The geology of Ragged Top Caldera

Abstract

The geologic history of the Ragged Top area has been one of sedimentation, intrusion, volcanism, and resurgent caldera formation. Prior to Ragged Top Caldera formation, this area underwent sedimentation of the Auld Lang Syne Group. These sediments were later intruded by Cretaceous plutons. Andesitic to siliceous volcanism covered the area and was followed by Ragged Top Caldera collapse producing a crater 6.5 km. by 5 km. Tuffaceous and clastic units filled the caldera after collapse. Subsequent resurgence produced a structural dome. Post-resurgent volcanism formed a number of dikes, all oriented north-northeast. Possibly related to this diking was a dacite erupted along the southern portion of the ring fracture and deposited to the south of the caldera. Mineralization is lacking due to the non-highly- differentiated nature of the igneous products following caldera collapse.