A high-precision Ar-40/(39) Ar age for the Nordlinger Ries impact crater, Germany, and implications for the accurate dating of terrestrial impact events

作者：Schmieder Martin^*; Kennedy Trudi; Jourdan Fred; Buchner Elmar; Reimold Wolf Uwe

来源：Geochimica et Cosmochimica Acta, 2018, 220: 146-157.

DOI：10.1016/j.gca.2017.09.036

• Ries crater
• Impact melt
• Tektites
• Moldavites
• Ar-40/(39) Ar dating
• Hydrothermal alteration

Ar-40/(39) Ar dating of specimens of moldavite, the formation of which is linked to the Ries impact in southern Germany, with a latest-generation ARGUS VI multi-collector mass spectrometer yielded three fully concordant plateau ages with a weighted mean age of 14.808 +/- 0.021 Ma (+/- 0.038 Ma including all external uncertainties; 2 sigma; MSWD = 0.40, P = 0.67). This new best-estimate age for the Nordlinger Ries is in general agreement with previous Ar-40/(39) Ar results for moldavites, but constitutes a significantly improved precision with respect to the formation age of the distal Ries-produced tektites. Separates of impact glass from proximal Ries ejecta (suevite glass from three different surface outcrops) and partially melted feldspar particles from impact melt rock of the SUBO 18 Enkingen drill core failed to produce meaningful ages. These glasses show evidence for excess 40 Ar introduction, which may have been incurred during interaction with hydrothermal fluids. Only partially reset Ar-40/(39) Ar ages could be determined for the feldspathic melt separates from the Enkingen core. The new Ar-40/(39) Ar results for the Ries impact structure constrain the duration of crater cooling, during the prevailing hydrothermal activity, to locally at least similar to 60 kyr. With respect to the dating of terrestrial impact events, this paper briefly discusses a number of potential issues and effects that may be the cause for seemingly precise, but on a kyr-scale inaccurate, impact ages.

• 出版日期2018-1-1