B. R. Doe H.J. Prostka Z. E. Peterman 1970 <div id="Abs1-section" class="c-article-section"><div id="Abs1-content" class="c-article-section__content"><p>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.</p></div></div> application/pdf 10.1007/BF00371979 en Springer Lead and strontium isotopes in rocks of the Absaroka volcanic field, Wyoming article