Reduction of Systematic Errors in 40Ar/39Ar Geochronology

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9814378RenneThis grant supports research aimed at improving the accuracy of the highly precise and very widely used 40Ar/39Ar method of geochronology. Precision of the method is often better than 0.1%, but systematic errors from decay constants, data for standards, and the isotopic composition of potassium combine to limit the method's absolute accuracy to no better than 2%. In this project, the investigators will conduct detailed comparisons between 40Ar/39Ar and U-Pb methods for carefully selected samples that are free of geologic complexities. In ideal cases, the U-Pb method is accurate to about 0.3%, thus accuracy approaching this limit may be obtained for the 40Ar/39Ar system through intercalibration. This work will be combined with experiments that will calibrate 40Ar/39Ar dating standards for the first time with the modern calendar through detailed analysis of potassium-rich minerals from the historic eruption of Vesuvius in 79 AD. The expected results of the project are a factor of ten or better improvement in accuracy of the 40Ar/39Ar dating method.***