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

限制供给火山超级爆发的巨大岩浆库从静止状态到能够爆发的状态的速度对于全面了解大型岩浆系统及其可能构成的火山危险非常重要。为了探测岩浆活动的时间尺度，可以提取在岩浆库中生长的晶体中包含的化学信息，并用于深入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。该项目将调查在巨大的（2800立方公里）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活动的潜在信号，该凝灰岩于74，000年前从印度尼西亚苏门答腊岛的多巴火山爆发。这项研究将在新加坡的南洋理工大学进行，由Fidel Costa博士指导。Fidel Costa博士是将晶体中的化学分区和扩散应用于岩浆系统过程时间尺度的著名专家。在阴极发光成像下，YTT石英晶体内存在显著的近边缘环带，这表明这些晶体的生长期不同，并且通常在不同的温度或压力条件下具有最终阶段。晶体带之间的边界代表了化学不平衡，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。在本项目中，将测量整个晶区边界的钛和铝浓度，以确定已发生的扩散弛豫的幅度。然后将产生的扩散曲线与数值模拟的时间相关曲线进行匹配，以确定区域生长和喷发之间所经过的时间。钛扩散弛豫与铝在石英中的耦合是一种新的方法，应该产生更强大的时间约束和解释比单独一个元素。研究结果将使研究人员能够确定近喷发石英结晶事件的发生，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。该奖项是在东亚和太平洋夏季研究所计划下设立的，旨在支持美国研究生的夏季研究，由NSF和新加坡国家研究基金会共同资助。

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.