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Late-to-post collisional brittle–ductile deformation in the Himalayan orogen: Evidences from structural studies in the Lesser Himalayan Crystallines, Kumaon Himalaya, India

Authors
Journal
Journal of Asian Earth Sciences
1367-9120
Publisher
Elsevier
Publication Date
Volume
27
Issue
5
Identifiers
DOI: 10.1016/j.jseaes.2005.06.010
Keywords
  • Main Central Thrust
  • Main Boundary Thrust
  • South Chiplakot Thrust
  • North Chiplakot Thrust
  • Chiplakot Crystalline Belt
Disciplines
  • Earth Science
  • Mathematics

Abstract

Abstract The Chiplakot Crystalline Belt (CCB) is a broad shear zone located within the meta-sedimentary zone of the Lesser Himalaya. Evidence from mesostructures and microstructures reveals development of this shear zone in a compressional ductile tectonic regime during continental collision in the Himalaya by top-to-SW shearing along NE-dipping shear surfaces. The shear surfaces are parallel to both the upper and basal thrust planes of the CCB. A hitherto unrecognized, late-to-post collisional brittle–ductile tectonic regime, comprised of two discrete phases is established from dynamic analysis of the kink bands, extensional shear fractures, foliation boudinage, competent layer boudinage, quartz veins and associated flanking folds, and brittle normal and reverse faults in the CCB. Kink bands, foliation parallel slip and general shear were major consequences of this late-to-post-collisional brittle–ductile tectonic episode, and were associated with the intrusion of a swarm of quartz veins. Quartz veins associated with flanking folds are developed at high angles with respect to the mylonitic foliation and parallel to the axial plane of the kink bands throughout the CCB. The geometry of the flanking folds along the quartz veins is a consequence of the fracturing and not vice-versa. The precise shape of the folds depends on the nature of general shearing along the wall of quartz veins and various orientations to the shear direction.

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