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

Sigurdsson9909769Ignimbrite耀斑是发生在汇聚边缘的爆炸性岩浆喷发。Ignimbrite事件对于理解大规模喷发火山作用对环境的影响、火山灾害的可能性以及俯冲带的地球化学循环具有重要意义。褐煤事件的记录作为火山灰在海洋沉积物中的落层保存得很好。最近在加勒比海钻探的ODP165航段发现了一个长达76英里的特殊层序，其中有2000多个火山灰落层。两次主要的火山爆发--一次发生在中新世中期，另一次发生在始新世中期--起源于中美洲火山弧，尼加拉瓜、洪都拉斯、萨尔瓦多和危地马拉的火山弧喷发了大量的硅质褐斑岩。这是一个为期两年的项目，以中美洲和加勒比地区的矿床为主要例子，解决火山爆发或燃煤爆发的性质。这项研究的主要目标是：1)利用高分辨率年代地层学评估爆炸事件的频率和性质；2)利用电子探针和ICPMS激光烧蚀分析玻璃和矿物，表征主要火山幕中具有代表性的特弗拉岩层的组成和挥发分含量；3)模拟火山灰层的迁移和沉积；4)收集和分析尼加拉瓜和洪都拉斯主要沸石矿床的样品，以便开始建立一个地球化学数据库，以便将海洋和陆地记录与之相结合。这项研究的结果将提供关于中美洲新生代大规模火山喷发的频率、主要火山爆发时期硅质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、个别来源喷发的火山学性质及其对火山灰扩散和沉积的影响的重要新信息。

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.