Abstract Electron backscatter diffraction analysis of quartz grains and imaging of void spaces at grain boundaries in two orthogonal sections of a sample from the plastically deformed and dynamically recrystallized Harkless quartzite reveals the presence of void spaces at quartz-quartz grain boundaries. The distribution of these voids correlates with the crystallographic orientation of neighboring quartz grains relative to the grain boundary. Void spaces are more prevalent along grain boundaries where the a-axis of quartz is normal to the grain boundary. These void spaces likely formed during the exhumation (decrease in temperature and pressure) of the Harkless quartzite as a consequence of the volume change associated with an anisotropic elastic change in quartz crystal lattice dimensions, in which the length of the a-axis decreases by more than that of the c-axis. This volume change results in void space preferentially forming at grain boundaries neighbored by quartz with the a-axis normal to the grain boundary. The preferred orientation of the void spaces thus matches the preferred crystal orientation of quartz in the samples, suggesting that the preexisting rock microstructure and crystal fabric plays an important role in controlling the development and distribution of porosity during exhumation, which more generally may have important implications for fluid migration and the strength of exhumed rocks.

中文翻译：

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Harkless 石英岩中晶界处的晶体学控制空隙空间

摘要 对来自塑性变形和动态再结晶的 Harkless 石英岩样品的两个正交截面中的石英颗粒进行电子背散射衍射分析和晶界空隙空间成像揭示了石英-石英晶界处空隙空间的存在。这些空隙的分布与相邻石英晶粒相对于晶界的结晶取向相关。空隙空间沿晶界更为普遍，其中石英的 a 轴垂直于晶界。由于与石英晶格尺寸各向异性弹性变化相关的体积变化，这些空隙空间可能在 Harkless 石英岩的折返（温度和压力降低）期间形成，其中 a 轴的长度比 c 轴的长度减少更多。这种体积变化导致空隙空间优先在与石英相邻的晶界处形成，a 轴垂直于晶界。因此，空隙空间的优选取向与样品中石英的优选晶体取向相匹配，表明预先存在的岩石微观结构和晶体结构在控制折返过程中孔隙度的发展和分布方面起着重要作用，更普遍地可能具有重要意义用于流体迁移和挖掘岩石的强度。