Cenozoic Potassium-Rich Mafic Volcanism in the Western U.S.A.: Its Relationship to Deep Subduction

Cenozoic potassium-rich volcanism, characterized by K₂O > Na₂O and SiO₂ < 60 wt %, follows a northeast to southwest younging trend in the western U.S.A. Correlation of this trend with the outer limits of arc-related magmatism, based on variable dip subduction models, suggests that potassium-rich volcanism may be related to deep subduction rather than intraplate tectonics.