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首页> 外文期刊>Contributions to Mineralogy and Petrology >Garnet polycrystals and the significance of clustered crystallization
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Garnet polycrystals and the significance of clustered crystallization

机译：石榴石多晶体及其成簇结晶的意义

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Polycrystalline garnets are common in metamorphic rocks and may form as a result of close spacing of nuclei (if clustering is early) or impingement of larger grains (if clustering occurs later in the growth history). The timing of clustering relative to garnet growth is relevant to understanding the formation and evolution of porphyroblasts and evaluating the significance (if any) of clustering. Electron backscattered diffraction (EBSD) analysis of garnet-bearing metamorphic rocks reveals the presence of polycrystalline garnet in nine localities examined in this study: the northern Appalachians (Vermont, Maine, New York, USA); North American Cordillera (North Cascades Range, Washington; Snake Range, Nevada, USA); western Rocky Mountains (British Columbia, Canada); southern Menderes Massif (Turkey); Santander Massif (Colombia); and the Sanandaj–Sirjan zone (Hamadan, Iran). In some samples, polycrystals comprise ~20–30% of garnets analyzed, and chemical and textural evidence suggests that early coalescence of garnet polycrystals is common. Some early-coalescing polycrystals exhibit growth zoning that is concentric about the geometric center of the polycrystal. In thin section, these garnets may be undetectable as polycrystals based on morphology or zoning. In some polycrystals, zoning is unrelated to the location of internal grain boundaries; in others, Fe–Mn–Mg zoning has a different pattern than that of Ca; zoning patterns may vary on the scale of a single thin section. In addition, some polycrystals are characterized by high-angle misorientation boundaries that may be in special (non-random) orientations, an observation that indicates that these polycrystals are not random clusters of grains. The presence of internal grain boundaries may affect diffusion pathways and length scales, and may facilitate communication of porphyroblast interiors with matrix phases, thereby influencing reaction history of the rock and the composition/zoning of garnet.
机译：多晶石榴石在变质岩中很常见，并且可能是由于原子核紧密间隔（如果聚簇较早）或撞击较大的晶粒（如果聚簇发生于生长历史的后期）而形成的。相对于石榴石生长的成簇时间与了解成卟啉细胞的形成和演化以及评估成簇的重要性（如果有）有关。含石榴石的变质岩的电子背散射衍射（EBSD）分析表明，在这项研究中检测的9个地区中都存在多晶石榴石：北部的阿巴拉契亚山脉（佛蒙特州，缅因州，美国纽约）；北美山脉（华盛顿州北喀斯喀特山脉；美国内华达州蛇岭）；落基山脉西部（加拿大不列颠哥伦比亚省）；南部Menderes地块（土耳其）；桑坦德山地块（哥伦比亚）；以及Sanandaj–Sirjan地区（伊朗哈马丹）。在某些样品中，多晶体占被分析的石榴石的约20％至30％，化学和质地证据表明，石榴石多晶体的早期聚结是常见的。一些早期聚集的多晶表现出围绕多晶的几何中心同心的生长区带。在薄截面中，基于形态或分区，这些石榴石可能无法检测为多晶。在某些多晶中，分区与内部晶界的位置无关。在其他地区，Fe-Mn-Mg的分区模式与Ca的模式不同；分区模式可能会因单个薄片的规模而异。此外，某些多晶的特征是可能具有特殊（非随机）取向的大角度取向错误边界，这一观察表明这些多晶不是晶粒的随机簇。内部晶界的存在可能影响扩散途径和长度尺度，并可能促进卟啉内部与基质相的连通，从而影响岩石的反应历史和石榴石的组成/分区。

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