Microtektites from the Northern Victoria Land Transantarctic Mountains: An Update (original) (raw)
Related papers
Tektites are natural silicate glasses produced by the melting associated with hypervelocity impacts of extraterrestrial bodies on Earth. They are found only in certain areas of the Earth known as strewn fields, the material being mostly projected melt from target rocks at the site of impact. Microtektites are distal ejecta which are found up to several thousands km from their source crater. Microtektite strewn fields documented in literature include the North American (35 Ma), Ivory Coast (1.1 Ma) and Australasian (0.8 Ma). We report here on the discovery of microtektites from several summit plateaus (~2700 m) of the Transantarctic Mountains in northern Victoria Land. They have a Late Miocene 40 Ar/ 39 Ar age and identify a new microtektite strewn field associated with an impact crater yet to be located. This finding has important implications for both the collisional history of our planet and for the denudation history of the Antarctic bedrock. Citation: Folco, L., P. Rochette, N. Perchiazzi, M. D'Orazio, M.A. Laurenzi, and M. Tiepolo (2007), Microtektites from the northern Victoria Land
Microtektites from Victoria Land transantarctic mountains
We report on the discovery of a microtektite (microscopic impact glass particles) strewn fi eld from the Victoria Land Transantarctic Mountains, Antarctica. Microtektites were found trapped in the local detritus accumulated in weathering pits and in joints of several glacially eroded summits (~2600 m above sea level [asl]) distributed latitudinally for 520 km. Their physical and chemical properties defi ne a coherent population with a geochemical affi nity to Australasian microtektites and compatible Quaternary 40 Ar-39 Ar formation age. We therefore suggest that Transantarctic Mountain microtektites (TAMM) defi ne the southern extension of the Australasian strewn fi eld. The margin of the Australasian strewn fi eld is thus shifted southward by ~3000 km and the maximum distance from the putative parent impact site in Indochina by ~2000 km. This emphasizes the paradox of the missing parent crater of the largest (>10% of the Earth's surface) and youngest tektite strewn fi eld discovered on Earth. Furthermore, TAMM are depleted in volatile elements (i.e., Pb, Na, K, Rb, Sr, Rb, and Cs) rela tive to Australasian ones, suggesting a possible relationship between high-temperature-time regimes in the microtektite-forming process and high-angle trajectories in the ejecta plume.
Geoscience Frontiers, 2021
The~790 ka Australasian (micro)tektite strewn field is one of the most recent and best-known examples of impact ejecta emplacement as the result of a large-scale cratering event across a considerable part of Earth's surface (>10% in area). The Australasian strewn field is characterized by a tri-lobe pattern consisting of a large central distribution lobe, and two smaller side lobes extending to the west and east. Here, we report on the discovery of microtektite-like particles in sedimentary traps, containing abundant micrometeorite material, in the Sør Rondane Mountain (SRM) range of East Antarctica. The thirty-three glassy particles display a characteristic pale yellow color and are predominantly spherical in shape, except for a single dumbbell-shaped particle. The vitreous spherules range in size from 220 to 570 μm, with an average diameter of~370 μm. This compares relatively well with the size distribution (75-778 μm) of Australasian microtektites previously recovered from the Transantarctic Mountains (TAM) and located ca. 2500-3000 km from the SRM. In addition, the chemical composition of the SRM particles exhibits limited variation and is nearly identical to the 'normal-type' (i.e., <6% MgO) TAM microtektites. The Sr and Nd isotope systematics for a single batch of SRM particles (n = 26) strongly support their affiliation with TAM microtektites and the Australasian tektite strewn field in general. Furthermore, Sr isotope ratios and Nd model ages suggest that the target material of the SRM particles was composed of a plagioclase-or carbonate-rich lithology derived from a Paleo-or Mesoproterozoic crustal unit. The affiliation to the Australasian strewn field requires long-range transportation, with estimated great circle distances of ca. 11,600 km from the hypothetical source crater, provided transportation occurred along the central distribution lobe. This is in agreement with the observations made for the Australasian microtektites recovered from Victoria Land (ca. 11,000 km) and Larkman Nunatak (ca. 12,000 km), which, on average, decrease in size and alkali concentrations (e.g., Na and K) as their distance from the source crater increases. The values for the SRM particles are intermediate to those of the Victoria Land and Larkman Nunatak microtektites for both parameters, thus supporting this observation. We therefore interpret the SRM particles as 'normal-type' Australasian microtektites, which significantly extend the central distribution lobe of the Australasian strewn field westward. Australasian microtektite distribution thus occurred on a continent-wide scale across Antarctica and allows for the identification of new, potential recovery sites on the Antarctic continent as well as the southeastern part of the Indian Ocean. Similar to volcanic ash layers, the~790 ka distal Australasian impact ejecta are thus a record of an instantaneous event that can be used for time-stratigraphic correlation across Antarctica.
