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

Sigurdson 9909769灰晶闪焰是发生在会聚边缘的岩浆爆发性喷出。火山灰岩幕对于了解大规模爆发性火山作用的环境影响、潜在的火山灾害和俯冲带的地球化学循环具有根本的重要性。熔结凝灰岩幕的记录作为火山灰下落层保存在海洋沉积物中。最近在加勒比地区钻探ODP 165航次，有两千多个火山灰层的长序列。两个主要的爆发性火山事件-一个是中新世中期，另一个是始新世中期-起源于中美洲火山弧，在尼加拉瓜、洪都拉斯、萨尔瓦多和危地马拉爆发了大量的火山灰凝灰岩。 这是一个为期两年的项目，以中美洲和加勒比矿床为主要实例，探讨爆发性火山事件或熔结凝灰岩爆发的性质。研究的主要目的是：1）利用高分辨率年代地层学评估爆发事件的频率和性质; 2）利用电子探针和ICPMS激光烧蚀分析玻璃和矿物，表征主要火山事件的火山碎屑层的组成和挥发物含量; 3）模拟灰层的迁移和沉积; 4）收集和分析尼加拉瓜和洪都拉斯主要熔结凝灰岩矿床的样品，开始建立地球化学数据库，以整合海洋和陆地记录。 这项研究的结果将提供重要的新资料，说明中美洲新生代大规模爆发的频率、爆发性火山活动重大事件期间火山岩浆和形成气溶胶的挥发物的产生率及其对全球气候的潜在影响、个别火山源爆发的火山学性质及其对火山碎屑散布和沉积的影响。

Sigurdsson9909769Ignimbrite 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.