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

俯冲带？一个构造板块被推到另一个板块下面的火山活动区？是地球上大部分地区的家园？火山爆发。在很大程度上，这是因为在俯冲带产生和喷发的岩浆往往富含水和二氧化硅，这两者都增加了喷发的爆炸性。喀斯喀特边缘，从加利福尼亚北部的拉森山一直延伸到不列颠哥伦比亚省南部，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，以及许多其他火山大楼，该地区的大部分地区也人口稠密。喀斯喀特山脉最近的历史上也发生过爆发，例如1980年的圣海伦斯火山和大约7700年前在火山口湖的马扎马火山的史前喷发。然而，尽管这些较年轻的喷发有很好的记录，但对于喀斯喀特俯冲带在更长的时间尺度上的长期爆炸记录，以及影响这种爆炸行为的力量，人们知之甚少。这个项目将通过观察保存在俄勒冈中部的Deschutes和Simtustus地层中的火山岩，帮助建立俄勒冈中部喀斯喀特火山在过去1500万年里的长期喷发历史。这些层序中保存了许多由大爆炸喷发引起的灰落和灰流沉积的实例，它们可以用来估计俯冲带这段大爆炸喷发的频率、组成、年龄和规模。这项研究将采用多种方法，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率、喷发规模、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。

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.