Melt in the impact breccias from the eyreville drill cores, Chesapeake Bay impact structure, USA
- Author(s)
- Katerina Bartosova, Lutz Hecht, Christian Koeberl, Eugen Libowitzky, Wolf Uwe Reimold
- Abstract
The center of the 35.3 Ma Chesapeake Bay impact structure (85 km diam.) was drilled during 2005/2006 in an ICDP-USGS drilling project. The Eyreville drill cores include polymict impact breccias and assocd. 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 crystn. and alteration. The different melt types also vary in their abundance with depth in the drill core. Based on the chem. data, mixing calcns. were performed to det. possible precursors of these melt particles. The calcns. suggest that most melt types formed mainly from the thick sedimentary section of the target sequence (mainly the Potomac Formation), but an addnl. cryst. basement (schist/gneiss) precursor is likely for the most abundant melt types m2 and m5. Sedimentary rocks with compns. 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 compn. of the melt particles is not only the result of the precursor compn. 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 compns. reflects the variety of target rocks and indicates that there was no uniform melt source.
- Organisation(s)
- Department of Lithospheric Research, Department of Mineralogy and Crystallography
- External organisation(s)
- Humboldt-Universität zu Berlin
- Journal
- Meteoritics and Planetary Science
- Volume
- 46
- Pages
- 396-430
- No. of pages
- 35
- ISSN
- 1086-9379
- Publication date
- 2011
- Peer reviewed
- Yes
- Austrian Fields of Science 2012
- 105105 Geochemistry
- Portal url
- https://ucrisportal.univie.ac.at/en/publications/e4edce94-365e-4007-9e88-40cdd4914e1e