Implications for behavior of volatile elements during impacts—Zinc and copper systematics in sediments from the Ries impact structure and central European tektites

1,2Zuzana Rodovská, 1Tomáš Magna, 3Karel Žák, 4Chizu Kato, 4,5,6Paul S. Savage, 4Frédéric Moynier, 3Roman Skála, 2Josef Ježek
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12922]
1Czech Geological Survey, Prague 1, Czech Republic
2Faculty of Science, The Charles University in Prague, Prague 2, Czech Republic
3Institute of Geology, The Czech Academy of Sciences, Prague 6, Czech Republic
4Institut de Physique du Globe de Paris, Université Paris Diderot, Paris, France
5Department of Earth Sciences, Durham University, Science Labs, Durham, UK
6Department of Earth and Environmental Sciences, University of St. Andrews, St. Andrews, Fife, UK
Published by arrangement with John Wiley & Sons

Moldavites are tektites genetically related to the Ries impact structure, located in Central Europe, but the source materials and the processes related to the chemical fractionation of moldavites are not fully constrained. To further understand moldavite genesis, the Cu and Zn abundances and isotope compositions were measured in a suite of tektites from four different substrewn fields (South Bohemia, Moravia, Cheb Basin, Lusatia) and chemically diverse sediments from the surroundings of the Ries impact structure. Moldavites are slightly depleted in Zn (~10–20%) and distinctly depleted in Cu (>90%) relative to supposed sedimentary precursors. Moreover, the moldavites show a wide range in δ66Zn values between 1.7 and 3.7‰ (relative to JMC 3-0749 Lyon) and δ65Cu values between 1.6 and 12.5‰ (relative to NIST SRM 976) and are thus enriched in heavy isotopes relative to their possible parent sedimentary sources (δ66Zn = −0.07 to +0.64‰; δ65Cu = −0.4 to +0.7‰). In particular, the Cheb Basin moldavites show some of the highest δ65Cu values (up to 12.5‰) ever observed in natural samples. The relative magnitude of isotope fractionation for Cu and Zn seen here is opposite to oxygen-poor environments such as the Moon where Zn is significantly more isotopically fractionated than Cu. One possibility is that monovalent Cu diffuses faster than divalent Zn in the reduced melt and diffusion will not affect the extent of Zn isotope fractionation. These observations imply that the capability of forming a redox environment may aid in volatilizing some elements, accompanied by isotope fractionation, during the impact process. The greater extent of elemental depletion, coupled with isotope fractionation of more refractory Cu relative to Zn, may also hinge on the presence of carbonyl species of transition metals and electromagnetic charge, which could exist in the impact-induced high-velocity jet of vapor and melts.

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