Deformation trail tracking in S-tectonites of the Darjeeling-Sikkim Himalaya: The kink band perspective

Small-scale structures are the primary source of information in interpreting the tectonic evolution of an orogen. However, due to the obliteration and discrete nature of small-scale structures, it is often challenging to ascertain the deformation events. Kink bands are one of the most frequently occurring small-scale structures in foliated rocks and varied tectonic settings, especially in contractional deformational zones. Kink bands in the S-tectonites of Darjeeling-Sikkim Himalaya (DSH) preserve evidence of at least three stages of development of kink bands. The angular parameters of the kink bands (alpha, beta and kappa) are used for paleostress reconstruction, estimating volume change and shortening percentages in kink bands developed on the Daling phyllites of the Ramgarh Thrust Sheet in the Tista half-window. Detailed studies on the morphological characteristics of kink bands coupled with structural analysis confirm the formation of kink bands progressively in stages under a hybrid kinking mechanism in a protracted history of deformation. Canonical discriminant analysis of data acquired from microscopic kink bands is employed for erecting a classification scheme with similar to 90% success rate in predicting the stages of infinitesimal deformation, and validated with mesoscale kink bands in DSH and compared with global examples. The adopted methodology depicts that kink bands can be utilized as a proxy to delineate the extent of volume change and shortening in orogenic belts.