Clues as to the possible origin of tektites are found by studying the chemical composition, sites where they are found, and shapes. An important chemical fact of tektites is that they are extremel dry. Tektites lie in four major areas and in three isolated regions. They are distributed as if they fell from the skies. By studying the flanged shapes of the australites, it was concluded that their shape was due to a fast, hot trip through the atmosphere. Tektites show no cosmic ray tracks which implies their space exposure time was short. This rules out the possibility that they are a form of meteorite with these clues in mind, four theories on their possible origin are discussed in this paper. The theories are: (1) terrestial impact by meteorite or comet; (2) lunar impact; (3) terrestial volcanoes; and (4) lunar volcanoes. This article rules out the first three theories for reasons which are given and leans toward the fourth theory as the most probable of the four
O'Keefe, John A.
The origin of tektites has been obscure because of the following dilemma. The application of physical principles to the data available on tektites points strongly to origin from one or more lunar volcanoes; but few glasses of tektite composition have hitherto been reported from the lunar samples. Instead, the lunar silicic glasses consist chiefly of a material very rich in K2O and poor in MgO. The ratio of K2O/MgO is higher in these glasses than in any tektites reported. The solution of the dilemma seems to come from the study of some recently discovered terrestrial deposits of tektite glass with high values of K2O/MgO at the Cretaceous Tertiary boundary. These glasses are found to be very vulnerable to crystallization into sandine or to alteration to smectite. These end products are known and are more abundant than any terrestrial deposits of tektite glass. It seems possible that, in fact, the moon produces tektite glass, mostly of the high K2O-low MgO type; but on Earth these deposits are destroyed. The much less abundant deposits with lower K and higher Mg are observed because they survive. Other objections to the lunar origin hypothesis appear to be answerable.
OKeefe, J. A.
Tektites are probably extraterrestrial, rather than the result of heating some terrestrial materials, because they are a chemically homogeneous group with definite peculiarities (high silica, excess of alkaline earths over alkalis, excess of potash over soda, absence of water), and because some of them (the australites) appear to have undergone ablation in flight through the atmosphere. Since comparatively slow heating is required to explain the liquefaction of the tektite material, it is suggested that the tektites arrived along orbits which were nearly parallel to the surface of the earth, and which resulted from the decay of the orbit of a natural satellite. The great meteor procession of February 9, 1913, is an example of such an object. Comparison with the reentry phenomena of the artificial satellite 1957 Beta suggests that the 1913 shower consisted of a single large stone weighing about 400 kilograms, and a few dozen smaller bodies weighing about 40 grams each, formed by ablation from the larger body. It is shown that under the observed conditions considerable liquid flow would be expected in the stone, which would be heated to about 2100 K. Objects falling from such a shower near the perigee point of the orbit would have a considerable distribution along the orbit as a result of slight variations in height or drag coefficient. The distribution in longitude would be made wider by the turning of the earth under the orbit during the time of fall. The ultimate source of the body which produces a tektite shower is probably the moon, which appears, by virtue of its polarization and the phase distribution of the returned light, to contain high-silica materials. It is suggested that the Igast object alleged to have fallen in 1855 is in fact genuine and represents an unmelted portion of the lunar crust.
ShyamPrasad, M.; Mislankar, P.G.; Charan, S.N.; Prasad, K.
On the basis of various lines of evidence, tektites are now considered as glassy objects generated by meteorite impacts, distributed in four known strewn fields, of which, the Australasian tektite strewn field is the youngest (0.77 Ma...
Izokh, E. P.
As Fig. 1 shows, the widespread belief that the age of the Australasian tektite strewn field (AATSF) is ~0.7 m.y. appeared to be conventional. Tektites of different fission-track ages were found within the AATSF: 0.83 m.y. , 3.54-4.25 m.y. , and ~11 m.y. . The first systematic investigation of the tektites, which were collected from a single stratigraphic layer in Vietnam, revealed three statistically discrete tektite age groups: 0.4, 0.6, and 0.8 m.y. . Similar tektites 0.75 m.y. and 1.1 m.y. in age are typical of the Zhamanshin impact crater, which represents an eminent part of the AATSF . Fig. 1, which appears here in the hard copy, shows radiogenic dating: 1-2: AATSF; 3-4: Zhamanshin; 1,3: data with known annealing correction. Compiled after Zahringer, 1963; Fleischer and Price, 1964; Gentner et al., 1969; McDougal and Lovering, 1969; Fleischer et al., 1969; Storzer and Wagner, 1979, 1980; Watanabe et al., 1985; Virk, 1985; Shukolukov et al., 1986; Kashkarov et al, 1986, 1987; Kolesnikov et al., 1987; Storzer and Muller-Sonhius, 1986; Arakelyants et al., 1988; etc. The very young geological age of the AATSF was established in Australia, and was confirmed by the author in Vietnam and in the Zhamanshin impact crater. This well-known tektite age paradox strongly supports an extraterrestrial origin of tektites. The paradox is fatal to the currently dominating Earth- impact theory of tektite origin, and we are not surprised that there are no continued attempts to either silence or disavow its significance. As a matter of fact, the formation of the gigantic AATSF can be considered as the main reason for the abrupt catastrophic climatic global changes and mass extinction of species on the Pleistocene/Holocene boundary 10,000 years ago [5,6]. The age-paradox scope dictates that tektites have been periodically formed and accumulated somewhere on an as-yet-unknown planetary body and then delivered to the Earth. The extraterrestrial volcanic eruptions seem
Senftle, F. E.; Thorpe, A. N.; Grant, J. R.; Hildebrand, A.; Moholy-Nagy, H.; Evans, B. J.; May, L.
Certain glass nodules found at the archeological site at Tikal, Guatemala, have been considered as possible tektites. To test this possibility, magnetic studies have been made on three of the glass specimens. These specimens are similar to tektites, both visually and also because they contain very little Fe3+ as detected by Mössbauer spectroscopy. The magnetic Curie constants are similar in magnitude to those found for normal tektites but show some variation from point to point in the same specimen. This variation reflects an inhomogeneity in the iron concentration. The Fe2+ calculated from the Curie constants accounts for most of the iron. The temperature-independent component of the total dc magnetic susceptibility is several times higher than that found in tektites from other strewn fields. The high values can be explained if the glass contains metallic iron spherules with Fe in the parts per million range and/or a ferromagnetic component which does not saturate in a low magnetic field. The magnetic properties resemble those of Muong Nong type tektites and suggest that the Tikal glass specimens are tektites of the Muong Nong type.
Beran, Anton; Koeberl, Christian
To improve the scarce data base of water content in tektites and impact glasses, we analyzed 26 tektites from all four strewn fields and 25 impact glass samples for their water content. We used the fourier transformed IR (FTIR) spectrometry method, which permits measurement of areas of about 40 mm in diameter. Our results show that the tektites have water contents ranging from 0.002 to 0.030 wt% (average 0.014+/-0.008 wt%). Ivory Coast tektites have the lowest water abundances (0.002-0.003 wt%), and Muong Nong-type indochinites and some North American tektites having the highest contents (up to about 0.03 wt%). Impact glass samples (from the Zhamanshin, Aouelloul, and Rio Cuarto craters) yielded water contents of 0.008 to 0.13 wt% H2O. Typical impact glasses from the Aouelloul and Zhamanshin craters have low water contents (0.008 to 0.063 wt%). Libyan Desert Glasses and Rio Cuarto glasses have higher water contents (about 0.11 wt%). We also analyzed glasses of unknown origin (e.g., urengoites; glass fragments from Tikal), which showed very low water contents, in agreement with an origin by impact. Our data confirm that all tektites found on land have very low water contents (<0.03 wt% water), while impact glasses have slightly higher water contents. Both glass types are very dry compared to volcanic glasses. This study confirms that the low water contents (<0.05 wt%) of such glasses can be considered good evidence for an origin by impact.
Chao, E.C.T.; Adler, I.; Dwornik, E.J.; Littler, J.
Iron-nickel spherules, as much as 0.5 mm in diameter, have been found completely embedded in some philippinites. The spherules consist mainly of kamacite with unidentified pink inclusions. The meteoritic origin of these spherules seems reasonable, suggesting that the tektites containing them were formed by asteroidal or meteoritic impact.
Herzog, G. F.; O'D. Alexander, C. M.; Berger, E. L.; Delaney, J. S.; Glass, B. P.
We report electron microprobe determinations of the elemental compositions of 11 Australasian layered tektites and 28 Australasian microtektites; and ion microprobe determinations of the 41K/39K ratios of all 11 tektites and 13 of the microtektites. The elemental compositions agree well with literature values, although the average potassium concentrations measured here for microtektites, 1.1 1.6 wt%, are lower than published average values, 1.9 2.9 wt%. The potassium isotope abundances of the Australasian layered tektites vary little. The average value of δ41K, 0.02 ± 0.12‰ (1σ mean), is indistinguishable from the terrestrial value (= 0 by definition) as represented by our standard, thereby confirming four earlier tektite analyses of Humayun and Koeberl (2004). In agreement with those authors, we conclude that evaporation has significantly altered neither the isotopic nor the elemental composition of Australasian layered tektites for elements less volatile than potassium. Although the average 41K/39K ratio of the microtektites, 1.1 ± 1.7‰ (1σ mean), is also statistically indistinguishable from the value for the standard, the individual ratios vary over a very large range, from -10.6 ± 1.4‰ to +13.8 ± 1.5‰ and at least three of them are significantly different from zero. We interpret these larger variations in terms of the evaporation of isotopically light potassium; condensation of potassium in the vapor plume; partial or complete stirring and quenching of the melts; and the possible uptake of potassium from seawater. That the average 41K/39K ratio of the microtektites equals the terrestrial value suggests that the microtektite-forming system was compositionally closed with respect to potassium and less volatile elements. The possibility remains open that 41K/39K ratios of microtektites vary systematically with location in the strewn field.
Khaweerat, Sasiphan; Tangpitayakul, Pisarn; Pimjun, Surapong; Chongkum, Somporn; Sangsuriya, Sineenart; Wiseatsri, Pojanee
The discoveries of suspicious meteorite or tektite around Chaiyapum province and surrounding area were sent to Physics Division, Office of Atoms for Peace (OAP). Fourteen samples were analyzed by 3 nuclear techniques; the measurement of natural radiation, x-ray fluorescence analysis and neutron activation analysis. The result shows that the samples can be classified according to the level of natural radiation, the elemental composition and there quantity
O'Keefe, John A.
It is shown that the enhanced abundance of siderophile elements and chromium in tektite-like glasses from the two impact craters of Zhamanshin and Aouelloul cannot be explained as a result of contamination of the country rock by meteorites nor, probably, comets. The pattern is, however, like that found in certain Australasian tektites, and in Ivory Coast tektites. It is concluded, in agreement with earlier suggestions by Campbell-Smith and Hey, that these craters were formed by the impact of large masses of tektite-like glass, of which the glasses which were studied are fragments. It follows that it is necessary, in considering an impact crater, to bear in mind that the projectile may have been a glass.
WANG Wei; MO JinYou; HUANG ZhiTao
This paper reports the recent discovery of 176 stone artifacts, including two handaxes (bifacial large cutting tools), which are preserved in the laterized sediments of terrace 4 of the Youjiang River at the Nanbanshan locality of the Damei site in the Bose basin, south China. Their characteristics are similar to Paleolithic stone artifacts discovered from other sites in this basin. The handaxes, picks and other stone artifacts are associated with 155 tektite pieces found in the same horizontal layer. These fresh, unabraded and sharp-edged tektites were buried immediately after the airfall event. This provides fur-ther evidence that the Bose stone artifacts and the tektites were deposited simultaneously around 0.8 Ma. More stone artifacts were also unearthed above the tektite layer, indicating that early humans in the area survived the event.
Walter, Louis S.; Carron, M.K.
The total vapor pressure of Philippine tektite melts of approximately 70 per cent silica has been determined at temperatures ranging from 1500 to 2100??C. This pressure is 190 ?? 40 mm Hg at 1500??C, 450 ?? 50 mm at 1800??C and 850 ?? 70 mm at 2100?? C. Determinations were made by visually observing the temperature at which bubbles began to form at a constant low ambient pressure. By varying the ambient pressure, a boiling point curve was constructed. This curve differs from the equilibrium vapor pressure curve due to surface tension effects. This difference was evaluated by determining the equilibrium bubble size in the melt and calculating the pressure due to surface tension, assuming the latter to be 380 dyn/cm. The relative volatility from tektite melts of the oxides of Na, K, Fe, Al and Si has been determined as a function of temperature, total pressure arid roughly, of oxygen fugacity. The volatility of SiO2 is decreased and that of Na2O and K2O is increased in an oxygen-poor environment. Preliminary results indicate that volatilization at 2100??C under atmospheric pressure caused little or no change in the percentage Na2O and K2O. The ratio Fe3 Fe2 of the tektite is increased in ambient air at a pressure of 9 ?? 10-4 mm Hg (= 106.5 atm O2, partial pressure) at 2000??C. This suggests that tektites were formed either at lower oxygen pressures or that they are a product of incomplete oxidation of parent material with a still lower ferricferrous ratio. ?? 1964.
