Dynamics of crystal mush: Insight from 2D and 3D analysis of drill cores from Kilauea Iki lava lake, Hawaii

钻探炽热的熔岩听起来像是科幻小说，但它不仅是一种被建议的清洁能源，而且实际上在1960年至1988年期间曾多次这样做。然后，夏威夷火山天文台的科学家们探测了1959年火山喷发期间形成的一个熔岩湖。他们的目标是通过收集钻探岩心样本来“观察”湖水的冷却和凝固。早期的钻探岩心只采集了湖的上地壳，湖中既有完全结晶的岩石，也有晶体，其中含有高达45%的熔体(在取芯过程中被水冷却成玻璃)。后来，在整个湖中钻取了岩芯，对上、下固体地壳以及内部泥浆进行了采样。对得到的钻芯进行的化学分析表明，在凝固过程中，熔体、气泡和晶体在熔岩湖内四处移动。知道是什么过程控制了这些运动，可以提高我们对火山下岩浆系统中熔化、气泡和晶体如何、何时以及为什么重新排列的理解。它还可能揭示气泡和晶体的运动如何为火山喷发做准备并引发火山喷发。该团队将使用x射线扫描技术来获得岩芯的3D图像，这些图像将显示自1959年以来玻璃+晶体+气泡作为湖中位置和时间的函数的空间分布。单独的岩心图像可以用来模拟控制熔体运动的属性，如熔体百分比、连通性和渗透率。在空间和时间上跟踪这些过程不仅将提供对火山的前所未有的观察，还将有助于未来的钻探工作。一个世纪以来，(1)岩浆系统中的熔体演化和(2)可喷发(富含熔体)岩浆体的形成的概念模型一直围绕着大型、长寿、熔体主导的岩浆室的概念而框架。然而，对岩浆系统的地球物理成像和岩石学分析都表明，它们是由含有熔体透镜的晶体ʻʻ主导的。这两种观点的协调一致是提高我们对为火山喷发提供动力的岩浆系统的理解的关键，并要求更好地理解控制熔体、晶体和挥发分在以泥浆为主的系统中重新分布的物理过程和化学后果。该项目将使用一套岩心的微CT扫描来解决这个问题，这些岩心是通过钻探到夏威夷固化的Kilauea Iki熔岩湖中而获得的。1960年至1988年收集的18个岩芯包括高达45%的熔体(现在是玻璃)的样品，跟踪冷却地壳的初始增长，后来横切上地壳和下地壳以及中间的晶体碎屑。岩芯的岩石学研究记录了湖中熔体、晶体和气泡复杂而多样的运动。新的3D数据将被用来绘制晶体泥在空间和时间上的物理性质。另外的2D分析将检查熔体和晶体分布的化学后果，特别是寻找与不同类型的熔体通道相关的反应流动的证据。伴随着2D模拟实验和建模，将跟踪当气体通过粘性液体+光弹性固体颗粒的悬浮液流动时的颗粒-颗粒相互作用。联合工作的结果将提高对熔岩湖(和岩床)凝固的理解，并有助于解释来自部分熔融系统的地球物理信号。钻探火山的想法也激发了公众的想象力，并对开发“清洁”的热液能源具有实际应用价值。研究人员将在史密森学会关于钻探热岩主题的虚拟展览中开发这些主题。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Drilling hot lava sounds like science fiction, but it is not only a suggested source of clean energy but was actually done multiple times between 1960 and 1988. Then scientists at the Hawaiian Volcano Observatory probed a lava lake that formed during an eruption in 1959. The goal was to ‘watch’ the lake cool and solidify by collecting drill core samples. Early drill cores sampled only the upper crust of the lake, which comprised both fully crystalline rock and crystal ‘mush’ comprising crystals with up to 45% melt (quenched to glass by water during coring). Later cores were drilled through the entire lake, sampling both upper and lower solid crust as well as interior mush. Chemical analysis of the resulting drill cores showed that during solidification, melt, bubbles and crystals were moving around within the lava lake. Knowing what processes control those movements could improve our understanding of how, when and why melt, bubbles and crystals are rearranged in magmatic systems under volcanoes. It may also reveal how the movement of bubbles and crystals prepare for and trigger volcanic eruptions. The team will use x-ray scanning technology to get 3D images of the cores that will show the spatial distribution of glass plus crystals plus bubbles as a function of position in the lake and time since 1959. Individual core images can be used to model properties - such as melt percentage, connectivity and permeability - that control melt movement. Tracking these processes through space and time will not only provide an unprecedented look into a volcano but also aid future drilling efforts. For a century, conceptual models of (1) melt evolution in magmatic systems and (2) formation of eruptible (melt-rich) magma bodies were framed around the concept of large, long-lived, melt-dominated magma chambers. However, both geophysical imaging and petrologic analysis of magmatic systems suggest that they dominated by crystal ʻmushʻ that contains lenses of melt. Reconciliation of these two perspectives is key to improving our understanding of the magma systems that feed volcanic eruptions and requires improved understanding of the physical processes that control, and the chemical consequences of, redistribution of melt, crystals and volatiles within mush-dominated systems. This project will address this problem using µCT scans of a suite of cores obtained by drilling into the solidifying Kilauea Iki lava lake, Hawaii. 18 cores collected between 1960 and 1988 include samples with up to 45% melt (now glass), track the initial growth of a cooling crust and later transected both the upper and lower crust as well as intervening crystal mush. Petrologic studies of the cores have documented complex and diverse movements of melt, crystals and bubbles within the lake. New 3D data will be used to map the physical properties of crystal mush in space and time. Additional 2D analysis will examine the chemical consequences of melt and crystal distribution and, specifically, look for evidence of reactive flow associated with different types of melt channels. Accompanying 2D analog experiments and modeling will track particle-particle interactions when gas is fluxed through suspensions of viscous liquid + photoelastic solid particles. The results of the combined work will improve understanding of lava lake (and sill) solidification and aid interpretation of geophysical signals from partially molten systems. The idea of drilling into volcanoes also captures the public imagination and has practical applications to the development of “clean” hydrothermal energy. The researchers will develop these themes in a virtual exhibit for the Smithsonian Institution on the topic of Drilling Hot Lava.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.