The ševĚtín astrobleme, southern Bohemia, Czechoslovakia

Vrána, Stanislav

doi:10.1007/bf01821089

Cited by 6 publications

(3 citation statements)

References 12 publications

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“…These occur in either primary or reworked impact ejecta and are postulated to have formed within the turbulent ejecta cloud (Pope et al, 1999). First recognized from the Ries crater (Graup, 1981), they have since been described associated with the Sevetin (Vrana, 1987), Azuara (Ernstson and Fiebag, 1992), Alamo (Warme and Kuehner, 1998), and Chicxulub (Ocampo et al, 1996;Pope et al, 1999) impact sites. Accreted grains from the latter three sites are composed largely or completely of fi ne carbonate fragments in a carbonate matrix, refl ecting bedrock at the impact sites.…”

Section: Accreted Grains In Other Settingsmentioning

confidence: 99%

“…Calcite is also present in accreted grains at Ries although it is described as being a secondary infi ltration (Graup, 1981). No carbonate is present at Sevetin, but the impact breccia there is silicifi ed (Vrana, 1987), and thus its original composition is uncertain. These examples are from ancient impact sites and the composition of the contemporaneous cement is not known.…”

Section: Accreted Grains In Other Settingsmentioning

confidence: 99%

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Catastrophic emplacement of the Heart Mountain block slide, Wyoming and Montana, USA

Beutner

Gerbi

2005

Geol Soc America Bull

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The mechanism that allowed many tens of km of movement of the enormous block slide fl oored by the rootless Heart Mountain detachment fault in NW Wyoming has long been a puzzle. Carbonate-rich microbreccia that is widespread along the fault and in dikes in the upper plate contains accreted grains indistinguishable from those observed as fallout from volcanic eruption clouds (accretionary lapilli) and impact ejecta clouds and in intrusive diatremes. In these settings and also in industrial processing, accreted grains form when particles in a turbulent gaseous suspension containing limited water adhere to a nucleating grain or to each other. Elongate grains in thick microbreccia have strong but diverse shape-preferred orientations unlike those reported from other fault rocks but instead suggestive of turbulent fl ow, and the microbreccia contains layering and other features of sedimentary character that appear to record deposition from suspension rather than frictional processes along a fault. We suggest that frictional heating led to dissociation of carbonate rock along the fault, producing supercritical CO 2 as the suspending medium. High CO 2 pressure drastically reduced friction along the fault and allowed continuation of catastrophic movement, probably initiated by a volcanic or phreatomagmatic explosion, resulting in very large displacement on a lowdipping surface. Earlier slower sliding may have occurred but fi nal emplacement was rapid (minutes) and spectacular.

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Section: Accreted Grains In Other Settingsmentioning

confidence: 99%

Section: Accreted Grains In Other Settingsmentioning

confidence: 99%

Catastrophic emplacement of the Heart Mountain block slide, Wyoming and Montana, USA

Beutner

Gerbi

2005

Geol Soc America Bull

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“…However, using a standard petrographic microscope, it can be difficult to distinguish between PDFs and nonshock‐related planar microstructures in quartz. On several occasions, lamellar microstructures in quartz have been identified as PDFs, but have subsequently been disproved to be shock‐related, or they remain controversial (e.g., Vrána 1987 versus Cordier et al. 1994; Surenian 1988 versus Leroux and Doukhan 1993; Ernstson and Fiebag 1992 versus Langenhorst and Deutsch 1996; Becker et al.…”

Section: Introductionmentioning

confidence: 99%

Scanning electron microscope‐cathodoluminescence (SEM‐CL) imaging of planar deformation features and tectonic deformation lamellae in quartz

Hamers¹,

Drury

2011

Meteorit & Planetary Scien

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Abstract-Planar deformation features (PDFs) in quartz are essential proof for the correct identification of meteorite impact structures and related ejecta layers, but can be confused with tectonic deformation lamellae. The only completely reliable method to demonstrate the shock origin of suspected (sub-) planar microstructures, transmission electron microscope (TEM) observations, is costly and time consuming. We have used a cathodoluminescence (CL) detector attached to a scanning electron microscope (SEM) to image both PDFs and tectonic deformation lamellae in quartz to demonstrate the potential of a simple method to identify PDFs and define characteristics that allow their distinction from tectonic deformation lamellae. In both limited wavelength grayscale and composite color SEM-CL images, PDFs are easily identified. They are straight, narrow, well-defined features, whereas tectonic deformation lamellae are thicker, slightly curved, and there is often no clear boundary between lamella and host quartz. Composite color images reveal two types of CL behavior in PDFs: either they emit a red to infrared CL signal or they are nonluminescent. The color of the CL signal emitted by tectonic deformation lamellae ranges from blue to red. For comparison, we also imaged several shocked quartz grains at cryogenic temperature. In most cases, the PDF characteristics in cryo-CL images do not differ significantly from those in images recorded at room temperature. We conclude that SEM-CL imaging, especially when color composites are used, provides a promising, practical, low cost, and nondestructive method to distinguish between PDFs and tectonic lamellae, even when the simplest CL techniques available are used.

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The Azuara impact structure (Spain): new insights from geophysical and geological investigations

Ernstson

Fiebag

1992

Geol Rundsch

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The ševĚtín astrobleme, southern Bohemia, Czechoslovakia

Cited by 6 publications

References 12 publications

Catastrophic emplacement of the Heart Mountain block slide, Wyoming and Montana, USA

Catastrophic emplacement of the Heart Mountain block slide, Wyoming and Montana, USA

Scanning electron microscope‐cathodoluminescence (SEM‐CL) imaging of planar deformation features and tectonic deformation lamellae in quartz

The Azuara impact structure (Spain): new insights from geophysical and geological investigations

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