Quaternary volcanism in northwestern Colorado: Implications for the roles of asthenosphere and lithosphere in the genesis of continental basalts

Quaternary volcanic rocks were erupted at four locations in NW Colorado; Dotsero (4150 y.B.P.), Willow Peak (undated), McCoy (0.64 m.y. B.P.), and Triangle Peak (1.98-1.87 m.y.B.P.). At Triangle Peak, there are at least eleven lava flows, but eruptions at the other locations were monogenetic. Dotsero was the only hydrovolcanic eruption. The volcanic rocks are alkali basalts, containing the phenocryst assemblage: olivine, Fe-Ti oxide, ± …