Experimental and Microstructural Study of Garnet Fracture Mechanics

一种用于确定山区拆顶过程中减压机制、速率和幅度的新技术，包括量化高温减压幅度和原深部岩石的拆顶压力-温度轨迹，涉及解释石榴石中的微裂纹模式。特别令人感兴趣的是从矿物包裹体中辐射出来的微裂纹，因为它们的形成可能是由减压引起的。通过记录矿物包裹体上静岩压力和内部压力的差异使宿主石榴石在包裹体周围呈放射状破裂的条件，可以计算出与中下地壳岩石发掘有关的构造变量。本研究包括(1)确定硅酸盐石榴石的断裂韧性作为温度、成分和晶体取向的函数，以及(2)记录和比较具有良好构造历史的石榴石中富含和无包裹体区域的石榴石微观结构。比较了夹杂物周围有微裂纹和没有微裂纹的夹杂物附近的显微组织。石榴石的性质将使用微力学测试仪器来确定，微观结构将使用高分辨率透射电子显微镜来观察，结构域将使用电子背散射衍射技术来评估。该研究结果可应用于其他解压材料（如含石榴石的地幔捕虏体），并提供有关石榴石脆性行为的基本信息。

Whitney 0106673 A novel technique for determining the mechanisms, rates, and magnitude of decompression during unroofing of mountain belts, including quantifying the magnitude of high-temperature decompression and the unroofing pressure-temperature trajectory of formerly deep rocks, involves interpreting microcrack patterns in garnet. Of particular interest are microcracks that radiate from mineral inclusions, as their formation is likely initiated by decompression. By documenting the conditions at which the difference between lithostatic pressure and the internal pressure on mineral inclusions will fracture a host garnet in a radial pattern about the inclusion, it may be possible to calculate tectonic variables related to exhumation of mid- to lower-crustal rocks. This research involves (1) determination of the fracture toughness of silicate garnets as a function of temperature, composition, and crystal orientation, and (2) documentation and comparison of garnet microstructures in inclusion-rich and inclusion-free regions of garnets with well-constrained tectonic histories. Microstructures in the vicinity of inclusions surrounded by microcracks are compared with those near inclusions with no microcracks. Garnet properties will be determined using micromechanical testing apparatus, microstructures will be observed with high-resolution transmission electron microscopy, and structural domains will be assessed using electron backscatter diffraction techniques. Results from this research have applications to other decompressed materials (e.g., garnet-bearing mantle xenoliths) and provide fundamental information about the brittle behavior of garnet.