Sigmoidal en-echelon tension gashes developed during this deformation, that were oblique to bedding parallel worm burrows and bedding planes themselves. Bulk top to NW shearing transformed initially symmetrical NNE–SSW trending meso to macroscopic folds from asymmetric to overturned ones without changing their trend. The anisotropy of dissolution and growth rates may have been responsible for the development of the specific grain boundaries.ĭetailed micro–meso to macroscopic structural analyses reveal two deformation phases in the western limb of the Hazara-Kashmir Syntaxis (HKS). These suggest that neither dislocation creep nor dislocation-accommodated grain boundary sliding (GBS) produced the plagioclase CPOs but rather grain rotation via GBS along specific grain boundaries parallel or subparallel to crystallographic planes of (010), (100) or (110), which led to an alignment of the easy-slip grain boundaries in the flow direction that produced the observed CPO patterns. In some domains of the drag fold, plagioclase CPOs are more distinct, but the majority of inferred slip systems are not consistent with the main slip systems in plagioclase.

Other than deformation twinning, they do not show any indications of intracrystalline plasticity or dynamic recrystallization.

These grains have developed weak crystallographic preferred orientations (CPOs). To clarify the rheological properties and deformational mechanisms that operate within lower-crustal shear zones, we analyzed deformation microstructures and fabrics in plagioclase grains from high-strain regions of intrafolial drag folds of an anorthositic ultramylonite from Langøya, Vesterålen, northern Norway.

A tale in the desert macro