Impact-shocked zircons: discovery of shock-induced textures reflecting increasing degrees of shock metamorphism

Bohor, B. F.; Betterton, W. J.; Krogh, T. E.

doi:10.1016/0012-821x(93)90149-4

Cited by 113 publications

(94 citation statements)

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“…Three grains displayed strawberry texture, and this texture has previously been interpreted as a product of recrystallization under high-T conditions after shock-induced amorphization [41][42]. As for zircon from North American sites (e.g., [40,43]), the granular texture in the porous zircon from the European sites occurs beneath the original planar surface of subhedral grains (Fig. 4c).…”

Section: Figurementioning

confidence: 87%

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Analyses of shocked quartz at the global K-P boundary indicate an origin from a single, high-angle, oblique impact at Chicxulub

Morgan

Lana

Kearsley

et al. 2006

Earth and Planetary Science Letters

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Section: Figurementioning

confidence: 87%

“…The aggregates are mostly seen on broken surfaces of the grains and are porous, similar in many aspects to the granular (strawberry) textures reported for shocked zircon in K-P samples from North America (Figs. 3c, d) (e.g., [40]). …”

Section: Shock Featuresmentioning

confidence: 99%

Analyses of shocked quartz at the global K-P boundary indicate an origin from a single, high-angle, oblique impact at Chicxulub

Morgan

Lana

Kearsley

et al. 2006

Earth and Planetary Science Letters

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“…Granular-textured zircon grains are frequently observed in impact-related lithologies (Bohor et al 1993;Krogh et al 1993bKrogh et al , 1996Glass and Liu 2001). Such polycrystalline grains represent crystallites of zircon in a glassy ZrSiO 4 matrix (Bohor et al 1993;Kamo et al 1996;Glass 2000) that resulted from shock-induced amorphization and subsequent recrystallization.…”

Section: Granular Texturesmentioning

confidence: 99%

“…Naturally shocked zircons appear turbid to opaque in color (Krogh et al 1984;Bohor et al 1993;Corfu et al 2003) and exhibit a decrease of the refractive index, which indicates amorphization (Dobretsov et al 1969). Amorphous lamellae of diaplectic ZrSiO 4 glass were confirmed by transmission electron microscopy (TEM) analyses of experimentally shocked ZrSiO 4 (Leroux et al 1999).…”

Section: Reidite and Planar Microstructuresmentioning

confidence: 99%

“…Optically recordable planar microstructures have been identified as microcracks and microtwinning features (Leroux et al 1999;Reimold et al 2002). They occur as single or multiple sets of parallel bands with a spacing below 5 µm (Krogh and Davis 1984;Bohor et al 1993) and are interpreted to form along with the transition of zircon to the high pressure polymorph reidite (Kusaba et al 1986;Leroux et al 1999;Finch and Hanchar 2003). The shock-induced martensitic, i.e., solid-state transition of zircon to reidite starts at ∼20 GPa and is complete at 52 GPa (Fiske et al 1994).…”

Section: Reidite and Planar Microstructuresmentioning

confidence: 99%

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Shock‐metamorphosed zircon in terrestrial impact craters

Wittmann

Kenkmann

Schmitt

et al. 2006

Meteorit & Planetary Scien

156

201

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Shock-metamorphosed zircon in terrestrial impact cratersAbstract-To ascertain the progressive stages of shock metamorphism of zircon, samples from three well-studied impact craters were analyzed by optical microscopy, scanning electron microscopy (SEM), and Raman spectroscopy in thin section and grain separates. These samples are comprised of well-preserved, rapidly quenched impactites from the Ries crater, Germany, strongly annealed impactites from the Popigai crater, Siberia, and altered, variably quenched impactites from the Chicxulub crater, Mexico. The natural samples were compared with samples of experimentally shock-metamorphosed zircon. Below 20 GPa, zircon exhibits no distinct shock features. Above 20 GPa, optically resolvable planar microstructures occur together with the high-pressure polymorph reidite, which was only retained in the Ries samples. Decomposition of zircon to ZrO 2 only occurs in shock stage IV melt fragments that were rapidly quenched. This is not only a result of post-shock temperatures in excess of ∼1700 °C but could also be shock pressure-induced, which is indicated by possible relics of a high-pressure polymorph of ZrO 2 . However, ZrO 2 was found to revert to zircon with a granular texture during devitrification of impact melts. Other granular textures represent recrystallized amorphous ZrSiO 4 and reidite that reverted to zircon. This requires annealing temperatures >1100 °C. A systematic study of zircons from a continuous impactite sequence of the Chicxulub impact structure yields implications for the post-shock temperature history of suevite-like rocks until cooling below ∼600 °C.

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Shock Metamorphism

Ferrière

Osinski

2012

Impact Cratering

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A requirement for the recognition and confirmation of meteorite impact structures is the presence of shock metamorphic indicators, either megascopic (e.g. shatter cones) or microscopic (e.g. planar deformation features in minerals), or high-pressure polymorphs (e.g. coesite and stishovite) and/or siderophile element (e.g. iridium) or isotopic (osmium) anomalies in specific geological settings. Crater morphology is not a sufficient argument, because a variety of circular features can be formed by completely different geological processes (e.g. volcanism or salt diapirism). The terms 'shock effects' or 'shock-metamorphic effects' cover all types of shock-induced changes, such as the formation of planar microstructures and phase transformations. Impact metamorphism is essentially the same as shock metamorphism, except that it also encompasses the melting, decomposition and vaporization of target rocks (Stöffler and Grieve, 2007). These irreversible changes are produced when rocks are subjected to shock pressures above their Hugoniot elastic limit (HEL). This limit is defined as 'the critical shock pressure at which a solid yields under the uniaxial strain of a plane shock wave' (Stöffler, 1972). The HEL of quartz is in the range of 5-8 GPa and ranges from approximately 1 to 10 GPa for most geological materials (e.g. Stöffler, 1972;Stöffler and Langenhorst, 1994). In nature, at the surface of the Earth, only hypervelocity impacts can generate such high shock pressures.A great diversity of shock effects in minerals are known and have been abundantly described in the literature during the last 40 years mostly for quartz (e.g.

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Impact-shocked zircons: discovery of shock-induced textures reflecting increasing degrees of shock metamorphism

Cited by 113 publications

References 10 publications

Analyses of shocked quartz at the global K-P boundary indicate an origin from a single, high-angle, oblique impact at Chicxulub

Analyses of shocked quartz at the global K-P boundary indicate an origin from a single, high-angle, oblique impact at Chicxulub

Shock‐metamorphosed zircon in terrestrial impact craters

Shock Metamorphism

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