Collaborative Research: Caldera Collapse and Subsequent Evolution of Long-lived Silicic Supervolcanoes: A Case Study of the Tshirege Member, Bandelier Tuff, NM

智力上的优点。从火山口喷出的流纹岩超级喷发是罕见的事件，超出了人类的经验记录，但可以肯定的是，它们将继续发生。对过去事件喷发产物的岩石学研究提供了对伴随流纹质岩浆的生成、储存和喷发的岩浆过程的见解。科学界目前正在形成一种共识，即体积为100 - 1 000立方公里的贫晶体流纹岩喷发在地表下留下更多数量的补充性非喷发富晶体残留物。这种残余物可能能够再生，并产生随后可喷发的贫结晶岩浆体。该提案寻求资金，以详细研究一个例子，其中两次贫晶体流纹岩的超级爆发发生在同一地点，时间间隔约36万年。班德尔凝灰岩的Otowi（下）和Tshirege（上）段分别于1.61和1.25 Ma从新墨西哥州的Valles破火山口喷发。两者都表现出强烈的化学分带性。从以前的工作，前破火山口岩浆的历史是很好的理解，因为是奥托维岩浆体的发展和喷发前的建筑。Otowi的高度富集，但相对简单的地球化学特征意味着它从大量晶体中分离出来。后来的Tshirege成员与Otowi有许多岩石学和地球化学相似之处，但要复杂得多。初步的数据是一致的模型，其中Tshirege部分来自Otowi晶体残留物与添加古地壳。这种混合物在产生Tshirege岩浆之前没有被均质化。这一假设将通过分析浮岩，玻璃和晶体的主要，微量元素和放射性同位素，以确定贡献的组件和他们组装形成Tshirege岩浆的过程进行测试。另外两个关键方面是：（1）相关的模拟实验，以限制由下落的破火山口块引起的晶体堆的同喷发干扰的程度;（2）石英斑晶中Ti分布的高分辨率成像和分析，这将限制可能通过晶体堆的热再生引发超级喷发的补给和加热事件的时间。考虑到流纹岩超级喷发可能对全球造成的破坏性影响，提前几十年预测下一次此类事件的必要性是不言而喻的。这种可以在地表探测到的前兆性指标必须了解超级喷发之前岩浆过程的性质和时间。这反过来又要求对这些过程进行基础研究，这就是本研究的主题。本提案中概述的研究还将用于培养本科生和研究生掌握与岩石学和地球化学调查相关的现代方法。此外，它将有助于发展一个年轻的研究科学家和一个职业生涯早期的西班牙裔科学家谁刚刚采取了终身职位。

Intellectual merit. Rhyolitic super-eruptions from calderas are rare events that lie outside recorded human experience, but it is quite certain that they will continue to occur. Insights into the magmatic processes that accompany the generation, storage, and eruption of large bodies of rhyolitic magma are provided by petrologic study of the eruptive products of past events. A consensus is now emerging among the scientific community that eruptions of crystal-poor rhyolite with volumes of the order of 100 - 1,000 km3 leave still greater quantities of complementary non-erupted crystal-rich residue beneath the surface. This residue may be capable of rejuvenation and production of subsequent eruptible bodies of crystal-poor magma. This proposal seeks funding for a detailed study of an example where two super-eruptions of crystal-poor rhyolite occurred on exactly the same site, separated in time by ~360,000 years. The Otowi (Lower) and Tshirege (Upper) Members of the Bandelier Tuff were erupted from the Valles caldera, New Mexico, in two episodes at 1.61 and 1.25 Ma respectively. Both exhibit strong chemical zonation. From prior work, the pre-caldera magmatic history is well understood, as are the development and pre-eruptive architecture of the Otowi magma body. The highly enriched, yet relatively simple, geochemical character of the Otowi implies that it parted from a large mass of crystals. The later Tshirege Member shares many petrologic and geochemical similarities with the Otowi, yet is considerably more complex. Preliminary data are consistent with a model in which the Tshirege is partly derived from Otowi crystal residue with added ancient crust. This mixture was not homogenized prior to production of the Tshirege magma. This hypothesis will be tested by analyzing pumices, glasses and crystals for major, trace elements and radiogenic isotopes to identify contributing components and the process by which they were assembled to form the Tshirege magma. Two additional key aspects are (1) associated analog experiments to constrain the extent of syn-eruptive disturbance of the crystal pile induced by the downdropping caldera block, and (2) high resolution imaging and analysis of Ti distributions in quartz phenocrysts, which will constrain the timing of recharge and heating event(s) that may trigger super-eruptions by thermal rejuvenation of the crystal pile.Broader impacts. Given the potentially devastating global impact of rhyolitic super-eruptions, the need to forecast the next such event several decades beforehand is self-evident. Such premonitory indicators as may be detectable at the surface must necessarily be informed by an understanding of the nature and timing of magmatic processes that precede supereruptions. This in turn demands basic research into these processes, which is the subject of this research. The research outlined in this proposal will additionally serve to train undergraduates and a graduate student in modern methods associated with petrologic and geochemical investigations. Additionally, it will contribute to the development of a young research scientists and an early-career Hispanic scientist who has just taken a tenure-track position.