The structure and rheology of crystal mushes

晶体糊的结构和流变学

• 批准号: NE/J021210/1
• 负责人: Alison Rust
• 金额: $ 1.39万
• 依托单位: University of Bristol
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2013
• 资助国家: 英国
• 起止时间: 2013 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FJ021210%2F1
• 关键词: structure; rheology; crystal; mushes

As molten rock (magma) cools, it crystallizes and a 'crystal mush' forms on the margins of the magma body. The mush contains a mixture of crystals and volcanic liquid. Continued cooling steadily converts the remaining liquid to crystals, and the mush layer grows until the entire body is solid. The way this mush layer responds to stress (its strength, or 'rheology') controls volcanic processes on all scales, from the evolution of large magma chambers under super-volcanoes, to the eruption of magma at mid-ocean ridges, the emplacement of lava flows, and the dynamics and explosivity of hazardous volcanic eruptions. An understanding of mush rheology is therefore vital if we are to understand many volcanic processes. Knowing how mixtures of liquid and particles respond to external stresses is also important to a wide range of problems, including making ice-cream, pouring concrete and understanding the behaviour of mud-flows.Much progress has been made in understanding the rheology of magmas with few suspended crystals (>50% liquid) and of rocks containing very little melt (<5% liquid). However, relatively little has been done to investigate the rheology of mushes with approximately 10-50% liquid, and it is difficult to scale up or down from previous studies because the rheology changes strongly. This intermediate case is important because many volcanic processes involve rocks with these intermediate liquid contents. For example, we don't know how important crystal mush compaction is in controlling basalt magma evolution, because of a lack of suitable data on rheology. We propose to address this gap by investigating the bulk rheology of crystal mushes with intermediate liquid contents, by combining experimental results with observations on the structure of natural crystal mushes. The rheology of a mush depends on its crystal-scale structure. For example, the size and shape of the particles has an effect on how rigid and strong the mush is. We will therefore focus on quantifying the mush structure, which will also help us to link together natural and experimental results. Firstly we will describe and quantify the microstructure of crystal mushes that we can be sure haven't been deformed, using natural examples of gabbro. Once we know the structure of a typical gabbro mush, we will design simple experiments using low-temperature analogue materials that mimic the gabbro mush. These experiments will show us how the mush structure changes when it is deformed and how various parameters (e.g. grain size, shape and the amount of liquid) affect the mush strength and the way it deforms. We will finally examine natural rocks that have been deformed, in order to calibrate our results and determine the importance of processes such as compaction. In this way we will build a quantitative understanding of rheology during cooling and crystallisation of magma. The results will have broad applicability for other areas of Earth science, and will also be relevant to a range of problems in chemical engineering, food processing and metallurgy.

当熔融的岩石（岩浆）冷却时，它会结晶，并在岩浆体的边缘形成“水晶泥”。这种糊状物含有晶体和火山液体的混合物。持续的冷却稳定地将剩余的液体转化为晶体，糊状层不断生长，直到整个身体都是固体。这一层对压力的反应方式（其强度或“流变性”）控制着所有规模的火山过程，从超级火山下大型岩浆库的演变，到大洋中脊岩浆的喷发，熔岩流的就位，以及危险火山爆发的动力学和爆炸性。因此，如果我们要了解许多火山过程，了解泥浆流变学是至关重要的。了解液体和颗粒的混合物如何对外部应力作出反应，对于许多问题也很重要，包括制作冰淇淋、浇注混凝土和了解泥流的行为。在了解含有少量悬浮晶体（>50%液体）的岩浆和含有很少熔体（<5%液体）的岩石的流变学方面，已经取得了很大进展。然而，对具有大约10-50%液体的糊状物的流变学进行的研究相对较少，并且由于流变学变化强烈，因此难以从先前的研究按比例放大或缩小。这种中间状态的情况很重要，因为许多火山作用都涉及到具有这种中间液体含量的岩石。例如，由于缺乏合适的流变学数据，我们不知道晶体泥压实在控制玄武岩岩浆演化中的重要性。我们建议通过研究具有中等液体含量的水晶浆的整体流变学，将实验结果与对天然水晶浆结构的观察相结合，来解决这一差距。糊状物的流变性取决于其晶体结构。例如，颗粒的大小和形状对糊状物的刚性和强度有影响。因此，我们将专注于量化糊状结构，这也将有助于我们将自然和实验结果联系起来。首先，我们将描述和量化的晶体mushes，我们可以肯定没有变形的微观结构，使用自然的辉长岩的例子。一旦我们知道了典型辉长岩浆的结构，我们将设计简单的实验，使用低温模拟材料来模拟辉长岩浆。这些实验将向我们展示糊状物结构在变形时如何变化，以及各种参数（例如颗粒大小，形状和液体量）如何影响糊状物强度及其变形方式。最后，我们将检查已经变形的天然岩石，以校准我们的结果并确定压实等过程的重要性。通过这种方式，我们将建立一个定量的了解流变学在冷却和结晶的岩浆。这些结果将广泛适用于地球科学的其他领域，也将与化学工程、食品加工和冶金学中的一系列问题有关。

项目成果

The formation of vesicular cylinders in pahoehoe lava flows

帕霍霍熔岩流中气泡柱的形成

• DOI: 10.1080/03091929.2014.955799
• 发表时间: 2014
• 期刊: Geophysical & Astrophysical Fluid Dynamics
• 影响因子: 1.3
• 作者: Fowler A