Experimental constraints on shock-induced microstructures in naturally deformed silicates

Huffman, Alan R.; Reimold, W. U.

doi:10.1016/0040-1951(95)00162-x

Cited by 99 publications

(147 citation statements)

References 77 publications

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“…The presence of minor melt particles indicates limited admixture of material shocked to even higher pressures (>45 GPa; e.g., Stöffler and Langenhorst 1994;Huffman and Reimold 1996). A slight overall increase in the degree of shock metamorphism appears to occur from the top to the bottom of the upper impactites as the proportions of diaplectic quartz glass and melt particles increase slightly (Table 2).…”

Section: Shock Variationmentioning

confidence: 99%

“…8 GPa (1 set of PDFs per host quartz grain) and 30 GPa (multiple sets of PDFs, incipient isotropization) (e.g., Stöffler and Langenhorst 1994;Huffman and Reimold 1996) for non-porous crystalline rocks, while the presence of diaplectic quartz glasses in the suevites lower in the borehole indicates higher shock pressures of >30-45 GPa (e.g., Stöffler and Langenhorst 1994;Huffman and Reimold 1996). The presence of minor melt particles indicates limited admixture of material shocked to even higher pressures (>45 GPa; e.g., Stöffler and Langenhorst 1994;Huffman and Reimold 1996).…”

Section: Shock Variationmentioning

confidence: 99%

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Lithostratigraphic and petrographic analysis of ICDP drill core LB‐07A, Bosumtwi impact structure, Ghana

Coney

Gibson

Reimold

et al. 2007

Meteorit & Planetary Scien

100

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Abstract-Lithostratigraphic and petrographic studies of drill core samples from the 545.08 m deep International Continental Scientific Drilling Program (ICDP) borehole LB-07A in the Bosumtwi impact structure revealed two sequences of impactites below the post-impact crater sediments and above coherent basement rock. The upper impactites (333.38-415.67 m depth) comprise an alternating sequence of suevite and lithic impact breccias. The lower impactite sequence (415.67-470.55 m depth) consists essentially of monomict impact breccia formed from meta-graywacke with minor shale, as well as two narrow injections of suevite, which differ from the suevites of the upper impactites in color and intensity of shock metamorphism of the clasts. The basement rock (470.55-545.08 m depth) is composed of lower greenschist-facies metapelites (shale, schist and minor phyllite), meta-graywacke, and minor meta-sandstone, as well as interlaminated quartzite and calcite layers. The basement also contains a number of suevite dikelets that are interpreted as injection veins, as well as a single occurrence of granophyric-textured rock, tentatively interpreted as a hydrothermally altered granitic intrusion likely related to the regional pre-impact granitoid complexes.Impact melt fragments are not as prevalent in LB-07A suevite as in the fallout suevite facies around the northern crater rim; on average, 3.6 vol% of melt fragments is seen in the upper suevites and up to 18 vol% in the lower suevite occurrences. Shock deformation features observed in the suevites and polymict lithic breccias include planar deformation features in quartz (1 to 3 sets), rare diaplectic quartz glass, and very rare diaplectic feldspar glass. Notably, no ballen quartz, which is abundant in the fallout suevites, has been found in the within-crater impact breccias. An overall slight increase in the degree of shock metamorphism occurs with depth in the impactites, but considerably lower shock degrees are seen in the suevites of the basement rocks, which show similar features to each other. The bulk of the suevite in LB-07A appears to have been derived from the <35 GPa shock zone of the transient crater.

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Section: Shock Variationmentioning

confidence: 99%

Section: Shock Variationmentioning

confidence: 99%

Lithostratigraphic and petrographic analysis of ICDP drill core LB‐07A, Bosumtwi impact structure, Ghana

Coney

Gibson

Reimold

et al. 2007

Meteorit & Planetary Scien

100

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“…They are generally found as small grains, 1-5 mm in size, and typically have 1 to 3 sets of PDFs (Fig. 9a) that are indicative of shock pressures of 15 to ~30 GPa (e.g., Stöffler 1974;Langenhorst and Deutsch 1994;Huffman and Reimold 1996). Point count analyses indicate that the proportion of quartz grains with multiple sets of PDFs appears to increase with depth in the impactite interval (Table 3).…”

Section: Shock Metamorphismmentioning

confidence: 99%

First petrographic results on impactites from the Yaxcopoil‐1 borehole, Chicxulub structure, Mexico

