Textures and Tectonics of Metamorphic Crystallization

该项目的总体目标是通过整合矿物化学和微观结构数据来理解变质结构的动力学：调和变质结构的几何和化学方面的岩石学和构造应用。这些数据是通过多种方法获得和整合的：电子背散射衍射来确定晶体取向，电子显微探针分析来记录矿物成分和分带，x射线计算机断层扫描和连续切片/图像分析来获得纹理的三维视图，以及建模方法来探索变形背景下的晶体生长（例如Elle微结构建模）。石榴石是记录变质过程中压力、温度、时间、流体和变形等信息的重要变质矿物，是许多变质结晶过程研究的基础。正在研究的具体问题是：在石榴石形态相干晶体中存在的高角度错取向边界对石榴石的成核和生长有什么指示作用？而且，由于这些边界在其他成卟细胞中很少见：石榴石的生长机制与其他成卟细胞不同吗？一个有待验证的假设是，在生长带发育之前，石榴石在早期聚结时形成边界，并且边界代表特殊的低能取向。该项目是明尼苏达大学研究生Eric Goergen博士论文的一部分，涉及与Mark Jessell博士（图卢兹）的国际合作。这项研究还包括明尼苏达大学的本科生研究助理和来自其他机构的暑期实习生，作为NSF-REU网站的一部分。结果将被纳入一个新的教学模块，该模块侧重于纽约州达奇斯县的巴罗维亚序列；该模块通过教学岩石学网站发布。

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.