High Precision Isotope Dilution Determination of Potassium by Thermal Ionisation Mass Spectrometry

Two independent articles published more than a decade ago pointed to the potential of the somewhat neglected K‐Ca system for very precise K‐Ca dating and thermochronology, but have not been followed up since. In the first of these articles, highly precise determination of K and hence the K/Ca ratio in lunar granites showed the feasibility of K‐Ca dates of micas with an analytical precision known so far in only U‐Pb and Ar/Ar dating. In the second article, it was shown that responses of the K‐Ca and Rb‐Sr isotopic systems in micas subjected to a slow post‐metamorphic cooling could provide new insights into thermochronology. Crucial to the follow‐up of these two promising leads is the development of a simple and user‐friendly method for routine high precision K determination in real samples, such as the one described in this report.