Experimental and Microanalytical Study of Dendritic Crystal Growth in CMAS and Basaltic Magma

CMAS 和玄武岩浆中枝晶生长的实验和显微分析研究

• 批准号: 1220084
• 负责人: Julia Hammer
• 金额: $ 27.09万
• 依托单位: University of Hawaii
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-07-15 至 2015-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1220084&HistoricalAwards=false
• 关键词: Experimental; Microanalytical; Study; Dendritic; Crystal

Petrogenetic and geochemical models generally assume that magmas crystallize under near equilibrium conditions, and that crystal growth occurs firmly in the interface-limited (as opposed to diffusion-limited) regime. However, mounting textural and compositional evidence points toward incipient magma crystallization characterized by rapid growth and formation of dendritic crystals ? in which case diffusion rates of the incorporated elements can significantly influence crystal growth. This proposal outlines a plan for studying the mechanics and petrologic consequences of dendritic crystal growth in two mafic crystalline phases, olivine and clinopyroxene, utilizing dynamic crystallization experiments and frontier compositional and microtextural analysis techniques. Intellectual Merit. The experimental and analytical study of Module 1, targets olivine crystallization in a thermal gradient under dynamic temperature conditions, utilizing a novel experimental geometry to enhance formation of defects. Activities in this module will test hypotheses regarding the origin of curved olivine-melt interfaces, development of subgrain boundaries (low angle lattice misorientations) in the absence of anisotropic stress, and the process of melt inclusion entrapment. The anticipated results have important implications for geochemical ?crystal stratigraphy? as well as geophysical models of ocean island magmatic plumbing systems. The microanalytical study in Module 2, targets clinopyroxene dendrites to investigate a style of progressive lattice rotation that is previously unrecognized in crystals growing freely from a liquid, and unexplained by existing crystal growth theory. Electron backscatter diffraction (EBSD) mapping will be used to characterize the incidence of lattice misorientations in previously-synthesized experimental samples as well as naturally-occurring clinopyroxene dendrites and polyhedral crystals. Selected materials will be further interrogated in TEM foils using diffraction contrast imaging, high resolution phase contrast imaging, and enegy-dispersive x-ray spectroscopy to determine the defect microstructure that accommodates the lattice rotation. Broader Impacts. We will continue offering a professional development program for Hawaii K-12 teachers developed during prior and current award periods. The program, Research Experience for Teachers in Volcano-Petrology (RET/V-P) emphasizes geoscience fundamentals and exposure to geology in a field setting. We will develop and disseminate educational materials intended for 6-8th grade instruction, composed of pre- and post-assessment instruments, classroom activities, field trips to several Oahu sites, and resources for deeper investigation. We will work with Dr. Lehnert, Director of the Integrated Earth Data Applications (IEDA), to develop schema appropriate for incorporation of novel textural and analytical data in the Geochemical Resource Library catalog. Tasks include incorporating (a) analytical data collected from non-equilibrated (i.e., kinetics-focused) experiments, (b) metadata such as tabulated analytical data that is contextualized with imagery, and (c) microcrystallographic orientation data, e.g., as generated during EBSD analysis and Xray element mapping.

岩石成因和地球化学模型通常假设岩浆结晶在接近平衡的条件下，晶体生长发生坚定的界面限制（而不是扩散限制）制度。然而，越来越多的纹理和成分的证据指向早期岩浆结晶的特点是快速增长和形成的树枝状晶体？在这种情况下，掺入元素的扩散速率可显著影响晶体生长。该建议概述了一个计划，研究力学和岩石学后果的树枝状晶体生长在两个镁铁质结晶相，橄榄石和单斜辉石，利用动态结晶实验和前沿成分和显微结构分析技术。智力优势。模块1的实验和分析研究，目标橄榄石结晶在动态温度条件下的热梯度，利用一种新的实验几何形状，以提高缺陷的形成。本模块中的活动将测试关于弯曲橄榄石熔体界面的起源、在无各向异性应力的情况下亚晶界（低角度晶格取向差）的发展以及熔体夹杂物截留过程的假设。预期的结果具有重要的意义，地球化学？结晶地层学以及大洋岛屿岩浆管道系统的地球物理模型。模块2中的微观分析研究，针对单斜辉石枝晶，以研究一种以前在从液体中自由生长的晶体中未识别的渐进晶格旋转方式，并且无法用现有的晶体生长理论解释。电子背散射衍射（EBSD）映射将被用来表征在先前合成的实验样品，以及自然发生的单斜辉石枝晶和多面体晶体的晶格取向不良的发病率。选定的材料将进一步询问TEM箔使用衍射对比成像，高分辨率相衬成像，和能量色散X射线光谱，以确定缺陷的微观结构，容纳晶格旋转。更广泛的影响。我们将继续提供一个专业的发展计划，为夏威夷K-12教师在以前和目前的奖励期间开发。该计划，火山岩石学教师的研究经验（RET/V-P）强调地球科学基础知识和在现场环境中接触地质学。我们将开发和传播用于6- 8年级教学的教育材料，包括评估前和评估后的工具，课堂活动，实地考察几个Occupy网站，以及更深入的调查资源。我们将与综合地球数据应用（IEDA）主任Lehnert博士合作，开发适合将新的纹理和分析数据纳入地球化学资源库目录的模式。任务包括合并（a）从非平衡（即，动力学聚焦的）实验，（B）元数据，例如与图像相关联的列表分析数据，以及（c）微晶取向数据，例如，如在EBSD分析和X射线元素绘图期间生成的。