Eruptive style of Mesoproterozoic a-type calderas in southeastern Missouri, USA

Abstract

Mesoproterozoic volcanism in southeastern Missouri was dominated by eruption of high temperature rhyolite ignimbrites and lavas with anorogenic chemical signatures. Incremental caldera collapse accompanied Plinian-Pelean-Effusive cycles that were erupted at structurally controlled sites along developing caldera walls. At least four ash flow calderas in the 20-40 km diameter class appeared at about 1.48 Ga and all exhibit features at variance with classic models for caldera subsidence. The collective traits of the Missouri calderas suggest that cyclic saturation explosive eruption subsidences quenching shift-of-site play a prominent role in the evolution of A-type calderas. Deviation of the Missouri calderas from the classic models is attributed to the physical and chemical peculiarities of A-type melts and control of synvolcanic extension by the pre-existing regional fault pattern.