Volcanic Centers of the Sunlight Area Park County, Wyoming

Abstract

The Sunlight area is located in the northern Absaroka Mountains of northwestern Wyoming. The rocks are dominantly Tertiary pyroclastics and basalt flows which rest on flat-lying Paleozoic limestones. The pyroclastics were thrown out from a large number of vents in explosive eruptions and were later modified by mud flows. Two major volcanic centers and one small explosive vent have been found in the Sunlight area. Intrusions of stocks, laccoliths, plugs, cone sheets, and radial dike systems are closely related to the volcanic centers. The radial dikes were formed by magma moving horizontally outward from the intrusive centers in vertical cracks. The Sunlight centers are similar in many respects to the Scottish Tertiary volcanoes. The rock types in general show a normal differentiation series from olivine gabbro and basalt through diorite and andesite to sodic syenite and trachyte. Several unusual orthoclase-bearing basalts, known as the absarokite series, are also present.