Geochemical evolution of a mid-miocene synextensional volcanic complex: The Dolan Springs volcanic field, northwestern Arizona
The Dolan Springs volcanic field (DSV), of northwestern Arizona, is dominated by andesite and basaltic-andesite flows and breccias, with minor amounts of basalt, rhyolite, and ash-flow tuff. Geochemistry is used here as a tool to evaluate the roles and contributions of the lithospheric and asthenospheric mantles to magmatism related to Miocene extension in the Colorado River extension corridor (CREC). The majority of synextensional volcanic rocks in the DSV are geochemically similar to regional trends, but rare tholeiitic basalts erupted near the end of extension. The tholeiites have trace element signatures similar to ocean island basalt (OIB), but have isotopic values indicative of a source in the lithosphere. The tholeiites represent the endpoint in a progressive decrease in the depth of lithospheric melting (22-8 Ma) that occurs just prior to the onset of asthenospheric volcanism at 6 Ma. Using geochemical arguments, models are presented here for trace element stratification in the lithospheric mantle and magma genesis in the CREC.