Vorticity estimates based on porphyroclasts analysis are limited by the extrapolation to three dimensions of two‐dimensional data. We describe a 3D approach based on the use of X‐ray micro‐computed tomography that better reflects the real 3D geometry of the porphyroclasts population. This new approach for kinematic vorticity analysis in the Munsiari Thrust mylonites, the lower boundary of the Main Central Thrust zone (MCTz) in Indian Himalaya, indicates a large pure shear component during non‐coaxial shearing. ⁴⁰Ar/³⁹Ar ages of micas along the mylonitic foliation of the Munsiari and Vaikrita thrusts (the upper boundary of the MCTz) constrain thrust activity to 5–4 and 8–9 Ma, respectively. Available kinematic vorticity analyses of the Vaikrita mylonites suggest the dominance of a simple shear component. Combining these data, we suggest that the southward and structurally downward shift of deformation along the MCTz was accompanied by a progressive increase in the pure shear component in a general shear flow.

中文翻译：

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主要中部逆冲带的三维涡度和受时间限制的演化，Garhwal喜马拉雅山（印度西北部）

基于卟啉弹性体分析的涡度估计受限于二维数据的三个维度的外推。我们描述了一种基于X射线微计算机断层扫描技术的3D方法，该方法可以更好地反映卟啉菌种群的真实​​3D几何形状。在印度喜马拉雅山中部主要冲断带（MCTz）的下边界，Munsiari冲断白垩岩运动涡度分析的这种新方法表明，在非同轴剪切过程中，纯剪切分量很大。⁴⁰氩/ ³⁹沿着Munsiari和Vaikrita逆冲断层（MCTz的上边界）的髓质化叶脉的云母Ar年龄分别将逆冲断层活动限制为5-4 Ma和8-9 Ma。现有的Vaikrita lon石运动涡度分析表明，简单剪切分量占主导地位。结合这些数据，我们认为沿MCTz的变形向南和结构上的向下偏移伴随着普通剪切流中纯剪切分量的逐渐增加。