Upper crustal shortening and forward modeling of the Himalayan fold-thrust belt along the Budhi-Gandaki river, central Nepal

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University of Alabama Libraries

Geologic mapping along the Budhi-Gandaki River in central Nepal reveals 6 significant structures: 1) South Tibetan Detachment system; 2) Main Central thrust; 3) Ramgarh thrust; 4) Lesser Himalayan duplex including the Trishuli thrust; 5) Main Boundary thrust; and 6) Main Frontal thrust system. A balanced cross-section between the South Tibetan Detachment system and Main Frontal thrust reveals that the region has a minimum total shortening of 76% or 420 km. The breakdown of the accommodation of shortening on each thrust is as follows: Main Central thrust - 115 km; Ramgarh thrust - 120 km; Lesser Himalayan duplex including the Trishuli thrust - 156 km; Main Boundary thrust - 10 km; Main Frontal thrust system - 19 km. In order to validate the balanced cross-section, a reconstruction program was used to forward model the system. By moving faults with appropriate amounts of displacement over a reasonable configuration of undeformed stratigraphy from the hinterland to foreland, the deformation of the Himalayan thrust belt along the Budhi-Gandaki River cross-section is reproduced. The forward modeling program moves hanging wall rock over stationary footwall rock using each individual fault identified in the balanced crosssection. Hanging wall rock deforms as it is thrust over footwall structures. Using forward modeling, the cross-section has a shortening estimate of 412 km or 75%. The two shortening estimates are virtually identical indicating the balanced cross-section along the Budi-Gandaki River is viable and admissible.

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