Petrographic and shock metamorphic studies of the impact breccia section (1397–1551 m depth) of the Eyreville drill core, Chesapeake Bay impact structure, USA

Bartošová, Kateřina; Ferrière, L.; Koeberl, Christian; Reimold, W. U.; Gier, Susanne

doi:10.1130/2009.2458(15)

Cited by 10 publications

(50 citation statements)

References 40 publications

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“…It consists mostly of suevite and large blocks of gneiss (Fig. 2) (Bartosova et al. 2009a; Horton et al.…”

Section: Introductionmentioning

confidence: 99%

“…2009). In the deeper part of the impact breccia section (below 1474 m) melt‐poor suevite and polymict lithic impact breccia alternate with large blocks of cataclastic gneiss (Bartosova et al. 2009a; Horton et al.…”

Section: Introductionmentioning

confidence: 99%

“…It contains a variety of rock and mineral clasts, melt particles, as well as secondary minerals. The lithic clasts in the suevite comprise abundant clasts of pre‐impact sediments of the Atlantic coastal plain (e.g., sandstones, siltstones, and mudstones), as well as clasts from the crystalline basement (e.g., granite, gneiss, and schist; Bartosova et al. 2009a), which is a distal part of the Appalachian orogen (Thomas et al.…”

Section: Introductionmentioning

confidence: 99%

“…2009). The melt‐poor bottom part of the impact breccia sequence with larger basement‐derived clasts and gneiss blocks, and generally scarce melt particles, with no evidence of aerial transport, is thought to be of ground‐surge origin (Bartosova et al. 2009a; Horton et al.…”

Section: Introductionmentioning

confidence: 99%

“…2009b). Toward the top of the impact breccia section the proportion of fallback material increases and the uppermost section, with small clasts of all different types and abundant melt particles, some of which are shard‐like, is clearly a fallback material (Bartosova et al. 2009a; Horton et al.…”

Section: Introductionmentioning

confidence: 99%

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Melt in the impact breccias from the Eyreville drill cores, Chesapeake Bay impact structure, USA

Bartošová

Hecht

Koeberl

et al. 2011

Meteorit & Planetary Scien

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Abstract– The center of the 35.3 Ma Chesapeake Bay impact structure (85 km diameter) was drilled during 2005/2006 in an ICDP–USGS drilling project. The Eyreville drill cores include polymict impact breccias and associated rocks (1397–1551 m depth). Tens of melt particles from these impactites were studied by optical and electron microscopy, electron microprobe, and microRaman spectroscopy, and classified into six groups: m1—clear or brownish melt, m2—brownish melt altered to phyllosilicates, m3—colorless silica melt, m4—melt with pyroxene and plagioclase crystallites, m5—dark brown melt, and m6—melt with globular texture. These melt types have partly overlapping major element abundances, and large compositional variations due to the presence of schlieren, poorly mixed melt phases, partly digested clasts, and variable crystallization and alteration. The different melt types also vary in their abundance with depth in the drill core. Based on the chemical data, mixing calculations were performed to determine possible precursors of these melt particles. The calculations suggest that most melt types formed mainly from the thick sedimentary section of the target sequence (mainly the Potomac Formation), but an additional crystalline basement (schist/gneiss) precursor is likely for the most abundant melt types m2 and m5. Sedimentary rocks with compositions similar to those of the melt particles are present among the Eyreville core samples. Therefore, sedimentary target rocks were the main precursor of the Eyreville melt particles. However, the composition of the melt particles is not only the result of the precursor composition but also the result of changes during melting and solidification, as well as postimpact alteration, which must also be considered. The variability of the melt particle compositions reflects the variety of target rocks and indicates that there was no uniform melt source. Original heterogeneities, resulting from melting of different target rocks, may be preserved in impactites of some large impact structures that formed in volatile‐rich targets, because no large melt body exists, in which homogenization would have taken place.

