The fate of moderately volatile elements in impact events—Lithium connection between the Ries sediments and central European tektites

Abstract

Lithium abundances and isotope compositions are presented for a suite of sediments from the surroundings of the Ries Impact structure, paralleled by new Li data for central European tektites (moldavites) from several substrewn fields (South Bohemia, Moravia, Cheb Basin, Lusatia), including a specimen from the newly discovered substrewn field in Poland. The data set was supplemented by three clay fractions isolated from sedimentary samples. Moldavites measured in this study show a very narrow range in δ7Li values (−0.6 to 0.3‰ relative to L‐SVEC) and Li contents (23.9–48.1 ppm). This contrasts with sediments from the Ries area which show remarkable range in Li isotope compositions (from −6.9 to 13.4‰) and Li contents (0.6–256 ppm). The OSM sediments which, based on chemical similarity, formed the major part of moldavites, show a range in δ7Li values from −2.0 to 7.9‰ and Li contents from 5.8 to 78.9 ppm. Therefore, the formation of moldavites was apparently accompanied by large‐scale mixing, paralleled by chemical and isotope homogenization of their parent matter. The proposed Li mixing model indicates that sands, clayey sediments, and low volumes of carbonates are the major components for tektite formation whereas residual paleokarst sediments could have been a minor but important component for a subset of moldavites. Striking homogenization of Li in tektites, combined with limited Li loss during impacts, may suggest that moderately volatile elements are not scavenged and isotopically fractionated during large‐scale collisions, which is consistent with recent models. In general, whether homogenization of bodies with distinct Li isotope systematics takes place, or collision of bodies with similar Li systematics operates cannot be resolved at present stage but Li isotope homogeneity of solar system planets and asteroidal bodies tentatively implies the latter.

Zhamanshin astrobleme provides evidence for carbonaceous chondrite and post-impact exchange between ejecta and Earth’s atmosphere

“…3 ). The dolomitic carbonate, present as a minor clastic component in some types of OSM sands 4 , was clearly present but only at quantities of a few per cent, at maximum 63 . Such a small admixture of high-δ 18 O carbonate was thus only one of several factors controlling the δ 18 O range of moldavites.…”

An experimental model for the tektite fluvial transport based on the most distal Polish moldavite occurrences

“…Minor differences in chemical structure indicate local variability of source sediments (Rodovská et al. ; Skála et al. ; Žák et al.…”

“…Moldavites and “Tertiary” sediments in the surroundings of the Ries structure are characterized by a very high geochemical homogeneity (Rodovská et al. ; Skála et al. ; Žák et al.…”

The most distal moldavite findings from Lower Silesia, Poland

“…B. and C. General view of the Gozdnica Formation in the western part of the Nowa Wieś Kącka sandpit. (d'après BRACHANIEC et al, 2014b(d'après BRACHANIEC et al, , 2015(d'après BRACHANIEC et al, , 2016 2012SKÁLA et al, 2016;RODOVSKÁ et al, 2016). BRACHANIEC et al (2014bBRACHANIEC et al ( , 2015BRACHANIEC et al ( , 2016 and SZOPA et al (2017a) recently described moldavite finds in SW Poland.…”