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

超级喷发的晶液动力学：最年轻的多巴凝灰岩及其后果，印度尼西亚苏门答腊岛

• 批准号: 1322077
• 负责人: Mary Reid
• 金额: $ 22.93万
• 依托单位: Northern Arizona University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-08-01 至 2019-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1322077&HistoricalAwards=false
• 关键词: Crystal; Liquid; Dynamics; Supereruption; Youngest

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.

印度尼西亚苏门答腊岛多巴火山口复合体或美国黄石火山口等巨型火山系统的喷发活动的消长，引发了有关这些系统的克里思和物理演变以及可能引发的现象的根本性问题。下一次喷发。该项目的目标是高度爆炸性的75 ka最年轻的多巴凝灰岩（YTT）-在2800 km 3的岩浆中，人类经历的最大的喷发-以及随后的更平静的喷发，这可能标志着次火山系统的更新，或其垂死挣扎。像YTT这样的火山岩中所含的晶体是岩浆系统起源、组合和热历史的有效记录者。对于YTT，水晶记录是非常复杂的，现有的结果是支离破碎的，有时是矛盾的。例如，对近喷发结晶间隔的估计从几百年到几万年不等，对火山动荡的规模和持续时间的影响截然不同。本研究的目的是调和晶体尺度记录中的各种差异，使用战略选择的样本和分析来补充，扩展和更仔细地检查以前的工作。调查将侧重于晶体生长环境的长期变化，YTT和后YTT喷发之间的矿物亲和力，以及晶体在以液体为主而不是以固体为主的条件下的停留时间，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。这项研究将测试的假设，不同部分的YTT和后YTT喷发选择性地采样不同部分的岩浆系统在空间和时间，包括一个以液体为主的盖水库，再活化的富含晶体的域（糊状物），和背景的岩浆输入系统，并检查是否一个居民的储层正在开发或多巴火山口复杂的下方死亡。PI和克雷格切斯纳博士（EIU），对多巴火山口复杂系统的领先专家，将在这个项目上合作，培训研究生在NAU与一个新的博士。Toba Caldera Complex是一个天然实验室，研究高度爆炸性的火山系统是如何产生的;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，大体积喷发的成分环带的起源，以及矿物生长的时间尺度，存储，并在高，低体积喷发从同一岩浆系统发出的糊状物再活化是本研究的主要焦点。正在对矿物石英、褐帘石和锆石中的代表性样品进行系统表征（通过浮石的连续切片、岩相学研究、SEM和CL成像）和战略性原位化学和同位素矿物分析（通过对选定的微量元素和238 U-232 Th-230 Th-207 Pb-206 Pb进行电子和离子微探针分析），并对其他矿物进行补充分析。需要一个全面的方法来区分同源矿物和在喷发期间或之前意外合并的矿物，并检查越来越多地使用的温度和化学代理的保真度-彼此和岩浆条件。确定岩浆再活动的持续时间和破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，以及与多巴破火山口复合体有关的未来火山灾害的可能性。