Crystal-Liquid Dynamics of a Supereruption: The Youngest Toba Tuff and its Aftermath, Sumatra, Indonesia

在印度尼西亚苏门答腊岛的Toba火山口杂岩或美国黄石火山口这样的大型火山系统，喷发活动的兴衰引发了关于这些系统的节奏和物理演化，以及可能引发下一次喷发的现象的根本问题。该项目的目标是高度爆炸性的75卡最年轻的托巴凝灰岩(YTT)-2800千米的岩浆，这是人类经历过的最大的喷发-以及随后更平静的喷发，这可能预示着次火山系统的更新，或其死亡痛苦。像YTT这样的火山岩中含有的晶体是负责它们的岩浆系统的起源、组装和热史的有效记录器。对于YTT来说，晶体记录异常复杂，现有的结果是支离破碎的，有时甚至相互矛盾。例如，对近喷发结晶间隔的估计从几百年到数万年不等，对火山动乱的规模和持续时间的影响截然不同。这项研究的目的是利用战略性地选择样本和分析来补充、扩展和更仔细地检查先前的工作，以协调晶体规模记录中的各种差异。调查将侧重于晶体生长环境的长期变化、YTT喷发和YTT喷发后的矿物亲和力，以及晶体在液体为主而不是固体主导条件下的停留时间，包括从接近喷发矿物生长的条件和持续时间开始的系统(重新)激活的持续时间。这项研究将检验YTT和YTT后喷发的不同部分在空间和时间上选择性地对岩浆系统的不同部分进行采样的假设，包括以液体为主的盖层储集层、可再活化的富晶区(MUSH)和岩浆输入系统的背景，并检验在Toba火山口杂岩下是否有常驻的硅质储集层正在发育或死亡。国际和平研究所和Topa火山口复杂系统的领先专家Craig Chesner(EIU)博士将在这个项目上合作，结合一个新的博士项目重点是地球和行星系统，培训NAU的研究生，并指导NAU和EIU的本科生。Toba Caldera复杂体是一个天然实验室，在其中研究高爆炸性硅系统是如何产生的；许多调查也推测了它对重大气候和人类学事件的影响。岩浆组合的化学动力学、大喷发成分分带的起源以及同一岩浆系统喷发的高、低喷发的矿物生长、储存和重新激活的时间尺度是本研究的重点。目前正在对具有代表性的样品进行系统的表征(通过连续的浮石切片、岩石学研究以及扫描电子显微镜和化学发光成像)，以及战略性的原位化学和同位素矿物分析(通过对选定的微量元素和238U-232Th-230Th-207Pb-206Pb的电子和离子探针分析)，并对其他矿物进行补充分析。需要一种全面的方法来区分同源矿物与喷发期间或喷发前意外并入的矿物，并检查越来越多使用的温度和化学替代物彼此之间以及对岩浆条件的保真度。划分岩浆再活动的持续时间和火山口后岩浆活动的频率也将有助于了解火山喷发前的岩浆信号，以及未来可能发生的与托巴火山口杂岩有关的火山灾害。

The waxing and waning of eruptive activity at giant volcanic systems like the Toba Caldera Complex of Sumatra, Indonesia or at Yellowstone Caldera, USA, raise fundamental questions about the tempo and physical evolution of these systems, and about the phenomena that could trigger the next eruption. This project targets the highly explosive 75 ka Youngest Toba Tuff (YTT) - at 2800 km3 of magma, the largest eruption experienced by the human race - and the subsequent, more quiescent eruptions that could signal renewal of the sub-volcanic system, or its death throes. Crystals contained within volcanic rocks like the YTT are effective recorders of the origin, assembly, and thermal history of the magmatic systems responsible for them. For the YTT, the crystal record is extraordinarily complicated, and existing results are fragmental and sometimes contradictory. Estimates for the interval of near-eruption crystallization, for example, range from a few hundred years to several tens of thousands of years, with drastically different implications for the magnitude and duration of volcanic unrest. This study aims to reconcile the various disparities in crystal-scale records using samples and analyses strategically selected to complement, extend, and more carefully examine previous work. Investigations will focus on long term changes in crystal growth environments, mineral affinities between the YTT and post-YTT eruptions, and the residence time of crystals at liquid-dominated rather than solid-dominated conditions including the duration of system (re)activation from the conditions and duration of near-eruption mineral growth. This study will test the hypothesis that different portions of the YTT and post-YTT eruptions selectively sample distinct portions of the magmatic system in space and time, including a liquid-dominated cap reservoir, remobilized crystal-rich domains (mush), and the background of magmatic inputs into the system, and examine whether a resident silicic reservoir is developing or dying beneath the Toba Caldera Complex. The PI and Dr. Craig Chesner (EIU), the leading expert on the Toba Caldera Complex system, will collaborate on this project, train graduate students at NAU in conjunction with a new Ph.D. program emphasis in Earth and Planetary Systems, and mentor undergraduates at NAU and EIU.The Toba Caldera Complex is a natural laboratory in which to investigate how highly explosive silicic systems are generated; numerous investigations have also speculated about its impact on major climatic and anthropologic events. The chemical dynamics of magma assembly, the origin of compositional zonation in large volume eruptions, and the timescales of mineral growth, storage, and mush reactivation in high- and low-volume eruptions emitted from the same magmatic system are the main foci of this study. Systematic characterization of representative samples (via serial sectioning of pumices, petrographic studies, and SEM and CL imaging) and strategic in situ chemical and isotopic mineral analyses (via electron and ion microprobe analyses of selected trace elements and 238U-232Th-230Th-207Pb- 206Pb) in the minerals quartz, allanite, and zircon are being undertaken, with complementary analyses of other minerals. A comprehensive approach is needed to distinguish cognate minerals from minerals accidentally incorporated during or before eruption, and to examine the fidelity - to each other and to magmatic conditions - of increasingly-used temperature and chemical proxies. Delimiting the duration of magma remobilization and the frequency of post-caldera magmatism will also contribute to understanding magmatic signals in the lead-up to eruptions, and the potential for future volcanic hazards associated with the Toba Caldera Complex.