Spiral garnet porphyroblasts are known to record lengthy periods of deformation and metamorphism by preserving single or multiple FIAs (Foliation Intersection Axis) formed normal to tectonic shortening directions. Thanks to technological advances in X-ray computed micro-tomography (XCMT), FIAs can now be readily determined in relatively large samples in contrast to previous methods that require the preparation of a set of radial vertical and horizontal thin sections of samples. XCMT scanning not only alleviates tedious thin section based procedures but also illuminates the complete internal architecture of a rock sample allowing three-dimensional (3D) quantitative shape analysis of an individual porphyroblast as well as precise measurement of FIAs. We applied the technique to a sample from the Hunza Valley in the Karakoram metamorphic complex (KMC), NW Himalayas, containing numerous garnet porphyroblasts with spiral-shaped inclusion trails. The XCMT imaging reveals an E–W trending FIA within the sample, which is consistent with orthogonal N–S collision of the India-Kohistan Island Arc with Asia. Garnet long axes (X_GT) have variable plunges that define a broad sub-vertical maximum and a small sub-horizontal maximum. The X_GT principle maxima lie at N-090 and N-120. Smaller maxima lie at N-020 and N-340. Geometric relationships between X_GT axes and FIA orientation in the sample suggest that porphyroblast shapes are controlled by the geometry of the lens-shaped microlithons in which they tend to nucleate and grow. The orientation of inclusion trails and matrix foliations in the sample are correlated with three discrete tectono-metamorphic events that respectively produced andalusite, sillimanite and kyanite in the KMC. Late staurolite growth in the sample reveals how the rocks extruded to the surface via a significant role of roll-on tectonics, which can be correlated with the Central Himalayas.

众所周知，螺旋石榴石成纤维细胞通过保留垂直于构造缩短方向形成的单个或多个FIA（叶片交点轴）来记录较长的变形和变质期。由于X射线计算机显微断层扫描（XCMT）的技术进步，与以前的方法（需要准备一组径向的垂直和水平的薄截面样品）相比，现在可以在相对较大的样品中轻松确定FIA。XCMT扫描不仅减轻了繁琐的基于薄层的程序，而且还阐明了岩石样品的完整内部结构，从而可以对单个成矿细胞进行三维（3D）定量形状分析以及FIA的精确测量。我们将该技术应用于来自喜马拉雅西北部Karakoram变质复合体（KMC）的Hunza谷的样本，该样本包含大量带有螺旋形包裹体痕迹的石榴石成卟啉。XCMT成像显示样品中的E-W趋势FIA，这与印度-科希斯坦岛弧与亚洲的正交N-S碰撞相一致。石榴石长轴（X_GT）具有可变的跌落幅度，这些跌落幅度定义了较宽的次垂直最大值和较小的次水平最大值。X _GT原则的最大值位于N-090和N-120。较小的最大值位于N-020和N-340。X _GT之间的几何关系样品中的X轴和FIA方向表明，成卟啉的形状受晶状微石的几何形状控制，微晶在其中趋于成核并生长。样品中夹杂物踪迹和基质叶的取向与三个离散的构造变质事件相关，分别在KMC中产生红柱石，硅线石和蓝晶石。样品中的星形胶石晚期生长揭示了岩石如何通过滚动构造的显着作用挤出到地面，这可能与喜马拉雅中部地区相关。