Lithium in tektites and impact glasses: Implications for sources, histories and large impacts

0363169 - GLÚ 2012 RIV GB eng J - Journal Article
Magna, T. - Deutsch, A. - Mezger, K. - Skála, Roman - Seitz, H.-M. - Mizera, Jiří - Řanda, Zdeněk
Lithium in tektites and impact glasses: Implications for sources, histories and large impacts.
Geochimica et Cosmochimica Acta. Roč. 75, č. 8 (2011), s. 2137-2158. ISSN 0016-7037. E-ISSN 1872-9533
R&D Projects: GA ČR GA205/09/0991
Institutional research plan: CEZ:AV0Z30130516; CEZ:AV0Z10480505
Keywords : crater * glass * isotopic composition * isotopic fractionation * lithium * lithology * mafic rock * moldavite * suevite * tektite * trace element
Subject RIV: DD - Geochemistry
Impact factor: 4.259, year: 2011

Lithium abundances and isotope compositions were determined in a suite of tektites (moldavites, Muong Nong-type tektites and an australite, Ivory Coast tektites and bediasites), impact-related glasses (Libyan Desert Glass, zhamanshinites and irghizites), a glass fragment embedded in the suevite from the Ries impact crater and sedimentary materials in order to test a possible susceptibility of Li to fractionation during hypervelocity impact events and to de-convolve links to their potential parental sources. The overall data show a large spread in Li abundance (4.7-58ppm Li) and δ⁷Li values (-3.2> to 26.0>) but individual groups of tektites and impact glasses have distinctive Li compositions. Most importantly, any significant high-temperature Li isotope fractionation can be excluded by comparing sedimentary lithologies from central Europe with moldavites. Instead, we suggest that Li isotope compositions in tektites and impact-related glasses are probably diagnostic of the precursor materials and their pre-impact geological histories. The Muong Nong-type tektites and australite specimen are identical in terms of Li concentrations and δ⁷Li and we tentatively endorse their common origin in a single impact event. Extreme shock pressures and the related extreme post-shock temperatures alone appear not to have any effect on the Li isotope systematics; therefore, useful information on parental lithologies and magmatic processes may be retrieved from analyses of Martian and lunar meteorites. Moreover, lack of significant Li depletion in tektites provides further constraints on the loss of moderately volatile elements during the Moon-forming impact.
Permanent Link: http://hdl.handle.net/11104/0199224