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首页> 外文期刊>Contributions to Mineralogy and Petrology >The effect of Dauphiné twinning on plastic strain in quartz
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The effect of Dauphiné twinning on plastic strain in quartz

机译：Dauphiné孪晶对石英塑性应变的影响

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We present an electron backscatter diffraction analysis of five quartz porphyroclasts in a greenschist facies (T = 300–400°C) granitoid protomylonite from the Arolla unit of the NW Alps. Mechanical Dauphiné twinning developed pervasively during the incipient stage of deformation within two porphyroclasts oriented with a negative rhomb plane {z} almost orthogonal to the compression direction (z-twin orientation). Twinning was driven by the anisotropy in the elastic compliance of quartz and resulted in the alignment of the poles of the planes of the more compliant positive rhomb {r} nearly parallel to the compression direction (r-twin orientation). In contrast, we report the lack of twinning in two porphyroclasts already oriented with one of the {r} planes orthogonal to the compression direction. One twinned porphyroclast has been investigated with more detail. It shows the localization of much of the plastic strain into discrete r-twins as a consequence of the higher amount of elastic strain energy stored by r-twins in comparison to z-twins. The presence of Dauphiné twins induced a switch in the dominant active slip systems during plastic deformation, from basal (regions without twinning) to {π} and {π′} (pervasively twinned regions). Dynamic recrystallization is localized along an r-twin and occurred dominantly by progressive subgrain rotation, with a local component of bulging recrystallization. Part of the recrystallized grains underwent rigid-body rotation, approximately about the bulk vorticity axis, which accounts for the development of large misorientation angles. The recrystallized grain size piezometer for quartz yields differential stress of 100 MPa. The comparison of this palaeostress estimate with literature data suggests that mechanical Dauphiné twinning could have a potential use as palaeopiezometer in quartz-bearing rocks.
机译：我们介绍了来自西北阿尔卑斯山Arolla单元的绿片岩相（T = 300–400°C）花岗岩类原生质岩中的五个石英卟啉的电子背散射衍射分析。机械的Dauphiné孪生孪晶在变形的初始阶段普遍发展，在两个具有负菱形平面{z}且几乎垂直于压缩方向（z双胞胎）的卟啉中。孪晶是由石英弹性柔度的各向异性驱动的，并导致更柔顺的正菱形{r}的平面的极点几乎与压缩方向（r双取向）平行。相比之下，我们报道了在已经与正交于压缩方向的{r}平面之一定向的两个卟啉中没有孪晶。已对一种双卟啉进行了更详细的研究。它显示，由于与Z型双绞线相比，R型双绞线存储的弹性应变能更高，因此许多塑性应变都定位在离散的R型双绞线中。 Dauphiné孪晶的存在在塑性变形期间在主要的主动滑动系统中引起了一个转换，从基部（没有孪生的区域）到{π}和{π'}（普遍的孪生区域）。动态再结晶沿r-孪晶局部化，并主要通过渐进的亚晶粒旋转而发生，并具有凸起的再结晶的局部成分。重结晶晶粒的一部分经历了刚体旋转，大约围绕整体涡度轴旋转，这导致了大的取向错误角的产生。石英的再结晶晶粒尺寸压强计产生100 MPa的压差。将该古地应力估算值与文献数据进行比较表明，机械的Dauphiné孪晶可能具有潜在的用途，可以用作含石英岩石中的古比兹计。

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