Assessing silicate melt behaviour with granite microstructure

岩浆(熔岩)的向上流动和结晶是地壳形成和演化中最重要的两个过程。这些过程在大陆地壳中尤其重要，那里的大多数岩浆成分是花岗岩。了解花岗岩浆的演化至关重要，因为(A)花岗岩是许多经济矿物的主要载体，包括金、铜、锡、钨和铀，以及(B)花岗岩浆的成因和侵位对前寒武纪至今的大陆演化具有重大影响。 关于花岗岩岩浆迁移和结晶的细节，我们知之甚少，因为我们还没有开发出一套严格的方法来测量和评价这些过程。因此，我们目前无法描述在任何给定的花岗岩体内，岩浆的晶体和液体部分是如何表现的，以及冷却速度如何影响晶体生长和颗粒尺寸。这种认识上的差距严重限制了我们对花岗岩形成的最基本的物理、化学、空间和时间条件的了解，进而限制了我们对大陆地壳演化的了解。在拟议的研究计划中，我将通过应用岩石微结构分析和解释方面的最新进展来研究花岗岩岩浆的内部行为。这些调查将对计划在加拿大和南非进行的新实地工作期间收集的样本进行。我的研究计划的一个直接结果将是一套新的方法：(1)识别花岗岩结晶过程中晶体和液体的流动性，(2)量化花岗岩侵入体的结晶速率。这些方法将被用于花岗岩岩浆演化的参数化，并最终提高我们对大型大陆岩浆系统的理解。 拟议的研究将包括两个相互关联的主题：i.高硅花岗岩(&gt；70wt.%SiO_2)的内部行为；以及ii.花岗岩侵入体的热演化。我们将使用矿物石英的晶体取向关系来确定晶体在结晶过程中是否移动，以及是否发生晶体熔体分离。这一结果将使我们能够评估侵入体的成分和尺寸对花岗岩体物理演化的影响。为了解决我们对花岗岩岩浆冷却行为的认识上的空白，我们将开发和校准一种新的结晶速率测速仪，该测速仪基于矿物斜长石的形态和花岗岩的化学成分。鉴于斜长石在花岗岩中几乎无处不在，该方法将适用于世界范围内岩浆动力学和岩浆杂岩热历史的研究。我的研究成果也将为认识与花岗岩有关的矿床提供一个新的平台。

The upward flow and crystallization of magma (molten rock) are two of the most important processes in the formation and evolution of Earth's crust. These processes are particularly important within the continental crust, where the majority of magmas are granitic in composition. Understanding the evolution of granitic magma is critical because (a) granite is a principal carrier of many economic minerals, including gold, copper, tin, tungsten and uranium, and (b) the genesis and emplacement of granitic magma has had a significant bearing on continental evolution from the Precambrian to the present day. Little is known about the details of granitic magma migration and crystallization because we have not yet developed a set of rigorous methods to measure and evaluate these processes. As such, we are currently unable to describe, in any given body of granite, how the crystal and liquid parts of the magma behaved, and how the rate of cooling affected crystal growth and grain dimensions. This gap in knowledge severely limits our understanding of the most fundamental physical, chemical, spatial and temporal conditions of granite formation and, in turn, the evolution of the continental crust. In the proposed program of research, I will investigate the internal behaviour of granitic magma by applying recent advances in the analysis and interpretation of rock microstructures. These investigations will be made on samples collected during new field work planned for Canada and South Africa. An immediate result of my research program will be a new set of methods to (1) identify the mobility of crystals and liquid during granite crystallization, and (2) quantify the crystallization rate of granitic intrusions. These methods will be used to parameterize the evolution of granitic magma and ultimately improve our understanding of large continental magmatic systems. The proposed research will consist of two interrelated themes: I. the internal behaviour of high-silica granites (>70 wt.% SiO2); and II. the thermal evolution of granitic intrusions. We will use crystallographic orientation relationships of the mineral quartz to determine if crystals were mobile during crystallization and if crystalmelt segregation occurred. The results will allow us to evaluate the influence of intrusion composition and dimensions on the physical evolution of granitic bodies. To address gaps in our understanding of cooling behaviour of granitic magma, we will develop and calibrate a new crystallization rate speedometer, based on the morphology of the mineral plagioclase and the chemical composition of the granite. Given the nearly ubiquitous occurrence of plagioclase in granitic rocks, this method will be applicable to the study of magma dynamics and thermal histories of magmatic complexes worldwide. The results of my research will also provide a new platform for the understanding of granite-related mineral deposits.