Vorticity analysis and recognition of ductile extension in the Sanbagawa belt, SW Japan
Vorticity analysis and recognition of ductile extension in the Sanbagawa belt, SW Japan
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DOI：
10.1016/0191-8141(95)00005-x
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发表时间：
1995-08
影响因子：
3.1
通讯作者：
S. Wallis
中科院分区：
文献类型：
--
作者：
S. Wallis
山带内部的变质带往往经历区域性的渗透变形。这种变形可能是由于两个基本上刚性的板块之间的整体简单剪切的结果，或者是由于韧性增厚或变薄的结果。研究变形过程中的非同轴度（涡度分析）有助于区分所产生的运动学历史。非同轴度的可能指标包括：（一）旋转的碎斑与不同的纵横比;（二）的分布集的材料线与不同的拉伸历史;（三）几何结构的晶体结构;和（四）倾斜的晶粒形状织物的取向。应用这些方法在三坝川变质带，日本西南部的建议，占主导地位的区域构造组构，与造山带平行剪切，作为韧性伸展的结果形成。定量分析表明，相关的变薄是50%的顺序。与整体简单剪切的主要区别还与共轭剪切的形成有关，共轭剪切在不同尺度上具有相反的剪切方向。在三坝川带的韧性变形过程中发生的大量减薄表明，这一构造阶段与折返过程有关，而与俯冲过程中的埋藏无关。减薄及其相关的拉伸方向（大致平行于造山带）可能与斜向会聚有关，其走滑分量沿造山带长度方向沿着具有梯度。
Metamorphic belts in the internal parts of mountain belts have invariably undergone regional penetrative deformation. Such deformation may form as the result of bulk simple shear between two essentially rigid plates or, alternatively, as a result of ductile thickening or thinning. Studies of the degree of non-coaxiality during deformation (vorticity analyses) can help distinguish between the resulting kinematic histories. Possible indicators of the degree of non-coaxiality include:(i) the rotation of porphyroclasts with different aspect ratios;(ii) the distribution of sets of material lines with different stretch histories;(iii) geometries of crystallographic fabrics; and (iv) the orientation of oblique grain shape fabrics. Application of such methods in the Sanbagawa metamorphic belt, SW Japan suggests that the dominant regional tectonic fabric, associated with orogen-parallel shearing, formed as a result of ductile extension. Quantitative analyses suggest the associated thinning was of the order of 50%. The major departure from bulk simple shear can also be related to the formation of conjugate shears with opposed senses of shear on various scales. The significant amount of thinning that took place during ductile deformation of the Sanbagawa belt shows that this tectonic phase is related to exhumation processes and not to burial during subduction. Both the thinning and its associated stretching direction (roughly orogenparallel) may be related to oblique convergence with a gradient in the strike-slip component along the length of the orogen.