Space-time relations of Cenozoic silicic volcanism in the Great Basin of the western United States

Abstract

Physical stratigraphy and more than 250 K-Ar dates demonstrate a definite space-time pattern of Cenozoic silicic volcanism in the Great Basin. Known vent areas of voluminous ash flows and approximate source areas for sheets provide the control points. Volcanism began about 40 m.y. ago and volcanic rocks are most abundant in east-central Nevada. The locus of activity then shifted outward toward the margins of the Great Basin. Silicic activity ceased in east-central Nevada about 25 m.y. ago and by 20 m.y. ago was restricted to the margins of the basin. Intensity has decreased progressively for the last 10 m.y. East-central Nevada is less seismic and possibly has a thicker crust than the rest of the basin. The outward migration of volcanism may have been the result of convection within the mantle with a rising current centered on the east-central part of the Great Basin.