Experimental Evidence of Basal Slip in Quartz
Experimental Evidence of Basal Slip in Quartz
复制标题
石英基底滑移的实验证据
DOI：
10.1086/627030
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发表时间：
1964
期刊：
影响因子：
--
通讯作者：
N. Carter
中科院分区：
文献类型：
--
作者：
J. Christie;D. Griggs;N. Carter
抛光石英晶体在高温和围压下变形，基面上具有高剪切应力，在其表面上形成平行于基面轨迹的滑移带，指示在该平面上的滑移。柱面上滑移痕的分布表明a轴是滑移方向。抛光晶体的薄切片含有平行于基底的变形薄片。因此，在这些晶体中，变形层平行于滑移区。光学研究的基础变形lamadium与相衬照明表明，它们是尖锐的边界，小于0.2微米厚，分离区域的折射率高于和低于石英在一定距离的lamadium。补偿器的测量也揭示了在这些边界的相对侧上比正常情况高和低的双折射。折射率和双折射率的变化是一致的光弹性效应，这将是预期从一个阵列的基底边缘位错与伯格斯矢量平行的a轴。计算应力场和由此产生的应力光学效应，需要位错密度为8 × 10^{4}/cm（平均层厚）。该模型的有效性得到了电子显微镜照片的蚀刻抛光表面的晶体含有实验产生的laminate。薄层表现为一排排金字塔形的蚀坑，在50 μ m范围内是精确的线性。凹坑的密度范围为每厘米5至13 × 10^{4}。平行于c轴的变形带的几何特征表明它们是由基底滑移产生的扭折带;它们相对于a轴的取向支持a轴是滑移方向的结论。带边界被假定为由锁定的基底刃位错的“壁”组成。这个模型是一致的，缺乏可测量的光学变化在附近的大多数带边界;沿沿着一些带边界的折射率和双折射率的变化，定性类似于层状，在不对称的边界处的残余弹性应力的结果。这些弹性应力通常通过未变形的主晶体中的拉伸断裂来缓解，并且可以通过扭结带边界处的棱柱位错的发展来部分缓解。迄今所研究的大多数自然光晶体在相衬照明下都表现出实验光晶体中所发现的双折射现象和变化。含纹层的天然石英岩的蚀刻抛光薄片的电子显微镜显示与纹层一致的蚀刻坑带。这些层状带内的蚀坑的分布比实验层状带中的蚀坑的分布不规则得多，但是如果蚀坑主要代表正确符号的位错，则蚀坑的密度是给出所观察到的光学效应所需的数量级。它的结论是，自然lamantics通常是由不规则阵列的锁定位错。讨论了自然和实验近基底层错之间的取向差异;得出的结论是，自然层错最初可能平行于基底，随后由其他滑移系内部旋转，或者它们可能起源于一个角度的基底位错的盘形阵列。
Polished crystals of quartz, deformed at high temperature and confining pressure with high shear stress on the basal plane, develop slip bands on their surfaces parallel to the trace of the basal planes, indicating slip on this plane. The distribution of the slip markings on cylindrical surfaces shows that the a-axes are the slip directions. Thin sections of the polished crystals contain deformation lamellae parallel to the base. The deformation lamellae are therefore parallel to slip zones in these crystals. Optical studies of basal deformation lamellae with phase-contrast illumination indicate that they are sharp boundaries, less than 0.2 micron thick, separating regions with higher and lower refractive indices than the quartz at some distance from the lamellae. Compensator measurements also reveal birefringences higher and lower than normal on opposite sides of these boundaries. Changes of indices and birefringence are consistent with the photoelastic effects which would be expected from an array of basal edge dislocations with Burgers vector parallel to an a-axis. Calculations of the stress field and resultant stress-optical effects due to such an array require a density of dislocations of $$8 \times 10^{4}$$ per centimeter in average lamellae. The validity of this model is supported by electron micrographs of etched polished surfaces of crystals containing experimentally produced lamellae. The lamellae appear as rows of pyramidal etch pits which are exactly linear within 50 Å. The density of pits ranges from 5 to $$13 \times 10^{4}$$ per centimeter. The geometrical characteristics of deformation bands parallel to the c-axis indicate that they are kink bands originating by basal slip; their orientations relative to the a-axes support the conclusion that the a-axes are the slip directions. The band boundaries are presumed to consist of "walls" of locked basal edge dislocations. This model is consistent with the lack of measurable optical changes in the vicinity of most band boundaries; changes of indices and birefringence along some band boundaries, qualitatively similar to lamellae, result from residual elastic stresses at asymmetrical boundaries. These elastic stresses are commonly relieved by tensile fracture in the undeformed host crystal and may be partially relieved by the development of prismatic dislocations at the kink-band boundary. Most natural lamellae so far studied exhibit the appearance in phase-contrast illumination and the changes in birefringence which have been found in experimental lamellae. Electron microscopy of etched polished thin sections of natural quartzite containing lamellae shows bands of etch pits coincident with the lamellae. The distribution of etch pits within these lamellar bands is much less regular than in experimental lamellae, but the density of etch pits is of the order required to give the observed optical effect if the etch pits represent dislocations predominantly of the correct sign. It is concluded that natural lamellae are typically comprised of irregular arrays of locked-in dislocations. Differences of orientation between natural and experimental near-basal lamellae are discussed; and it is concluded that natural lamellae may be initially parallel to the base, with subsequent internal rotation by other slip systems, or they may originate at an angle to the base as en échelon arrays of basal dislocations.