New fission‐track age determinations on impact glasses

Bigazzi, G.; Michele, Vincenzo De

doi:10.1111/j.1945-5100.1996.tb02017.x

Cited by 45 publications

(31 citation statements)

References 10 publications

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“…In terms of chemical composition, LDG is very silica-rich (approximately 98 wt% of SiO 2 content) and has low abundances of most major oxides. The age of LDG was determined by fission-track analysis giving ages ranging from 28.5 ± 2.3 Ma to 29.4 ± 0.5 Ma (plateau age) (e.g., Bigazzi and de Michele 1996;Horn et al 1997). The origin of LDG has been the subject of much debate since it was discovered early in the 20th century.…”

Section: Samplesmentioning

confidence: 99%

Infrared, Raman, and cathodoluminescence studies of impact glasses

Gucsik

Koeberl

Brandstätter

et al. 2004

Meteorit & Planetary Scien

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Abstract-We studied the infrared reflectance (IR), Raman, and cathodoluminescence (CL) spectroscopic signatures and scanning electron microscope-cathodoluminescence (SEM-CL) images of three different types of impact glasses: Aouelloul impact glass, a Muong Nong-type tektite, and Libyan desert glass. Both backscattered electron (BSE) and CL images of the Muong Nong-type tektite are featureless; the BSE image of the Libyan desert glass shows only weak brightness contrasts. For the Aouelloul glass, both BSE and CL images show distinct brightness contrast, and the CL images for the Libyan desert glass show spectacular flow textures that are not visible in any other microscopic method. Compositional data show that the SiO 2 composition is relatively higher and the Al 2 O 3 content is lower in the CL-bright areas than in the CL-dark regions. The different appearance of the three glass types in the CL images indicates different peak temperatures during glass formation: the tektite was subjected to the highest temperature, and the Aouelloul impact glass experienced a relatively low formation temperature, while the Libyan desert glass preserves a flow texture that is only visible in the CL images, indicating a medium temperature.All IR reflectance spectra show a major band at around 1040 to 1110 cm −1 (antisymmetric stretching of SiO 4 tetrahedra), with minor peaks between 745 and 769 cm −1 (Si-O-Si angle deformation). Broad bands at 491 and 821 cm −1 in the Raman spectra in all samples are most likely related to diaplectic glass remnants, indicating early shock amorphization followed by thermal amorphization. The combination of these spectroscopic methods allows us to deduce information about the peak formation temperature of the glass, and the CL images, in particular, show glass flow textures that are not preserved in other more conventional petrographic images.

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Section: Samplesmentioning

confidence: 99%

Infrared, Raman, and cathodoluminescence studies of impact glasses

Gucsik

Koeberl

Brandstätter

et al. 2004

Meteorit & Planetary Scien

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“…According to isotope and fission track studies LDG formed about 29 million years ago (e.g., Gentner et al 1969;Mu¨ller-Sohnius et al 1993;Bigazzi and de Michele 1996), most likely during an asteroid impact that caused shock-induced melting of Nubian sandstone Kleinmann et al 2001) or sandy material derived from a Precambrian crystalline basement (Schaaf and Mu¨ller-Sohnius 2002). This view is strengthened by the finding of shock metamorphic features present in sandstones from the Libyan Desert Glass strewn field (Kleinmann et al 2001;C.…”

Section: Introductionmentioning

confidence: 99%

Brownish inclusions and dark streaks in Libyan Desert Glass: Evidence for high-temperature melting of the target rock

