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

印度尼西亚苏门答腊岛的多巴火山复合体或美国黄石火山等大型火山系统的喷发活动的兴衰，提出了有关这些系统的速度和物理演化的基本问题，以及可能引发下一次喷发的现象。这个项目的目标是高度爆炸性的75 ka最年轻的多巴凝灰岩(YTT) -岩浆2800立方公里，是人类经历过的最大的喷发-以及随后的，更安静的喷发，可能预示着次火山系统的更新，或者它的死亡痛苦。YTT等火山岩中的晶体是形成它们的岩浆系统的起源、组合和热历史的有效记录者。对于YTT，晶体记录是非常复杂的，现有的结果是零碎的，有时是相互矛盾的。例如，对近喷发结晶间隔的估计，从几百年到几万年不等，对火山不稳定的程度和持续时间有截然不同的含义。本研究旨在利用样品和分析来调和晶体尺度记录中的各种差异，以补充、扩展和更仔细地检查以前的工作。研究将集中在晶体生长环境的长期变化，YTT和YTT爆发后的矿物亲和力，以及晶体在液体主导而不是固体主导条件下的停留时间，包括系统（再）激活的持续时间和近喷发矿物生长的持续时间。本研究将测试YTT和YTT后喷发的不同部分在空间和时间上有选择地采样岩浆系统的不同部分的假设，包括液体主导的盖层储层，重新激活的富含晶体的区域（mush），以及岩浆输入系统的背景，并检查多巴火山口复合体下是否存在一个永久的硅储层正在发育或死亡。PI和Toba火山口复杂系统的首席专家Craig Chesner博士（EIU）将在该项目上合作，在NAU培训研究生，并结合新的地球和行星系统博士课程重点，并指导NAU和EIU的本科生。多巴火山口复合体是一个天然实验室，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主要气候和人类学事件的影响。岩浆组合的化学动力学、大体积喷发中成分分带的成因以及同一岩浆系统大、小体积喷发中矿物生长、储存和浆液再活化的时间尺度是本研究的重点。对代表性样品进行系统表征（通过浮石连续切片、岩石学研究、SEM和CL成像），对石英、allanite和锆石矿物进行战略性原位化学和同位素矿物分析（通过电子和离子探针分析选定的微量元素和238U-232Th-230Th-207Pb- 206Pb），并对其他矿物进行补充分析。需要一种综合的方法来区分同源矿物和在喷发期间或之前偶然结合的矿物，并检查越来越多使用的温度和化学代用物相互之间和对岩浆条件的保真度。划定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爆发前的岩浆信号，以及与多巴火山口复群相关的未来火山危险的可能性。

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.