Abstract
Rb Sr whole rock/biotite ages of crystalline basement rocks from Ries Crater are 323 ± 8Ma; initial 87Sr/ 86Sr rat are 0.7081 ± 0.0007. These values compare perfectly with those for Moldanubian rocks exposed in the Bayerischer Wald and Schwarzwald. It is demonstrated that impact-related shock pressures up to 15 GPa and temperatures as high as 300°C did not disturb the Rb Sr isotopic systems of the rocks. Comparison of Sr isotopic compositions of Tertiary Upper Freshwater Molasse sediments with those of moldavites suggests that such sediments can be regarded as source material of these tektites. Our data for components of the sediments show that a mixture of clay (weathered crystalline rocks) and secondary carbonates, in addition to detrital quartz, can explain the observed range of 87Sr/ 86Sr ratios in moldavites. A similar comparison of moldavites with bentonites from the Tertiary molasse definitely rules out a genetical relationship between these two materials. We regard liquid/gas-filled bubbles in bentonite glasses as proof of their volcanic nature.
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