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evidence for a meteoritic component in impact melt rock from the chicxulub structureThe Chicxulub structure in Yucatan, Mexico, has recently been recognized as a greater then 200-km-diameter multi-ring impact crater of K-T boundary age. Crystalline impact melt rocks and breccias from within the crater, which have compositions similar to those of normal continental crustal rocks and which show shock metamorphic effects, have been studied for trace element and Re-Os isotope compositions. Re-Os isotope systematics allow the sensitive and selective determination of an extraterrestrial component in impact-derived rocks. A melt rock sample shows elevated iridium concentrations, an osmium concentration of 25 ppb, and a low Os-187/Os-188 ratio of 0.113, which are incompatible with derivation from the continental crust. Even though the Os-187/Os-188 ratio is slightly lower than the range so far measured in meteorites, a mantle origin seems unlikely for mass balance reasons and because the cratering event is unlikely to have excavated mantle material. The data support the hypothesis of a heterogeneously distributed meteoritic component in the Chicxulub melt rock. A sample of impact glass from the Haitian K-T boundary at Beloc yielded about 0.1 ppb osmium and an Os-187/0s-188 ratio of 0.251, indicating the presence of a small meteoritic component in the impact ejecta as well.
Document ID
19970024923
Document Type
Reprint (Version printed in journal)
Authors
Koeberl, Christian
(Wien Univ. Austria)
Sharpton, Virgil L.
(Lunar and Planetary Inst. Houston, TX United States)
Schuraytz, Benjamin C.
(Lunar and Planetary Inst. Houston, TX United States)
Shirey, Steven B.
(Carnegie Institution of Washington Washington, DC United States)
Blum, Joel D.
(Dartmouth Coll. Hanover, NH United States)
Marin, Luis E.
(Universidad Nacional Autonoma de Mexico Mexico City, Mexico)
Date Acquired
August 17, 2013
Publication Date
January 19, 1994
Publication Information
Publication: Geochimica et Cosmochimica Acta
Volume: 58
Issue: 6
ISSN: 0016-7037
Subject Category
Astrophysics
Report/Patent Number
NAS 1.26:203366
NASA-CR-203366
LPI-Contrib-828
Funding Number(s)
PROJECT: Proj. P8794
PROJECT: Proj. P9026-GEO
CONTRACT_GRANT: NSF EAR-92-18847
CONTRACT_GRANT: NASw-4066
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