Sample records for australites

  1. Beryllium-10 in Australasian tektites - Evidence for a sedimentary precursor (United States)

    Pal, D. K.; Moniot, R. K.; Kruse, T. H.; Herzog, G. F.; Tuniz, C.


    Each of seven Australasian tektites contains about 100 micron atoms of beryllium-10 (half-life, 1.53 million years) per gram. Cosmic-ray bombardment of the australites cannot have produced the measured amounts of beryllium-10 either at the earth's surface or in space. The beryllium-10 contents of these australites are consistent with a sedimentary precursor that adsorbed from precipitation beryllium-10 produced in the atmosphere. The sediments must have spent several thousand years at the earth's surface within a few million years of the tektite-producing event.

  2. Coeval ages of Australasian, Central American and Western Canadian tektites reveal multiple impacts 790 ka ago (United States)

    Schwarz, Winfried H.; Trieloff, Mario; Bollinger, Klemens; Gantert, Niklas; Fernandes, Vera A.; Meyer, Hans-Peter; Povenmire, Hal; Jessberger, Elmar K.; Guglielmino, Massimo; Koeberl, Christian


    High resolution 40Ar-39Ar step heating dating of australites and indochinites, representing a large area of the Australasian strewn field, and more recently discovered tektite-like glasses from Central America (Belize) and Western Canada, were carried out. Precise plateau ages were obtained in all cases, yielding indistinguishable ages of 789 ± 9 ka for four australites, 783 ± 5 ka for four indochinites, 783 ± 17 ka for one Western Canadian and 769 ± 16 ka for one Belize impact glass. Concerning major elements and REEs, australites and the Western Canadian impact glass are indistinguishable. If the Western Canadian sample was transported by impact ejection and belongs to the Australasian strewn field, this implies extremely far ballistic transport of 9000 km distance, assuming a source crater in southern Asia. The distinct major element and REE composition of the Belize impact glass suggests formation in another separate impact event. We conclude that the Australasian/Western Canadian impact glasses formed 785 ± 7 ka ago in a single event and Belize impact glass in a separate event 769 ± 16 ka ago. The two impact events forming these two strewn fields occurred remarkably closely related in time, i.e., separated by <30 ka.

  3. Boron content and isotopic composition of tektites and impact glasses: Constraints on source regions (United States)

    Chaussidon, Marc; Koeberl, Christian


    Abundances of Li, Be, and B, as well as boron isotopic compositions, were determined in twenty-seven tektite and impact glass samples, using an ion microprobe. Samples included tektites from the Australasian, North American, and Ivory Coast strewn fields, and Aouelloul and Darwin impact glasses. Variations of B abundance and isotopic composition in a flanged australite were also studied. δ 11B variations of only a few permil were found within the australite flange. The isotopic composition shows no correlation with the B contents or with the distance from the rim of the flange. The mean δ 11B value for the flanged australite is very similar to that of Muong-Nong type tektites (-1.9 ± 1.9‰). Thus, vapor fractionation has been unimportant during tektite formation. This is supported by the observation that B contents and the δ 11B values of the different samples from the Australasian tektite strewn field are not correlated with each other. Most tektites show a rather limited range of δ 11B values (-9.3 ± 1.5 to +2.7 ± 1.5%o), which is small compared to the range observed for common terrestrial rocks (-30 to +40‰). The B abundance and isotopic data can be used to place constraints on the tektite source rocks. Australasian tektites have high B and Li abundances; only clay-rich sediments, such as pelagic and neritic sediments, as well as river and deltaic sediments have B contents (up to 100 ppm) and δ 11B values that are in agreement with the range shown by Australasian tektites (-4.9 to + 1.4‰). 10Be and RbSr data indicate continental crustal source rocks and exclude pelagic and neritic sediments. However, deltaic sediments, e.g., from the Mekong river, which are of continental crustal origin, agree with 10Be, RbSr, and B data, and support a possible source locality close to the coast of SE Indochina in the South China Sea. On the other hand, one bediasite sample has a very high δ 11B value of +15.1 ± 2.1‰, requiring the presence of marine

  4. Comparing investigations on the surface structures of irghizites and pyroclastics by SEM (United States)

    Heide, K.; Volksch, G.; Florenski, P. W.


    An electron microscope was used in an investigation which compared the surface structures of irghizites from the Zhamanshin crater in Kazachstan, USSR, with those of such typical tektites as australites and pyroclastics such as obsidians and lapilli. The results indicate no unambiguous genetic relationships between irghizite morphology and tektite and pyroclastic surface features. Irghizite surfaces instead result from simultaneous or successive processes in the course of which variously-dimensioned globules melted, fused and were eaten into by corrosive gases after solidification. The assumption that the verrucose glass globule swellings, which are identical in chemical composition to the glass bulk of the irghizites, were caused by expanding glass bubbles immediately below the glass bulk surface may be discounted.