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“…It consists mostly of suevite and large blocks of gneiss (Fig. 2) (Bartosova et al. 2009a; Horton et al.…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Melt in the impact breccias from the Eyreville drill cores, Chesapeake Bay impact structure, USA

Bartošová

Hecht

Koeberl

et al. 2011

Meteorit & Planetary Scien

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Origin of two Verwey transitions in different generations of magnetite from the Chesapeake Bay impact structure, USA

Mang

Kontny

2013

JGR Solid Earth

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[1] We observed two different Verwey transition temperatures in fragments of crystalline basement rocks and impact sediments from the Chesapeake Bay impact structure, USA. Our study aims to the question if this feature can be used as shock indicator in impact craters. We distinguished three generations of magnetite. (1) Primary magnetite in crystalline basement rocks has average grain sizes up to several hundreds of micrometers and shows a regular T V at ≈ 121 K. (2) Shocked magnetite occurs in fragments of crystalline basement rocks and also in the suevite and impact breccia. These magnetites show two Verwey transitions-a regular one and a "low-temperature transition" (LT V ) at around 89 K. LT V is related to a small grain size fraction, whereas a larger grain size fraction (some hundreds of micrometers) causes the regular T V . The small grain size fraction contains a distinctly higher amount of superficially oxidized material due to the high surface/volume ratio, which causes a decrease of the Verwey transition temperature (LT V ). (3) A secondary magnetite generation shows also two Verwey transition temperatures, one at 121 K and a LT V range between 91 and 105 K. The LT V in this generation is also linked to thin oxidized surface layers. This study shows that especially the Verwey transition temperature of small magnetite grains reacts very sensitively to surface oxidation and can therefore not be used as a reliable pressure indicator for impact structures on Earth.Citation: Mang, C., and A. Kontny (2013), Origin of two Verwey transitions in different generations of magnetite from the Chesapeake Bay impact structure, USA,

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Petrography, mineralogy, and geochemistry of deep gravelly sands in the Eyreville B core, Chesapeake Bay impact structure

Bartošová

Gier

Horton

et al. 2010

Meteoritics &Amp; Planetary Science

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Abstract-The ICDP-USGS Eyreville drill cores in the Chesapeake Bay impact structure reached a total depth of 1766 m and comprise (from the bottom upwards) basement-derived schists and granites ⁄ pegmatites, impact breccias, mostly poorly lithified gravelly sand and crystalline blocks, a granitic slab, sedimentary breccias, and postimpact sediments. The gravelly sand and crystalline block section forms an approximately 26 m thick interval that includes an amphibolite block and boulders of cataclastic gneiss and suevite. Three gravelly sands (basal, middle, and upper) are distinguished within this interval. The gravelly sands are poorly sorted, clast supported, and generally massive, but crude size-sorting and subtle, discontinuous layers occur locally. Quartz and K-feldspar are the main sand-size minerals and smectite and kaolinite are the principal clay minerals. Other mineral grains occur only in accessory amounts and lithic clasts are sparse (only a few vol%). The gravelly sands are silica rich (80 wt% SiO 2 ). Trends with depth include a slight decrease in SiO 2 and slight increase in Fe 2 O 3 . The basal gravelly sand (below the cataclasite boulder) has a lower SiO 2 content, less K-feldspar, and more mica than the higher sands, and it contains more lithic clasts and melt particles that are probably reworked from the underlying suevite. The middle gravelly sand (below the amphibolite block) is finer-grained, contains more abundant clay minerals, and displays more variable chemical compositions than upper gravelly sand (above the block). Our mineralogical and geochemical results suggest that the gravelly sands are avalanche deposits derived probably from the nonmarine Potomac Formation in the lower part of the target sediment layer, in contrast to polymict diamictons higher in the core that have been interpreted as ocean-resurge debris flows, which is in agreement with previous interpretations. The mineralogy and geochemistry of the gravelly sands are typical for a passive continental margin source. There is no discernible mixing with marine sediments (no glauconite or Paleogene marine microfossils noted) during the impact remobilization and redeposition. The unshocked amphibolite block and cataclasite boulder might have originated from the outer parts of the transient crater.

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Petrographic and shock metamorphic studies of the impact breccia section (1397–1551 m depth) of the Eyreville drill core, Chesapeake Bay impact structure, USA

Cited by 10 publications

References 40 publications

Melt in the impact breccias from the Eyreville drill cores, Chesapeake Bay impact structure, USA

Melt in the impact breccias from the Eyreville drill cores, Chesapeake Bay impact structure, USA

Origin of two Verwey transitions in different generations of magnetite from the Chesapeake Bay impact structure, USA

Petrography, mineralogy, and geochemistry of deep gravelly sands in the Eyreville B core, Chesapeake Bay impact structure

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