Textures and Tectonics of Metamorphic Crystallization

该项目的总体目标是通过整合矿物、化学和微结构数据来了解变质结构的动力学：将变质结构的几何和化学方面协调起来，用于岩石学和构造应用。这些数据是使用各种方法获得和整合的：用来确定晶体取向的电子背散射衍射法、用来记录矿物成分和分带的电子探针分析、用来获得纹理的三维视图的X射线计算机层析和连续切片/图像分析，以及用来在变形的情况下探索晶体生长的建模方法(如ELLE微结构建模)。石榴石是一种记录变质过程中压力、温度、时间、流体和变形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：在形态上一致的石榴石晶体中存在的高角度取向错位边界意味着石榴石的成核和生长？而且，因为这些边界在其他成斑细胞中是罕见的：石榴石的生长机制是否与其他成斑细胞不同？一个需要检验的假设是，石榴石在生长环带形成之前生长的早期融合中的边界形式，以及边界代表特殊的低能量取向。这个项目代表了明尼苏达大学研究生埃里克·戈尔根的博士论文的一部分，并涉及到与马克·杰塞尔博士(图卢兹)的国际合作。这项研究还包括明尼苏达州的本科生研究助理和其他机构的暑期实习生，这是NSF-REU网站的一部分。结果正在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分发。

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.