Isotopic evidence on the structure and origin of subcontinental lithospheric mantle in southern Nevada

The trace element and Nd, Sr, and Pb isotopic compositions of extension-related late Cenozoic basalts in southern Nevada were determined in order to constrain models for the tectonic evolution of the subcrustal mantle in the southern Great Basin since 10 Ma. Basalts in southern Nevada between latitudes 36°N and 37°N have low ε_Nd (-8 to -10), high Δ8/4 (+70 to +107) and Δ7/4 (+8 to +12), high ⁸⁷Sr/⁸⁶Sr, and low high field strength element (HFSE) concentrations relative to other Basin and Range basalts. Basalts with these chemical and isotopic traits have erupted semicontinuously in southern Nevada since 10 Ma. During the same period of time, basalts in central Nevada and east central California have shifted toward higher ε_Nd, lower ⁸⁷Sr/⁸⁶Sr, lower Δ8/4 and Δ7/4, and higher HFSE contents than observed for the southern Nevada basalts. The latter isotopic characteristics are similar to other basalts in the western United States that are interpreted to have been derived from asthenospheric mantle similar isotopically to the sources of ocean island basalts. The isotopic and chemical characteristics of the southern Nevada basalts are not attributed to asthenospheric mantle but to lithospheric mantle that has been preserved beneath this region despite late Cenozoic extension. -from Authors