The In Vacuo Release of Ar from Minerals: 4—Polymineralic Samples

The in vacuo release of Ar and other noble gases is well understood for single minerals. However, natural samples, even those seemingly pure under the optical microscope, mostly consist of mm-to-µm scale intergrowths of different minerals. Typically, relict phases and retrogression products are contained in minerals that are studied in sufficient detail. Only exceptionally can the number of different mineral generations be as low as two; single-generation gems (diamonds, rubies, emeralds) are not routinely used in geochronology. In polygenetic mixtures, the systematics of temperature-dependent release of artificial Ar isotopes used as compositional indicators (38Ar and 37Ar) can be linked to the 40Ar/39Ar ratio and disambiguate the ages of individual mineral generations.