RbSr study on langbeinite and other salt minerals from a Zechstein diapir in Northern Germany

Due to its very low Rb and high Sr contents, the polyhalite studied was found to be unsuitable for RbSr dating. In the case of halite, concentrations of Rb and Sr in the ppb range cannot be distinguished from the blanks. Langbeinite, on the other hand, is very promising as its contents in Rb and Sr in the ppm range are very suitable for dating. In addition, langbeinite seems to retain its radiogenic Sr over geologically long periods. A 9-point errorchron (plus 1 outlier) corresponds to an age of 135 ± 11 Ma (2σ). It is argued that the scatter of the experimental points was most probably caused by recent Rb loss and that the mineral langbeinite formed a closed system for Rb and Sr over most of its history. The results presented in this study show that langbeinite is most probably not a recent product and that its minimum age must be Cretaceous. However, KAr ages of 180–200 Ma on the same samples render the final interpretation of the RbSr results difficult: It is possible that the age of 135 Ma is either the age of formation, the age of a disturbing event or a cooling age.