The structure and rheology of crystal mushes

晶体糊的结构和流变学

基本信息

批准号：
NE/J020877/1
负责人：
Madeleine Humphreys
金额：
$ 1.41万
依托单位：
University of Oxford
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%2FJ020877%2F1
关键词：
structure rheology crystal mushes

项目摘要

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.

随着熔融岩石（岩浆）冷却，它在岩浆体的边缘上结晶并形成了“晶体糊状”。糊含有晶体和火山液体的混合物。继续冷却将剩余的液体稳步转换为晶体，糊状层生长直到整个身体固体。该糊状层对压力（其强度或“流变学”）的响应方式控制着各个尺度上的火山过程，从超级伏尔加诺人的大型岩浆腔室的演变到岩浆中山脊的岩浆喷发，Lava Flow的增气量，以及危险的火山冲突的动力学和爆炸性。因此，如果我们要了解许多火山过程，对穆斯流变学的理解至关重要。知道液体和颗粒的混合物对外部压力的反应如何对于多种问题，包括制作冰淇淋，倒入混凝土和理解泥流的行为。在理解很少的悬浮晶体（> 50％液体）和含量很小的岩石（<5％液体）的岩浆的流变方面，已经取得了成功的进步（<5％）。但是，对研究液体约10-50％的蘑菇的流变学进行了相对较少的作用，并且由于流变学的变化很大，因此很难从先前的研究中进行比例缩放。这种中间情况很重要，因为许多火山过程都涉及具有这些中间液体含量的岩石。例如，由于缺乏关于流变学数据的合适数据，我们不知道Crystal Mush压实在控制玄武岩岩浆演化中有多重要。我们建议通过将实验结果与关于天然晶体糊的结构的观察结合，通过研究晶体糊与中间液体含量的大量流变来解决这一差距。糊的流变学取决于其晶体尺度的结构。例如，颗粒的大小和形状对糊状的刚性和强度有影响。因此，我们将专注于量化糊状结构，这也将帮助我们将自然和实验结果联系在一起。首先，我们将使用GABBRO的自然示例来描述和量化晶体糊的微观结构，我们确定没有变形。一旦我们知道了典型的Gabbro Mush的结构，我们将使用模仿Gabbro Mush的低温模拟材料设计简单的实验。这些实验将向我们展示糊状结构在变形时如何变化，以及各种参数（例如晶粒尺寸，形状和液体量）如何影响糊状强度及其变形的方式。我们最终将检查已变形的天然岩石，以校准我们的结果并确定诸如压实等过程的重要性。这样，我们将在冷却和岩浆结晶过程中对流变学建立定量的理解。结果将对地球科学的其他领域具有广泛的适用性，也将与化学工程，食品加工和冶金学方面的一系列问题有关。