Mizera, Jiří; Řanda, Zdeněk; Kameník, Jan
Roč. 154, MAR (2016), s. 123-137 ISSN 0012-8252 R&D Projects: GA ČR GA13-22351S; GA MŠk(CZ) LM2011019 Institutional support: RVO:67985891 ; RVO:61389005 Keywords : Australasian tektite * Parent crater * Geochemical analysis * Isotope analysis * Chinese loess * Badain Jaran Subject RIV: BG - Nuclear, Atomic and Molecular Physics, Colliders; DD - Geochemistry (USMH-B) Impact factor: 7.051, year: 2016
Magna, T.; Deutsch, A.; Mezger, K.; Skála, Roman; Seitz, H.-M.; Mizera, Jiří; Řanda, Zdeněk
Roč. 75, č. 8 (2011), s. 2137-2158 ISSN 0016-7037 R&D Projects: GA ČR GA205/09/0991 Institutional research plan: CEZ:AV0Z30130516; CEZ:AV0Z10480505 Keywords : crater * glass * isotopic composition * isotopic fractionation * lithium * lithology * mafic rock * moldavite * suevite * tektite * trace element Subject RIV: DD - Geochemistry Impact factor: 4.259, year: 2011
Nowlis, D. P.
Because it is widely agreed that the field of environmental psychology is quite young, it was determined that a sample of recorded observations from a representative mission should be included in the report on Tektite to give the professional reader a better feeling of normal day-to-day life in the isolated habitat. Names of the crew members have been replaced with numbers and some off-color words have been replaced by more acceptable slang; some remarks have been omitted that might lead to easy identification of the subjects. Otherwise, the following pages are exactly as transcribed during the late afternoons and the evenings of the mission.
Rodovská, Z.; Magna, T.; Žák, Karel; Skála, Roman; Brachaniec, T.; Visscher, Ch.
Roč. 51, č. 12 (2016), s. 2403-2415 ISSN 1086-9379 R&D Projects: GA ČR GA13-22351S Institutional support: RVO:67985831 Keywords : tektites * Ries sediments * Li Subject RIV: DB - Geology ; Mineralogy Impact factor: 2.391, year: 2016
Thorpe, A. N.; Senftle, F. E.; May, L.; Barkatt, A.; Adel-Hadadi, M. A.; Marbury, G. S.; Izett, G. A.; Maurrasse, F. R.
The magnetic properties of black Beloc glass have been measured. The Curie constant, the magnetization, and the magnetic susceptibility of the Beloc glass fall within the known ranges observed for tektites. However, the temperature-independent component of the magnetic susceptibility is slightly higher than that found for tektites. Moreover, it is not possible to match the experimental magnetic data for the Beloc glass with the calculated values using the previously reported Fe(3+)/Fe(2+) ratio of 0.7. The oxidation state of Fe was therefore redetermined by Mossbauer measurements, and the Fe(3+)/Fe(2+) ratio was found to be 0.024 plus or minus 0.015. Using the redetermined value of the ratio, the magnetic parameters were again calculated using formulas that are applicable to tektites, and good agreement was found between the calculated and experimental values. The experimental magnetic measurements and the redetermined Fe(3+)/Fe(2+) ratio of the Beloc glass specimens are essentially the same as those found for tektite glass.
Wang, Kai-Tuo; Tang, Qing; Cui, Xue-Min; He, Yan; Liu, Le-Ping
The environment on the lunar surface poses some difficult challenges to building long-term lunar bases; therefore, scientists and engineers have proposed the creation of habitats using lunar building materials. These materials must meet the following conditions: be resistant to severe lunar temperature cycles, be stable in a vacuum environment, have minimal water requirements, and be sourced from local Moon materials. Therefore, the preparation of lunar building materials that use lunar resources is preferred. Here, we present a potential lunar cement material that was fabricated using tektite powder and a sodium hydroxide activator and is based on geopolymer technology. Geopolymer materials have the following properties: approximately zero water consumption, resistance to high- and low-temperature cycling, vacuum stability and good mechanical properties. Although the tektite powder is not equivalent to lunar soil, we speculate that the alkali activated activity of lunar soil will be higher than that of tektite because of its low Si/Al composition ratio. This assumption is based on the tektite geopolymerization research and associated references. In summary, this study provides a feasible approach for developing lunar cement materials using a possible water recycling system based on geopolymer technology.
Mizera, Jiří; Řanda, Zdeněk
Roč. 9, č. 1 (2013), s. 150-150 ISSN 1336-7242. [65. zjazd chemikov. 09.09.2013-13.09.2013, Tatranské Matliare] R&D Projects: GA ČR GA205/09/0991; GA ČR GA13-22351S Institutional support: RVO:61389005 Keywords : tektite * impact glass * moldavite * irghizite * Australasian tektite * activation analysis Subject RIV: BG - Nuclear, Atomic and Molecular Physics, Colliders
Koeberl, C.; Kluger, F.; Kiesl, W.
Elemental ratios constitute an important geochemical tool for the evaluation of genetic correlations between different materials. We have investigated the behaviour of several trace element ratios and their correlations in some terrestrial impact glasses (tektites and impactites from the Australasian and moldavite strewn field, a Darwin glass sample and material from Zhamanshin and Aouelloul impact crater). Some well known geochemical pairs are discussed: K/Sc, K/Rb, K/Zr, K/Cs, K/Ba, K/U, Ti/Zr, Cr/Ni, Rb/Zr, Ba/Rb, Ba/Zr, La/Yb and Th/Sm. Correlation coefficients for some of the pairs have also been calculated. In all these pairs we see a clear distinction between different bodies of the solar system, which is due to the different stages of differentiation of the respective bodies, since the elements discussed here behave differently in various geochemical processes. (author)
Graham, D. G.; Muenow, D. W.; Gibson, E. K., Jr.
Mass pyrograms obtained from high-temperature, mass psectrometric pyrolysis of a glassy theoleiitic submarine basalt and a tektite, ground in air to less than 64 microns, have shown N2 and SO release patterns very similar to those from the pyrolysis of mature lunar soil fines. The N2 and CO release behavior from the terrestrial samples reproduces the biomodal, high-temperature (approximately 700 and 1050 C) features from the lunar samples. Unground portions of the basalt and tektite show no release of N2 and CO during pyrolysis. Grinding also alters the release behavior and absolute amounts of H2O and CO2. It is suggested that adsorption of atmospheric gases in addition to solar wind implantation of ions may account for the wide range of values in previously reported concentrations of carbon and nitrogen from lunar fines.
Ackerman, Lukáš; Magna, T.; Žák, Karel; Skála, Roman; Jonášová, Šárka; Mizera, Jiří; Řanda, Zdeněk
Roč. 210, 1 August (2017), s. 59-70 ISSN 0016-7037 R&D Projects: GA ČR GA13-22351S; GA MŠk LM2015056 Institutional support: RVO:67985831 ; RVO:61389005 Keywords : highly siderophile elements * meteoritic component * Osmium isotopes * Ries impact structure * tektite Subject RIV: DB - Geology ; Mineralogy; CB - Analytical Chemistry, Separation (UJF-V) OBOR OECD: Geology; Analytical chemistry (UJF-V) Impact factor: 4.609, year: 2016
Rodovská, Z.; Magna, T.; Žák, Karel; Kato, C.; Savage, P. S.; Moynier, F.; Skála, Roman; Ježek, J.
Roč. 52, č. 10 (2017), s. 2178-2192 ISSN 1086-9379 R&D Projects: GA ČR GA13-22351S Institutional support: RVO:67985831 Keywords : moldavites * tektites * Ries impact structure Subject RIV: DB - Geology ; Mineralogy OBOR OECD: Geology Impact factor: 2.391, year: 2016
Skála, Roman; Jonášová, Šárka; Žák, Karel; Ďurišová, Jana; Brachaniec, T.; Magna, T.
Roč. 66, č. 2 (2016), s. 171-191 ISSN 1802-6222 R&D Projects: GA ČR GA13-22351S Institutional support: RVO:67985831 Keywords : moldavites * tektites * Lower Silesia * Lower Silesia * Poland * Ries impact structure * geochemistry Subject RIV: DB - Geology ; Mineralogy Impact factor: 0.609, year: 2016
Smit, J.; Montanari, A.; Swinburne, N. H.; Alvarez, W.; Hildebrand, A. R.; Margolis, S. V.; Claeys, P.; Lowrie, W.; Asaro, F.
The hypothesis of Cretaceous-Tertiary (K-T) boundary impact on Yucatan, Mexico, predicts that nearby sites should show evidence of proximal impact ejecta and disturbance by giant waves. An outcrop along the Arroyo el Mimbral in northeastern Mexico contains a layered clastic unit up to 3 m thick that interrupts a biostratigraphically complete pelagic-marl sequence deposited at more than 400 m water depth. The marls were found to be unsuitable for determining magnetostratigraphy, but foraminiferal biostratigraphy places the clastic unit precisely at the K-T boundary. We interpret this clastic unit as the deposit of a megawave or tsunami produced by an extraterrestrial impact. The clastic unit comprises three main subunits. (1) The basal "spherule bed" contains glass in the form of tektites and microtektites, glass spherules replaced by chlorite-smectite and calcite, and quartz grains showing probable shock features. This bed is interpreted as a channelized deposit of proximal ejecta. (2) A set of lenticular, massive, graded "laminated beds" contains intraclasts and abundant plant debris, and may be the result of megawave backwash that carried coarse debris from shallow parts of the continental margin into deeper water. (3) At the top, several thin "ripple beds" composed of fine sand are separated by clay drapes; they are interpreted as deposits of oscillating currents, perhaps a seiche. An iridium anomaly (921 +/- 23 pg/g) is observed at the top of the ripple beds. Our observations at the Mimbral locality support the hypothesis of a K-T impact on nearby Yucatan.
ShyamPrasad, M.; Rao, P.S.
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Rodovská, Zuzana; Magna, TomáÅ.¡; Žák, Karel; Kato, Chizu; Savage, Paul S.; Moynier, Frédéric; Skála, Roman; Ježek, Josef
Moldavites are tektites genetically related to the Ries impact structure, located in Central Europe, but the source materials and the processes related to the chemical fractionation of moldavites are not fully constrained. To further understand moldavite genesis, the Cu and Zn abundances and isotope compositions were measured in a suite of tektites from four different substrewn fields (South Bohemia, Moravia, Cheb Basin, Lusatia) and chemically diverse sediments from the surroundings of the Ries impact structure. Moldavites are slightly depleted in Zn ( 10-20%) and distinctly depleted in Cu (>90%) relative to supposed sedimentary precursors. Moreover, the moldavites show a wide range in δ66Zn values between 1.7 and 3.7‰ (relative to JMC 3-0749 Lyon) and δ65Cu values between 1.6 and 12.5‰ (relative to NIST SRM 976) and are thus enriched in heavy isotopes relative to their possible parent sedimentary sources (δ66Zn = -0.07 to +0.64‰; δ65Cu = -0.4 to +0.7‰). In particular, the Cheb Basin moldavites show some of the highest δ65Cu values (up to 12.5‰) ever observed in natural samples. The relative magnitude of isotope fractionation for Cu and Zn seen here is opposite to oxygen-poor environments such as the Moon where Zn is significantly more isotopically fractionated than Cu. One possibility is that monovalent Cu diffuses faster than divalent Zn in the reduced melt and diffusion will not affect the extent of Zn isotope fractionation. These observations imply that the capability of forming a redox environment may aid in volatilizing some elements, accompanied by isotope fractionation, during the impact process. The greater extent of elemental depletion, coupled with isotope fractionation of more refractory Cu relative to Zn, may also hinge on the presence of carbonyl species of transition metals and electromagnetic charge, which could exist in the impact-induced high-velocity jet of vapor and melts.
Glass, B.P.; Chapman, D.R.; ShyamPrasad, M.
stream_size 100 stream_content_type text/plain stream_name Meteor_Planet_Sci_31_365.pdf.txt stream_source_info Meteor_Planet_Sci_31_365.pdf.txt Content-Encoding ISO-8859-1 Content-Type text/plain; charset=ISO-8859-1 1996...
Mizera, Jiří; Řanda, Zdeněk; Kameník, Jan; Klokočník, Jaroslav; Kostelecký, J.
Roč. 51, AUG (2016), A467-A467 ISSN 1086-9379. [79th Annual Meeting of the Meteoritical-Society. 07.08.2016-12.08.2016, Berlin] R&D Projects: GA ČR GA13-22351S; GA MŠk LM2015056 Institutional support: RVO:61389005 ; RVO:67985815 Keywords : ATT * Indochina * crater Subject RIV: DD - Geochemistry; BN - Astronomy, Celestial Mechanics, Astrophysics (ASU-R)
Žák, Karel; Skála, Roman; Řanda, Zdeněk; Mizera, Jiří
Roč. 47, č. 6 (2012), s. 1010-1028 ISSN 1086-9379 R&D Projects: GA ČR GA205/09/0991 Institutional research plan: CEZ:AV0Z30130516; CEZ:AV0Z10480505 Keywords : moldavites * geochemistry * ries * carbon stable isotopes * moldavites (Germany) Subject RIV: DD - Geochemistry Impact factor: 2.800, year: 2012
ShyamPrasad, M.; Sudhakar, M.
and the microtektites are found to have similar major element compositions conforming to the Australasian tektite/microtektite chemistry. Earlier studies based on isotopic evidence, dating, and chemistry had provided evidence of a single large tektite strewn field...
Rivera, Tiffany; Storey, Michael; Palike, Heiko
Recent high-resolution δ18O records from North Atlantic (I)ODP cores, with reliable paleomagnetic signals, have placed the mean age of the Matuyama-Brunhes (MB) geomagnetic polarity reversal ca. 8 ka younger than previous estimates when correlated to ice-volume age models (Channell et al., 2010...... with sedimentation rates determined through drill core analysis, we approach the MB boundary from both sides to arrive at a boundary age that is consistent with independent astronomical ages proposed for the polarity transition. This novel approach provides a best-fit age for the MB boundary that incorporates radio......-isotopic dating, astrochronologies, and sedimentation rates. The research leading to these results has received funding from the European Community's Seventh Framework Programme [FP7/2007-2013] under grant agreement no. 215458....
