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

University Of Hawaii, Honolulu

Investigators

Abstract

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.