Tuchscherer¹,

Reimold²,

Koeberl³

et al. 2004

Meteorit & Planetary Scien

Self Cite

109

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Abstract-The ICDP Yaxcopoil-1 (Yax-1) borehole located 60 km south-southwest of the center of the Chicxulub impact structure intercepted an interval of allogenic impactites (depth of 795-895 m). Petrographic analysis of these impactites allows them to be differentiated into five units based on their textural and modal variations. Unit 1 (795-922 m) comprises an apparently reworked, poorly sorted and graded, fine-grained, clast-supported, melt fragment-bearing suevitic breccia. The interstitial material, similar to units 2 and 3, is permeated by numerous carbonate veinlets. Units 2 (823-846 m) and 3 (846-861 m) are groundmass-supported breccias that comprise green to variegated angular and fluidal melt particles. The groundmass of units 2 and 3 comprises predominantly fine-grained calcite, altered alkali element-, Ca-, and Si-rich cement, as well as occasional lithic fragments. Unit 4 (861-885 m) represents a massive, variably devitrified, and brecciated impact melt rock. The lowermost unit, unit 5 (885-895 m), comprises highly variable proportions of melt rock particles (MRP) and lithic fragments in a fine-grained, carbonate-dominated groundmass. This groundmass could represent either a secondary hydrothermal phase or a carbonate melt phase, or both. Units 1 and 5 contain well-preserved foraminifera fossils and a significantly higher proportion of carbonate clasts than the other units. All units show diagnostic shock deformation features in quartz and feldspar clasts. Our observations reveal that most felsic and all mafic MRP are altered. They register extensive K-metasomatism. In terms of emplacement, we suggest that units 1 to 3 represent fallout suevite from a collapsing impact plume, whereby unit 1 was subsequently reworked by resurging water. Unit 4 represents a coherent impact melt body, the formation of which involved a significant proportion of crystalline basement. Unit 5 is believed to represent an initial ejecta/ground-surge deposit.

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“…Controlled shockwave experiments, which allow the collection of shocked samples for further studies, using various techniques, have led to a good understanding of the conditions for the formation of shock metamorphic products and a pressure-temperature calibration of the effects of shock pressures up tõ 100 GPa (see e.g. French and Short, 1968;Stöffler, 1972Stöffler, , 1974Stöffler and Langenhorst, 1994;Huffman and Reimold, 1996;Langenhorst and Deutsch, 1998; and references therein). Shock metamorphic effects are best studied in the various breccia types that are found within and around the crater structure (see above).…”

Section: Shock Metamorphismmentioning

confidence: 99%

Mineralogical and geochemical aspects of impact craters

Koeberl¹

2002

Mineral. mag.

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The importance of impact cratering on terrestrial planets is obvious from the abundance of craters on their surfaces. On Earth, active geological processes rapidly obliterate the cratering record. To date only about 170 impact structures have been recognized on the Earth's surface. Mineralogical, petrographic, and geochemical criteria are used to identify the impact origin of such structures or related ejecta layers. The two most important criteria are the presence of shock metamorphic effects in mineral and rock inclusions in breccias and melt rocks, as well as the demonstration, by geochemical techniques, that these rocks contain a minor extraterrestrial component. There is a variety of macroscopic and microscopic shock metamorphic effects. The most important ones include the presence of planar deformation features in rock-forming minerals, high-pressure polymorphs (e.g. of coesite and stishovite from quartz, or diamond from graphite), diaplectic glass, and rock and mineral melts. These features have been studied by traditional methods involving the petrographic microscope, and more recently with a variety of instrumental techniques, including transmission electron microscopy, Raman spectroscopy, cathodoluminescence imaging and spectroscopy, and high-resolution X-ray computed tomography. Geochemical methods to detect an extraterrestrial component include measurements of the concentrations of siderophile elements, mainly of the platinum-group elements (PGEs), and, more recently, chromium and osmium isotopic studies. The latter two methods can provide confirmation that these elements are actually of meteoritic origin. The Cr isotopic method is also capable of providing information on the meteorite type. In impact studies there is now a trend towards the use of interdisciplinary and multi-technique approaches to solve open questions.

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Experimental constraints on shock-induced microstructures in naturally deformed silicates

Cited by 99 publications

References 77 publications

Lithostratigraphic and petrographic analysis of ICDP drill core LB‐07A, Bosumtwi impact structure, Ghana

Lithostratigraphic and petrographic analysis of ICDP drill core LB‐07A, Bosumtwi impact structure, Ghana

First petrographic results on impactites from the Yaxcopoil‐1 borehole, Chicxulub structure, Mexico

Mineralogical and geochemical aspects of impact craters

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