Geochemical studies of the SUBO 18 (Enkingen) drill core and other impact breccias from the Ries crater,Germany |
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| Authors: | Wolf Uwe Reimold Iain McDonald Ralf‐Thomas Schmitt Birgit Hansen Juliane Jacob Christian Koeberl |
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| Institution: | 1. Museum für Naturkunde—Leibniz‐Institut für Evolutions‐ und Biodiversit?tsforschung, , 10115 Berlin, Germany;2. Humboldt Universit?t zu Berlin, , 10099 Berlin, Germany;3. School of Earth & Ocean Sciences, Cardiff University, , Cardiff, CF10 3YE UK;4. Department of Lithospheric Research, University of Vienna, , 1090 Vienna, Austria;5. Natural History Museum, , 1010 Vienna, Austria |
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| Abstract: | Suevite and melt breccia compositions in the boreholes Enkingen and Polsingen are compared with compositions of suevites from other Ries boreholes and surface locations and discussed in terms of implications for impact breccia genesis. No significant differences in average chemical compositions for the various drill cores or surface samples are noted. Compositions of suevite and melt breccia from southern and northeastern sectors of the Ries crater do not significantly differ. This is in stark contrast to the published variations between within‐crater and out‐of‐crater suevites from northern and southern sectors of the Bosumtwi impact structure, Ghana. Locally occurring alteration overprint on drill cores—especially strong on the carbonate‐impregnated suevite specimens of the Enkingen borehole—does affect the average compositions. Overall, the composition of the analyzed impact breccias from Ries are characterized by very little macroscopically or microscopically recognized sediment‐clast component; the clast populations of suevite and impact melt breccia are dominated consistently by granitic and intermediate granitoid components. The Polsingen breccia is significantly enriched in a dioritic clast component. Overall, chemical compositions are of intermediate composition as well, with dioritic‐granodioritic silica contents, and relatively small contributions from mafic target components. Selected suevite samples from the Enkingen core have elevated Ni, Co, Cr, and Ir contents compared with previously analyzed suevites from the Ries crater, which suggest a small meteoritic component. Platinum‐group element (PGE) concentrations for some of the enriched samples indicate somewhat elevated concentrations and near‐chondritic ratios of the most immobile PGE, consistent with an extraterrestrial contribution of 0.1–0.2% chondrite‐equivalent. |
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