ShyamPrasad, M.; Gupta, S.M.; Kodagali, V.N.
34:369–384.Storzer D. and Wagner G. A. 1980. Two discrete tektite formingevents 140,000 years apart in the Australian-Southeast Asian area (abstract). Meteoritics 15:372.Storzer D., Jessberger E. K., Klay N., and Wagner G. A. 1984. 40Ar/39Ar... evidence for 2 discrete tektite-forming events in theAustralian-Southeast Asian area (abstract). Meteoritics 19:317. Schnetzler C. C. and Pinson W. H., Jr. 1963. The chemical composition of tektites. In Tektites, edited by O’Keefe J. A...
Bunch, T. E.; Hermes, R. E.; Moore, A. M. T.; Kennett, D. J.; Weaver, J. C.; Wittke, J. H.; DeCarli, P. S.; Bischoff, J. L.; Hillman, G. C.; Howard, G. A.; Kimbel, D. R.; Kletetschka, Günther; Lipo, C. P.; Sakai, S.; Revay, Z.; West, A.; Firestone, R. B.; Kennett, J. P.
Roč. 109, č. 28 (2012), E1903-E1912 ISSN 0027-8424 Institutional support: RVO:67985831 Keywords : tektite * miocrocraters * oxygen fugacity * trinitite Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 9.737, year: 2012
Wittke, J. H.; Weaver, J. C.; Bunch, T. E.; Kennett, J. P.; Kennett, D. J.; Moore, A. M. T.; Hillman, G. C.; Tankersley, K. B.; Goodyear, A. C.; Moore, Ch. R.; Daniel Jr., I. R.; Ray, J. H.; Lopinot, N. H.; Ferraro, D.; Israde-Alcántara, I.; Bischoff, J. L.; DeCarli, P. S.; Hermes, R. E.; Kloosterman, J. B.; Revay, Z.; Howard, G. A.; Kimbel, D. R.; Kletetschka, G.; Nábělek, Ladislav; Lipo, C. P.; Sakai, S.; West, A.; Firestone, R. B.
Roč. 110, č. 23 (2013), E2088-E2097 ISSN 0027-8424 Institutional support: RVO:67985831 Keywords : Clovis-Folsom * lechatelierite * tektite * wildfires Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 9.809, year: 2013
King, E. A.
The suggestion of O'Keefe (1980) that the terminal Eocene event was caused by rings of tektite material encircling the earth is discussed. It is argued that the assumption that the tektites are of lunar volcanic origin is unwarranted and contrary to existing data, including the lack of lunar rocks of suitable composition, the lack of lunar rocks of the correct age, the lack of evidence that the North American tektites fell throughout a sedimentary rock column of a few million years, and the nondetection of a tektite with a measurable cosmic ray exposure age. Alternatively, it is suggested that the terminal Eocene event may be associated with volcanic ash, air-fall tuff and bentonite in the late Eocene. O'Keefe replies that the hypothesis of the terrestrial origin of the tektites conflicts with the laws of physics, for example in the glass structure and shaping of the tektites. Furthermore, evidence is cited for lunar rocks of the proper major-element composition and ages, and it is noted that the proposed solar Poynting-Robertson effect would account for the particle fall distributions and cosmic ray ages.
Macris, C. A.; Young, E. D.; Kohl, I. E.; zur Loye, T. E.
Tektites are natural glasses formed as quenched impact melt ejecta. Because they experienced extreme heating while entrained in a hot impact vapor plume, tektites allow insight into the nature of these ephemeral events, which play a critical role in planetary accretion and evolution. During tektite formation, the chemical and isotopic composition of parent materials may be modified by (1) vapor/liquid fractionation at high T in the plume, (2) incorporation of meteoric water at the target site, (3) isotope exchange with atmospheric oxygen (if present), or some combination of the three. Trends from O isotope studies reveal a dichotomy: some tektite δ18O values are 4.0-4.5‰ lower than their protoliths (Luft et al. 1987; Taylor & Epstein 1962), opposite in direction to a vaporization induced fractionation; increases in δ18O with decreasing SiO2 in tektites (Taylor & Epstein 1969) is consistent with vapor fractionation. Using an aerodynamic levitation laser furnace (e.g. Macris et al. 2016), we can experimentally determine the contributions of processes (1), (2) and (3) above to tektite compositions. We conducted a series of evaporation experiments to test process (1) using powdered tektite fused into 2 mm spheres and heated to 2423-2473 K for 50-90 s while levitated in Ar in the furnace. Mass losses were from 23 to 26%, reflecting evaporation of Si and O from the melt. The starting tektite had a δ18O value of 10.06‰ (±0.01 2se) and the residues ranged from 13.136‰ (±0.006) for the least evaporated residue to 14.30‰ (±0.02) for the most evaporated (measured by laser fluorination). The increase in δ18O with increasing mass loss is consistent with Rayleigh fractionation during evaporation, supporting the idea that O isotopes are fractionated due to vaporization at high T in an impact plume. Because atmospheric O2 and water each have distinctive Δ17O values, we should be able to use departures from our measured three-isotope fractionation law to evaluate
Lo, Ching-Hua; Howard, Kieren T.; Chung, Sun-Lin; Meffre, Sebastien
Three samples of Darwin Glass, an impact glass found in Tasmania, Australia at the edge of the Australasian tektite strewn field were dated using the 40Ar/39Ar single-grain laser fusion technique, yielding isochron ages of 796-815 ka with an overall weighted mean of 816 ± 7 ka. These data are statistically indistinguishable from those recently reported for the Australasian tektites from Southeast Asia and Australia (761-816 ka; with a mean weighted age of 803 ± 3 ka). However, considering the compositional and textural differences and the disparity from the presumed impact crater area for Australasian tektites, Darwin Glass is more likely to have resulted from a distinct impact during the same period of time.
A Czechoslovakian tektite or moldavite shows clear, indirect evidence of aerodynamic ablation. This large tektite has the shape of a teardrop, with a strongly convex, deeply corroded, but clearly identifiable front and a planoconvex, relatively smooth, posterior surface. In spite of much erosion and corrosion, demarcation of the posterior and the anterior part of the specimen (the keel) is clearly preserved locally. This specimen provides the first tangible evidence that moldavites entered the atmosphere cold, probably at a velocity exceeding 5 kilometers per second; the result was selective heating of the anterior face and perhaps ablation during the second melting. This provides evidence of the extraterrestial origin of moldavites.
Senftle, F. E.; Thorpe, A. N.; May, L.; Barkatt, A.; Adel-Hadadi, M. A.; Marbury, G. S.; Izett, G.; Sigurdsson, H.; Maurasse, F. J.-M. R.
The experimental magnetic susceptibility, the temperature-independent component of the magnetic susceptibility, the magnetization, and the Curie constant have been measured for a number of specimens of glass from the K-T boundary found at Beloc, Haiti, and the results are compared with those of similar measurements of tektites. Because the Fe(3+)/Fe(2+) ratio is needed to calculate the magnetic parameters, Moessbauer spectroscopic measurements were also made. The data were consistent with the classification of the Beloc glasses as tektites.
Skála, Roman; Jonášová, Šárka; Žák, Karel; Ďurišová, Jana; Brachaniec, T.; Magna, T.
Roč. 51, SI, Supplement 1 (2016), A581-A581 ISSN 1086-9379. [Annual Meeting of the Meteoritical Society /79./. 07.08.2016-12.08.2016, Berlin] Institutional support: RVO:67985831 Keywords : moldavites * tektites * Lower Silesia, Poland * Ries impact structure * geochemistry Subject RIV: DD - Geochemistry
Pratesi, G.; Caporali, S.; Loglio, F.; Giuli, G.; Dziková, L.; Skála, Roman
Roč. 7, č. 4 (2014), s. 3319-3336 ISSN 1996-1944 R&D Projects: GA ČR GA205/09/0991 Institutional support: RVO:67985831 Keywords : tomography * tektites * moldavites * Muong Nong * plastic deformation Subject RIV: DB - Geology ; Mineralogy Impact factor: 2.651, year: 2014
O'Keefe, J. A., III
Supporting evidence for the fission hypothesis for the origin of the moon is offered. The maximum allowable amount of free iron now present in the moon would not suffice to extract the siderophiles from the lunar silicates with the observed efficiency. Hence extraction must have been done with a larger amount of iron, as in the mantle of the earth, of which the moon was once a part, according to the fission hypothesis. The fission hypothesis gives a good resolution of the tektite paradox. Tektites are chemically much like products of the mantle of the earth; but no physically possible way has been found to explain their production from the earth itself. Perhaps they are a product of late, deep-seated lunar volcanism. If so, the moon must have inside it some material with a strong resemblance to the earth's mantle.
Carling, Paul; Songtham, Wickanet; Tada, Riuji; Tada, Toshihiro; Duangkrayon, Jaa
Effects of meteoroid impacts on terrestrial geology primarily have been considered with respect of proximal effects near the impact location; such as cratering, fracturing and melt. However, other than the use of rare elements (iridium) as event markers and tektite chemistry for dating control, distal effects of impacts are less-well documented. Distal effects might include: fireball, air blast, heat, water vaporization, catastrophic flooding, earthquakes, ejecta fallout (tektites & dust), large quantities of N2O from shock heating of the atmosphere, release of CO2 and sulphur aerosols causing heating or cooling of atmosphere, IR radiation causing vegetation fires, smoke and pyrotoxins, and altered native rock geochemistry. Such processes may affect the distal surface geology, degrade vegetation cover and cause extirpation of flora and fauna. Quaternary sedimentary sections have been examined in northern and central Cambodia, in southern China and in north-east Thailand. These locality lie within the Australian strewn tektite field ̶ reliably dated to 0.77-0.78Ma BP ̶ just before the 0.80Ma BP Brunhes/Matayama reversal. The location of the primary impact crater (if any) is uncertain but a local major crater probably lies within central Laos or just offshore to the east. The described sections are considered distal from the main impact. Stratigraphic evidence indicates a temporal sequence of catastrophic stripping of alluvial-gravel surfaces followed by catastrophic redistribution of gravel (incorporating tektites), followed by deposition of atmospheric dust. Grain-size and grain-density trends, XRD, spherule distributions, luminescence profiles, tektite, and microtektite and shock quartz assay, are used to with the stratigraphic evidence to examine an hypothesis that the sections represent the distal effects of a meteorite. Additional insight is gained with respect to prior claims that large accumulations of woody debris in Thai Quaternary river terraces were due
Carey, S.; Sigurdsson, H.; Dhondt, S.; Espindola, J. M.
The K/T boundary sequence is exposed in uplifted carbonate sediments of the southwest peninsula of Haiti. It is found at 15 localities within the Beloc formation, a sequence of limestone and marls interpreted as a monoclinal nappe structure thrust to the north. This tectonic deformation has affected the K/T boundary deposit to varying degrees. In some cases the less competent K/T deposit has acted as a slip plane leading to extensive shearing of the boundary layer, as well as duplication of the section. The presence of glassy tektites, shocked quartz, and an Ir anomaly directly link the deposit to a bolide impact. Stratigraphic and sedimentological features of the tripartite sequence indicate that it was formed by deposition from ballistic fallout of coarse tektites, emplacement of particle gravity flows and fine grained fallout of widely dispersed impact ejecta.
Thorpe, A. N.; Sullivan, S.; Alexander, C. C.; Senftle, F. E.; Dwornik, E. J.
Magnetic susceptibility of 11 glass spherules from the Apollo 14 lunar fines have been measured from room temperature to 4 K. Data taken at room temperature, 77 K, and 4.2 K, show that the soft saturation magnetization was temperature independent. In the temperature range 300 to 77 K the temperature-dependent component of the magnetic susceptibility obeys the Curie law. Susceptibility measurements on these same specimens and in addition 14 similar spherules from the Apollo 11 and 12 mission show a Curie-Weiss relation at temperatures less than 77 K with a Weiss temperature of 3-7 degrees in contrast to 2-3 degrees found for tektites and synthetic glasses of tektite composition. A proposed model and a theoretical expression closely predict the variation of the susceptibility of the glass spherules with temperature.
estimates of the total abundance of cosmic dust and also quantitative estimates of the flux of stony spherules on earth. Brownlee et al. (1975) and Blanchard and Davis (1978) simulated atmospheric entry conditions on natural and artificial analogs... obliterated/masked these important events in the earth’s history. 89 References Barnes V.E. (1989), Origin of tektites, Texas J. of Sci.,41, 5-33. Blanchard M.B. and Cunningham G. (1974) Artificial meteor ablation studies - olivine. J. Geophys...
study for two reasons: (i) Both materials are compositionally high in SiO2 and (ii) form similarly to glass formed by a nuclear explosion, which...creates massive pressures and temperatures. As an example, trinitite is a glass formed by a post-nuclear event with SiO2 making up 50%-75% of its...processing, characterization, obsidian, tektite, natural glass 15. NUMBER OF PAGES 89 16. PRICE CODE 17. SECURITY CLASSIFICATION OF REPORT
Okeefe, J. A.
It is suggested that the formation of a ring system about the earth by particles and debris related to the North American strewn tektite field is responsible for the terminal Eocene event of 34 million years ago, in which severe climatic changes accompanied by widespread biological extinctions occurred. Botanical data is cited which implies a 20-C decrease in winter temperature with no change in summer temperature, and evidence of the correlation of the North American tektite fall, which is estimated to have a total mass of 10 to the 9th to 10 to the 10th tons, with the disappearance of five of the most abundant species of radiolaria is presented. The possible connection between the tektites and climatic change is argued to result from the screening of sunlight by an equatorial ring of trapped particles of extraterrestrial origin in geocentric orbit which would cut off sunlight only in the winter months. Such a ring, located at a distance of between 1.5 and 2.5 earth radii (the Roche limit) is estimated to have a lifetime of a few million years.
