High precision multi-collector 40Ar-39Ar dating of moldavites (central Eurepean tekties)
Moldavites (Central European tektites) are genetically related to the meteorite impact event that produced the 24-km diameter Ries crater (Germany) during the Langhian, and representing one of the youngest large impact structures on Earth. Despite the numerous geochronological studies over the last decades and the potential implications for stratigraphic, paleontological and paleoclimatic studies, the age of the Ries impact is still debated. In this study, I investigate in detail moldavite samples by multicollector 40Ar/39Ar laser dating in order to address the age of the Ries impact. Data were obtained relative to the key Fish Canyon sanidine (FCs) and Alder Creek sanidine (ACs) reference materials, over a period of nearly two years, in 4 irradiations of different duration. Results, completed through the step-heating and the total fusion techniques, demonstrate an excellent intrasample and intersample reproducibility of moldavites and prove that analytical performances of moldavites in terms of uncertainties on the 40Ar*/39ArK ratios are in line with those achievable by the most widely used FCs and ACs reference minerals. Using the most recent astronomically calibrated age for FCs (28.176 ± 0.023 Ma) yields an age of 14.7355 ± 0.0039 Ma (±2σ – ± 0.013 Ma, including uncertainties in the age of the reference material and 40K total decay constant). Results place definitively the age of the Ries impact in the reverse polarity chron C5ADr of the ATNTS2022, and suggest that the Ries impact preceded the switch from reversed to normal chron by at least 127 ± 15 ka. The analytical performance in terms of uncertainties on the 40Ar*/39ArK ratios, together with the easy availability and the simplicity of preparation, make moldavites an ideal intralaboratory reference material for the 40Ar/39Ar dating method.
Di Vincenzo G. (2022). High precision multi-collector 40Ar/39Ar dating of moldavites (Central European tektites) reconciles geochrological and paleomagnetic data. Chemical Geology, https://doi.org/10.1016/j.chemgeo.2022.121026.
For more information: Gianfranco Di Vincenzo, CNR-IGG (gianfranco.divincenzo(at)igg.cnr.it).