Collaborative Research: The Tumalo Volcanic Center - Probing the Origin of Explosive Pleistocene Silicic Volcanism in Central Oregon

为什么在10万到80万年前，在俄勒冈州喀斯喀特山脉中部爆发了一次火山爆发，在过去的10万年里，这个地方一直被贝尔克纳普火山口这样的玄武岩火山和南姐妹火山这样的平流层火山所主导？这是这项研究背后的基本问题，该研究考察了俄勒冈州中部的图马洛火山中心（TVC），在现代三姐妹火山和本德市之间的景观中，至少有三次大爆发，每次喷发至少1到10立方公里。这些大规模喷发的岩浆来源是什么？它与现代喀斯喀特的火山活动有什么最密切的关系？是由北美与胡安·德·富卡板块碰撞引起的火山活动，还是北美在俄勒冈州高喀斯喀特和盆地及山脉的持续拉伸引起的火山活动？在不知道火山喷发的确切年龄和喷出物质中发现的晶体的情况下，TVC无法被置于喀斯喀特山脉的演变中，也无法评估俄勒冈州中部爆发火山活动的可能性。通过将化学成分数据添加到混合物中，可以了解形成这些喷发的过程，以及TVC与世界上其他硅质爆炸性喷发的相似程度。这将是对俄勒冈喀斯喀特中部这个主要火山地区的详细研究。尽管TVC先前已经被绘制出来，但它在几乎所有其他方面都知之甚少：火山喷发的年表；单个喷发单元的体积；高质量的地球化学或岩石年代学资料；以及岩石学对岩浆成因过程/条件的制约。这项详细的年代学、岩石学和地球化学研究将为这些岩浆形成的测试模型提供基础，帮助评估未来主要爆炸性TVC喷发的可能性，并为喀斯喀特和其他俯冲系统中产生硅岩浆的过程提供重要的见解。这项研究将通过以下方式解决这些问题：实地文件和基于地理信息系统的数量估计；40 ar / 39 ar地质年代学;锆石U-Pb（和U-Th）定年及微量元素系统；大块岩石、玻璃、矿物和熔融包裹体的地球化学；以及基于相平衡的岩浆形成和储存的密集参数估计。本研究也有四个主要的更广泛的影响：(1)研究生和本科生在研究1和文科院校之间的相互指导和培训；(2)由于德舒特县人口超过14万，对火山灾害的认识增加，TVC中与再次喷发有关的危害目前尚不清楚；(3)广泛的宣传，包括博客文章、Twitter、演讲、新的TVC网站和现场标志，这将提供一个重要的机会，提高人们对俄勒冈中部火山危害的认识；(4)本研究将支持一名博士生、一名拉丁裔研究人员和本科生，其中许多人将从STEM领域代表性不足的群体中招募。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Why was there a burst of explosive volcanism between 100,000 and 800,000 years ago in the middle of the central Oregon Cascades, a location that over the last 100,000 years has been dominated by basaltic volcanoes like Belknap Crater and stratovolcanoes like South Sister? This is the fundamental question behind this study to examine the Tumalo Volcanic Center (TVC) in central Oregon, where at least three major explosive eruptions that disgorged each at least 1 to 10 cubic kilometers mantle the landscape between the modern Three Sisters volcanoes and the city of Bend. What is the source of the magma that fed these massive eruptions and what is it most closely related to: the volcanism of modern Cascades caused by the collision of North America with the Juan de Fuca plate or ongoing stretching of North America in Oregon High Cascades and the Basin and Range? Without knowing the precise ages of the eruptions themselves and the crystals found in the materials ejected, the TVC can't be placed into the evolution of the Cascade Range or assessed for the likelihood of renewed explosive volcanism in central Oregon. By adding chemical compositional data to the mix, the processes that formed these eruptions can be understood, along with how similar the TVC is to other silicic explosive eruptions around the world. This will be a detailed study of this major volcanic region in the central Oregon Cascades. Although the TVC has been previous mapped, it is poorly known in almost all other respects: the chronology of eruptions; the volumes of individual eruptive units; high quality geochemical or petrochronologic data; and petrological constraints on the processes/conditions of magma genesis. This detailed chronological, petrological and geochemical study will provide a basis for testing models for the formation of these magmas, assist in assessing the future likelihood for major explosive TVC eruptions, and provide important insight into the processes that produce silicic magmas in the Cascades and in other subduction systems. This study will address these points through: field documentation and GIS-based volume estimates; 40Ar/39Ar geochronology; zircon U-Pb (and U-Th) dating and trace element systematics; geochemistry of bulk rocks, glasses, minerals and melt inclusions; and phase equilibria-based estimates of intensive parameters of magma formation and storage. There are also four main Broader Impacts to this study: (1) mutual mentoring and training of graduate and undergraduate students shared across Research 1 and Liberal Arts institutions; (2) increased understanding of volcanic hazards as the population of Deschutes County is over 140,000 and the hazard related to renewed eruption in the TVC is currently unclear; (3) extensive outreach, including blog posts, Twitter, talks, new TVC website and signs in the field that will provide an important opportunity to increase awareness of volcanic hazards in Central Oregon; (4) this research will support a Ph.D. student, a Latino researcher and undergraduate research students, many of which will be recruited from groups underrepresented in STEM fields.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.