Harris, T. H. S.; Davais, M. E.
Several elements of the 786 ka Australasian (AA) tektite imprint bear close scrutinyin order to locate the parent impact site or structure. The unique Carolina bays unit geologic formation is indicated as a large "medial" ejecta blanket from a large cosmic impact during a period containing 786 ka. Coincidence? Kg-scale sub-spherical hollow splash form AA tektites implies prolonged atmospheric blow out-scale momentum current with a core of sub-parallel or divergent flow volume having essentially zero turbulence. This would allow for plasma entrainment and heating of target mass at prolonged low dynamic pressure during outflow, where adiabatic expansion could deliver both semi-solid Muong Nong-type and inviscid melts above the atmosphere for gentle release upon rarefaction in vacuum. Within a large atmospheric blow-out scale momentum current, target mass becomes entrained at the speed of adiabatic outflow. 10+ km/s ejecta entrainment yields inter-hemispheric emplacement from launch per governing suborbital mechanics, without question. Oblique impact into a thick ice sheet explains reduced excavation volume and shearing disruption in the form of hypersonic steam plasma scouring. Adiabatic expansion would be immediately available to accelerate and further heat proto-tektite target mass. With shock no longer the sole transport engine, kg-scale splash forms and tektite speeds above the post-shock vaporization velocity of quartz are explained by expansion of shocked ice, in agreement with the observed imprint. The 6 Carolina bay shapes or "Davias Archetypes" are reproducible using conic perturbation in Suborbital Analysis, conforming to a formative mechanism of suborbital transport and ballistic emplacement: "Suborbital Obstruction Shadowing" needs only 3 parts in 10,000 of VEL variation around a circular EL-AZ-VEL launch cone, before considering re-entry effects. Transport energy of the Carolina bay sand, calculated using the 3.5 to 4 km/s launch VEL required for its
Randa, Z.; Benada, J.; Kuncir, J.; Vobecky, M.
A description is presented of sampling, calibration standards, the method of activation and measurement, activation product identification, the respective nuclear reactions, interfering admixtures, and pre-activation operations. The analysis is described of sulphides, halogenides, oxides, sulphates, carbonates, phosphates, silicates, aluminosilicates, composite minerals containing lanthanides, rocks, tektites, meteors, and plant materials. The method allows determining mainly F, Mg, Al, Ti, V, Nb, Rh, and I which cannot be determined by long-term activation (LTA). It is more sensitive than LTA in determining Ca, Cu, In, and Dy. The analysis takes less time, irradiation and measurement are less costly. The main mineral components are quickly found. (M.K.)
Komarov, A.N.; Krylov, A.Ya.
The method is described of the determination of the thermostability of tracks applied to oceanic basalts and the comparison is carried out of age values obtained for the same samples by the track method and by the potassium-argon method. The obtained results allow to consider that the track method is quite practicable for the dating of oceanic basalts on the condition that natural annealing of a part of tracks of the spontaneous uranium fission is taken into accout. For glasses of the other origin - tektites - such approach results in the agreement of the obtained values with the results of potassium-argon method
Iunes, P.J.; Bigazzi, G.; Hadler Neto, J.C.; Laurenzi, M.A.; Balestrieri, M.L.; Norelli, P.; Osorio Araya, A.M.; Guedes, S.; Tello S, C.A.; Paulo, S.R.; Moreira, P.A.F.P.; Palissari, R.; Curvo, E.A.C.
Neutron dosimetry based on U and Th thin films was used for fission-track dating of the age standard Moldavite, the central European tektite, from the Middle Miocene deposit of Jankov (southern Bohemia, Czech Republic). Our fission-track age (13.98+/-0.58Ma) agrees with a recent 40 Ar/ 39 Ar age, 14.34+/-0.04Ma, based on several determinations on Moldavites from different sediments, including the Jankov deposit. This result indicates that the U and Th thin film neutron dosimetry represents a reliable alternative for an absolute approach in fission-track dating
use a "plucking" process rather than a pruning " process with our established projects. In this way, the im- portant projects will be accomplished in...Enger, CEC, USN, Commander, NAVFAC 1000-1015 "Ocean Engineering Capt. W.A. Walls Policies" 1015-1030 Coffee Break 1030-1045 Conference Objectives Dr...of Structures a. SEALAB b. TEKTITE Dr. J.D. Stachiw, NCEL c. Concrete Structures D. Potter, NAVFAC d. Penetrations 0945-1000 Coffee Break 1000-1100 e
Hyodo, Masayuki; Matsu'ura, Shuji; Kamishima, Yuko; Kondo, Megumi; Takeshita, Yoshihiro; Kitaba, Ikuko; Danhara, Tohru; Aziz, Fachroel; Kurniawan, Iwan; Kumai, Hisao
A detailed paleomagnetic study conducted in the Sangiran area, Java, has provided a reliable age constraint on hominid fossil-bearing formations. A reverse-to-normal polarity transition marks a 7-m thick section across the Upper Tuff in the Bapang Formation. The transition has three short reversal episodes and is overlain by a thick normal polarity magnetozone that was fission-track dated to the Brunhes chron. This pattern closely resembles another high-resolution Matuyama–Brunhes (MB) transition record in an Osaka Bay marine core. In the Sangiran sediments, four successive transitional polarity fields lie just below the presumed main MB boundary. Their virtual geomagnetic poles cluster in the western South Pacific, partly overlapping the transitional virtual geomagnetic poles from Hawaiian and Canary Islands’ lavas, which have a mean 40Ar/39Ar age of 776 ± 2 ka. Thus, the polarity transition is unambiguously the MB boundary. A revised correlation of tuff layers in the Bapang Formation reveals that the hominid last occurrence and the tektite level in the Sangiran area are nearly coincident, just below the Upper Middle Tuff, which underlies the MB transition. The stratigraphic relationship of the tektite level to the MB transition in the Sangiran area is consistent with deep-sea core data that show that the meteorite impact preceded the MB reversal by about 12 ka. The MB boundary currently defines the uppermost horizon yielding Homo erectus fossils in the Sangiran area. PMID:22106291
Hyodo, Masayuki; Matsu'ura, Shuji; Kamishima, Yuko; Kondo, Megumi; Takeshita, Yoshihiro; Kitaba, Ikuko; Danhara, Tohru; Aziz, Fachroel; Kurniawan, Iwan; Kumai, Hisao
A detailed paleomagnetic study conducted in the Sangiran area, Java, has provided a reliable age constraint on hominid fossil-bearing formations. A reverse-to-normal polarity transition marks a 7-m thick section across the Upper Tuff in the Bapang Formation. The transition has three short reversal episodes and is overlain by a thick normal polarity magnetozone that was fission-track dated to the Brunhes chron. This pattern closely resembles another high-resolution Matuyama-Brunhes (MB) transition record in an Osaka Bay marine core. In the Sangiran sediments, four successive transitional polarity fields lie just below the presumed main MB boundary. Their virtual geomagnetic poles cluster in the western South Pacific, partly overlapping the transitional virtual geomagnetic poles from Hawaiian and Canary Islands' lavas, which have a mean (40)Ar/(39)Ar age of 776 ± 2 ka. Thus, the polarity transition is unambiguously the MB boundary. A revised correlation of tuff layers in the Bapang Formation reveals that the hominid last occurrence and the tektite level in the Sangiran area are nearly coincident, just below the Upper Middle Tuff, which underlies the MB transition. The stratigraphic relationship of the tektite level to the MB transition in the Sangiran area is consistent with deep-sea core data that show that the meteorite impact preceded the MB reversal by about 12 ka. The MB boundary currently defines the uppermost horizon yielding Homo erectus fossils in the Sangiran area.
Simmons, J.H.; Macedo, P.B.
In the search for an optimum glass matrix composition, we have determined that chemical durability and thermal stability are maximized, and that stress development is minimized for glass compositions containing large concentrations of glass-forming oxides, of which silica is the major component (80 mol%). These properties and characteristics were recently demonstrated to belong to very old geological glasses known as tektites (ages of 750,000 to 34 million years.) The barrier to simulating tektite compositions for the waste glasses was the high melting temperature (1600 to 1800 0 C) needed for these glasses. Such temperatures greatly complicate furnace design and maintenance and lead to an intolerable vaporization of many of the radioisotopes into the off-gas system. Research conducted at our laboratory led to the development of a porous high-silica waste glass material with approximately 80% SiO 2 by mole and 30% waste loading by weight. The process can handle a wide variety of compositions, and yields long, elliptical, monolithic samples, which consist of a loaded high-silica core completely enveloped in a high-silica glass tube, which has collapsed upon the core and sealed it from the outside. The outer glass layer is totally free of waste isotopes and provides an integral multibarrier protection system
Chakrabarti, R.; Basu, A. R.; Peterson, J.; Misra, S.
We report Raman spectra of shocked plagioclase grains from the Lonar impact Crater of India. The Lonar Crater, located in the Buldana district of Maharashtra, India (19° 58'N, 76° 31'E), is an almost circular depression in the 65Ma old basalt flows of the Deccan Traps. Age estimates of this impact crater range from 10-50ka. Tektite and basalt samples were collected for this study from the rim of the crater, which is raised about 20 meters above the surrounding plains. For comparison, a Manicouagan maskelynite and an unaltered mid-oceanic ridge basalt with plagioclase laths were also analyzed. Polished thin sections of all these samples were first petrographically studied. The MORB plagioglase as well as the plagioclase from Lonar host-basalts show first order interference colors and distinct multiple lamellar twinning. The Manicouagan maskelynite is isotropic under crossed-polars. The Lonar tektite samples characteristically demonstrate spherules which are identified by their perfectly circular cross-section and isotropic nature. The spherules also contain fragments of the host basalt with plagioclase laths showing lamellar twinning. The groundmass within the spherules shows lath shaped plagioclase grains, most of which show varying degrees of isotropism due to maskelynitization. Raman scattering measurements were performed using the 514.5 nm line of an argon ion laser at an intensity of 40 kW/cm2. An inverted microscope (Nikon TE3000) with 50x objective (NA 0.55) was used for confocal imaging. A holographic notch filter removed residual laser scatter and the Raman scattering was detected by a silicon CCD at -90° C (Princeton Instruments Spec10-400R). Raman spectra were collected from ~250 cm-1 through 2000 cm-1. Raman spectra of crystalline unshocked plagioclase feldspars from the MORB and the Lonar host basalt show strongest peaks at 265 cm-1, 410 cm-1, 510 cm-1 and 1110 cm-1. The results remain the same for different points in a single grain but vary slightly
Current ideas about the moon appear to be mistaken on two fundamental points. First, at least within certain large classes of lunar craters, internal origin (i.e., some form of volcanism) predominates over impact; this result raises questions about the reality of the era of violent bombardment. Second, the origin of tektites by meteoritic impact on the earth cannot be reconciled with physical principles and is to be abandoned. The only viable alternative is origin by lunar volcanism, which implies the following: continuance of (rare) explosive lunar volcanism to the present time; existence of silicic lunar volcanism and of small patches of silicic rock at the lunar surface; a body of rock in the lunar interior, probably at great depth, which is closely similar to the earth's mantle and which contains billions of tons of volatiles, probably including hydrogen; and origin of the moon from the earth after the formation of the earth's core. 42 references
The book treats astronomical objects and phenomena which remain unexplained or unproven by current investigators. Specific objects discussed include comets, satellite clouds surrounding the earth, tektites, the planet Vulcan (within the orbit of Mercury), Planet X (beyond Pluto), the Gum Nebula, planetary nebulae, supernovae, supernova remnants, transient X-ray sources, the possible extinction of the dinosaurs by an X-ray explosion and super-supernovae. Attention is also given to the star Eta Carinae, black holes, BL Lacertae objects, active galaxies, Markarian galaxies, N and compact galaxies, Seyfert galaxies, quasars, redshift anomalies, Stephan's quintet of galaxies, and intergalactic black holes or black dwarfs which may account for the mass necessary to bind together clusters of galaxies
Abrajano, T.A. Jr.; Ebert, W.L.; Luo, J.S.
This report reviews and summarizes studies performed to characterize the products and processes involved in the corrosion of natural glasses. Studies are also reviewed and evaluated on how well the corrosion of natural glasses in natural environments serves as an analogue for the corrosion of high-level radioactive waste glasses in an engineered geologic disposal system. A wide range of natural and experimental corrosion studies has been performed on three major groups of natural glasses: tektite, obsidian, and basalt. Studies of the corrosion of natural glass attempt to characterize both the nature of alteration products and the reaction kinetics. Information available on natural glass was then compared to corresponding information on the corrosion of nuclear waste glasses, specifically to resolve two key questions: (1) whether one or more natural glasses behave similarly to nuclear waste glasses in laboratory tests, and (2) how these similarities can be used to support projections of the long-term corrosion of nuclear waste glasses. The corrosion behavior of basaltic glasses was most similar to that of nuclear waste glasses, but the corrosion of tektite and obsidian glasses involves certain processes that also occur during the corrosion of nuclear waste glasses. The reactions and processes that control basalt glass dissolution are similar to those that are important in nuclear waste glass dissolution. The key reaction of the overall corrosion mechanism is network hydrolysis, which eventually breaks down the glass network structure that remains after the initial ion-exchange and diffusion processes. This review also highlights some unresolved issues related to the application of an analogue approach to predicting long-term behavior of nuclear waste glass corrosion, such as discrepancies between experimental and field-based estimates of kinetic parameters for basaltic glasses
Abrajano, T.A. Jr.; Ebert, W.L.; Luo, J.S.
