The Absaroka volcanic field is comprised of predominant andesitic volcaniclastic rocks and less abundant potassium-rich mafic lavas (shoshonites and absarokites). Strontium and lead isotopic variations preclude a simple derivation from an isotopically uniform source: Sr87/Sr86, 0.7042 to 0.7090; Pb206/Pb204, 16.31 to 17.30; Pb208/Pb204, 36.82 to 37.64. We postulate that these rocks were derived from a lower crust or upper mantle which underwent a preferential loss of uranium relative to lead approximately 2800±200 m.y. ago. Variations in lead and strontium isotopic compositions are thought to reflect small inhomogeneities in U/Pb and Rb/Sr ratios in the source.
|Title||Lead and strontium isotopes in rocks of the Absaroka volcanic field, Wyoming|
|Authors||Z. E. Peterman, B. R. Doe, H. J. Prostka|
|Publication Subtype||Journal Article|
|Series Title||Contributions to Mineralogy and Petrology|
|Record Source||USGS Publications Warehouse|