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

火成岩爆发是岩浆的爆炸性喷发，发生在会聚边缘。火成岩幕式对了解大规模爆发火山活动的环境影响、潜在的火山灾害以及俯冲带的地球化学循环具有重要意义。火山火山灰落在海洋沉积物层中，火成岩时期的记录保存得很好。最近在加勒比海的ODP Leg 165钻探发现了一个特殊的76米长的序列，其中有超过2000个火山灰落层。两次主要的火山爆发期——一次是中新世中期，另一次是始新世中期——起源于中美洲火山弧，在那里尼加拉瓜、洪都拉斯、萨尔瓦多和危地马拉爆发了大量的硅烟灰岩。这是一个为期两年的项目，以中美洲和加勒比地区的沉积物为主要例子，研究爆炸性火山事件或褐煤爆发的性质。研究的主要目的是：1)利用高分辨率年代地层学评估爆炸事件的频率和性质；2)利用电子显微探针和ICPMS激光烧蚀分析玻璃和矿物，表征主要火山事件中具有代表性的火山层组的组成和挥发性含量；3)模拟烟灰层的运输和沉积；4)收集和分析尼加拉瓜和洪都拉斯主要烟灰矿床的样本，开始建立一个地球化学数据库，将海洋和陆地记录整合起来。研究结果将为以下方面提供重要的新信息：中美洲新生代大规模爆炸性喷发的频率、爆炸性火山活动主要时期硅岩浆和气溶胶形成挥发物的产生速度及其对全球气候的潜在影响、单个火山源喷发的火山学性质及其对火山体扩散和沉积的影响。

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.