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.