Textures and Tectonics of Metamorphic Crystallization

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A general aim of this project is understanding the dynamics of metamorphic textures by integrating mineral chemical and microstructural data: reconciling geometric and chemical aspects of metamorphic textures for petrologic and structural applications. These data are obtained and integrated using a variety of approaches: electron back-scattered diffraction to determine crystallographic orietnation, electron microprobe analysis to document mineral composition and zoning, X-ray computed tomography and serial sectioning/image analysis to obtain 3-dimensional views of textures, and modeling methods to explore crystal growth in the context of deformation (e.g., Elle microstructural modeling). This investigation focuses on the growth of garnet, an important metamorphic mineral for recording pressure, temperature, time, fluid, and deformation information during metamorphism, and the basis for many studies of metamorphic crystallization processes. Specific questions being studied are: What does the presence of high-angle misorientation boundaries in morphologically coherent crystals of garnet indicate about garnet nucleation and growth? And, because these boundaries are rare in other porphyroblasts: Do garnets grow by different mechanisms than other porphyroblasts? A hypothesis to be tested is that the boundaried form during early coalescence of garnets that grow prior to development of growth zoning, and that the boundaries represent special low energy orientations.This project represents part of the Ph.D. thesis of a University of Minnesota graduate student, Eric Goergen, and involve international collaboration with Dr. Mark Jessell (Toulouse). The research also involves undergraduate research assistants at Minnesota and summer interns from other institutions as part of an NSF-REU site. Results are being incorporated into a new teaching module that focuses on the Dutchess County, NY, Barrovian sequence; the module is distributed through the Teaching Petrology website.