MARGINS: The Explosive Volcanic History of the Central Oregon Cascades: Probing the Changing State of the Neogene Cascade Arc

边缘：俄勒冈中部喀斯喀特火山爆发的历史：探索新近纪喀斯喀特弧的变化状态

• 批准号: 1144555
• 负责人: Adam Kent
• 金额: $ 36.01万
• 依托单位: Oregon State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-03-15 至 2018-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1144555&HistoricalAwards=false
• 关键词: MARGINS; Explosive; Volcanic; History; Central

Subduction zones ? volcanically active regions where one tectonic plate is pushed beneath another ? are home to most of the Earth?s explosive volcanic eruptions. In large part this is because the magmas that are produced and erupted in subduction zones tend to be both richer in water and in silica, both of which increase the propensity for eruptions to be explosive. The Cascade margin, running from Mount Lassen in northern California to southern British Columbia is host to a number of well-known volcanoes such as Mount Hood, Mount St Helens and Mount Rainier as well as numerous other volcanic edifices, and much of the region is also heavily populated. Explosive eruptions have occurred in the recent history of the Cascades, examples include Mount St Helens in 1980 and the prehistoric eruption of Mount Mazama at Crater Lake ~7700 years ago. However, although these younger eruptions are well documented, less is known about the long-term explosive record of the Cascade subduction zone over longer timescales, and the forces that influence such explosive behavior. This project will help establish the long-term eruptive history of the Cascades in Central Oregon over the last 15 million years, by looking at volcanic rocks preserved within the Deschutes and Simtustus Formations of central Oregon. Many examples of ash fall and ash flow deposits that result from large explosive eruptions are preserved in these sequences, and they can be used to estimate the frequency, composition, age and size of large explosive eruptions in this section of the subduction zone. This research will use a combination of approaches, including field, geochronological, geochemical and petrological studies and will enable us to study changes in eruption rate, eruption size and chemical and isotopic composition through time and to compare this to the more recent behavior of the subduction zone.

俯冲区？一个板块被推到另一个板块之下的火山活跃区？是地球大部分地区的家园吗？S火山爆发。这在很大程度上是因为在俯冲带产生和喷发的岩浆往往水和二氧化硅都更丰富，这两者都增加了喷发的爆炸性倾向。从加利福尼亚州北部的拉森山到不列颠哥伦比亚省南部的喀斯喀特边缘是许多著名火山的所在地，如胡德山、圣海伦斯山和雷尼尔山以及许多其他火山建筑，该地区的大部分地区也人口稠密。在喀斯特山脉的近代史上曾发生过爆炸性喷发，例如1980年的圣海伦斯火山和7700年前陨石坑湖的马扎马火山史前喷发。然而，尽管这些更年轻的喷发被很好地记录下来，但人们对喀斯喀特俯冲带在更长时间尺度上的长期爆炸性记录以及影响这种爆炸性行为的力量知之甚少。该项目将通过研究保存在俄勒冈州中部德舒特和西姆图斯图斯地层中的火山岩，帮助建立过去1500万年来俄勒冈州中部喀斯喀特山脉的长期喷发历史。在这些层序中保存了许多由大型爆炸性喷发引起的火山灰坠落和火山灰流沉积的例子，它们可以用来估计俯冲带这一段大型爆炸性喷发的频率、成分、年龄和大小。这项研究将使用多种方法，包括野外、地质年代学、地球化学和岩石学研究，使我们能够研究喷发速度、喷发规模以及化学和同位素组成随时间的变化，并将其与俯冲带最近的行为进行比较。