This report reviews and summarizes studies performed to characterize the products and processes involved in the corrosion of natural glasses. Studies are also reviewed and evaluated on how well the corrosion of natural glasses in natural environments serves as an analogue for the corrosion of high-level radioactive waste glasses in an engineered geologic disposal system. A wide range of natural and experimental corrosion studies has been performed on three major groups of natural glasses: tektite, obsidian, and basalt. Studies of the corrosion of natural glass attempt to characterize both the nature of alteration products and the reaction kinetics. Information available on natural glass was then compared to corresponding information on the corrosion of nuclear waste glasses, specifically to resolve two key questions: (1) whether one or more natural glasses behave similarly to nuclear waste glasses in laboratory tests, and (2) how these similarities can be used to support projections of the long-term corrosion of nuclear waste glasses. The corrosion behavior of basaltic glasses was most similar to that of nuclear waste glasses, but the corrosion of tektite and obsidian glasses involves certain processes that also occur during the corrosion of nuclear waste glasses. The reactions and processes that control basalt glass dissolution are similar to those that are important in nuclear waste glass dissolution. The key reaction of the overall corrosion mechanism is network hydrolysis, which eventually breaks down the glass network structure that remains after the initial ion-exchange and diffusion processes. This review also highlights some unresolved issues related to the application of an analogue approach to predicting long-term behavior of nuclear waste glass corrosion, such as discrepancies between experimental and field-based estimates of kinetic parameters for basaltic glasses.
Putthapiban, P.; Zolensky, M.; Jull, T.; Demartino, M.; Salyapongse, S.
Tha Chang sand pits, Nakhon Ratchasima Province and many other sand pits in the area adjacent to the Mun River are characterized by their fluviatile environment in association with mass wasting deposits, along the paleo-river channel and the flood plain of the Mun River. Sediments of these deposits are characterized by clasts of various rock types especially the resistant ones with frequent big tree trunks, logs and wood fragments in different sizes and various stages of transformation from moldering stage to lignification and petrification. Widespread pyritization of the lower horizon suggests strongly reducing environment during burial. The Tha Chang deposits have been received much attention from geoscientists especially paleontologist communities, as they contain fragments of some distinct vertebrate species such as Stegadon sp., hominoid primate, rhinoceros Aceratherium and others. Based on the associated mammal fauna and hominoid fossils, the late Miocene ( 9 - 6 Ma) was given for the time of deposition of this sand and gravel unit. Some other reports believed that sediments and materials of these sand and gravel quarries (pits) were deposited by high-energy flood pulses contemporaneous with the tektites forming event during mid-Pleistocene at c. 0.8 Ma. Interpretation from Palynostratigraphical study suggested that the lower horizon of Tha Chang sand pit was deposited during Pliocene/Pleistocene period and the upper horizons are Pleistoncene/Holocene. It is crystal clear that all the fluviatile sediments including tektites and almost all fossil fragments being deposited in these sand pits were, likely a multiple times reworked materials. Only some old bamboo trees, some old crowling trees and fossils grasses observed on the old river bank are considered in situ. C-14 dating of 5 old wood specimens from Tha Chang Sand Pits, 15 old wood specimens from Chumpuang Sand Pits and one sample of old pottery from a Chumpuang Sand Pit were carried out in the NSF
Papelis, Charalambos; Um, Wooyong; Russel, Charles E.; Chapman, Jenny B.
The specific surface area of natural and manmade solid materials is a key parameter controlling important interfacial processes in natural environments and engineered systems, including dissolution reactions and sorption processes at solid-fluid interfaces. To improve our ability to quantify the release of trace elements trapped in natural glasses, the release of hazardous compounds trapped in manmade glasses, or the release of radionuclides from nuclear melt glass, we measured the specific surface area of natural and manmade glasses as a function of particle size, morphology, and composition. Volcanic ash, volcanic tuff, tektites, obsidian glass, and in situ vitrified rock were analyzed. Specific surface area estimates were obtained using krypton as gas adsorbent and the BET model. The range of surface areas measured exceeded three orders of magnitude. A tektite sample had the highest surface area (1.65 m2/g), while one of the samples of in situ vitrified rock had the lowest surf ace area (0.0016 m2/g). The specific surface area of the samples was a function of particle size, decreasing with increasing particle size. Different types of materials, however, showed variable dependence on particle size, and could be assigned to one of three distinct groups: (1) samples with low surface area dependence on particle size and surface areas approximately two orders of magnitude higher than the surface area of smooth spheres of equivalent size. The specific surface area of these materials was attributed mostly to internal porosity and surface roughness. (2) samples that showed a trend of decreasing surface area dependence on particle size as the particle size increased. The minimum specific surface area of these materials was between 0.1 and 0.01 m2/g and was also attributed to internal porosity and surface roughness. (3) samples whose surface area showed a monotonic decrease with increasing particle size, never reaching an ultimate surface area limit within the particle
Harting, M.; Deutsch, A.; Rickers, K.
Many K/T sections all over the world contain impact spherules supposed related to the Chicxulub event. This study focus on ejecta layers in NE-Mexican profiles. We carried out systematic XRF and synchrotron radiation measurements on such spherules at the HASYLAB and ANKA facilities as well as microprobe analyses (CAMECA SX50). Area scans on tektite-like material of the Bochil section reveal a pronounced zonation in the inner part, dominated by Ba and Sr whereas secondary CaCO3 dominates in the altered margin. The composition of the spherules from the Mesa-Juan Perez section differ significantly from the Beloc (Haiti) and Bochil tektite glasses. At Mesa-Juan Perez, spherules are either extremely rich in Fe and Ca or consist of smectite, some of those carry carbonate inclusions. Yttrium, La and Ce are zoned within the smectite with concentrations below the detection limit and up to 20 æg/g The Ca-rich inclusions are enriched in Y (up to 35 æg/g) and La (18 æg/g) and, compared to the surrounding smectite, also in Ce (up to 34 æg/g). The Ce enrichment in spherules from the Mesa-Juan Perez section indicates impact-melted carbonates of the Yucatan carbonate platform as possible precursor rocks. Recent investigations focus on the chemistry of melt rock samples from the PEMEX wells Yucatan-6 and Chicxulub-1: Their average composition (mean of 250 data points in wt-percent ) is 61.6 for SiO2, 0.16 for TiO2, 18.07 for Al2O3, 0.01 for Cr2O3, 1.98 for Na2O, 1.5 for FeO, 0.05 for MnO, 0.01 for NiO, 0.31 for MgO, 9.14 for K2O, 3.44 for CaO, and 0.01 for SO2. These results are in some cases comparable to the geochemistry of ejecta glasses, e.g. from Beloc (Haiti).
Macris, C. A.; Badro, J.; Eiler, J. M.; Stolper, E. M.
The aerodynamic levitation laser apparatus is an instrument in which spherical samples are freely floated on top of a stream of gas while being heated with a CO2laser to temperatures up to about 3500 °C. Laser heated samples, ranging in size from 0.5 to 3.5 mm diameter, can be levitated in a variety of chemically active or inert atmospheres in a gas-mixing chamber (e.g., Hennet et al. 2006; Pack et al. 2010). This allows for containerless, controlled-atmosphere, high temperature experiments with potential for applications in earth and planetary science. A relatively new technique, aerodynamic levitation has been used mostly for studies of the physical properties of liquids at high temperatures (Kohara et al. 2011), crystallization behavior of silicates and oxides (Arai et al. 2004), and to prepare glasses from compositions known to crystallize upon quenching (Tangeman et al. 2001). More recently, however, aerodynamic levitation with laser heating has been used as an experimental technique to simulate planetary processes. Pack et al. (2010) used levitation and melting experiments to simulate chondrule formation by using Ar-H2 as the flow gas, thus imposing a reducing atmosphere, resulting in reduction of FeO, Fe2O3, and NiO to metal alloys. Macris et al. (2015) used laser heating with aerodynamic levitation to reproduce the textures and diffusion profiles of major and minor elements observed in impact ejecta from the Australasian strewn field, by melting a powdered natural tektite mixed with 60-100 μm quartz grains on a flow of pure Ar gas. These experiments resulted in quantitative modeling of Si and Al diffusion, which allowed for interpretations regarding the thermal histories of natural tektites and their interactions with the surrounding impact vapor plume. Future experiments will employ gas mixing (CO, CO2, H2, O, Ar) in a controlled atmosphere levitation chamber to explore the range of fO2applicable to melt-forming impacts on other rocky planetary bodies
Lebofsky, Larry A.; Cañizo, Thea L.; Buxner, Sanlyn
Hands-on learning allows students to understand science concepts by directly observing and experiencing the topics they are studying. The Planetary Science Institute (PSI) has created instructional rock kits that have been introduced to elementary and middle school teachers in Tucson, in our professional development workshops. PSI provides teachers with supporting material and training so that they can use the kits as tools for students’ hands-on learning. Use of these kits provides an important experience with natural materials that is essential to instruction in Earth and Space Science. With a stronger knowledge of science content and of how science is actually conducted, the workshops and kits have instilled greater confidence in teachers’ ability to teach science content. The Next Generation Science Standards (NGSS) Performance Expectations includes: “What makes up our solar system?” NGSS emphasizes the Crosscutting Concepts—Patterns Scale, Portion, and Quantity; and Systems and System Models. NGSS also states that the Nature of Science (NOS) should be an “essential part” of science education. NOS topics include understanding that scientific investigations use a variety of methods, that scientific knowledge is based on empirical evidence, that scientific explanations are open to revision in light of new evidence, and an understanding of the nature of scientific models.Addressing a need expressed by teachers for borrowing kits less expensive than our $2000 option, we created a Meteorite Mini-Kit. Each Mini-Kit contains eight rocks: an iron-bearing chondrite, a sliced chondrite (showing iron and chondrules), a tektite, a common Tucson rock, a river-polished rock, pumice, a small iron, and a rounded obsidian rock (false tektite). Also included in the Mini-Kits are magnets and a magnifier. The kits cost $40 to $50, depending on the sizes of the chondrites. A teacher can check out a classroom set of these which contains either 10 or 20 Mini-Kits. Each
Bureau research programs and projects are designed to address many of the State's major concerns in the areas of geologic, energy, mineral, land, and environmental resouces. Research programs incorporate geologic concepts that will build toward an understanding of a specific resource and its impact on human activities. In addition to resource assessments in uranium, lignite, and geopressured geothermal energy, the Bureau continued research into analysis of governmental policy related to energy. Systemic geologic mapping, coastal studies, basin analysis projects, and investigations in other areas of economic geology further indicate the range of research programs carried forward in 1978. Specifically, research on mineral resources and land resources, coastal studies, hydrogeology, basin studies, geologic mapping, and other research (tektites and meteorites, carboniferous of Texas, depositional environments of the Marble Falls Formation, Central Texas) are reported. The establishment of the Mining and Mineral Resources Research Institute is followed. Contracts and grant support and contract reports are listed. The publications eminating from the Bureau are listed. Services rendered by the Bureau and personnel information are included. (MCW)
Magna, Tomáš; Žák, Karel; Pack, Andreas; Moynier, Frédéric; Mougel, Bérengère; Peters, Stefan; Skála, Roman; Jonášová, Šárka; Mizera, Jiří; Řanda, Zdeněk
Chemical fingerprints of impacts are usually compromised by extreme conditions in the impact plume, and the contribution of projectile matter to impactites does not often exceed a fraction of per cent. Here we use chromium and oxygen isotopes to identify the impactor and impact-plume processes for Zhamanshin astrobleme, Kazakhstan. ε 54 Cr values up to 1.54 in irghizites, part of the fallback ejecta, represent the 54 Cr-rich extremity of the Solar System range and suggest a CI-like chondrite impactor. Δ 17 O values as low as -0.22‰ in irghizites, however, are incompatible with a CI-like impactor. We suggest that the observed 17 O depletion in irghizites relative to the terrestrial range is caused by partial isotope exchange with atmospheric oxygen (Δ 17 O = -0.47‰) following material ejection. In contrast, combined Δ 17 O-ε 54 Cr data for central European tektites (distal ejecta) fall into the terrestrial range and neither impactor fingerprint nor oxygen isotope exchange with the atmosphere are indicated.Identifying the original impactor from craters remains challenging. Here, the authors use chromium and oxygen isotopes to indicate that the Zhamanshin astrobleme impactor was a carbonaceous chrondrite by demonstrating that depleted 17O values are due to exchange with atmospheric oxygen.
Mizera, J.; Academy of Sciences of the Czech Republic, Prague; Randa, Z.; Tomandl, I.
