The Darjeeling-Sikkim Himalaya lies in a zone where the convergence vector between the Indian and Eurasian plates is almost perpendicular to the Himalayan deformation front. Current outcrop pattern preserves high-grade hanging wall rocks of the Main Central thrust (MCT) and the Pelling thrust (PT) within 5km of the mountain front. U-Pb SHRIMP analysis on zircon grains from MCT sheet record two 206Pb/238U age groups of ca. 2575 and ca. 943Ma and from the PT 1835±13Ma. The Lesser Himalayan duplex in the footwall of the MCT is composed of two duplex systems; a structurally higher hinterland dipping duplex, and a lower duplex system that varies from hinterland dipping in the north to an antiformal stack in the middle and foreland dipping duplex in the south. The foreland-dipping horses and reactivation of the roof thrust resulted in large translation of the overlying MCT and Pelling thrust sheets. The duplex also resulted in a plunge culmination forming a broad N-S trending anticline. A transport-parallel, restorable, balanced cross section reveals a minimum shortening of ~450km (~81%) south of the South Tibetan Detachment system, and an average long-term shortening rate ~20mm/yr. Although the study area lies in a zone of high convergence angle with the deformation front, the surface structures do not record the greatest shortening of the orogen. The Shillong plateau and a tranverse zone lying southeast of the study area have accommodated a part of the convergence-related shortening, thereby under-representing the shortening in the Sikkim Himalayan fold-thrust belt. Lateral variations in the original width of the Lesser Himalayan basin may have played a role in partitioning the shortening in the fold-thrust belt.
Bibliographical noteFunding Information:
This work was supported by IISER Kolkata Start-up grant to K. Bhattacharyya, and NSF Grant EAR – 0439999 to G. Mitra. We acknowledge S. Kim for his help with the SHRIMP analysis, F. Ahmed for his help in drafting Figs. 10 and 11 . We thank S. Long, D. Robinson, D. Grujic and L. Imamura for their detailed and critical comments on an earlier version of this manuscript. Critical reviews by two anonymous reviewers improved the quality of the paper. We have used only field data that we collected ourselves, for this work. The data for this paper are available by contacting the corresponding author.
© 2015 Elsevier Ltd.
All Science Journal Classification (ASJC) codes
- Earth-Surface Processes