Preferred orientation in experimentally deformed limestone
Preferred orientation in experimentally deformed limestone
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实验变形石灰石中的优选取向
DOI：
10.1007/bf00373875
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发表时间：
1973
影响因子：
3.5
通讯作者：
F. J. Turner
中科院分区：
文献类型：
--
作者：
H. Wenk;C. S. Venkitasubramanyan;D. Baker;F. J. Turner
在方解石I、方解石II和文石稳定区内，对细粒灰岩进行了60多次同构造单轴压缩变形实验。X射线技术和球谐分析的数据被用来确定优先取向定量，并推导出这些轴对称标本的逆极图。它们在大多数情况下显示出强烈的择优取向，其作为实验条件的函数而变化，主要是温度和压力。在低于350° C的温度下，没有再结晶，并且扁平的晶粒表明平移、孪晶滑动和扭结是主要的变形机制。反极图显示了在c处的最大值，其肩部朝向或在e处的第二个最大值。这与在实验变形的Yule大理石中观察到的优选取向一致，并且可以解释为e上的主导孪晶滑动和r上的平移滑动的产物（Turner等人，1956年）。在高温（900-1000° C）下，强烈的晶粒生长（从4微米到50微米）表明织物再结晶。颗粒是等维的，清晰的，有大理石般的纹理。反极图显示在r处有一个最大值，c轴在压缩轴σ1周围的一个小圆圈内。根据热力学原理，假定再结晶晶粒的取向方式使应变能达到最大值，则可以预期会出现这种择优取向模式（如MacDonald，1960）。围压的降低导致c处的最大值减小，并在反极图的高角度正菱形处形成次极大值。这可以解释为r平移超过e孪生。在所有的变形实验中，在20%缩短后达到择优取向的平衡。择优取向强度随温度的升高而降低。文石是在500° C以上的温度下在其流体静力学稳定区内生成的。在相界附近，粗晶织构显示出择优取向，其极点为（010），平行于σ1。在较高的压力下，组构是细粒的，[001]平行于σ1排列。有证据表明，在这些变形实验中，从方解石到文石的相变是一种扩散，而不是马氏体相变。
Over sixty syntectonic deformation experiments in uniaxial compression have been done on fine-grained limestones in the stability fields of calcite I, calcite II and aragonite. X-ray techniques and spherical harmonic analysis of the data were used to determine preferred orientation quantitatively, and inverse pole-figures were derived for these axially symmetric specimens. They display in most cases strong preferred orientation which varies as a function of the experimental conditions, mainly temperature and pressure. At temperatures below 350° C recrystallization is lacking and flattened grains indicate that translation, twin gliding and kinking have been the dominant deformation mechanisms. The inverse pole-figure shows a maximum at c with a shoulder towards or a second maximum at e. This is in agreement with preferred orientation observed in experimentally deformed Yule marble and can be explained as the product of dominant twin gliding on e and translation gliding on r (Turner et al., 1956). At high temperatures (900–1000° C) strong grain growth (from 4 to 50 microns) indicates that the fabric recrystallized. Grains are equidimensional and clear with a marble-like texture. The inverse pole-figure shows a single maximum at r, and c-axes are oriented in a small circle around the axis of compression, σ1. Such a pattern of preferred orientation would be expected on thermodynamic grounds assuming that recrystallized grains will be oriented in such a way that the strain energy is a maximum (e.g. MacDonald, 1960). Decrease in confining pressure caused a decrease of the maximum at c and the formation of a secondary maximum at highangle positive rhombs in the inverse pole-figure. This can be interpreted as r translation dominating over e twinning. In all deformation experiments an equilibrium in preferred orientation was reached after 20 percent shortening. The strength of preferred orientation decreased with increasing temperature. Aragonite was produced within its hydrostatic stability field at temperatures above 500° C. Close to the phase boundary, coarse-grained textures showed preferred orientation with poles to (010) parallel to σ1. At higher pressures the fabric is fine-grained and [001] is aligned parallel to σ1. Evidence is given that the phase change from calcite to aragonite in these deformation experiments is a diffusive and not a martensitic transformation.