Experimental and Microstructural Study of Garnet Fracture Mechanics

惠特尼0106673 一种新的技术，用于确定机制，速率和减压幅度在山带的去顶，包括量化的高温减压和去顶压力温度轨迹以前深岩石的幅度，涉及解释石榴石中的微裂纹图案。特别感兴趣的是从矿物包裹体辐射的微裂纹，因为它们的形成可能是由减压引发的。 通过记录岩石静压力和矿物包裹体的内部压力之间的差异将在包裹体周围以放射状模式破裂宿主石榴石的条件，可以计算与中地壳至下地壳岩石折返有关的构造变量。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，和（2）文档和石榴石的微观结构在包含丰富的和无包含区的约束构造历史的比较。对被微裂纹包围的夹杂物附近的显微组织与未被微裂纹包围的夹杂物附近的显微组织进行了比较。石榴石的性能将确定使用微机械测试仪器，微观结构将观察高分辨率透射电子显微镜，和结构域将使用电子背散射衍射技术进行评估。 这项研究的结果可应用于其他减压材料（例如，含石榴子石的地幔捕虏体），并提供有关石榴子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.