Pb isotope measurements of sanidine monitor standards: implications for provenance analysis and tephrochronology

Samples of Fish Canyon and Cobb Mountain sanidine monitor standards, irradiated and fused with 7 W of CO2 laser power for 40Ar/39Ar geochronology analyses, give Pb isotope composition and Pb concentrations that are indistinguishable from unprocessed aliquots of the same monitors. The absence of measurable change in Pb isotope composition indicates the feasibility of measuring the Pb isotope composition of feldspar grains that have been previously analyzed for their 40Ar/39Ar ages. Therefore, it should be possible to fingerprint datable volcanic ash layers for purposes of correlating noncontiguous layers with similar ages. Application of this combined technique to detrital feldspar grains (most detrital grains would not be sanidine, so further tests are necessary) should also improve the sensitivity of provenance analysis.