Earth and Planetary Science Letters, 2010
Australasian microtektites volatile elements tektites impact melting impact glass impact cratering We studied the variations of the volatile major elements Na and K in Transantarctic Mountain microtektites and Australasian microtektites with distance from the putative source crater location in Indochina. The dataset includes 169 normal-type Australasian microtektites (101 from this study and 68 from the literature) from 24 deep-sea sediment cores up to 8000 km from Indochina, and 54 Transantarctic Mountain microtektites from northern Victoria Land, 11 000 km due southeast of Indochina. Normal-type (MgOb 5.5 wt.% and SiO 2 =60-78 wt.%) Transantarctic Mountain microtektites and Australasian microtektites share a common volatilization trend with Na and K contents decreasing with distance from Indochina. The average total alkali (Na 2 O+K 2 O) concentrations at distance ranges of 1000-2000 km, 2000-4000 km, 4000-8000 km and N8000 km are 4.27± 0.67 wt.% (n = 84), 3.20 ± 1.21 wt.% (n = 50), 2.10 ± 0.25 wt.% (n = 35) and 1.25 ± 0.25 wt.% (n = 54), respectively. The trend highlights a relationship between increasing loss of volatiles in microtektites with longer trajectories and higher temperature-time regimes which should be taken into account in microtektite formation modeling. The trend is consistent with a previous hypothesis that Transantarctic Mountain microtektites belong to the Australasian strewn field and that Indochina is the target region for the parent catastrophic impact.
Tektites, minitektites and microtektites from the Kalgoorlie region, Western Australia
2012
Introduction About 790 ka (Schneider et al. 1992), an asteroid or comet impacted in southeast Asia, melting crustal rocks (and regolith) and producing glassy impact debris, known as tektites or australites, which are found over more than 10% of the Earth’s surface (Schnetzler & McHone 1996), including much of Australia and surrounding oceans (Fig. 1). The tektites formed as molten “splash” material cooled during high-velocity movement through the air and range in size from spheres less than 1 mm (microtektites, found mainly in deep sea cores) to irregular blocks weighing up to more than 20 kg (Muong Nong tektites in SE Asia). The distribution, size and concentration of tektites in the Australasian strewn field indicate a likely impact site somewhere in southern Laos, northern Cambodia or eastern Thailand, but the location of the impact site has not yet been discovered.
Transantarctic Mountain microtektites: Geochemical affinity with Australasian microtektites
Geochimica Et Cosmochimica Acta, 2009
We extended the petrographic and geochemical dataset for the recently discovered Transantarctic Mountain microtektites in order to check our previous claim that they are related to the Australasian strewn field. Based on color and composition, the 465 microtektites so far identified include two groups of transparent glass spheres less than ca. 800 lm in diameter: the most abundant pale-yellow, or normal, microtektites, and the rare pale-green, or high-Mg, microtektites. The major element composition of normal microtektites determined through electron microprobe analysis is characterized by high contents of silica (SiO 2 = 71.5 ± 3.6 (1r) wt%) and alumina (Al 2 O 3 = 15.5 ± 2.2 (1r) wt%), low total alkali element contents (0.50-1.85 wt%), and MgO abundances <6 wt%. The high-Mg microtektites have a distinctly higher MgO content >10 wt%. Transantarctic Mountain microtektites contain rare silica-rich (up to 93 wt% SiO 2 ) glassy inclusions similar to those found in two Australasian microtektites analyzed here for comparison. These inclusions are interpreted as partially digested, lechatelieritelike inclusions typically found in tektites and microtektites. The major and trace element (by laser ablation -inductively coupled plasma -mass spectrometry) abundance pattern of the Transantarctic Mountain microtektites matches the average upper continental crust composition for most elements. Major deviations include a strong to moderate depletion in volatile elements including Pb, Zn, Na, K, Rb, Sr and Cs, as a likely result of severe volatile loss during the high temperature melting and vaporization of crustal target rocks. The normal and high-Mg Transantarctic Mountain microtektites have compositions similar to the most volatile-poor normal and high-Mg Australasian microtektites reported in the literature. Their very low H 2 O and B contents (by secondary ion mass spectrometry) of 85 ± 58 (1r) lg/g and 0.53 ± 0.21 lg/g, respectively, evidence the extreme volatile loss characteristically observed in tektites. The Sr and Nd isotopic compositions of multigrain samples of Transantarctic Mountain microtektites are 87 Sr/ 86 Sr % 0.71629 and 143 Nd/ 144 Nd % 0.51209, and fall into the Australasian tektite compositional field. The Nd model age calculated with respect to the chondritic uniform reservoir (CHUR) is T Nd CHUR % 1.1 Ga, indicating a Meso-Proterozoic crustal source rock, as was derived for Australasian tektites as well.
