Anorthite in Magmatic Systems

要满足我们日益增长的对自然资源稳定供应的需求，就需要对形成和储存这种资源的过程有越来越深入的了解。要深入了解这些过程，需要进行研究，从地质材料转化为可开采的地面资源的各个方面，从最初从地球内部带出来的东西，到资源集中在地表的最终机制的性质。这个项目的重点是促进我们对地球内部有什么东西，比人类直接接触到的更深，以及在大洋中脊海底静止的火山活动期间和陆地上猛烈的火山喷发期间，这种地幔物质的哪一部分被带到地球表面的基本理解。通过研究在这两种地质环境中发现的一种矿物--钙长石，将收集到对这些地区的地幔和将岩浆移动到地表的机制的新见解。钙长石的起源仍然是个谜，不能用我们目前对地幔中工作的地质过程的理解来解释。这项研究利用了通过对这种矿物的合成版本进行研究而获得的一系列新观察结果，这些观察结果表明，岩浆在岩浆中的行为与广泛假设的截然不同，并有可能极大地改变我们对地幔如何产生岩浆以及它们在上升过程中经历的变化的看法。这项研究包括模拟地球内部条件的实验、模拟和观察岩石样品中的天然钙长石晶体的组合。这种多方面的方法对于培养各级下一代地球科学家至关重要，将用于向大学新生介绍跨学科科学，为本科生提供研究经验，并最终提供博士水平的研究机会。具体地说，这项拟议的工作使用实验和热力学模拟方法来研究自鲍文时代以来，人们很少认识到的与经典熔环拓扑结构的偏差，该拓扑结构被认为是决定火成岩中斜长石成分行为的。这种偏差是以斜长石富集区和斜长-橄榄石组成空间的假共沸物形式在高压下破坏斜长石的稳定性，并阻止斜长岩在岩浆冷却时正常向富钠方向演化。拟议的研究将限制这种行为在上升地幔的组成空间内，这样做将为大洋中脊和俯冲带岩浆中高度斜长石晶体的起源提供新的见解。此外，这种拓扑结构上的压力效应决定了斜长石与熔体稳定性关系的变化，这意味着存在一个高熔体生成量的高压区，并对涉及铝尖晶石的包晶反应起着重要作用。由于目前在这些环境中岩浆产生的模型都无法预测这些影响，这项研究有可能打开各种关于挤压和伸展板块边缘岩浆起源和演化的新研究之门，这些研究可以将这种行为整合到下一代地球地幔岩浆形成的机制模型中。

Meeting our ever increasing need for a steady supply of natural resources requires an increasingly sophisticated understanding of processes that form and store such resources. Gaining insights into these processes requires research that spans all aspects of the transformation of geologic material into exploitable ground-based resources, from what is originally brought up from the Earth's interior, to the nature of the final mechanisms of concentration of resources on the surface. This project focuses on furthering our fundamental understanding of what lies in the Earth's interior, deeper than humans can directly access, and what portion of this mantle material is brought to the Earth's surface during quiescent volcanic activity beneath the sea at mid-ocean ridges and during violent volcanic eruptions on land. New insights into the mantle in these regions and the mechanisms of moving magma to the surface will be gleaned by studying a mineral found in both of these geologic environments, the mineral anorthite, whose origin remains enigmatic and cannot be explained by our current understanding of the geologic processes at work in the Earth's mantle. This research capitalizes upon a set of new observations obtained through research on a synthetic version of the mineral that suggests very different behavior in magmas than has been broadly assumed and has the potential to dramatically change our view on how magmas are produced in the mantle and the changes they undergo as they ascend. This research involves a combination of experiments simulating conditions within the Earth, modeling, and looking at natural anorthite crystals in rock samples. This multi-faceted approach is vital for training the next generation of geoscientists at all levels and will be used to introduce college freshmen to interdisciplinary science, provide research experiences for undergraduates, and finally to provide Ph.D. level research opportunities. In specific, the proposed work uses experimental and thermodynamic modelling approaches to investigate a little-recognized deviation from the classic melting loop topology accepted as dictating plagioclase compositional behavior in igneous rocks since the time of Bowen. This deviation is in the form of a pseudo-azeotrope in the anorthite-rich region of plagioclase and plagioclase-olivine compositional space at elevated pressure that destabilizes plagioclase and inhibits anorthitic plagioclase from evolving normally towards Na-enrichment as the magma cools. The proposed research will constrain this behavior in the compositional space of upwelling mantle and by doing so will provide new insights into the origin of highly anorthitic plagioclase crystals in mid-ocean ridge and subduction zone magmas. Furthermore, the change in plagioclase and melt stability relations dictated by the pressure effect on this topology implies an elevated pressure region of high melt production and an important role for a peritectic reaction involving aluminous spinel. As neither of these implications can be predicted by current models of magma production in these environments, this research has the potential to open the door to a variety of new studies on the origin and evolution of magmas at compressional and extensional plate margins that can integrate such behavior into a next-generation mechanistic model of magma formation in the Earth's mantle.