A large set of impact glasses from the Zhamanshin crater in Kazakhstan was analyzed by various modes of instrumental neutron activation analysis, supplemented by instrumental photon activation analysis and prompt gamma-ray activation analysis. Results of the determination of more than forty major and trace elements have shown that the analyzed set of homogeneous, tektite-like impact glasses with size of several centimeters and of various forms could be divided into two geochemically different groups. The lustrous, silica rich (acidic) glasses with high Ni content have been classified conventionally as irghizites. The dull, silica poor (basic) glasses with very low Ni content should not be confused with the large, heterogeneous impactite forms-zhamanshinites, but considered as a separate type of impact glass. Within both primary groups, further division has been suggested based on lower contents of Ni in an irghizite subgroup, and evidence of mixing of source materials for both primary groups in a part of the basic glasses. Based on the contents of Ni, Cr, Mn, Fe and Co, an ordinary chondrite impactor has been suggested with its contribution to the irghizite matter ranging between 4 and 21%. Possible source materials and impact processes leading to irghizite formation have been outlined. (author)
Solid State Nuclear Track Detectors (SSNTDs) - A class of passive detectors, developed by R.L. Fleischer, P.B. Price and R.M. Walker in the early 1960s have found numerous applications in various fields of science and technology. SSNTDs have been recognized as very potential and effective tools in exploring various areas of research. The intrinsic features of SSNTDs like low cost , availability, versatility and their remarkable stability have contributed to applications in a wide range of fields opening up new vistas which were practically unthinkable and unbelievable about a decade or two ago. Apart from the direct applications of far reaching consequences in nuclear physics, other areas as diverse as bio-medical sciences, cosmic rays and space physics, environmental research, geochronology and geophysics, materials sciences, lunar science, meteorites and tektites; microanalysis, mine safety, nuclear technology, uranium prospecting and most recently nano/micro technology etc., have been greatly influenced by SSNTDs. They have a very important role to play in radiation measurement, micro technology and dosimetry and thus are potential enough in spreading awareness about the radiation environment and its impact on the general public and the academic peers. In order to disseminate the knowledge generated in this fast growing field, there is a need to bring material science and radiation community on a common platform and discuss various operational and radiation protection aspects. Papers relevant to INIS are indexed separately
O'Keefe, J. A.; Barkatt, A.; Glass, B. P.; Alterescu, S.
J. J. Crovisier and J. Honnorez  discuss an article by W. W. Maggs, “Mg May Protect Waste Under Glass” [Maggs, 1988] summarizing work by A. Barkatt (Catholic University, Washington, D.C.), B. P. Glass (University of Delaware, Newark), and S. Alterescu and J. A. O'Keefe (NASA/GSFC, Greenbelt, Md.). We found that seawater is orders of magnitude less corrosive t h an fresh water in attacking tektite glass; traced the protective effect to the presence of magnesium, at a level of about 1.3 g/L in seawater; and suggested that the effect might be useful in protecting nuclear waste glasses from corrosion.Crovisier and Honnorez first make the point that the rate of corrosion of glass is, in principle, a function of the ratio of surface area 5 to the effective volume V. This concept, which is usually discussed in American literature under the name of S/V effects, is discussed by Crovisier and Honnorez in terms of the “permeability of the environment.” These effects have been carefully considered throughout our work (see, for example, Barkatt et al. [19867rsqb;). It turns out that in the sea the effective S/V is so small that the effects referred to by Crovisier and Honnorez can be ignored.
Alvarez, W.; Asaro, F.; Alvarez, L. W.; Michel, H. V.
Large-body impact on the Earth is a rare but indisputable geologic process. The impact rate is approximately known from objects discovered in Earth-crossing orbits and from the statistics of craters on the Earth's surface. Tektite and microtektite strewn fields constitute unmistakable ejecta deposits that can be due only to large-body impacts. The Cretaceous-Tertiary (K-T) boundary coincides with an unusually severe biological trauma, and this stratigraphic horizon is marked on a worldwide basis by anomalous concentrations of noble metals in chondritic proportions, mineral spherules with relict quench-crystallization textures, and mineral and rock grains showing shock deformation. These features are precisely compatible with an impact origin. Although only impact explains all the types of K-T boundary evidence, the story may not be as simple as once thought. The original hypothesis envisioned one large impact, triggering one great extinction. Newer evidence hints at various complications. Different challenges are faced by the occupants of each apex of a three-cornered argument over the K-T event. Proponents of a non-impact explanation must show that the evidence fits their preferred model better than it fits the impact scenario. Proponents of the single impact-single extinction view must explain away the complications. Proponents of a more complex impact crisis must develop a reasonable scenario which honors the new evidence.
Helmreich, Robert L.
A cost-reward model is used to frame a discussion of differences in observed behavior of individuals and groups in confined environments. It has been observed that the high cost of functioning in a stressful environment is likely to produce poor performance when anticipated rewards are low but that participants can manage the stress and achieve high performance if they anticipate high rewards. The high-reward environment is exemplified by early undersea habitats such as Sealab and Tektite and by early space missions. Other aspects of behavior occur in all confined environments and point to an important area for future research. Of particular interest are intergroup conflicts arising between the confined group and its external control. Also, individual differences in personality seem always to have an impact in confined environments. Recent research has focused on: (1) predicting performance and adjustment based on instrumental and expressive aspects of the self; (2) the differential predictive power of achievement striving and irritation/irritability in Type A personalities; and (3) the nature and role of leadership in small, isolated groups.
Hazel, Joseph E.
The scientific controversy over the origin of upper Eocene tektites, microtektites and other microspherules cannot be logically resolved until it is determined just how many events are involved. The microspherule-bearing beds in marine sediments have been dated using standard biozonal techniques. Although a powerful stratigraphic tool, zonal biostratigraph has its limitations. One is that if an event, such as a microspherule occurrence, is observed to occur in a zone at one locality and then a similar event observed in the same zone at another locality, it still may be unwarranted to conclude that these events exactly correlate. To be in a zone a sample only need be between the fossil events that define the zone boundaries. It is often very difficult to accurately determine where within a zone one might be. Further, the zone defining events do not everywhere occur at the same points in time. That is, the ranges of the defining taxa are not always filled. Thus, the length of time represented by a zone (but not, of course, its chronozone) can vary from place to place. These problems can be offset by use of chronostratigraphic modelling techniques such as Graphic Correlation. This technique was used to build a Cretaceous and Cenozoic model containing fossil, magnetopolarity, and other events. The scale of the model can be demonstrated to be linear with time. This model was used to determine the chronostratigraphic position of upper Eocene microspherule layers.
Macleod, N.; Kitchell, J. A.
While it is well known that the cosmic impact event at or near the Cretaceous-Tertiary boundary coincides with an interval of mass extinction, a similar impact (or series of impacts) near the Eocene-Oligocene boundary presents a more complex picture, in terms of associated fluctuations in marine biotic diversity. Tektites, microtektites, and mineral grains exhibiting features of shock metamorphism found in Eocene sediments of the western N. Atlantic, Caribbean, and Gulf of Mexico (comprising the North American microtektite strewn field) offer compelling evidence for a catastrophic impact event. Despite the magnitude of this event, however, few extinctions in the planktic marine fauna are known to have occurred coincident with this event. Instead, changes in relative abundance, morphology, and development occurred. Cosmic impacts generally have been interpreted as influencing the course of evolution through the wholesale elimination of significant portions of standing biotic diversity. Indeed, extinction traditionally has been viewed as the negative side of evolution. In some instances, it is suggested such impact events can serve instead to increase, rather than decrease, morphological and ecological diversity, by altering the developmental programs within species at the level of the local population.
Kurosawa, Kosuke; Okamoto, Takaya; Genda, Hidenori
Hypervelocity ejection of material by impact spallation is considered a plausible mechanism for material exchange between two planetary bodies. We have modeled the spallation process during vertical impacts over a range of impact velocities from 6 to 21 km/s using both grid- and particle-based hydrocode models. The Tillotson equations of state, which are able to treat the nonlinear dependence of density on pressure and thermal pressure in strongly shocked matter, were used to study the hydrodynamic-thermodynamic response after impacts. The effects of material strength and gravitational acceleration were not considered. A two-dimensional time-dependent pressure field within a 1.5-fold projectile radius from the impact point was investigated in cylindrical coordinates to address the generation of spalled material. A resolution test was also performed to reject ejected materials with peak pressures that were too low due to artificial viscosity. The relationship between ejection velocity veject and peak pressure Ppeak was also derived. Our approach shows that "late-stage acceleration" in an ejecta curtain occurs due to the compressible nature of the ejecta, resulting in an ejection velocity that can be higher than the ideal maximum of the resultant particle velocity after passage of a shock wave. We also calculate the ejecta mass that can escape from a planet like Mars (i.e., veject > 5 km/s) that matches the petrographic constraints from Martian meteorites, and which occurs when Ppeak = 30-50 GPa. Although the mass of such ejecta is limited to 0.1-1 wt% of the projectile mass in vertical impacts, this is sufficient for spallation to have been a plausible mechanism for the ejection of Martian meteorites. Finally, we propose that impact spallation is a plausible mechanism for the generation of tektites.
Synthesized glasses provide an opportunity to study natural corrosion processes which are intermediate in time span between geological examples of natural glasses, such as obsidians and tektites, and relatively short term laboratory tests lasting a few hours to several decades. In addition, synthesized glasses can usually be tracked to particular archaeological find sites with known dates of production and often burial. Environmental conditions are routinely measured at archaeological sites as a part of the excavation-process, such that information is available on the yearly cycling of temperature and relative humidity, sometimes at the depth at which the artifact was found. Whether the artifacts were excavated in an air enclosure, such as a tomb, or in the soil can also be reconstructed, such that one can determine whether aqueous or atmospheric corrosion was involved in the degradation process. For instance, so-called open-quotes Roman glassclose quotes may span a time period of production of 800 years and a geographical range from Germany to North Africa and from Britain to Afghanistan. One example is the storage during World War II of glass from the British Museum in underground metro stations. Some of these glasses have been in collections for over 100 years. Thus, populations of glasses can be chosen for experimentation which compare variations in bulk composition, dopants, microstructure, heat treatment, ground vs. fire polished surfaces, aqueous vs. atmospheric corrosion, geographic, geological as well as recent storage conditions. Glasses in museums are generally considered to have had their corrosion arrested and be stable because changes in visual appearance are not obvious. However, if we attempt to measure the range of surface water content in these glasses using Fourier transform infrared analysis, a considerable variability is found, as shown
It is well known in the sedimentary record of several parts of the world that during the Younger Dryas interval (YD) ocurred an abrupt environmental change between 12,900 and 11,700 cal yr BP (10,900 to 10,000 14C BP). In the lacustrine basins this changes are often preserved and in some Mexican lakes this is a distinctive stratigraphic marker for the YD. We analized the proxies of this event in cores of two lakes (Chapala, Cuitzeo) and three trenches of ex-lakes (Acambay,Texcoco and El Cedral). Deposits consist of fine detrital material with often Pleistocene fossil vertebrate assemblages. At the Chapala, Cuitzeo, Acambay, and Tocuila lacustrine environments are found in association with a distinctive dark organic layer showing sharp changes in the diatom, pollen, mineralogical and geochemical record. Includes also microscopic magnetic, Fe-rich spherules, silica melted droplets with aerodynamic shapes (tektites), followed by large amounts of charcoal, and sometimes nanodiamonds (Cuitzeo), that were deposited at the onset of the YD or in the limit Pleistocene-Holocene. These unusual materials are buried more than 2.50 meters and were not observed above or below the Younger Dryas sediments at these sites. The geochemistry of the microspherules indicates that they are not volcanic, anthropogenic or authigenic origin. A very distinctive feature is the shape of the spherules, ovoid, polygonal, filigreed or dendritic indicating melting and quenching infering that are product of an impact event. Their morphologies includes hollow shells caused by de-gassing of elements at very high temperatures causing a flattened side with a "skirt" structure by a high-velocity collision.Our results are consistent with the Firestone hypothesis.
Folco, L.; Glass, B. P.; D'Orazio, M.; Rochette, P.
Impactor identification is one of the challenges of large-scale impact cratering studies due to the dilution of meteoritic material in impactites (typically ratios in a Co/Ni vs Cr/Ni space (46 microtektites analyzed in this work by Laser Ablation-Inductively Coupled Plasma -Mass Spectrometry and 31 from literature by means of Neutron Activation Analyses with Cr, Co and Ni concentrations up to ∼370, 50 and 680 μg/g, respectively). Despite substantial overlap in Cr/Ni versus Co/Ni composition for several meteorite types with chondritic composition (chondrites and primitive achondrites), regression calculation based on ∼85% of the studied microtektites best fit a mixing line between crustal compositions and an LL chondrite. However, due to some scatter mainly in the Cr versus Ni ratios in the considered dataset, an LL chondrite may not be the best fit to the data amongst impactors of primitive compositions. Eight high Ni/Cr and five low Ni/Cr outlier microtektites (∼15% in total) deviate from the above mixing trend, perhaps resulting from incomplete homogenization of heterogeneous impactor and target precursor materials at the microtektite scale, respectively. Together with previous evidence from the ∼35 Myr old Popigai impact spherules and the ∼1 Myr old Ivory Coast microtektites, our finding suggests that at least three of the five known Cenozoic distal impact ejecta were generated by the impacts of large stony asteroids of chondritic composition, and possibly of ordinary chondritic composition. The impactor signature found in Australasian microtektites documents mixing of target and impactor melts upon impact cratering. This requires target-impactor mixing in both the two competing models in literature for the formation of the Australasian tektites/microtektites: the impact cratering and low-altitude airburst plume models.