  5. Lithium in tektites and impact glasses: Implications for sources, histories and large impacts (United States)

    Magna, T.; Deutsch, A.; Mezger, K.; Skála, R.; Seitz, H.-M.; Mizera, J.; Řanda, Z.; Adolph, L.


    Lithium (Li) abundances and isotope compositions were determined in a representative suite of tektites (moldavites, Muong Nong-type tektites and an australite, Ivory Coast tektites and bediasites), impact-related glasses (Libyan Desert Glass, zhamanshinites and irghizites), a glass fragment embedded in the suevite from the Ries impact crater and sedimentary materials in order to test a possible susceptibility of Li to fractionation during hypervelocity impact events and to de-convolve links to their potential parental sources. The overall data show a large spread in Li abundance (4.7-58 ppm Li) and δ 7Li values (-3.2‰ to 26.0‰) but individual groups of tektites and impact glasses have distinctive Li compositions. Most importantly, any significant high-temperature Li isotope fractionation can be excluded by comparing sedimentary lithologies from central Europe with moldavites. Instead, we suggest that Li isotope compositions in tektites and impact-related glasses are probably diagnostic of the precursor materials and their pre-impact geological histories. The Muong Nong-type tektites and australite specimen are identical in terms of Li concentrations and δ 7Li and we tentatively endorse their common origin in a single impact event. Evidence for low-temperature Rayleigh fractionation, which must have operated prior to impact-induced melting and solidification, is provided for a subset of Muong Nong-type tektites. Although Li isotope variations in most tektites are broadly similar to those of the upper continental crust, Libyan Desert Glass carries high δ 7Li ⩾24.7‰, which appears to mirror the previous fluvial history of parental material that was perhaps deposited in lacustrine environment or coastal seawater. Lithium isotopes in impact-related glasses from the Zhamanshin crater define a group distinct from all other samples and point to melting of chemically less evolved mafic lithologies, which is also consistent with their major and trace element

  6. Neodymium and strontium isotopic study of Australasian tektites - New constraints on the provenance and age of target materials (United States)

    Blum, Joel D.; Papanastassiou, D. A.; Wasserburg, G. J.; Koeberl, C.


    The Nd and Sr isotopic compositions of Australasian tectites (including two flanged Australian tectites, two low-SiO2 Muong Nong-type tectites, and three high-SiO2 Muong Nong-type tectites) and the Nd, Sm, Sr, and Rb concentrations were investigated by isotope-dilution thermal ionization mass spectrometry, and the Sm-Nd and Rb-Sr isotope systematics were used to study the characteristics of the parental material. It is shown that the Nd and Sr isotopic data provide evidence that all Australasian tektites were derived from a single sedimentary formation with a narrow range of stratigraphic ages close to 170 Ma. It is suggested that all of the Australasian tektites were derived from a single impact event and that the australites represent the upper part of a melt sheet ejected at high velocity, whereas the indochinites represent melts formed at a lower level in the target material distributed closer to the area of the impact.

  7. Tektite origin by hypervelocity asteroidal or cometary impact: The quest for the source craters (United States)

    Koeberl, Christian

    Tektites are natural glasses that are chemically homogeneous, often spherically symmetrical objects several centimeters in size, and occur in four known strewn fields on the surface of the Earth: the North American, moldavite (or Central European), Ivory Coast, and Australasian strewn fields. Tektites found within such strewn fields are related to each other with respect to their petrological, physical, and chemical properties as well as their age. A theory of tektite origin needs to explain the similarity of tektites in respect to age and certain aspects of isotopic and chemical composition within one strewn field, as well as the variety of tektite materials present in each strewn field. In addition to tektites on land, microtektites (which are generally less than 1 mm in diameter) have been found in deep-sea cores. Tektites are classified into three groups: (1) normal or splash-form tektites, (2) aerodynamically shaped tektites, and (3) Muong Nong-type tektites (sometimes also called layered tektites). The aerodynamic ablation results from partial remelting of glass during atmospheric passage after it was ejected outside the terrestrial atmosphere and quenched from a hot liquid. Aerodynamically shaped tektites are known mainly from the Australasian strewn field where they occur as flanged-button australites. The shapes of splash-form tektites (spheres, droplets, teardrops, dumbbells, etc., or fragments thereof) are the result of the solidification of rotating liquids in the air or vacuum. Mainly due to chemical studies, it is now commonly accepted that tektites are the product of melting and quenching of terrestrial rocks during hypervelocity impact on the Earth. The chemistry of tektites is in many respects identical to the composition of upper crustal material.