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Journal of the Geological Society; 2009; v. 166; issue.2; p. 261-275;
DOI: 10.1144/0016-76492008-097
© 2009 Geological Society of London

Research Article

Pre-Miocene deformation of the Himalayan superstructure, Hidden valley, central Nepal

Dawn A. Kellett1,2 & Laurent Godin1

1 Department of Geological Sciences and Geological Engineering, Queen's University, Kingston, Ont. K7L 3N6, Canada
2 Present address: Department of Earth Sciences, Dalhousie University, Halifax, N.S. B3H 4J1, Canada

*Corresponding author (e-mail: Dawn.Kellett{at}Dal.Ca)

Throughout the Himalaya, the Tethyan sedimentary sequence forms the detached carapace, or superstructure, to exhumed mid-crustal rocks. In central Nepal, low metamorphic-grade Cambrian to Jurassic rocks of this carapace preserve five phases of deformation, structurally dominated by second phase (D2) north-verging back folds that oppose the vergence of the orogen. The folds are overprinted and cross-cut by the c. 22 Ma South Tibetan detachment system and the Manaslu leucogranite. New structural mapping in Hidden valley provides further constraints on the character of D2: megascopically, large asymmetric north-verging folds define D2; microscopically, it is characterized by an axial-planar cleavage. Balanced cross-sections and bed-length restoration of F2 folds indicate a minimum of 32–38% shortening and 180% thickening during D2. These data indicate that north-verging folds played a significant role in pre-Miocene crustal thickening of the Himalayan superstructure. The formation of these folds is compatible with wedge extrusion or channel flow of the underlying mid-crustal rocks, whereby their geometry reflects early coupling between the upper and middle crust.





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D. A. Kellett, D. Grujic, and S. Erdmann
Miocene structural reorganization of the South Tibetan detachment, eastern Himalaya: Implications for continental collision
Lithosphere, 2009; 1: 259 - 281.
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