database recording magnetic signatures of tektites, impactites, and various types of natural glasses, Hoffmann et al. (2016) found that the Belize tektite-like glasses are most similar to impactite glass. Belize glasses are compositionally distinct from other known tektites (see TAS diagram below).

Total Alkali vs. Silica (TAS) Plot
standby for silica vs. total alkali diagram
Diagram credit: Koeberl et al., GCA, vol. 325 (2022, open access link)
'Tektites glasses from Belize, Central America: Petrography, geochemistry, and search for a possible meteoritic component'

Comprehensive petrographic, geochemical (major and trace elements), isotopic, spectrographic, and other analyses (e.g., Fe oxidation state, 10Be concentrations) of Belize tektites by Koeberl et al. (2022) have determined that the source material is consistent with Central American arc parental magmas, particularly with volcanic rocks found in Honduras and Guatemala. Features observed in the tektites, such as schlieren, vesicles, and lechatelierite, and a water content of 82–133 ppm, are comparable to other tektites from the Australasian, Ivory Coast, North American, and other recognized tektite strewn fields. The combined results of Koeberl et al. (2022) are less favorable for an origin from the Pantasma Crater in Nicaragua. Photos of typical belizite specimens can be found in the Meteorite Times Magazine article 'Belize Tektites' by Brian C. Burrer (2011), and in the Communications Earth & Environment article 'Impact glasses from Belize represent tektites from the Pleistocene Pantasma impact crater in Nicaragua' by Rochette et al. (2021), the latter article showing typical splash-forms including elongate, teardrop, and dumbbell morphologies (see their photo of large specimens [5 mm lines]). The 6.9 g Belize tektite shown below was formerly in the Povenmire Collection.

standby for belize tektite photo
Photo courtesy of Katie Povemmire

Other impact-related glasses have been found around the world. Three specimens of a 24 m.y. old impact glass were recovered in Western Siberia near Novy Urengoi, known as Urengoites. A single 6.2 m.y. old piece of impact glass has been found near Magnitogorsk in the Urals, named South-Ural glass. Besides their petrographic characteristics, these glasses contain very low water contents compared to glasses of volcanic origin, and are therefore suspected to be of impact origin. Bottle-green-colored microtektites have been found in a core sample from the South Tasman Rise in the Indian Ocean, which have been dated to 4.6–12.1 m.y. ago (D. Kelly and L. Elkins-Tanton, 2004). These microtektites have been geochemically associated with impact glasses from Bahía Blanca, Argentina, dated at ~5.28 (±0.04) m.y. ago, and indicate that a large impact event occurred. Basaltic clasts analysed from this impact-melt glass show close similarities to known angrites (Harris and Schultz, 2009). Lastly, three different locations feature large areas of vesicular impact glass with incorporated meteoritic particles, likely associated with cometary low-altitude airburst events (Harris and Schultz, 2020 #2229; Schultz et al., 2021): 1) Pica glass found in the Atacama Desert near Pica, Chile, aged ~12 t.y.; 2) Dakhleh glass found in the Dakhleh Oasis, southwestern Egypt, aged 100–200 t.y.; and 3) Edeowie glass found in South Australia, aged ~700 t.y.

Pictured at the top of the page (bottom row, middle) is a tektite-like glass commonly referred to as a Colombianite (or Amerikanite), which has generally been considered to be of terrestrial volcanic origin due to a high water content, in spite of its strong resemblance to a tektite. Recently, Vajda et al. (2017), Gómez et al. (2017), and Ocampo et al. (2017) described impact-related materials including microspherules as well as these tektites, or "Calitites" (photo credit: Ocampo et al., 2017, #2832) associated with a buried elliptical (36 × 26 km) impact crater—Cali Crater—located near Cali, Columbia and dated at 3.25 (±0.04) m.y. (weighted mean age). Nevertheless, analyses by Ferrière et al. (2019 #5111; 2021) led them to conclude that an impact origin of the Cali glass can be excluded in favor of a volcanic origin as represented by rhyolitic glass or obsidian (see TAS diagram below). They also found that high Nd and low Sr isotope values in Cali glass are consistent with a mantle signature rather than the crustal signature observed in verified tektites.

Total Alkali vs. Silica (TAS) Plot
standby for silica vs. total alkali diagram
Diagram credit: Ferrière et al., Large Meteorite Impacts VI, #5111 (2019)

standby for lodran photo
click on image for a magnified view
Image credit: Aubrey Whymark—tektites.co.uk