Microscopic lamellar deformation features in quartz: Discriminative characteristics of shock-generated varieties

Alexopoulos, J. S.; Grieve, R. A. F.; Robertson, P. B.

doi:10.1130/0091-7613(1988)016<0796:mldfiq>2.3.co;2

Cited by 99 publications

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“…Quartz with PDFs is generally considered reliable evidence of meteorite impact (French and Short 1968;Stöffler 1972Stöffler , 1974Alexopoulos et al 1988), as are high pressure silica polymorphs (Stöffler 1971). Being the best criterion for distinguishing between various stages of shock metamorphism, the shock deformation of quartz (quartz without PDFs, quartz with PDFs, quartz with partial isotropization, quartz with complete isotropization (diaplectic quartz glass), quartz with ballen structure, and shock melted) has been used to estimate the shock pressure in the Bosumtwi suevite samples In shocked shale and graywacke, quartz is completely transformed to diaplectic glass, whereas adjacent individual feldspar grains are not (Figs.…”

Section: Shock Metamorphismmentioning

confidence: 99%

Petrographic studies of “fallout” suevite from outside the Bosumtwi impact structure, Ghana

Boamah

Koeberl

2006

Meteorit & Planetary Scien

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Abstract-Field studies and a shallow drilling program carried out in 1999 provided information about the thickness and distribution of suevite to the north of the Bosumtwi crater rim. Suevite occurrence there is known from an ~1.5 km 2 area; its thickness is ≤15 m. The present suevite distribution is likely the result of differential erosion and does not reflect the initial areal extent of continuous Bosumtwi ejecta deposits.Here we discuss the petrographic characteristics of drill core samples of melt-rich suevite. Macroscopic constituents of the suevites are melt bodies and crystalline and metasedimentary rock (granite, graywacke, phyllite, shale, schist, and possibly slate) clasts up to about 40 cm in size. Shock metamorphic effects in the clasts include multiple sets of planar deformation features (PDFs), diaplectic quartz and feldspar glasses, lechatelierite, and ballen quartz, besides biotite with kink bands. Basement rock clasts in the suevite represent all stages of shock metamorphism, ranging from samples without shock effects to completely shock-melted material that is indicative of shock pressures up to ~60 GPa.

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Section: Shock Metamorphismmentioning

confidence: 99%

Petrographic studies of “fallout” suevite from outside the Bosumtwi impact structure, Ghana

Boamah

Koeberl

2006

Meteorit & Planetary Scien

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“…Such phases require the realization of abnormally high pressures in the upper parts of the crust; conditions normally met only within the deeper interiors of planets. The development of multiple planar deformation features (PDFs) in minerals is also considered an indication of shock (e.g., Alexopoulos et al, 1988). However, identification of high-pressure polymorphs and PDFs requires microscopy and/or sophisticated analysis in the laboratory: their presence cannot be verified in the field.…”

Section: Introductionmentioning

confidence: 99%

Shock‐induced melting and vaporization of shatter cone surfaces: Evidence from the Sudbury impact structure

Gibson

Spray

1998

Meteorit & Planetary Scien

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Abstract-Analytical scanning electron microscopy has been used to investigate the surface textures and compositions of newly exposed shatter cones from the 1.85 Ga Sudbury impact structure, Canada. Unusual surface microstructures are observed at the micron scale, including silicate melt smears, melt fibres and melt splats. Silicate and Ni-rich spherules up to 5 pm in diameter adorn earlier-formed surface features, and we interpret these to be condensates formed due to shock-induced vaporization of the shatter cone surfaces. The development of striations on the shatter cones is attributed to shock-related fracture and slip. Formation of melts and spherules indicates that the highest ranks of shock metamorphism (Stages IV and V) were realized, but only on a very localized scale. Shatter cone surfaces are, therefore, likely sites for the development of high-pressure polymorphs and, if the chemistry is appropriate, fillerenes. As such, they may be equivalent to "Type A" pseudotachylytes and shock veins in meteorites.

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“…In other recognized impact structures in the world, shock-metamorphic features are best developed in crystalline target rocks (Stöffler, 1971;Alexopoulos, Grieve & Robertson, 1988). The poorly consolidated, interbedded porous sandstones and argillaceous sedimentary rocks of the Yallalie structure may have absorbed much of the energy of the impact event.…”

Section: C D E N T I T H a N D Ot H E R Smentioning

confidence: 99%

Yallalie: a buried structure of possible impact origin in the Perth Basin, Western Australia

et al. 1999

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An enigmatic buried structure, located in Mesozoic sedimentary rocks in the Perth Basin, Western Australia, was discovered in 1990 by Ampol Exploration. The basin-like Yallalie structure (centred on 30° 26′ 40.3″ S, 115° 46′ 16.4″ E) is circular in plan view and about 12 km in diameter. High-resolution, seismic-reflection profiles across the structure show a basin-shaped area of chaotic reflections that extend to a depth of approximately 2 km below the surface. The structure has sharp boundaries with surrounding faulted, but otherwise relatively undisturbed, rocks. In the centre of the structure there is an uplifted area approximately 3–4 km across, similar to those described from complex meteorite impact structures. The seismically defined structure coincides with a circular topographic depression, and image processing of digital elevation data has allowed recognition of concentric and radial structures extending as far as 40 km from the centre of the depression. Gravity surveys show the structure to be associated with a positive gravity anomaly of about 30 gu. Aeromagnetic surveys have defined annular anomalies associated with the central uplifted section, and possibly margins, of the structure. A search for siderophile element enrichments (by neutron activation analysis) in the rocks of the structure, which would indicate the presence of a meteorite component, proved negative. Quartz grains in cores that penetrate the structure show the development of prismatic cleavage fractures and irregular, slightly curved planes formed by brittle fracture. An allochthonous breccia of Late Cretaceous rocks occurs a few kilometres west of the western margin of the structure. Quartz grains from a thin veneer of Tertiary sediments that drape the structure are essentially undeformed. However, multiple sets of closely spaced planar deformation features in quartz, characteristic of highly shocked rocks, have yet to be observed in the rocks of the Yallalie structure and the allochthonous breccia. The morphology of the Yallalie structure determined from topographic and geophysical data suggests strongly that it is of impact origin. Geological and geochemical evidence is equivocal, but is not inconsistent with this interpretation.

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Microscopic lamellar deformation features in quartz: Discriminative characteristics of shock-generated varieties

Cited by 99 publications

References 0 publications

Petrographic studies of “fallout” suevite from outside the Bosumtwi impact structure, Ghana

Petrographic studies of “fallout” suevite from outside the Bosumtwi impact structure, Ghana

Shock‐induced melting and vaporization of shatter cone surfaces: Evidence from the Sudbury impact structure

Yallalie: a buried structure of possible impact origin in the Perth Basin, Western Australia

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