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。来自火山口的流纹状超级喷发是有记录的人类经验之外的罕见事件，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着大量流纹岩岩浆的产生、储存和喷发的岩浆过程的洞察。科学界现在正在形成一种共识，即体积约为100-1000千米的贫晶流纹岩的喷发在地表下留下了更多补充的、未喷发的富含晶体的残留物。这些残留物可能能够恢复活力，并产生随后喷发的贫晶岩浆。这项提议寻求资助对一个例子进行详细研究，该例子中，两次贫晶流纹岩的超级喷发发生在完全相同的地点，时间上相隔约36万年。班德利耶凝灰岩的下部奥托伊和上部凝灰岩Tshirege分别于1.61 Ma和1.25 Ma分两幕从新墨西哥州的Valles火山口喷发。两者都表现出强烈的化学分带性。从以前的工作中，人们已经很好地了解了前火山口岩浆的历史，以及奥托伊岩浆体的发展和喷发前的结构。奥托伊的高度浓缩但相对简单的地球化学性质意味着它是从大量晶体中分离出来的。后来的Tshirege成员在岩石学和地球化学方面与奥托伊有许多相似之处，但要复杂得多。初步数据与Tshirege的模型一致，该模型认为Tshirege部分来自于添加了古壳的Oowi晶体残留物。在Tshirege岩浆产生之前，这种混合物没有被均化。这一假设将通过分析浮石、玻璃和晶体中的主要元素、微量元素和放射性同位素来验证，以确定贡献成分和它们组装形成Tshirege岩浆的过程。另外两个关键方面是(1)相关的模拟实验，以限制下落的火山口块体对晶堆的共生扰动的程度；(2)高分辨率成像和分析石英斑晶中的钛分布，这将约束可能通过晶堆的热回春而触发超喷发的补给和加热事件(S)的时间。考虑到流纹学超级喷发的潜在破坏性全球影响，提前几十年预测下一次此类事件的必要性是不言而喻的。必须了解超级喷发之前岩浆作用的性质和时间，才能了解在地表可探测到的这些先兆指标。这反过来又需要对这些过程进行基础研究，这也是本研究的主题。这项建议中概述的研究还将对本科生和研究生进行与岩石学和地球化学调查相关的现代方法培训。此外，它还将有助于培养一名年轻的研究科学家和一名职业生涯早期的西班牙裔科学家，他们刚刚获得终身教职。

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.