Explosive Volcanic Episodes: Integration of the Deep Sea and Terrestrial Record

University Of Rhode Island, Kingston RI

Investigators

Abstract

Sigurdsson 9909769 Ignimbrite flare-ups are explosive outpourings of magma that occur at convergent margins. Ignimbrite episodes are of fundamental importance in understanding the environmental impact of large scale explosive volcanism, the potential for volcanic hazards, and the geochemical cycling at subduction zones. The record of ignimbrite episodes is well preserved as volcanic ash fall layers in marine sediments. Recent drilling of ODP Leg 165 in the Caribbean recovered an exceptional 76 m.y.-long sequence with over two thousand ash fall layers. Two major explosive volcanic episodes - one of mid-Miocene and the other mid-Eocene age - originate from the Central American volcanic arc, where voluminous silicic ignimbrites were erupted in Nicaragua, Honduras, El Salvador and Guatemala. This is a two-year project to address the nature of explosive volcanic episodes, or ignimbrite flare-ups, using the Central American and Caribbean deposits as a primary example. The principal objectives of the research are to 1) assess the frequency and nature of explosive events by using a high resolution chronostratigraphy, 2) characterize the composition and volatile content of a representative suites of tephra layers from the main volcanic episodes by using electron microprobe and ICPMS laser ablation analysis of glasses and minerals; 3) model the transport and deposition of ash layers, and 4) collect and analyze samples from major ignimbrite deposits in Nicaragua and Honduras to begin to build up a geochemical database with which to integrate the marine and terrestrial records. The results of the study will provide important new information on the frequency of large-scale explosive eruptions in Central America during the Cenozoic, the production rate of silicic magma and aerosol-forming volatiles during major episodes of explosive volcanism and their potential impact on global climate, and the volcanological nature of individual source eruptions and their influence on tephra dispersal and deposition.