Many crystalline rocks of the continental crust contain coarse-grained quartz as a main mineral (e.g., granitoids). Incipient deformation of coarse quartz, which likely controls the accumulation of bulk strain in heterogeneously deformed crustal rock volumes, commonly develops microshear zones (MSZs) of localized recrystallization. At mid-crustal conditions, where quartz deformation is mostly accomplished by subgrain rotation recrystallization, grains of MSZs can show an abrupt change in crystallographic orientation (large misorientation angle) with respect to the host quartz that is still not fully understood. We analyzed MSZs (20–200 µm thick) from deformed coarse-grained (millimeter grain size) quartz veins in the Austroalpine Schobergruppe (Eastern Alps). Electron backscatter diffraction analysis reveals that the MSZs are characterized by a nearly 90° misorientation angle between the c-axes of the host and new grains, which also share one {m} and one {1122} pole, compatible with Japan twinning. This abrupt switch of the c-axis orientation can promote geometrical softening and shear localization. So far, Japan twinning has been interpreted as a growth feature. We show that deformation-induced twinning in quartz, including Japan and Dauphiné twinning, can play an important role in initiation of crystal-plastic deformation within the crust.

中文翻译：

---

早期糜棱化过程中石英中变形引起的日本孪晶

大陆地壳的许多结晶岩含有粗粒石英作为主要矿物（例如花岗岩）。粗石英的初始变形可能控制不均匀变形地壳岩石体积中体积应变的积累，通常会形成局部再结晶的微剪切带 (MSZ)。在中地壳条件下，石英变形主要是通过亚晶粒旋转再结晶完成的，MSZ 的晶粒可以显示出相对于主体石英的晶体取向的突然变化（大的取向差角），但仍未完全了解。我们分析了来自 Austroalpine Schobergruppe（东阿尔卑斯山）的变形粗粒（毫米粒度）石英脉的 MSZ（20-200 µm 厚）。电子背散射衍射分析表明，MSZ 的特征是主体和新晶粒的 c 轴之间的取向角接近 90°，它们也共享一个 {m} 和一个 {1122} 极，与日本孪晶兼容。c 轴方向的这种突然转换可以促进几何软化和剪切定位。迄今为止，日本结对一直被解读为一种增长特征。我们表明，石英中的变形诱导孪晶，包括日本孪晶和 Dauphiné 孪晶，可以在地壳内晶体塑性变形的启动中发挥重要作用。日本结对被解读为增长特征。我们表明，石英中的变形诱导孪晶，包括日本孪晶和 Dauphiné 孪晶，可以在地壳内晶体塑性变形的启动中发挥重要作用。日本结对被解读为增长特征。我们表明，石英中的变形诱导孪晶，包括日本孪晶和 Dauphiné 孪晶，可以在地壳内晶体塑性变形的启动中发挥重要作用。