The common observation of glasses persisting in natural environments for long periods of time (up to tens of millions of years) provides compelling evidence that these materials can be kinetically stable in a variety of subsurface environments. This paper reviews how natural and historical synthesized glasses can be employed as natural analogues for understanding and projecting the long-term alteration of high-level nuclear waste glasses. The corrosion of basaltic glass results in many of the same alteration features found in laboratory testing of the corrosion of high-level radioactive waste glasses. Evidence has also been found indicating similarities in the rate controlling processes, such as the effects of silica concentration on corrosion in groundwater and in laboratory leachates. Naturally altered rhyolitic glasses and tektites provide additional evidence that can be used to constrain estimates of long-term waste glass alteration. When reacted under conditions where water is plentiful, the corrosion for these glasses is dominated by network hydrolysis, while the corrosion is dominated by molecular water diffusion and secondary mineral formation under conditions where water contact is intermittent or where water is relatively scarce. Synthesized glasses that have been naturally altered result in alkali-depleted alteration features that are similar to those found for natural glasses and for nuclear waste glasses. The characteristics of these alteration features appear to be dependent on the alteration conditions which affect the dominant reaction processes during weathering. In all cases, care must be taken to ensure that the information being provided by natural analogues is related to nuclear waste glass corrosion in a clear and meaningful way
Schmieder, Martin; Kennedy, Trudi; Jourdan, Fred; Buchner, Elmar; Reimold, Wolf Uwe
40Ar/39Ar dating of specimens of moldavite, the formation of which is linked to the Ries impact in southern Germany, with a latest-generation ARGUS VI multi-collector mass spectrometer yielded three fully concordant plateau ages with a weighted mean age of 14.808 ± 0.021 Ma (± 0.038 Ma including all external uncertainties; 2σ; MSWD = 0.40, P = 0.67). This new best-estimate age for the Nördlinger Ries is in general agreement with previous 40Ar/39Ar results for moldavites, but constitutes a significantly improved precision with respect to the formation age of the distal Ries-produced tektites. Separates of impact glass from proximal Ries ejecta (suevite glass from three different surface outcrops) and partially melted feldspar particles from impact melt rock of the SUBO 18 Enkingen drill core failed to produce meaningful ages. These glasses show evidence for excess 40Ar introduction, which may have been incurred during interaction with hydrothermal fluids. Only partially reset 40Ar/39Ar ages could be determined for the feldspathic melt separates from the Enkingen core. The new 40Ar/39Ar results for the Ries impact structure constrain the duration of crater cooling, during the prevailing hydrothermal activity, to locally at least ∼60 kyr. With respect to the dating of terrestrial impact events, this paper briefly discusses a number of potential issues and effects that may be the cause for seemingly precise, but on a kyr-scale inaccurate, impact ages.
Reimold, Wolf Uwe; Koeberl, Christian
More than 50 years of space and planetary exploration and concomitant studies of terrestrial impact structures have demonstrated that impact cratering has been a fundamental process – an essential part of planetary evolution – ever since the beginning of accretion and has played a major role in planetary evolution throughout the solar system and beyond. This not only pertains to the development of the planets but to evolution of life as well. The terrestrial impact record represents only a small fraction of the bombardment history that Earth experienced throughout its evolution. While remote sensing investigations of planetary surfaces provide essential information about surface evolution and surface processes, they do not provide the information required for understanding the ultra-high strain rate, high-pressure, and high-temperature impact process. Thus, hands-on investigations of rocks from terrestrial impact craters, shock experimentation for pressure and temperature calibration of impact-related deformation of rocks and minerals, as well as parameter studies pertaining to the physics and chemistry of cratering and ejecta formation and emplacement, and laboratory studies of impact-generated lithologies are mandatory tools. These, together with numerical modeling analysis of impact physics, form the backbone of impact cratering studies. Here, we review the current status of knowledge about impact cratering – and provide a detailed account of the African impact record, which has been expanded vastly since a first overview was published in 1994. No less than 19 confirmed impact structures, and one shatter cone occurrence without related impact crater are now known from Africa. In addition, a number of impact glass, tektite and spherule layer occurrences are known. The 49 sites with proposed, but not yet confirmed, possible impact structures contain at least a considerable number of structures that, from available information, hold the promise to be able to
Varatharajan, I.; D'Amore, M.; Maturilli, A.; Helbert, J.; Hiesinger, H.
The Mercury Radiometer and Thermal Imaging Spectrometer (MERTIS) payload of ESA/JAXA Bepicolombo mission to Mercury will map the thermal emissivity at wavelength range of 7-14 μm and spatial resolution of 500 m/pixel . Mercury was also imaged at the same wavelength range using the Boston University's Mid-Infrared Spectrometer and Imager (MIRSI) mounted on the NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii with the minimum spatial coverage of 400-600km/spectra which blends all rocks, minerals, and soil types . Therefore, the study  used quantitative deconvolution algorithm developed by  for spectral unmixing of this composite thermal emissivity spectrum from telescope to their respective areal fractions of endmember spectra; however, the thermal emissivity of endmembers used in  is the inverted reflectance measurements (Kirchhoff's law) of various samples measured at room temperature and pressure. Over a decade, the Planetary Spectroscopy Laboratory (PSL) at the Institute of Planetary Research (PF) at the German Aerospace Center (DLR) facilitates the thermal emissivity measurements under controlled and simulated surface conditions of Mercury by taking emissivity measurements at varying temperatures from 100-500°C under vacuum conditions supporting MERTIS payload. The measured thermal emissivity endmember spectral library therefore includes major silicates such as bytownite, anorthoclase, synthetic glass, olivine, enstatite, nepheline basanite, rocks like komatiite, tektite, Johnson Space Center lunar simulant (1A), and synthetic powdered sulfides which includes MgS, FeS, CaS, CrS, TiS, NaS, and MnS. Using such specialized endmember spectral library created under Mercury's conditions significantly increases the accuracy of the deconvolution model results. In this study, we revisited the available telescope spectra and redeveloped the algorithm by  by only choosing the endmember spectral library created at PSL for unbiased model
Gohn, G.S.; Koeberl, C.; Miller, K.G.; Reimold, W.U.
The late Eocene Chesapeake Bay impact structure lies buried at moderate depths below Chesapeake Bay and surrounding landmasses in southeastern Virginia, USA. Numerous characteristics made this impact structure an inviting target for scientific drilling, including the location of the impact on the Eocene continental shelf, its threelayer target structure, its large size (??85 km diameter), its status as the source of the North American tektite strewn field, its temporal association with other late Eocene terrestrial impacts, its documented effects on the regional groundwater system, and its previously unstudied effects on the deep microbial biosphere. The Chesapeake Bay Impact Structure Deep Drilling Project was designed to drill a deep, continuously cored test hole into the central part of the structure. A project workshop, funding proposals, and the acceptance of those proposals occurred during 2003-2005. Initial drilling funds were provided by the International Continental Scientific Drilling Program (ICDP) and the U.S. Geological Survey (USGS). Supplementary funds were provided by the National Aeronautics and Space Administration (NASA) Science Mission Directorate, ICDP, and USGS. Field operations were conducted at Eyreville Farm, Northampton County, Virginia, by Drilling, Observation, and Sampling of the Earth's Continental Crust (DOSECC) and the project staff during September-December 2005, resulting in two continuously cored, deep holes. The USGS and Rutgers University cored a shallow hole to 140 m in April-May 2006 to complete the recovered section from land surface to 1766 m depth. The recovered section consists of 1322 m of crater materials and 444 m of overlying postimpact Eocene to Pleistocene sediments. The crater section consists of, from base to top: basement-derived blocks of crystalline rocks (215 m); a section of suevite, impact melt rock, lithic impact breccia, and cataclasites (154 m); a thin interval of quartz sand and lithic blocks (26 m); a
Davias, M. E.; Harris, T. H. S.
80 years after aerial photography revealed thousands of aligned oval depressions on the USA's Atlantic Coastal Plain, the geomorphology of the "Carolina bays" remains enigmatic. Geologists and astronomers alike hold that invoking a cosmic impact for their genesis is indefensible. Rather, the bays are commonly attributed to gradualistic fluvial, marine and/or aeolian processes operating during the Pleistocene era. The major axis orientations of Carolina bays are noted for varying statistically by latitude, suggesting that, should there be any merit to a cosmic hypothesis, a highly accurate triangulation network and suborbital analysis would yield a locus and allow for identification of a putative impact site. Digital elevation maps using LiDAR technology offer the precision necessary to measure their exquisitely-carved circumferential rims and orientations reliably. To support a comprehensive geospatial survey of Carolina bay landforms (Survey) we generated about a million km2 of false-color hsv-shaded bare-earth topographic maps as KML-JPEG tile sets for visualization on virtual globes. Considering the evidence contained in the Survey, we maintain that interdisciplinary research into a possible cosmic origin should be encouraged. Consensus opinion does hold a cosmic impact accountable for an enigmatic Pleistocene event - the Australasian tektite strewn field - despite the failure of a 60-year search to locate the causal astroblem. Ironically, a cosmic link to the Carolina bays is considered soundly falsified by the identical lack of a causal impact structure. Our conjecture suggests both these events are coeval with a cosmic impact into the Great Lakes area during the Mid-Pleistocene Transition, at 786 ka ± 5 k. All Survey data and imagery produced for the Survey are available on the Internet to support independent research. A table of metrics for 50,000 bays examined for the Survey is available from an on-line Google Fusion Table: https://goo.gl/XTHKC4 . Each bay
Rathbun, K.; Ukstins, I.; Drop, S.
Monturaqui Crater is a small ( 350 m diameter), simple meteorite impact crater located in the Atacama Desert of northern Chile that was emplaced in Ordovician granite overlain by discontinuous Pliocene ignimbrite. Ejecta deposits are granite and ignimbrite, with lesser amounts of dark impact melt and rare tektites and iron shale. The impact restructured existing drainage systems in the area that have subsequently eroded through the ejecta. Satellite-based mapping and modeling, including a synthesis of photographic satellite imagery and ASTER thermal infrared imagery in ArcGIS, were used to construct a basic geological interpretation of the site with special emphasis on understanding ejecta distribution patterns. This was combined with field-based mapping to construct a high-resolution geologic map of the crater and its ejecta blanket and field check the satellite-based geologic interpretation. The satellite- and modeling-based interpretation suggests a well-preserved crater with an intact, heterogeneous ejecta blanket that has been subjected to moderate erosion. In contrast, field mapping shows that the crater has a heavily-eroded rim and ejecta blanket, and the ejecta is more heterogeneous than previously thought. In addition, the erosion rate at Monturaqui is much higher than erosion rates reported elsewhere in the Atacama Desert. The bulk compositions of the target rocks at Monturaqui are similar and the ejecta deposits are highly heterogeneous, so distinguishing between them with remote sensing is less effective than with direct field observations. In particular, the resolution of available imagery for the site is too low to resolve critical details that are readily apparent in the field on the scale of 10s of cm, and which significantly alter the geologic interpretation. The limiting factors for effective remote interpretation at Monturaqui are its target composition and crater size relative to the resolution of the remote sensing methods employed. This
Savranskaia, T.; Valet, J. P.; Bassinot, F. C.; Meynadier, L.; Simon, Q.; Bourles, D. L.; Thouveny, N.; Thevarasan, A.; Villedieu, A.; Choy, S.; Gacem, L.
Two techniques can be used to determine the evolution of the geomagnetic field intensity in the past. The first one relies on records of relative paleointensity (RPI) in sediments. Although they remain relatively sparse detailed records of 10Be production (expressed in terms of 10Be/9Be) provide an alternative approach. However integration of 10Be within the sediment is not better understood than the magnetization process, and therefore paleofield studies should greatly benefit from the integration of both datasets. In order to achieve this goal, it is crucial to compare and analyze the signals over a common time period. We selected five sedimentary cores from the Indian, Pacific and Atlantic Oceans and focused on the last reversal which is characterized by the largest intensity changes. Since 10Be is homogenized in the atmosphere, the same amount of 10Be should be recorded everywhere. We found different amounts of 10Be at each site during the last reversal which appear roughly correlated with accumulation rate. In contrast the 10Be amplitude is similar at all locations while higher amplitude signals are expected for low deposition rates. Taking advantage of the distribution of tektites layers, the beryllium signals have been deconvolved, but this procedure did not strikingly change the results. Despite atmospheric mixing we wonder whether 10Be production was slightly different at each location in presence of a multipolar transitional field. The comparison between the 10Be and RPI signals reveals large similarities but also puzzling differences. In particular, the relationship between the two signals is not the same during periods of stable polarity as during the transitional interval. A precursor with low intensity is present in several RPI records but not clearly marked on the beryllium records. We also addressed the question of a possible offset between the two signals that would be indicative of a delayed magnetization acquisition. After correlating and
Marin, Yu. B.; Skublov, G. T.; Yushkin, N. P.
