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Tectonostratigraphy and Structural Evolution of the Himalayan Fold-Thrust Belt in Kumaon, NW India

Subhadip (Subho) Mandal and Delores M. Robinson
Geological Sciences, University of Alabama, Tuscaloosa, AL 35487, [email protected]

Early Cenozoic continental collision between Indian and Asian plates has created the vast Himalayan-Tibetan orogenic system, serving a natural laboratory to study continent-continent collision. The Himalayan fold-thrust belt (FTB), a diagnostic feature of this orogenic system, runs along the strike for ~2500 km. The Himalayan FTB consists of four major tectono-stratigraphic zones; Sub- himalaya, Lesser Himalaya, Greater Himalaya, and Tethyan Himalaya. Improper identification of various formations within each zone has led to erroneous structural and kinematic interpretations of the FTB evolution in Kumaon, NW India. New detailed mapping, accompanied by U-Pb zircon geochronologic data and a balanced structural cross-section define the tectono-stratigraphic architecture, and structural evolution of this area. *Depositional ages of various clastic units were better constrained using U-Pb detrital zircon analyses, which help to refine the stratigraphic architecture of this area. A balanced cross section along the eastern part of Kumaon reveals a minimum of 65% total upper-crustal shortening. In the southern part the structural geometry of the foreland is quite simple with widely spaced thrust ramps, and simple fault-bend folds in the Main Frontal Thrust hanging wall. In the central part, the structural geometry seen at the surface is mainly controlled by a buried hinterland dipping duplex. The Main Central thrust, a ductile shear zone occupies the northern part of the sector. The forward model and reconstruction reveals that the Lesser Himalayan duplex grew up by incorporating footwall rock and transferring it into the hanging wall along the Main Himalayan thrust, the main décollement of this FTB.

*New U-Pb detrital zircon analyses from various clastic units in the study sections have helped to redefine the stratigraphic architecture of this area.

AAPG Search and Discovery Article #90182©2013 AAPG/SEG Student Expo, Houston, Texas, September 16-17, 2013