Greshake

Koeberl

Fritz

et al. 2010

Meteoritics &Amp; Planetary Science

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Abstract-Dark streaks and different types of inclusions in Libyan Desert Glass (LDG) collected from the LDG strewn field in Egypt were investigated. Rare transparent spherules enclosed in the glassy matrix are characterized by concentric cracks, irregular internal cracks, intense twinning, and considerable amounts of Ti and Al. Raman spectra show that the spherules are a-cristobalite. Their occurrence together with lechatelierite indicates quick heating of the source rock to at least 1550°C, followed by rapid quenching leading to crystallization of b-cristobalite, which upon cooling inverted into a-cristobalite. Brownish inclusions are irregularly shaped, elongated objects with smooth contacts to the surrounding glass. They contain small roundish to elliptical droplets, and a few larger angular grains, which compositionally and according to their Raman spectra most closely resemble low-Ca, Al-rich orthopyroxene. Composition and texture of the orthopyroxene suggest that the brownish inclusions formed by incomplete melting of an Al-rich orthopyroxene bearing precursor, e.g., mafic phases present in desert surface sands or also of orthopyroxenebearing granulite dykes in the LDG target. Experimental data on Ca-poor enstatite also support that the inclusions were heated to about 1550°C. Analyses of dark streaks in LDG reveal high abundances of Al, Ti, Mn, Cr, Fe, and Ni and a pronounced correlation between the abundances of Cr, Mn, Fe, and Ni. As the Fe ⁄ Ni, Mn ⁄ Ni, and Cr ⁄ Ni ratios are all clearly nonchondritic, the source of this material is most likely terrestrial and the dark streaks studied here represent a different type of schlieren compared to those which contain a meteoritic component. These findings suggest LDG formation during a short high-temperature event. Melting of Al-rich orthopyroxene bearing target material seems to suggest an asteroid impact rather than a near-surface airburst.

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“…40 Ar/ 39 Ar Dating 40 Ar/ 39 Ar analyses were performed on a single moldavite specimen that had previously undergone FT dating (Bigazzi and De Michele 1996;Balestrieri et al 1997;Balestrieri et al 1998;Bouška et al 2000); the original weight of the samples is reported in Table 1. Pieces of green moldavites were lightly crushed in an agate mill, and small chips with no visible bubbles or surface alteration were selected under a microscope for analysis.…”

Section: Analytical Data Samplesmentioning

confidence: 99%

⁴⁰Ar/³⁹Ar laser probe dating of the Central European tektite‐producing impact event

Laurenzi

Bigazzi

Balestrieri

et al. 2003

Meteorit & Planetary Scien

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Abstract-A new 40 Ar/ 39 Ar data set is presented for tektites from the Central European strewn field (moldavites). This is the only strewn field that is entirely situated in a continental environment and still characterized by scattered ages (14-15.3 Myr). The main objectives of the study were to define more precisely the moldavite formation age and provide a good calibration for a glass standard proposed for fission-track dating. The laser total fusion ages obtained on chips from 7 individual specimens from the Southern Bohemian and Moravian subfields are restricted to a narrow interval of time, with an average of 14.34 ± 0.08 Myr relative to the 27.95 ± 0.09 Myr of the Fish Canyon Tuff biotite. This result gives a more precise age not only for the tektite field but also for its producing impact. If the genetic link between the moldavites and the Nördlinger Ries impact crater is maintained, then this new age has to be considered a reliable estimate for the Ries crater also.This new value places the formation of Central European tektites within the Lower Serravallian period in the latest geologic timescales. Evidence of their impact products, such as glass spherules or shocked minerals, can, therefore, be sought in sedimentary marine formations in a more precisely defined age interval.

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New fission‐track age determinations on impact glasses

Cited by 45 publications

References 10 publications

Infrared, Raman, and cathodoluminescence studies of impact glasses

Infrared, Raman, and cathodoluminescence studies of impact glasses

Brownish inclusions and dark streaks in Libyan Desert Glass: Evidence for high-temperature melting of the target rock

⁴⁰Ar/³⁹Ar laser probe dating of the Central European tektite‐producing impact event

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New fission‐track age determinations on impact glasses

Cited by 45 publications

References 10 publications

Infrared, Raman, and cathodoluminescence studies of impact glasses

Infrared, Raman, and cathodoluminescence studies of impact glasses

Brownish inclusions and dark streaks in Libyan Desert Glass: Evidence for high-temperature melting of the target rock

40Ar/39Ar laser probe dating of the Central European tektite‐producing impact event

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⁴⁰Ar/³⁹Ar laser probe dating of the Central European tektite‐producing impact event