Journal of Geophysical Research, 1994
Geographic variations in the concentration of Australasian microtektites in 42 cores from the Indian Ocean, western equatorial Pacific Ocean, and the Philippine, Celebes, and Sulo Seas were used to predict the location of the Australasian tektite source crater and to estimate its size. The location that seems to best explain the geographic variations in microtektite concentrations is located in central Cambodia at about 12øN latitude and 106øE longitude. The diameter of the source crater is estimated to be between 32 and 114 km based on thickness of the microtektite layer at each site and distance from the predicted source area in Cambodia. The large range in estimated size of the source crater is due to a lack of knowledge about the value of the exponent that describes the radial decrease in ejecta thickness. Additional microtektite/ejecta-bearing sites closer to the source region could help resolve this problem.
10Be in Australasian microtektites compared to tektites: Size and geographic controls
Geology, 2018
Large 10Be content in tektites has been shown to be evidence of a source material enriched in atmospheric 10Be, i.e. a soil or sediment. In Australasian tektites 10Be content increases with distance from the putative source crater in Indochina, with geographic averages from 69 to 136x106 at/g. Here we show that the same trend exists in microtektites by measuring samples from Antarctica and South China Sea. Moreover, microtektites are ~30x106 at/g richer than tektites from the same geographic area. Antarctic microtektites, with an average 10Be content of 184x106 at/g after correction for insitu-production, are the richest impact melt ever measured. The simpler hypothesis for such systematic size and geographic gradient is that the source depth of the melted material in the target soil surface decreases with ejection velocity. A higher initial kinetic energy indeed means a higher launch distance and a higher fragmentation. Alternative models invoking a marine sediment source or a secondary enrichment in the microtektite (either by atmospheric scavenging or host contamination) fail to reproduce the observed relationships.
Impact microcrater morphology on Australasian microtektites
Meteoritics & Planetary Science, 2003
Scanning electron microscopy of 137 Australasian microtektites and fragments from 4 sediment cores in the Central Indian Ocean reveals more than 2000 impact-generated features in the size range of 0.3 to 600 mm. Three distinct impact types are recognized: destructive, erosive, and accretionery. A large variation in impact energy is seen in terms of catastrophic destruction demonstrated by fragmented microtektites through erosive impacts comprising glass-lined pit craters, stylus pit craters, pitless craters, and a small number of accretionery features as well. The size range of observed microtektites is from 180 to 2320 mm, and not only are the smaller microtektites seen to have the largest number of impacts, but most of these impacts are also of the erosive category, indicating that target temperature is an important factor for retaining impact-generated features. Further, microcratering due to collisions in impact-generated plumes seems to exist on a larger and more violent scale than previously known. Although the microcraters are produced in a terrestrially generated impact plume, they resemble lunar microcraters in many ways: 1) the size range of impacts and crater morphology variation with increasing size; 2) dominant crater number densities in mm and sub-mm sizes. Therefore, tektite-producing impacts can lead to the generation of microcraters that mimic those found on lunar surface materials, and for the lunar rocks to qualify as reliable cosmic dust flux detectors, their tumbling histories and lunar surface orientations have to be known precisely.