Development of preferred orientation and microstructure in sheared quartzite: comparison of natural data and simulated results
Development of preferred orientation and microstructure in sheared quartzite: comparison of natural data and simulated results
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DOI：
10.1016/s0040-1951(99)00173-0
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发表时间：
1999-11
期刊：
影响因子：
2.9
通讯作者：
T. Takeshita;H. Wenk;R. Lebensohn
中科院分区：
文献类型：
--
作者：
T. Takeshita;H. Wenk;R. Lebensohn
使用经修改以纳入动态再结晶效应的粘塑性自洽模型，对在绿片岩相条件下剪切和广泛再结晶的石英岩样品中的 c 轴织物和微观结构进行了分析，并与理论预测进行了比较。样品中存在关于有限缩短 z 轴的不对称小圆 c 轴织物，具有小半张角 (35°)；它由四个方向分量组成，分别由主晶粒 c 轴方向（称为 A、B、C 和 D）表示：A 和 B 与叶理面成大角度，分别逆着剪切方向位移； C 位于有限应变 Y 轴和 Z 轴之间的中间方向，D 围绕中间应变 (Y) 轴形成辅助集中。 B 和 C 晶粒分别对基底 (0001) 和金字塔 {10 1 ̄ 1}<a> 滑移有利地取向，并且变形强烈，而 A 和 D 晶粒对滑移系不利取向，并且变形较小或中等。有的A粒甚至断裂了。动态再结晶的程度随着不同取向晶粒（按 A、D、C 和 B 晶粒的顺序）所承受的应变的增加而增加。微观结构证据和理论预测表明，较硬的 A、C 和 D 晶粒被较软的再结晶 B 成分的晶界迁移显着消耗（尽管石英岩样品中并未真正记录 A 晶粒的消耗）。该结论得到以下事实的支持：B 组分在再结晶中比在主体 c 轴织物中占主导地位得多。因此，c 轴最大值几乎垂直于剪切面，并且明显以自然剪切石英岩中常见的剪切感（与 B 分量相关）发生位移，这可能是由于大应变下晶界迁移导致基底 (0001) 滑移的软取向生长而形成的。
c-axis fabric and microstructures in a quartzite sample, sheared and extensively recrystallized under greenschist facies conditions, have been analyzed and compared with theoretical predictions using a viscoplastic self-consistent model modified to incorporate the effects of dynamic recrystallization. An asymmetric small-circle c-axis fabric about the finite shortening z-axis with a small half opening angle (35°) is present in the sample; it consists of four orientation components which are represented by host grain c-axis orientations (referred to as A, B, C and D): A and B are at high angles to the foliation plane, displaced against and with the sense of shear, respectively; C is in an intermediate direction between the Y- and Z-axis of finite strain, and D forms a subsidiary concentration around the intermediate strain (Y-) axis. B- and C-grains are favorably oriented for basal (0001) and pyramid {10 1 ̄ 1}〈a〉 slip, respectively, and strongly deformed, while A- and D-grains are unfavorably oriented for the slip systems and little or moderately deformed. Some of A-grains are even fractured. The degree of dynamic recrystallization increases with increasing strain undergone by differently oriented grains (in the sequence of A-, D-, C- and B-grains). Microstructural evidence and theoretical predictions indicate that harder A-, C- and D-grains were significantly consumed by the grain boundary migration of the softer recrystallized B-component (although the consumption of A-grains was not really documented in the quartzite sample). The conclusion is supported by the fact that the B-component is much more dominant in the recrystallized than in the host c-axis fabric. Hence, the c-axis maximum nearly perpendicular to the shear plane and apparently displaced with the sense of shear commonly found in naturally sheared quartzites (correlated with the B-component) is presumably developed by the growth of soft orientations for basal (0001) slip by grain boundary migration at large strains.