On the right-hand bank of the Volkhov River, in the natural area of tektite-like glasses (Volkhovites), fragments of shungites and slags with bunches of hairlike dark brownish enclosures were found. The filament thickness ranged from 20 to 100 μm, and separate “hairlines” were 3 cm in length. The composition of shungites and “hairlines” was found to be identical, which allowed us to consider the latter as aposhungite carbon formations. The high-carbon hairline structures associated with volkhovites are called kirishites. Kirishites are a new type of high-carbon structures that formed simultaneously with volkhovites in the case of explosion-type delivery of carbon slag and shungite fragments to the daylight surface during Holocene explosive activity. Under sharply reductive conditions, the slags partially melted, the melts were segregated, and carbonaceous-silicate and carbonaceous-ferriferous glasses formed with subsequent decompression-explosive liberation of carbon-supersaturated structures, which were extruded from shungite and slag fragments in the form of a resinoid mass. The “hairlines” were found to be zonal in structure: the central axial zones are composed of high-nitrogen hydrocarbon compounds, and peripheral regions are essentially carbonaceous with a high content of organic-mineral compounds and numerous microanomalies of petrogenic, volatile, rare, and ore elements. Infrared spectroscopy identified in kirishites proteinlike compounds, diagnosed in absorption bands (in cm-1) 600-720 (Amid V), 1200-1300 (Amid III), 1480-1590 (Amid II), 1600-1700 (Amid I), 3000-3800 (vibrations in NH2 and II groups). Gas chromatography, with the possibility of differentiation of left- and right-handed forms, revealed a broad spectrum of amino acids in kirishites, with their total content found to be the absolutely highest record for natural bitumens, an order of magnitude higher than the largest amino acid concentrations ever revealed in fibrous high
Thorpe, Arthur N.; Barkatt, Aaron
Experiments carried out during the progress period are summarized. Experiments carried out involving glass samples exposed to solutions of Tris have shown the appearance of 'spikes' upon monitoring glass dissolution as a function of time. The periodic 'spikes' observed in Tris-based media were interpreted in terms of cracking due to excessive stress in the surface region of the glass. Studies of the interactions of silicate glasses with metal ions in buffered media were extended to systems containing Al. Caps buffer was used to establish the pH. The procedures used are described and the results are given. Preliminary studies were initiated as to the feasibility of adding a slowly dissolving solid compound of the additive to the glass-water system to maintain a supply of dissolved additive. It appears that several magnesium compounds have a suitable combination of solubility and affinity towards silicate glass surfaces to have a pronounced retarding effect on the extraction of uranium from the glass. These preliminary findings raise the possibility that introducing a magnesium source into geologic repositories for nuclear waste glass in the form of a sparingly soluble Mg-based backfill material may cause a substantial reduction in the extent of long-term glass corrosion. The studies described also provide mechanistic understanding of the roles of various metal solutes in the leachant. Such understanding forms the basis for developing long-term predictions of nuclear waste glass durability under repository conditions. From what is known about natural highly reduced glasses such as tektites, it is clear that iron is dissolved as ferrous iron with little or no ferric iron. The reducing conditions were high enough to cause metallic iron to exsolve out of the glass in the form of submicroscopic spherules. As the nuclear waste glass is much less reduced, a study was initiated on other natural glasses in addition to the nuclear waste glass. Extensive measurements were
Pringle, Emily A.; Moynier, Frédéric; Beck, Pierre; Paniello, Randal; Hezel, Dominik C.
Volatile lithophile elements are depleted in the different planetary materials to various degrees, but the origin of these depletions is still debated. Stable isotopes of moderately volatile elements such as Zn can be used to understand the origin of volatile element depletions. Samples with significant volatile element depletions, including the Moon and terrestrial tektites, display heavy Zn isotope compositions (i.e. enrichment of 66Zn vs. 64Zn), consistent with kinetic Zn isotope fractionation during evaporation. However, Luck et al. (2005) found a negative correlation between δ66Zn and 1/[Zn] between CI, CM, CO, and CV chondrites, opposite to what would be expected if evaporation caused the Zn abundance variations among chondrite groups. We have analyzed the Zn isotope composition of multiple samples of the major carbonaceous chondrite classes: CI (1), CM (4), CV (2), CO (4), CB (2), CH (2), CK (4), and CK/CR (1). The bulk chondrites define a negative correlation in a plot of δ66Zn vs 1/[Zn], confirming earlier results that Zn abundance variations among carbonaceous chondrites cannot be explained by evaporation. Exceptions are CB and CH chondrites, which display Zn systematics consistent with a collisional formation mechanism that created enrichment in heavy Zn isotopes relative to the trend defined by CI-CK. We further report Zn isotope analyses of chondrite components, including chondrules from Allende (CV3) and Mokoia (CV3), as well as an aliquot of Allende matrix. All chondrules are enriched in light Zn isotopes (∼500 ppm on 66Zn/64Zn) relative to the bulk, contrary to what would be expected if Zn were depleted during evaporation, on the other hand the matrix has a complementary heavy isotope composition. We report sequential leaching experiments in un-equilibrated ordinary chondrites, which show sulfides are isotopically heavy compared to silicates and the bulk meteorite by ca. +0.65 per mil on 66Zn/64Zn. We suggest isotopically heavy sulfides were
The Nullarbor Region is a limestone desert in the south of Australia. It forms part of the larger Eucla Basin, which straddles the border between South Australia and Western Australia. The portion of the Eucla Basin lying in Westem Australia covers an area of about 104,000 km^2 (Bevan and Binns, 1989) and meteorites have been recovered from this region since 1971, new material being deposited at the Western Australia Museum. Between 21/3/92 and 6/4/92 a joint expedition between the Western Australia Museum and EUROMET recovered approximately 440 specimens of meteorites (total mass 13206 g) and 297 tektites. The expedition, whose members were Claude Perron (Paris), Christian Koeberl (Vienna), Georg Delisle (BGR Hannover), Gian- Paolo Sighinolfi (Modena), and Andrew Morse (OU) for Euromet, together with Wayne Smith (Australian Army) and Tom Smith (Perth Astronomical Observatory), was led by Dr Alex Bevan of the Western Australia Museum. Searching was carried out on foot with the participants spread out in a line with a 10-m spacing, walking along a compass bearing for approximately 10 km and back each day. Eight collecting regions were used, with a stop of about 2 days at each camp. Half of the searching was done near known strewn fields in order that the team become practised. Thus the expedition collected material at the following known sites. Camel Donga, Eucrite: The initial recovery was made in 1984 (Cleverly et al., 1986). The strewn field is about 8 km by 2-3 km at coordinates 30 degrees 19'S, 126 degrees 37'E. This expedition recovered 65 stones weighing a total of 2456 g, plus one stone of 4.8 g that was clearly chondritic in hand specimen. Mulga (north), H6: The initial recovery was made in 1964 (McCall, 1968). The strewn field is 8 km by 2 km at coordinates 30 degrees 11'S, 126 degrees 22'E and on this expedition 5 stones were recovered with a weight of 548 g. Also 110 stones (total mass 1535 g) that are certainly not H6 were found within a 100-m radius of
The Bosumtwi structure is a 1.07 milion year old, well-preserved, 10.5 km wide complex impact crater. It is associated with one of only four tektite strewn fields known on Earth and it is the source of the Ivory Coast tektites. It was drilled in 2004 by the International Continental Scientific Drilling Program (ICDP), and since then it has been the object of intensive research on various aspects of impact cratering process. This thesis is a continuation of those studies. Chapter 3 of this thesis presents a full and detailed characterization of the three granitoid intrusions and one mafic dike located in the vicinity of the Bosumtwi crater in terms of petrology, major and trace element geochemistry, geochronology, as well as isotopic composition. This allows us to characterize magmatic evolution of the West African Craton in this area and better understand the geological framework and target rocks of the impact. This study shows that the similar composition (strongly peraluminous muscovite granites and granodiorites) and age (between 2092±6 Ma and 2098±6 Ma) of granitic intrusions in the proximity of the Bosumtwi crater suggest that they are co-genetic. The granitoids were probably formed as a result of anatexis of TTGs (or rocks derived from them) at relatively low pressure and temperature. We propose that the intrusions from the Bosumtwi area are genetically related to the Banso granite occurring to the east of the crater and can be classified as basin-type, late-stage granitoids. Also a mafic dike located to the NE of the Bosumtwi crater seems to be genetically related to those felsic intrusions. Based on those findings a revised version of the geological map of the Bosumtwi crater area is proposed. Chapter 4 presents results of the investigation of the spatial relations between a statistically significant number of shocked quartz grains (278) showing PDFs (409) developed within a given area of a single thin section (⁓35 mm 2 ) from the Bosumtwi impact crater
Research over the past decades has shown that collisions between solid bodies govern many crucial phases of planetary origin and evolution. The accretion of the terrestrial planets was punctuated by planetary-scale impacts that generated deep magma oceans, ejected primary atmospheres and probably created the moons of Earth and Pluto. Several extrasolar planetary systems are filled with silicate vapor and condensed 'tektites', probably attesting to recent giant collisions. Even now, long after the solar system settled down from its violent birth, a large asteroid impact wiped out the dinosaurs, while other impacts may have played a role in the origin of life on Earth and perhaps Mars, while maintaining a steady exchange of small meteorites between the terrestrial planets and our moon. Most of these events are beyond the scale at which experiments are possible, so that our main research tool is computer simulation, constrained by the laws of physics and the behavior of materials during high-speed impact. Typical solar system impact velocities range from a few km/s in the outer solar system to 10s of km/s in the inner system. Extrasolar planetary systems expand that range to 100s of km/sec typical of the tightly clustered planetary systems now observed. Although computer codes themselves are currently reaching a high degree of sophistication, we still rely on experimental studies to determine the Equations of State (EoS) of materials critical for the correct simulation of impact processes. The recent expansion of the range of pressures available for study, from a few 100 GPa accessible with light gas guns up to a few TPa from current high energy accelerators now opens experimental access to the full velocity range of interest in our solar system. The results are a surprise: several groups in both the USA and Japan have found that silicates and even iron melt and vaporize much more easily in an impact than previously anticipated. The importance of these findings is
Liu, S.; Kyte, F. T.; Glass, B. P.; Gersonde, R.
Our two labs independently discovered upper Eocene microtektites and microkrystites at ODP Site 1090, a new South Atlantic locality near the Agulhus Ridge. This is a significant new data point for the strewn fields of these spherules, which were recently extended into the Atlantic sector of the Southern Ocean when they were reported at ODP Site 689 on the Maude Rise. The microtektites have been regarded as related to North American tektites and the microkrystites as belonging to the clinopyroxene-bearing (cpx) spherule strewn field. Initial reports indicate that Site 1090 contains a complete sequence of upper Eocene sediments composed of diatom and nannofossil oozes. The magneto- and bio-stratigraphy indicate that impact-age sediments should occur in core 30X of Hole 1090B. One of us (FTK) took 2 cc samples at 10 cm intervals over 600 cm of core for Ir analyses and the senior author (SL) took 3 cc samples at 20 cm intervals to search for spherules. Both studies proved successful and additional samples were obtained to confirm initial results and better define the Ir anomaly and spherule abundances. Peak Ir concentrations of 0.97 ng/g were found at 1090B-30X-5, 105-106cm and 0.78 ng/g at 115-116 cm. Anomalous Ir concentrations (greater than 0.1 ng/g) extend over about 100 cm of core. Preliminary results indicate that the excess Ir at this site is about 25 ng per sq cm. About 380 microtektites (>63 pm) and 2492 microkrystites (>63 pm) were recovered over a 1.8 m interval with a peak abundance of microtektites (106/gram) and microkrystites (562/gram) at 1090B-30X- 5, 114-115 cm. The largest microtektite is approximately 960 x 1140 micron in size. About 55 % are spherical, and the rest are disc, cylinder, dumbbell, teardrop, or fragments. Most of the microtektites are transparent colorless, but a few are transparent pale brown or green. Preliminary data indicate that the microtektites at Site 1090 have similar major oxide compositions to those at Site 689. About 50% of
Schultz, P. H.; Stickle, A. M.
The absence of a clearly identified crater (or craters) for the proposed YDB impact has raised questions concerning the reality of such an event. Geologic studies have identified impact deposits well before recognizing a causative crater (e.g., Chicxulub and Chesapeake Bay); some have yet to be discovered (e.g., Australasian tektite strewnfields). The absence of a crater, therefore, cannot be used as an argument against the reality of the YDB impact (and its possible consequences). The study here addresses how a large on-land impact during the late Pleistocene or early Holocene could avoid easy detection today. It does not argue the case for a YDB impact, since such evidence must come from the rock record. During the late Pleistocene, the receding Laurentide ice sheet still covered a significant portion of Canada. While a large (1km) body impacting vertically (90°) would penetrate such a low-impedance ice layer and excavate the substrate, an oblique impact couples more of its energy into the surface layer, thereby partially shielding the substrate. Three approaches address the effectiveness of this flak-jacket effect. First, hypervelocity impact experiments at the NASA Ames Vertical Gun Range investigated the effectiveness of low-impedance layers of different thicknesses for mitigating substrate damage. Second, selected experiments were compared with hydrocode models (see Stickle and Schultz, this volume) and extended to large scales. Third, comparisons were made with relict craters found in eroding sediment and ice covers on Mars. Oblique impacts (30 degrees) into soft particulates (no. 24 sand) covering a solid substrate (aluminum) have no effect on the final crater diameter for layer thicknesses exceeding a projectile diameter and result in only plastic deformation in the substrate. In contrast, a vertical impact requires a surface layer at least 3 times the projectile diameter to achieve the same diameter (with significant substrate damage). Oblique impacts
Abdel Monem, A.A.
conditions can be used to date groundwater and study circulation of water in the ocean. The cosmogenic noble gases nuclides 37 Ar, 39 Ar, 81 Kr and 85 Kr have long residence time in the atmosphere. The other cosmogenic ones, 10 Be, 26 AI and 32 Si, rapidly removed from the atmosphere by precipitation are deposited in marine or lacustrine sediments and in the polar ice sheets, where they are used to measure the rate of deposition of marine sediments. The group 10 Be, 26 AI and 36 CI are suitable for glaciological studies together with 14 C, 31 CI and 81 Kr which occur in air bubbles trapped in glacial ice. Also, the cosmogenic 10 Be, 26 AI and 36 CI accumulate in rocks exposed to cosmic rays at the surface of the Earth, which makes them useful to measure erosion rates and exposure ages. The existence of 10 Be in young volcanic rocks in island arcs and subduction zones has been attributed to the melting of deep sea sediments in the down going slab of oceanic crust. Similarly, the presence of 10 Be in tektites from Indochina and Australia can be attributed to melting of continental sediments containing 10 Be produced in the atmosphere. The use of these radionuclides for the study of geologic phenomena has been enhanced by ultra-sensitive mass spectrometers. This equipment may enable to detect time-dependent variations in the production rates of certain radionuclides that could be attributed to past fluctuations of the solar activity or of the geomagnetic field.