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，在俄勒冈州中部的喀斯喀特山脉爆发了一次火山爆发？在过去的10万年里，这个地方一直由像贝尔纳普火山口这样的玄武岩火山和像南姐妹这样的成层火山所主导。这是这项研究背后的基本问题，以检查俄勒冈州中部的图马洛火山中心（TVC），在那里，至少有三次主要的爆炸性喷发，每次喷发至少1到10立方公里，覆盖了现代三姐妹姐妹篇和弯曲市之间的景观。这些大规模喷发的岩浆来源是什么？它与什么最密切相关：北美与胡安·德富卡板块碰撞造成的现代喀斯喀特火山活动，或者北美在俄勒冈州高喀斯喀特山脉和盆地山脉的持续拉伸？在不知道喷发本身的确切年龄和喷出物质中发现的晶体的情况下，TVC不能被置于喀斯喀特山脉的演变中，也不能评估俄勒冈州中部火山爆发的可能性。通过将化学成分数据添加到混合物中，可以理解形成这些喷发的过程，沿着TVC与世界各地其他火山爆发的相似性。这将是对俄勒冈州喀斯喀特山脉中部这一主要火山区的详细研究。虽然TVC以前已被映射，它是鲜为人知的，在几乎所有其他方面：火山喷发的年表;个别喷发单位的体积;高品质的地球化学或岩石年代学数据;和岩石学的限制岩浆成因的过程/条件。这一详细的年代学、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，有助于评估未来重大爆炸性TVC喷发的可能性，并为在瀑布和其他俯冲系统中产生岩浆的过程提供重要的见解。本研究将通过以下方式解决这些问题：野外记录和基于GIS的体积估计; 40 Ar/39 Ar地质年代学;锆石U-Pb（和U-Th）测年和微量元素系统学;大块岩石、玻璃、矿物和熔融包裹体的地球化学;和基于相平衡的岩浆形成和储存密集参数估计。这项研究还有四个主要的更广泛的影响：（1）研究1和文科机构之间共享的研究生和本科生的相互指导和培训;（2）随着德舒特县人口超过140，000，对火山危害的了解增加，目前还不清楚与TVC重新爆发有关的危害;（3）广泛的宣传，包括博客文章，Twitter，会谈，新的TVC网站和现场标志，这将提供一个重要的机会，以提高对俄勒冈州中部火山危害的认识;（4）这项研究将支持博士学位。该奖项反映了NSF的法定使命，并通过使用基金会的智力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.