EAPSI: Probing the Pre-Eruption Magmatic Record of the Youngest Toba Tuff through Titanium and Aluminum Diffusion Timescales in Quartz Crystals

限制为火山超级喷发提供补给的巨大岩浆库从静止状态动员到能够喷发的状态的速度，对于全面了解大型岩浆系统及其可能造成的火山危险非常重要。为了探测岩浆动员的时间尺度，可以提取岩浆库中生长的晶体中包含的化学信息，并用于了解喷发前岩浆库中发生的条件和过程的任何变化的时间。该项目将研究在巨大的（2800 km3）最年轻的多巴凝灰岩（YTT）中发现的石英晶体喷发前生长记录中岩浆动员的潜在信号，该凝灰岩于74000年前在印度尼西亚苏门答腊岛的多巴火山口爆发。这项研究将在新加坡南洋理工大学进行，导师是菲德尔·科斯塔博士，他是一位著名的专家，擅长将晶体中的化学分区和扩散应用于岩浆系统过程的时间尺度。在阴极发光成像下，YTT石英晶体中存在明显的近边缘带状，表明这些晶体的生长周期不同，并且在不同的温度或压力条件下往往有一个最终阶段。晶体区域之间的边界代表了一种化学不平衡，在岩浆温度下，随着时间的推移，元素将在晶体中扩散以达到平衡。在这个项目中，钛和铝的浓度将跨越晶体带边界进行测量，以确定已经发生的扩散弛豫的大小。然后将得到的扩散曲线与数值模拟的随时间变化的曲线相匹配，以确定区域生长和喷发之间经过的时间。石英中钛扩散弛豫与铝扩散弛豫的耦合是一种新的方法，应该比单独的一种元素产生更强大的时间约束和解释。这些结果将使研究人员能够确定近喷发石英结晶事件的开始，以及这些事件与YTT岩浆系统动员和/或替代过程（如同喷发减压）的潜在关系。该奖项由美国国家科学基金会和新加坡国家研究基金会共同资助，隶属于东亚和太平洋暑期研究所项目，支持一名美国研究生进行暑期研究。

Constraining how quickly the enormous magma reservoirs that feed volcanic supereruptions can mobilize from a quiescent state to a state capable of eruption is important for overall understanding of large magma systems and the volcanic hazard they may pose. To probe the timescales of magma mobilization, chemical information contained within crystals that were growing in a magma reservoir can be extracted and used to gain insight into the timing of any changes in the conditions and processes that occurred in the magma reservoir before eruption. This project will investigate potential signals of magma mobilization in the pre-eruption growth record of quartz crystals found within the enormous (2800 km3) Youngest Toba Tuff (YTT), which explosively erupted 74,000 years ago from Toba Caldera in Sumatra, Indonesia. The research will be conducted at Nanyang Technological University in Singapore under the mentorship of Dr. Fidel Costa, a noted expert in applying chemical zoning and diffusion in crystals to timescales of magmatic system processes. Striking near-rim zonation present within YTT quartz crystals under cathodoluminescence imaging is indicative of distinct of periods of growth for these crystals, and often with a final stage under different temperature or pressure conditions. The boundary between crystal zones represents a chemical disequilibrium where, through time at magmatic temperatures, elements will diffuse in the crystal to attain equilibrium. For this project, titanium and aluminum concentrations will be measured across crystal zone boundaries to determine the magnitude of diffusional relaxation that has occurred. The yielded diffusion profiles will then be matched to numerically modeled time-dependent profiles to determine the time elapsed between zone growth and eruption. The coupling of titanium diffusional relaxation with that of aluminum in quartz is a novel approach that should yield more robust temporal constraints and interpretations than one element alone. The results will allow the researchers to determine the onset of near-eruption quartz crystallization events, and the potential relation of these events to YTT magma system mobilization and/or alternative processes, such as syn-eruptive decompression. This award, under the East Asia and Pacific Summer Institutes program, supports summer research by a U.S. graduate student and is jointly funded by NSF and the National Research Foundation of Singapore.